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Ribbon Mic - RCA 77D - worth messing with????

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September 6, 2005 9:09:01 AM

Archived from groups: rec.audio.pro (More info?)

Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
and wonder if its worth messing with... It is, I am sure well known
to many in this group.. Seems to work to a non-critical test, but I
wonder if years of storage in a hot attic and who-knows-what-other
insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
the mic can be wired to be 30, 150, or 250, and I wonder what this
degree of mismatch does to gain and noise (it did sound a bit hissy).

Seems like a great find, I look forward to any comments and
suggestions. Thanks in advance for the wisdom of the group! Peter
Anonymous
September 6, 2005 9:09:02 AM

Archived from groups: rec.audio.pro (More info?)

DUDE, CAREFUL! ribbon mics can be destroyed by phantom power. so make
sure you can disable phantom power on your onyx. (sorry if that is
obvious to you).

Wes Dooley at AEA could probably take it in and tell you if it's
trashed or not. Also, Scott Dorsey would be able to open it up and see
what's up with it.
Anonymous
September 6, 2005 9:09:02 AM

Archived from groups: rec.audio.pro (More info?)

phantom power and input impedance are two different things.

phantom power on a mic channel will "recognize" a mic once it's plugged
into the channel and then start supplying 48 volts to it (kind of like
when a computer recognizes that a printer has been plugged into a usb
port). the problem is that ribbon mics were never designed for phantom
power, and can easily be destroyed by it. it's not like overclocking a
computer where it's cool until it overloads and shuts down...it's just
plain bad for a ribbon mic.

dynamic mics (like a shure sm-57 or sm-58) don't need phantom power.
they won't be harmed if they are on a phantom powered mic channel..they
will just ignore it.

condenser mics are the ones that want phantom power. so mixers are
often made have the ability to deliver phantom power. some mixers have
a global phantom power, where a switch will provide phantom power to
all mic channels, or none. others have individual on/off phantom
power for each channel.

just be way careful. you may have found a mic worth about $2700. so
don't blow it!

impedance has to do with how a mic gets loaded. old school neumann
u-47 teuchel connector days built everything with 600 ohm. you
plugged a 600 ohm mic into a 600 ohm mic pre into a 600 ohm blah blah
blah..

contemporary thinking is that you have the mic deliver a very low
impedance (50-200ohms) and have it hit a preamp with a high impedance
(1000 ohms, 10,000ohms, etc.).

i've never owned a ribbon mic, but they belong do a different sort of
voodoo. some very elaborate mic pres like the Groove Tube Vipre allow
you to adjust the mic pre impedance. this can very significantly help
"dial-in" a mic. i heard Aspen Pitman do a demo of this at AES, and
was quite impressed how a ribbon mic can "come alive" when the preamp
is dialed into an impedance the mic "likes". you can use the impedance
to affect slew rate, but now we're getting off topic.

the main topics are these:
1) DO NOT plug it into a mic channel that has phantom power on it
2) send it out to a ribbon mic genius to have them tell you what kind
of condition it is in
3) if it's in good shape, consider investing in a separate mic pre that
has variable input impedance. then you can dial in your mic and always
keep the phantom power off on that device so you don't blow up the mic.
Related resources
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Anonymous
September 6, 2005 9:09:02 AM

Archived from groups: rec.audio.pro (More info?)

bohemian wrote:
> Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
> and wonder if its worth messing with...

It's a fine mic, and if it isn't fine now, it can be restored to new or
better-than-new condition.

> My Mackie Onyx mic preamps list input impedance at 2.4K and
> the mic can be wired to be 30, 150, or 250, and I wonder what this
> degree of mismatch does to gain and noise (it did sound a bit hissy).

The reason why it sounds hissy is because the sensitivity is farily low
and you're having to use a lot of gain. If you switch the tap to 250
ohms (if it isn't already set there) you'll get more voltage out of the
mic for a given sound pressure level so you may be able to use less
gain.

You don't "match" impedances between a mic and a preamp, but the input
impedance of the preamp interacts with the output transformer of the
mic, which changes the sound slightly. It'll probably work OK with your
Onyx.

As far as phantom power goes, you should be careful with that mic, at
least until you determine whether the transformer has its center tap
grounded. They were originally built that way (most have had the
connection removed) and if it's wired like that, the mic should never
see phantom power. At least the Onyx has a phantom power switch on each
channel so you can be sure it's off, but don't make any mistakes.
You're a little safer with the center tap ungrounded - you can switch
on phantom power IF THE MIC IS PLUGGED IN BEFORE APPLYING POWER!!! but
it's better to not risk it.

Wes Dooley is one of the RCA ribbon repair experts. Clarence Kane and
Stephen Sank are two others who have the parts, tools, and knowledge to
check it out and fix what needs to be fixed, if anything. It's worth
putting some money into the mic to have it checked out and fixed. At
least that way you'll know what it really sounds like, and if you don't
find it useful for your work, you can sell it in good condition rather
than unknown condition.
September 6, 2005 10:11:27 AM

Archived from groups: rec.audio.pro (More info?)

hey, thanks for the warning! I was aware of the phantom power issue,
and I DID read an article I think by Wes - got a little confused and
have to read more since I think it was he that said the input Z should
be at least 1500........

On 5 Sep 2005 23:07:07 -0700, genericaudioperson@hotmail.com wrote:

>DUDE, CAREFUL! ribbon mics can be destroyed by phantom power. so make
>sure you can disable phantom power on your onyx. (sorry if that is
>obvious to you).
>
>Wes Dooley at AEA could probably take it in and tell you if it's
>trashed or not. Also, Scott Dorsey would be able to open it up and see
>what's up with it.
Anonymous
September 6, 2005 12:50:34 PM

Archived from groups: rec.audio.pro (More info?)

bohemian <same> wrote:
>Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
>and wonder if its worth messing with... It is, I am sure well known
>to many in this group.. Seems to work to a non-critical test, but I
>wonder if years of storage in a hot attic and who-knows-what-other
>insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
>the mic can be wired to be 30, 150, or 250, and I wonder what this
>degree of mismatch does to gain and noise (it did sound a bit hissy).

The hot attic won't hurt it, but if it was stored in the wrong position
(ie. not upright), the ribbon can sag. If this is the case, you'll find
the low end is very flabby and out of control. Ribbon replacement is
under $100 and can be done by Steven Sank or Clarence Kane.

Strap the microphone for 250 ohms and use a preamp that can deal with
it. As you have noticed, the mike will be very noisy with the Mackie
and the top end might not be right, either. The 77D wants to see a
transformer input if at all possible.

>Seems like a great find, I look forward to any comments and
>suggestions. Thanks in advance for the wisdom of the group! Peter

It's a fun mike, and one of the old standbys that every studio used to
have around. Use it in figure-8 mode if you can... the pattern control
gadget isn't really all that good.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
September 6, 2005 1:17:46 PM

Archived from groups: rec.audio.pro (More info?)

"Scott Dorsey" <kludge@panix.com> wrote in message
news:D fk3aq$dji$1@panix2.panix.com...
> bohemian <same> wrote:
>>Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
>>and wonder if its worth messing with... It is, I am sure well known
>>to many in this group.. Seems to work to a non-critical test, but I
>>wonder if years of storage in a hot attic and who-knows-what-other
>>insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
>>the mic can be wired to be 30, 150, or 250, and I wonder what this
>>degree of mismatch does to gain and noise (it did sound a bit hissy).
>
> The hot attic won't hurt it, but if it was stored in the wrong position
> (ie. not upright), the ribbon can sag. If this is the case, you'll find
> the low end is very flabby and out of control. Ribbon replacement is
> under $100 and can be done by Steven Sank or Clarence Kane.
>
> Strap the microphone for 250 ohms and use a preamp that can deal with
> it. As you have noticed, the mike will be very noisy with the Mackie
> and the top end might not be right, either. The 77D wants to see a
> transformer input if at all possible.
>
>>Seems like a great find, I look forward to any comments and
>>suggestions. Thanks in advance for the wisdom of the group! Peter
>
> It's a fun mike, and one of the old standbys that every studio used to
> have around. Use it in figure-8 mode if you can... the pattern control
> gadget isn't really all that good.
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

This web site is very informative about the RCA 77 microphones:

http://www.coutant.org/3.html

Steve King
Anonymous
September 6, 2005 1:24:49 PM

Archived from groups: rec.audio.pro (More info?)

> impedance has to do with how a mic gets loaded. old school neumann
> u-47 teuchel connector days built everything with 600 ohm. you
> plugged a 600 ohm mic into a 600 ohm mic pre into a 600 ohm blah blah
> blah..

Neumanns were always supposed to be bridged, not matched. I'm not familiar
with a 600 Ohms Neumann of any kind...

JP
Anonymous
September 6, 2005 4:41:36 PM

Archived from groups: rec.audio.pro (More info?)

genericaudioperson@hotmail.com wrote in news:1125990102.002469.242790
@z14g2000cwz.googlegroups.com:

> phantom power on a mic channel will "recognize" a mic once it's plugged
> into the channel and then start supplying 48 volts to it (kind of like
> when a computer recognizes that a printer has been plugged into a usb
> port).

Good grief...
September 6, 2005 6:30:54 PM

Archived from groups: rec.audio.pro (More info?)

Thanks, Scott.... Assuming I send this off for a re-ribbon job for
$120 (thanks for the names!!), I read somewhere 700 to 1,000 bucks for
a proper pre-amp (way over budget), is there no good alternative?????
Thanks again!

Peter
On 6 Sep 2005 08:50:34 -0400, kludge@panix.com (Scott Dorsey) wrote:

>bohemian <same> wrote:
>>Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
>>and wonder if its worth messing with... It is, I am sure well known
>>to many in this group.. Seems to work to a non-critical test, but I
>>wonder if years of storage in a hot attic and who-knows-what-other
>>insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
>>the mic can be wired to be 30, 150, or 250, and I wonder what this
>>degree of mismatch does to gain and noise (it did sound a bit hissy).
>
>The hot attic won't hurt it, but if it was stored in the wrong position
>(ie. not upright), the ribbon can sag. If this is the case, you'll find
>the low end is very flabby and out of control. Ribbon replacement is
>under $100 and can be done by Steven Sank or Clarence Kane.
>
>Strap the microphone for 250 ohms and use a preamp that can deal with
>it. As you have noticed, the mike will be very noisy with the Mackie
>and the top end might not be right, either. The 77D wants to see a
>transformer input if at all possible.
>
>>Seems like a great find, I look forward to any comments and
>>suggestions. Thanks in advance for the wisdom of the group! Peter
>
>It's a fun mike, and one of the old standbys that every studio used to
>have around. Use it in figure-8 mode if you can... the pattern control
>gadget isn't really all that good.
>--scott
Anonymous
September 6, 2005 6:30:55 PM

Archived from groups: rec.audio.pro (More info?)

Peter <alias@snowcrest.net> wrote:
>Thanks, Scott.... Assuming I send this off for a re-ribbon job for
>$120 (thanks for the names!!), I read somewhere 700 to 1,000 bucks for
>a proper pre-amp (way over budget), is there no good alternative?????

Not really, but you'll find that a good preamp makes all your other
microphones sound better, too.

My first recommendations would be the original Great River preamp, the
John Hardy preamps, and maybe a (used) Peavey VMP-2. All of these do
a good job with ribbon mikes.

The parts costs for the transformers in these things probably is higher
than the retail price on that Mackie. They are expensive, but you're
getting an awful lot for your money with them.

When you hear an SM-57 through a transformer-input preamp, you'll be amazed.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
September 6, 2005 10:14:09 PM

Archived from groups: rec.audio.pro (More info?)

bohemian <alias@snowcrest.net> wrote:
> Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
> and wonder if its worth messing with... It is, I am sure well known
> to many in this group.. Seems to work to a non-critical test, but I
> wonder if years of storage in a hot attic and who-knows-what-other
> insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
> the mic can be wired to be 30, 150, or 250, and I wonder what this
> degree of mismatch does to gain and noise (it did sound a bit hissy).

"If it ain't broke, don't fix it". Your mic may be perfectly fine.
As Scott said, you probably want to set it to 250 ohms. This is
very simple to do. On a BK5 it is a matter of opening the back
part and moving a wire over. I imagine that a 77 is the same. Email
Doug Walker and he may reply with the instructions. But maybe yours
is already set to 250.

And test it out. Don't hit it with anything too loud like a bass guitar
or kick drum. Don't blow into it, because you can also wreck the ribbon
that way. I have heard that the phantom power risk is actually quite
rare and only happens if the mic is actually wired incorrectly, and
normally ribbon mics are safe with phantom.

Try it on your voice. Does it sound nice? Lots of top end and bottom
end with no weird artifacts? Then it it may actually be fine.

Yes, it will get better with a nice mic preamp, but it will still be very
useful with the built-in ones in your console.

Congratulations with your find!

Rob R.
Anonymous
September 6, 2005 10:33:04 PM

Archived from groups: rec.audio.pro (More info?)

On Tue, 6 Sep 2005 01:09:01 -0400, bohemian wrote
(in article <os2qh1ljhjjpehb7namhq8rhiehevoitlb@4ax.com>):

> Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
> and wonder if its worth messing with... It is, I am sure well known
> to many in this group.. Seems to work to a non-critical test, but I
> wonder if years of storage in a hot attic and who-knows-what-other
> insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
> the mic can be wired to be 30, 150, or 250, and I wonder what this
> degree of mismatch does to gain and noise (it did sound a bit hissy).
>
> Seems like a great find, I look forward to any comments and
> suggestions. Thanks in advance for the wisdom of the group! Peter

They are worth about $1200-$1500 in good shape and respond well to preamps
that have a big fat input transformer; like the Amek Neve 9098 and Jensen
Dual Servo.

Regards,

Ty Ford



-- Ty Ford's equipment reviews, audio samples, rates and other audiocentric
stuff are at www.tyford.com
Anonymous
September 6, 2005 10:58:58 PM

Archived from groups: rec.audio.pro (More info?)

"Peter" <alias@snowcrest.net> wrote in message
news:hn9rh1pimmqohijl3ir423qhh0uv5f027n@4ax.com...
> Thanks, Scott.... Assuming I send this off for a re-ribbon job for
> $120 (thanks for the names!!), I read somewhere 700 to 1,000 bucks for
> a proper pre-amp (way over budget), is there no good alternative?????

You *might* get good results with a Groove Tubes Brick (list $499). Try it
first; though; mic-to-preamp interface is a big deal on ribbons. Or look for
a used Peavey VMP2.

Peace,
Paul

> On 6 Sep 2005 08:50:34 -0400, kludge@panix.com (Scott Dorsey) wrote:
>
> >bohemian <same> wrote:
> >>Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
> >>and wonder if its worth messing with... It is, I am sure well known
> >>to many in this group.. Seems to work to a non-critical test, but I
> >>wonder if years of storage in a hot attic and who-knows-what-other
> >>insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
> >>the mic can be wired to be 30, 150, or 250, and I wonder what this
> >>degree of mismatch does to gain and noise (it did sound a bit hissy).
> >
> >The hot attic won't hurt it, but if it was stored in the wrong position
> >(ie. not upright), the ribbon can sag. If this is the case, you'll find
> >the low end is very flabby and out of control. Ribbon replacement is
> >under $100 and can be done by Steven Sank or Clarence Kane.
> >
> >Strap the microphone for 250 ohms and use a preamp that can deal with
> >it. As you have noticed, the mike will be very noisy with the Mackie
> >and the top end might not be right, either. The 77D wants to see a
> >transformer input if at all possible.
> >
> >>Seems like a great find, I look forward to any comments and
> >>suggestions. Thanks in advance for the wisdom of the group! Peter
> >
> >It's a fun mike, and one of the old standbys that every studio used to
> >have around. Use it in figure-8 mode if you can... the pattern control
> >gadget isn't really all that good.
> >--scott
>
Anonymous
September 6, 2005 11:02:39 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:

> Peter wrote:
> >Thanks, Scott.... Assuming I send this off for a re-ribbon job for
> >$120 (thanks for the names!!), I read somewhere 700 to 1,000 bucks for
> >a proper pre-amp (way over budget), is there no good alternative?????

> Not really, but you'll find that a good preamp makes all your other
> microphones sound better, too.

> My first recommendations would be the original Great River preamp, the
> John Hardy preamps, and maybe a (used) Peavey VMP-2. All of these do
> a good job with ribbon mikes.

GR NV series doesn't hurt 'em, either.

> The parts costs for the transformers in these things probably is higher
> than the retail price on that Mackie. They are expensive, but you're
> getting an awful lot for your money with them.

> When you hear an SM-57 through a transformer-input preamp, you'll be amazed.

While the RNP doesn't have an xfrmr input it seems to me to match mics
wanting to see that better than any other "affordable" no-xfrmr input
pre does. It still doesn't have all the gain one might want for a ribbon
mic, but there are downstream ways to deal with that if one has no other
options.

--
ha
Anonymous
September 7, 2005 12:45:13 AM

Archived from groups: rec.audio.pro (More info?)

Wire it for 150, listen to see if the ribbon is intact, do not, I
repeat, do not subject it to phantom power, and then hopefully, enjoy.
Anonymous
September 7, 2005 1:10:32 PM

Archived from groups: rec.audio.pro (More info?)

danger wrote:
> On Tue, 06 Sep 2005 05:09:01 GMT, bohemian <alias@snowcrest.net>

> 1. Dont worry about phanthom power it is transformer coupled.

Yes, worry. The center tap of the transformer might be grounded (and
connected to Pin 1). When connected to phantom power, it will put a
large voltage spike across the primary, which will appear at the
secondayr, and drive the ribbon into obilvion.

Given that this is an old mic of unknown history, it should be checked
first before it's "powered."
Anonymous
September 7, 2005 1:21:02 PM

Archived from groups: rec.audio.pro (More info?)

<genericaudioperson@hotmail.com> wrote in message ...
>
>
> phantom power on a mic channel will "recognize" a mic once it's plugged
> into the channel and then start supplying 48 volts to it (kind of like
> when a computer recognizes that a printer has been plugged into a usb
> port).

Or not... This has got to go into some sort of a hall of fame for one of
the furthest comments from the truth (and it isn't even political).

> the problem is that ribbon mics were never designed for phantom
> power, and can easily be destroyed by it. it's not like overclocking a
> computer where it's cool until it overloads and shuts down...it's just
> plain bad for a ribbon mic.

Ribbons don't need phantom because there is no active circuitry in them.
Period. Applying phatom to a mic can blow the ribbon. Now, with some
ribbons, you may be lucky and not blow the mic- but if you send phantom down
one pin and not the other (have a short or rock the connector as you are
plugging it in), you will blow the mic. Other ribbons (like RCAs) will be
blown in any case...


--Ben

--
Benjamin Maas
Fifth Circle Audio
Los Angeles, CA
http://www.fifthcircle.com

please remove "nospam" upon reply
September 7, 2005 3:42:28 PM

Archived from groups: rec.audio.pro (More info?)

On Tue, 06 Sep 2005 05:09:01 GMT, bohemian <alias@snowcrest.net>
wrote:

>Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
>and wonder if its worth messing with... It is, I am sure well known
>to many in this group.. Seems to work to a non-critical test, but I
>wonder if years of storage in a hot attic and who-knows-what-other
>insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
>the mic can be wired to be 30, 150, or 250, and I wonder what this
>degree of mismatch does to gain and noise (it did sound a bit hissy).
>
>Seems like a great find, I look forward to any comments and
>suggestions. Thanks in advance for the wisdom of the group! Peter

1. Dont worry about phanthom power it is transformer coupled.
2. Set the Impedance to 150 Ohms
3. It will sound a little dark that is normal.
4 Dont take it apart aside from the bottom cover. (where the
transformer cover is.)
If is it sounds a bit dark thats ok. Most 77's are in one of 2 classes
working and not.


enjoy.
Anonymous
September 7, 2005 6:20:49 PM

Archived from groups: rec.audio.pro (More info?)

danger wrote:

> Sorry I have about 15from 44a and 77a up and have never blown one

I've never won the lottery either. I guess we both have the same kind
of luck.

> please explain to me how the dc is going to fly over the transformer
> windings.

DC doen't couple through the transformer. It doesn't have to. A large
spike will do sufficient damage. When you plug in an XLR connector, pin
2 and pin 3 won't make contact at exactly the same time except by luck.
There's likely to be a couple of milliseconds between when the first
one makes contact and when the second one does. If the transformer
center tap is connected to pin 1, plugging in the mic with phantom
power turned on will apply the full phantom voltage across half the
winding until the other signal connects. A 48 volt spike will go
through the transformer quite nicely.
Anonymous
September 7, 2005 11:15:43 PM

Archived from groups: rec.audio.pro (More info?)

On 9/7/05 11:42 AM, in article 6g1uh1hdbf795nd1abp4uvqb0ueg6hpia5@4ax.com,
"danger" <fishfood@bway.net> wrote:

>
> 1. Dont worry about phanthom power it is transformer coupled.

FOOL! INFIDEL! ANTHRACITE!
Sure way to instantly kill a great mic.

PETER!-
RIGH NOW - put the 77 back in it;s' bag and case
and put it safely on a shelf or in a drawer (close the drawer SLOWLY... Not
kidding)
and Before you listen to folks who do NOT know what the speaketh of,
(or ANYBODY on some damned newgroup... Even ME!)
go find the facts,
In THIS case.. Get THIS pdf file-

http://www.wesdooley.com/pdf/4038C.pdf

read, capture, print and MEMORISE the instructions on PAGE-1 then go and do
the same for what's at the bottom of PAGE-8

When you have this stuff MEMORISED, go back and pick up the 77... NOT UNTIL.

You have something that (most likely) is in good shape and ORIGINAL and
should be dealt with VERY carefully.


> 2. Set the Impedance to 150 Ohms
> 3. It will sound a little dark that is normal.
> 4 Dont take it apart aside from the bottom cover. (where the
> transformer cover is.)
> If is it sounds a bit dark thats ok. Most 77's are in one of 2 classes
> working and not.


This stuiff is pretty on the mark. #1 up there , the NONSENSe about
"phantom power can;t hurt" is just DEAD DANGEROUSLY WRONG.

You Can Kill This Mic Easily With Phantom Power.
End of discussion.

NOW go do your homework and THEN enjoy!




>
September 7, 2005 11:15:44 PM

Archived from groups: rec.audio.pro (More info?)

On Wed, 07 Sep 2005 19:15:43 GMT, SSJVCmag <ten@nozirev.gamnocssj.com>
wrote:

>On 9/7/05 11:42 AM, in article 6g1uh1hdbf795nd1abp4uvqb0ueg6hpia5@4ax.com,
>"danger" <fishfood@bway.net> wrote:
>
>>
>> 1. Dont worry about phanthom power it is transformer coupled.
>

Sorry I have about 15from 44a and 77a up and have never blown one
please explain to me how the dc is going to fly over the transformer
windings.
Anonymous
September 7, 2005 11:32:06 PM

Archived from groups: rec.audio.pro (More info?)

On 9/7/05 3:15 PM, in article BF44B49C.10D53%ten@nozirev.gamnocssj.com,
"SSJVCmag" <ten@nozirev.gamnocssj.com> wrote:
> Get THIS pdf file-
>
> http://www.wesdooley.com/pdf/4038C.pdf
>
> read, capture, print and MEMORISE the instructions on PAGE-1 then go and do
> the same for what's at the bottom of PAGE-8
>
> When you have this stuff MEMORISED, go back and pick up the 77... NOT UNTIL.
>
> You have something that (most likely) is in good shape and ORIGINAL and
> should be dealt with VERY carefully.

> NOW go do your homework and THEN enjoy!

I'll add some Lessons Learned The Hard Way.

This mic is HEAVY.
DO NOT put it on a regular K&M boom stand arm. Even with an ADDED
counterweight the clutch isn;t up to it. Using the more ubiquitous cheap-ass
COPIES of the K&M stands is worse (though considering what K&M dunderheads
did to the clutch pads I can;t imagine how much worse).

Use a STRAIGHT STAND, unless you have one of the K&M 200 series WIDE TALL
tripod stands or the ATLAS rolling monster stand.

IF this thing falls over and hits the floor, it no longer is what you might
call 'pristine'. And you will hate yourself every time you look at it, or
try to use it.


The next suggestion wants Comments From The Peanut Gallery:
Should (as I think) Peter have someone qualified (pay them yes if they
demand) check the cable plugs (both ends) and the internal wiring BEFORE
firing this thing up? Having seen, reverssed and (mea culpa) DONE some
Less-Than-Wise mods in the course of working with pro gear, someone may have
messed things up in there... Or not...
Anonymous
September 8, 2005 12:36:35 AM

Archived from groups: rec.audio.pro (More info?)

Benjamin Maas wrote:

> if you send phantom down
> one pin and not the other (have a short or rock the connector as you are
> plugging it in), you will blow the mic.

There is no reason to connect any of the circuitry in a ribbon mic to
ground, so no current should flow anywhere as a result of phantom power.

Maybe a tiny spike charging up the capacitance of the cable if pins 2
and 3 don't make contact at the same time, current limited to a maximum
of 8 mA with a time constant of 10 microseconds. Does that really do any
damage?

Are ribbon mics really that badly designed?

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
September 8, 2005 12:36:36 AM

Archived from groups: rec.audio.pro (More info?)

anahata <anahata@treewind.co.uk> wrote:
>Benjamin Maas wrote:
>
>> if you send phantom down
>> one pin and not the other (have a short or rock the connector as you are
>> plugging it in), you will blow the mic.
>
>There is no reason to connect any of the circuitry in a ribbon mic to
>ground, so no current should flow anywhere as a result of phantom power.
>
>Maybe a tiny spike charging up the capacitance of the cable if pins 2
>and 3 don't make contact at the same time, current limited to a maximum
>of 8 mA with a time constant of 10 microseconds. Does that really do any
>damage?
>
>Are ribbon mics really that badly designed?

SOME of the RCA ribbon mikes had the center tap on the transformer
secondary grounded, for various noise reduction reasons that no longer
apply today. On a microphone with this configuration, Mr. Maas' statements
are quite accurate.

I know the 77DX wasn't shipped that way, but I don't know if the earlier
77D ever was. I know sometimes you see a 74B with the grounded tap, but
that most of them don't have it.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
September 8, 2005 4:52:31 AM

Archived from groups: rec.audio.pro (More info?)

On 9/7/05 5:14 PM, in article b0muh1lo6ag11q6t5djoniai3iqfmo2uq9@4ax.com,
"danger" <fishfood@bway.net> wrote:

> On Wed, 07 Sep 2005 19:15:43 GMT, SSJVCmag <ten@nozirev.gamnocssj.com>
> wrote:
>
>> On 9/7/05 11:42 AM, in article 6g1uh1hdbf795nd1abp4uvqb0ueg6hpia5@4ax.com,
>> "danger" <fishfood@bway.net> wrote:
>>
>>>
>>> 1. Dont worry about phanthom power it is transformer coupled.
>>
>
> Sorry I have about 15from 44a and 77a up and have never blown one
> please explain to me how the dc is going to fly over the transformer
> windings.

It's been mentioned briefly already, and if that didn;t perk your ears up
and make you nod in new understanding, you're more concerned about defending
yourself than getting smarter. It's like arguing with somebody about driving
with your eyes closed being perfectly safe "what could go wrong? I know
where the road goes and the other drivers will stay in their lanes"
Get a clue.

Please read the mentioned references. They're from a guy who's worked with
more ribbon mics than you'll ever see in your life for a longer time than
you've even known what they are. You can assume he's got more than a couple
of clues going, or you can continue to be ignorant and proud of it.
Your choice.
My choice is not to let you near any of mine.
Sheeshe...
Anonymous
September 8, 2005 5:29:57 AM

Archived from groups: rec.audio.pro (More info?)

On Wed, 07 Sep 2005 17:14:59 -0400, danger wrote:

> Sorry I have about 15from 44a and 77a up and have never blown one please
> explain to me how the dc is going to fly over the transformer windings.

Short answer: It takes a few milliseconds to rise from 0V
to +48V. The tranny won't recognize it as DC until it gets to +48 and
STAYS THERE. Meanwhile, your potentially very cool microphone has become
a paperweight.
Anonymous
September 8, 2005 5:40:33 AM

Archived from groups: rec.audio.pro (More info?)

On Wed, 07 Sep 2005 20:36:35 +0100, anahata wrote:

> Are ribbon mics really that badly designed?

The heyday of ribbons was a bit before my time, so I can't speak to design
issues. But the story I've always heard was that ribbons & dynamics were
popular early in the US, while condensers were the big thing in Europe. If
that's true, the early ribbon mic designers wouldn't have any real reason
to their mics to see DC voltage on pins 2&3.

Of course, SOME people don't think GWB had any real reason to expect the
head of FEMA would ever need any more relevant background than judging
horse shows. Go figure.
Anonymous
September 8, 2005 6:04:17 AM

Archived from groups: rec.audio.pro (More info?)

Agent 86 <maxwellsmart@control.gov> wrote:
> On Wed, 07 Sep 2005 17:14:59 -0400, danger wrote:

>> Sorry I have about 15from 44a and 77a up and have never blown one please
>> explain to me how the dc is going to fly over the transformer windings.

> Short answer: It takes a few milliseconds to rise from 0V
> to +48V. The tranny won't recognize it as DC until it gets to +48 and
> STAYS THERE. Meanwhile, your potentially very cool microphone has become
> a paperweight.

I am going to get into touch with Doug Walker and see what he has to
say about this issue.

In the meantime, it's the ribbon that gets cooked, right, not the
transformer? So in the end we are talking about a $100 mistake.
Not quite paperweight. Except mics like B&Os where the ribbons don't
exist anymore. (Actually I accidently phantom powered my B&O once
and nothing happened. But the mic was already connected so it
only would have been a factor if the output transformer was centre-
tapped.

Rob R.
Anonymous
September 8, 2005 6:04:18 AM

Archived from groups: rec.audio.pro (More info?)

Rob Reedijk <reedijk@hera.med.utoronto.ca> wrote:
>Agent 86 <maxwellsmart@control.gov> wrote:
>> On Wed, 07 Sep 2005 17:14:59 -0400, danger wrote:
>
>>> Sorry I have about 15from 44a and 77a up and have never blown one please
>>> explain to me how the dc is going to fly over the transformer windings.
>
>> Short answer: It takes a few milliseconds to rise from 0V
>> to +48V. The tranny won't recognize it as DC until it gets to +48 and
>> STAYS THERE. Meanwhile, your potentially very cool microphone has become
>> a paperweight.
>
>I am going to get into touch with Doug Walker and see what he has to
>say about this issue.

He'll tell you to lift the center tap on those few RCA mikes that have
them, and stop worrying so much.

>In the meantime, it's the ribbon that gets cooked, right, not the
>transformer? So in the end we are talking about a $100 mistake.
>Not quite paperweight. Except mics like B&Os where the ribbons don't
>exist anymore. (Actually I accidently phantom powered my B&O once
>and nothing happened. But the mic was already connected so it
>only would have been a factor if the output transformer was centre-
>tapped.

Right, but a $100 mistake is still a lot of money for something silly
that could easily have been avoided. Especially if you're also out
of use of your favorite mike for a couple weeks while it's being fixed.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
September 8, 2005 6:39:21 AM

Archived from groups: rec.audio.pro (More info?)

On 9/7/05 9:40 PM, in article pan.2005.09.08.01.40.31.153832@control.gov,
"Agent 86" <maxwellsmart@control.gov> wrote:

> On Wed, 07 Sep 2005 20:36:35 +0100, anahata wrote:
>
>> Are ribbon mics really that badly designed?
>
> The heyday of ribbons was a bit before my time, so I can't speak to design
> issues. But the story I've always heard was that ribbons & dynamics were
> popular early in the US, while condensers were the big thing in Europe.

Somebody needs to tell Lee Hirschberg
Somebody needs to tell Lew Layton.

Come on... Nobody on either side of the pond ignored EITHER type of mic.
Sure, MANUFACTURERS in the US pretty much let the Germans hgve their lead on
making marvelous capacitor mics, while SHURE and Western Electric (Altec)
kept advancing the ribbon and dynamics (and England's COLES) well into the
late 60's. But that has NOTHING to do with who bought what mics for their
studios... 67's and 87's, 84's and 56's were all over the US big studios
right along side the 44's, 639's and 77's.

> If
> that's true, the early ribbon mic designers wouldn't have any real reason
> to their mics to see DC voltage on pins 2&3.

That's correct but NOT because of the reason you stated above.

SET THE WAYBACK MACHINE FOR 1965::::
Capacitor mics were built around TUBES, each with its own dedicated external
power supply... Thus what connected to the recording preamp was out of a
transformer and simply an audio signal.
It wasn;t till transistor mics, mics that didin;t need filament and hi
voltages, came a cropper in the late 60's that you could think about
powering a mic with a simple single DC voltage and -then- the idea of
simplex (phantom) power was brought in. Ribbons had for decades never been
anywhere near a not-yet-existant preamp supplying phantom power... Wasn;t
any reason to have it.. Didin;t exist... Not an issue...
Once Phantom power started in, it was still in a situation where consoles
were custom-built wonders that cost like a small apartment building and
each channel was a complete set of circuits on its own including (if you
ordered the option installed) phantom power... And you turned it ON --only--
when you plugged in one of the newfangled nifty solid-state mics with that
mysterious Phontom Power thing. How Modern! After a string of ribbons
popped, the maintainance guys started yelling and making big new rules about
the PHANTOM POWER switches and console operations and folks started paying
attention. Or they got fired.

You don;t know this stuff,
you;re just a little ignorant and need to study up...
No big

Somebody (specially somebody with serious creds) TELLS you about this and
you ARGUE with them...
You;re on your own and deserve what you get.
The mic you kill better'd be YOURS.

You try and DEFEND this nonsense in front of some poor schlub trying REAL
hard to ask, listen and do The Right Thing by a great antique find,
Then you need to have your fingernails pounded by a dead cageless 639 motor
assembly till you apologise and start over without the bonehead streak.



> Of course, SOME people don't think GWB had any real reason to expect the
> head of FEMA would ever need any more relevant background than judging
> horse shows. Go figure.

I ain;t lettin' Shrub anywhere near my ribbons either...
Anonymous
September 8, 2005 7:56:18 AM

Archived from groups: rec.audio.pro (More info?)

Rob Reedijk wrote:

> I am going to get into touch with Doug Walker and see what he has to
> say about this issue.

You don't believe me, or John, or Wes? Trust who you choose, but be
careful.

> In the meantime, it's the ribbon that gets cooked, right, not the
> transformer? So in the end we are talking about a $100 mistake.

Is that the current price for re-ribboning a mic? Got a quote? But why
make even a $100 mistake when it's so easy to avoid?

> (Actually I accidently phantom powered my B&O once
> and nothing happened. But the mic was already connected so it
> only would have been a factor if the output transformer was centre-
> tapped.

This is why the more thoughtful replies suggested checking the wiring
before connecting the mic to a phantom powered input. Make no mistake -
many of these mics have been connected to phantom powered inputs in the
day when they were common in studios. Many consoles of that time had
phantom power, but no switch. But it was also pretty common (since
studios had a limited number of microphones) to leave them plugged in
all the time. And of course once the issue of the grounded center tap
was recognized, the information got around pretty quickly (they had
good magazines then, not the Internet - less to wade through) and the
center tap connection was removed, making the mics safe.

However, a mic owned privately by an uncle may not have been so
modified, if it was of the age when grounding the transformer center
tap was standard.
Anonymous
September 8, 2005 8:08:22 AM

Archived from groups: rec.audio.pro (More info?)

Peter wrote:

> I simply LOVE the threads that arise from what I presume to be
> relatively simple questions! So THANKS ALL for the comments...

That's because the REALLY simple questions usually have boring answers.
But many people don't realize how involved the answers to their
"simple" questions really are.

> I have NOT fried the mic with 48 VDC.. It had a 1/4 inch plug on it

OOOOOH! OOOOOOH! OOOOOH!

If it has a 1/4" plug on the end of the cables, and it came from your
uncle's attic (are we still on that track, or is this a different
person and a different mic?), he probably plugged it into the mic jack
his Webcor tape recorder that was designed to work with the high output
crystal mic that came with it. He said "This old thing doesn't work
very well - the recordings are so quiet." and put it back in the attic.


Check the wiring very carefully. Chances are it's a TS plug and phantom
power applied between the tip and sleeve will go directly across the
transformer. I'm pretty sure I've seen diagrams of the RCA mics on a
few websites. Look one up. If you're unsure about checking wiring (and
don't put an ohm meter across the transformer either), send it off to
one of the RCA specialists. It's worth putting into good shape even if
you decide you don't need it and choose to sell it. But there's no
point in breaking it if it's not already broken.

> ... my one big remaining question will
> be... since it *might* be in good shape, having never heard one, and
> not having a specifically designed pre-amp, how will I know if it
> needs to be re-ribboned??

Well, sending it to somoneone who does know is the simplest solution.
These guys love the mics and aren't going to rip you off. If all it
needs is a cleaning, rewiring, and checkout, they won't tell you that
it needs a new ribbon. Usually you can tell just by inspection. If the
ribbon is sagging or visibly torn, then it needs to be replaced.
Generally, if it looks good, it is good, and those who work on these
mics don't "hot rod" them like some people do with condenser mics.
September 8, 2005 8:35:41 AM

Archived from groups: rec.audio.pro (More info?)

I simply LOVE the threads that arise from what I presume to be
relatively simple questions! So THANKS ALL for the comments...

I have NOT fried the mic with 48 VDC.. It had a 1/4 inch plug on it
and I am going to replace with XLR and open the bottom to see that it
is wired at 250, check grounding, etc. after reading all the great
stuff I have been pointed to... my one big remaining question will
be... since it *might* be in good shape, having never heard one, and
not having a specifically designed pre-amp, how will I know if it
needs to be re-ribboned?? Assume it does and send it to Phoenix or LA
anyway?? I listened to a 36 string folk harp from about 3 feet away
through headphones, and other than the hiss, it sounded really good...
<cowering in the corner in anticipation!> :)  Thanks again to
all...Peter

On Tue, 06 Sep 2005 05:09:01 GMT, bohemian <alias@snowcrest.net>
wrote:

>Hi all.... just found in my dad's old junk an RCA Ribbon Mic type 77D
>and wonder if its worth messing with... It is, I am sure well known
>to many in this group.. Seems to work to a non-critical test, but I
>wonder if years of storage in a hot attic and who-knows-what-other
>insults. My Mackie Onyx mic preamps list input impedance at 2.4K and
>the mic can be wired to be 30, 150, or 250, and I wonder what this
>degree of mismatch does to gain and noise (it did sound a bit hissy).
>
>Seems like a great find, I look forward to any comments and
>suggestions. Thanks in advance for the wisdom of the group! Peter
Anonymous
September 8, 2005 12:47:54 PM

Archived from groups: rec.audio.pro (More info?)

SSJVCmag wrote:
> On 9/8/05 7:08 AM, in article
> 1126177702.236622.201710@g44g2000cwa.googlegroups.com, "Mike Rivers"
> <mrivers@d-and-d.com> wrote:
>
> > ... If you're unsure about checking wiring (and
> > don't put an ohm meter across the transformer either),
>
> And a word about WHY NOT TO... (for those who might not know)
> An ohmeter checks resistance by running a battery across the thing being
> tested... That'll send voltage INTO the transformer and the spipke is just
> like what we're trying to AVOID with phantom or ANY sort of applied voltage
> that would move and snap the ribbon!

Actually, worse.

If you're lucky (and you don't have a mic with a grounded center tap on
the mic output side its transformer), connecting the mic to a phantom
power source applies the same voltage to both signal pins
simultaneously, resulting in no current flow through the transformer.
An ohm meter, on the other hand, applies a potential difference between
the pins, assuring that some current will flow.
Anonymous
September 8, 2005 2:36:09 PM

Archived from groups: rec.audio.pro (More info?)

in article 8efvh1l8m6h4gr26ubjjm4vclbbj8e5db6@4ax.com, Peter at
alias@snowcrest.net wrote on 9/8/05 12:35 AM:

> it sounded really good...

There's your answer. Invest in a mic preamp capable of clean high gain.
Anonymous
September 8, 2005 5:16:23 PM

Archived from groups: rec.audio.pro (More info?)

On 9/8/05 12:35 AM, in article 8efvh1l8m6h4gr26ubjjm4vclbbj8e5db6@4ax.com,
"Peter" <alias@snowcrest.net> wrote:

> I simply LOVE the threads that arise from what I presume to be
> relatively simple questions! So THANKS ALL for the comments...
>
> I have NOT fried the mic with 48 VDC.. It had a 1/4 inch plug on it
> and I am going to replace with XLR and open the bottom to see that it
> is wired at 250, check grounding, etc.

BE REALLY CAREFUL!!!
If you don;t have brass tools, you;re about to find out why one would WANT
them... The magnet in there is going to really try and grab anything with
iron in it that you bring close.. Be Careful.

>...after reading all the great
> stuff I have been pointed to...

A gentleman and a scholar! (so few of us left... Sigh)

> ...my one big remaining question will
> be... since it *might* be in good shape, having never heard one, and
> not having a specifically designed pre-amp, how will I know if it
> needs to be re-ribboned??

It WILL need a LOT of gain...
It should sound clean and significantly WARM, shall we say over any other
modern mic you'd have to compare it with. There's a PATTERN control that ios
actually mechanical..it moves a metal shutter that closes off (in various
ways) the back side of the ribbon with associated changes in tone character,
the only setting I've ever been able to tolewrate on these is the fully-open
bidirectional setting... Use it there.. You'll know because the mic should
sound pretty much identical when you talk into the front or the back (DO NOT
TRY THIS WITH HEADPHONES>>> IT --WILL NOT-- sound the same front-and-back!
that's a HEADPHONE issue and we can go into that later if you want)

> Assume it does and send it to Phoenix or LA
> anyway?? I listened to a 36 string folk harp from about 3 feet away
> through headphones, and other than the hiss, it sounded really good...

BINGO!!! great test,,, when you get CLOSE to this thing, like 6" and less,
it gets really bass-heavy (in a nice sorta way). Farther back like you did
is a good overall test of character.

> <cowering in the corner in anticipation!> :)  Thanks again to
> all...Peter

Cower Not! Listen, read, learn!
Anonymous
September 8, 2005 5:19:58 PM

Archived from groups: rec.audio.pro (More info?)

On 9/8/05 7:08 AM, in article
1126177702.236622.201710@g44g2000cwa.googlegroups.com, "Mike Rivers"
<mrivers@d-and-d.com> wrote:

> ... If you're unsure about checking wiring (and
> don't put an ohm meter across the transformer either),

And a word about WHY NOT TO... (for those who might not know)
An ohmeter checks resistance by running a battery across the thing being
tested... That'll send voltage INTO the transformer and the spipke is just
like what we're trying to AVOID with phantom or ANY sort of applied voltage
that would move and snap the ribbon!
Anonymous
September 8, 2005 5:24:35 PM

Archived from groups: rec.audio.pro (More info?)

Found this ASTOUNDINGLY marvelous site... Best 77 site I've seen...
Downloadable manual pages and some GORGROUS photos of the mic and folks who
used it...

http://www.coutant.org/3.html
Anonymous
September 8, 2005 5:35:55 PM

Archived from groups: rec.audio.pro (More info?)

On Thu, 08 Sep 2005 02:39:21 +0000, SSJVCmag wrote:

> On 9/7/05 9:40 PM, in article pan.2005.09.08.01.40.31.153832@control.gov,
> "Agent 86" <maxwellsmart@control.gov> wrote:
>
>> The heyday of ribbons was a bit before my time, so I can't speak to
>> design issues. But the story I've always heard was that ribbons &
>> dynamics were popular early in the US, while condensers were the big
>> thing in Europe.
>
> Somebody needs to tell Lee Hirschberg Somebody needs to tell Lew Layton.

Thanks, I stand corrected.

--<snip>--

>> If
>> that's true, the early ribbon mic designers wouldn't have any real
>> reason to their mics to see DC voltage on pins 2&3.

This SHOULD have read "...any real reason to EXPECT their mics to se DC
voltage...". Thinking faster than I can type again.

> That's correct but NOT because of the reason you stated above.
>
--<history lesson snipped>--

> You don;t know this stuff,
> you;re just a little ignorant and need to study up... No big
>
> Somebody (specially somebody with serious creds) TELLS you about this
> and you ARGUE with them...
> You;re on your own and deserve what you get. The mic you kill better'd
> be YOURS.
>
> You try and DEFEND this nonsense in front of some poor schlub trying
> REAL hard to ask, listen and do The Right Thing by a great antique find,
> Then you need to have your fingernails pounded by a dead cageless 639
> motor assembly till you apologise and start over without the bonehead
> streak.

Where'd the hostility come from? I'm not arguing with anybody or trying to
defend anything. Are you sure you're replying to the right message?
Anonymous
September 8, 2005 8:55:55 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey <kludge@panix.com> wrote:
> Rob Reedijk <reedijk@hera.med.utoronto.ca> wrote:
>>Agent 86 <maxwellsmart@control.gov> wrote:
>>> On Wed, 07 Sep 2005 17:14:59 -0400, danger wrote:
>>
>>>> Sorry I have about 15from 44a and 77a up and have never blown one please
>>>> explain to me how the dc is going to fly over the transformer windings.
>>
>>> Short answer: It takes a few milliseconds to rise from 0V
>>> to +48V. The tranny won't recognize it as DC until it gets to +48 and
>>> STAYS THERE. Meanwhile, your potentially very cool microphone has become
>>> a paperweight.
>>
>>I am going to get into touch with Doug Walker and see what he has to
>>say about this issue.

> He'll tell you to lift the center tap on those few RCA mikes that have
> them, and stop worrying so much.

Hey! I AM NOT the one who was worrying. I was one who was saying
it likely wasn't a problem!

>>In the meantime, it's the ribbon that gets cooked, right, not the
>>transformer? So in the end we are talking about a $100 mistake.
>>Not quite paperweight. Except mics like B&Os where the ribbons don't
>>exist anymore. (Actually I accidently phantom powered my B&O once
>>and nothing happened. But the mic was already connected so it
>>only would have been a factor if the output transformer was centre-
>>tapped.

> Right, but a $100 mistake is still a lot of money for something silly
> that could easily have been avoided. Especially if you're also out
> of use of your favorite mike for a couple weeks while it's being fixed.
> --scott

True. But I was just pointing out that this is not catastrophic.
It is a survivable error. In fact, I was saying, "stop worrying
so much!"

Rob R.
Anonymous
September 8, 2005 9:03:30 PM

Archived from groups: rec.audio.pro (More info?)

Mike Rivers <mrivers@d-and-d.com> wrote:

> Rob Reedijk wrote:

>> I am going to get into touch with Doug Walker and see what he has to
>> say about this issue.

> You don't believe me, or John, or Wes? Trust who you choose, but be
> careful.

I believe lots of people including you for many things.

When it comes to microphones, I think Doug is at the top of the
list of experts. He is one of three guys (Wes is also) when it
comes to this in North America. The only problem is that now
that Stephen Paul is no longer with us, there is so much demand for
Doug's time in building and rebuilding condensor capsules that he
does not have as much time for ribbons.

Anyway, Doug has already sent me a response and I just am waiting for
one clarification and his permission to post it.

Rob R.
September 8, 2005 10:11:25 PM

Archived from groups: rec.audio.pro (More info?)

Been back to lurking mode for a while....& read thru a bunch of
responses on this thread. I'll throw in my 2 pennies of experience on
the RCA 77dx - I own and use 2 of them occasionally.

- I blew the ribbon on one when I thought phantom was off (it wasn't)
and plugged the cable on the mic end - turning the XLR until it clicked
in! My bad. These days I plug in the mic cable first - then go to the
mic pre to be sure the phantom switch is off before powering on the
pre. It's a habit kinda thing that works for me.

- If ribbons cost $100, replacing one might be a bit more. Clarence
Kane charged over $300 cuz his expertise is worth something. Then
there's the FEAR of shipping.

- I've used my 77's on Great River MP2-MH as well as GR NV. Both work
great. For the sources I usually mic, I can't get enuf gain out of my
Peavey VMP-2 to satisfy. But the OP (or others) might be interested in
trying their 77's on a Studio Projects VTB-1 mic preamp (cheap) but a
*suprisingly* good match for the 77 series. Personally, I keep the
"Tube Blend" very low or off. Learned about this one from The Pope.

===================
Note the new e-address:
Rich-at-
StolenMomentsAudio-dot-com
===================

Best...
Rich
Anonymous
September 10, 2005 9:09:07 AM

Archived from groups: rec.audio.pro (More info?)

with the value of 77's now days id put couple hundred into one any day
unless you want to sell it as-is

dnw


In article <1126228285.234310.197810@z14g2000cwz.googlegroups.com>,
rich@stolenmomentsaudio.com
> Been back to lurking mode for a while....& read thru a bunch of
> responses on this thread. I'll throw in my 2 pennies of experience on
> the RCA 77dx - I own and use 2 of them occasionally.
>
> - I blew the ribbon on one when I thought phantom was off (it wasn't)
> and plugged the cable on the mic end - turning the XLR until it clicked
> in! My bad. These days I plug in the mic cable first - then go to the
> mic pre to be sure the phantom switch is off before powering on the
> pre. It's a habit kinda thing that works for me.
>
> - If ribbons cost $100, replacing one might be a bit more. Clarence
> Kane charged over $300 cuz his expertise is worth something. Then
> there's the FEAR of shipping.
>
> - I've used my 77's on Great River MP2-MH as well as GR NV. Both work
> great. For the sources I usually mic, I can't get enuf gain out of my
> Peavey VMP-2 to satisfy. But the OP (or others) might be interested in
> trying their 77's on a Studio Projects VTB-1 mic preamp (cheap) but a
> *suprisingly* good match for the 77 series. Personally, I keep the
> "Tube Blend" very low or off. Learned about this one from The Pope.
>
> ===================
> Note the new e-address:
> Rich-at-
> StolenMomentsAudio-dot-com
> ===================
>
> Best...
> Rich
Anonymous
September 10, 2005 8:14:36 PM

Archived from groups: rec.audio.pro (More info?)

Rob Reedijk wrote:
> (Doug's initial reply)
> I note the comments below, but I
> am not clear on why there would be a voltage imbalance between pins 2 and 3,
> even momentarily. I suppose it could be argued that a capacitance exists
> between each audio lead and ground, and that if this capacitance was not
> exactly the same between each lead and ground, an imbalance could occur
> while the RC circuit is charging, but I think this would be a reach.

As long as the cable doesn't have a short between one of the signal
pins and pin 1, or the mic doesn't have a grounded center tap, it's
usually safe to turn on phantom power once the mic is connected. As
Doug suggests, if there is an imbalance between the voltage applied to
the two signal pins, it would be momentary and very small (assuming the
phantom power supply is properly designed and one of the resistors in
series with the phantom supply voltage hasn't changed value) and would
likely not damage the mic. However, there is greater risk (as I
mentioned in another message, I think) if the mic is plugged in to a
source of phantom power. If the two signal pins don't make contact at
the same time, current can flow until the second pin contacts the
socket.

> Having said this, it seems to me that the prudent thing to do when using a
> ribbon microphone is to ensure that phantom power is off.

I agree. If it's necessary to turn it on (for instance the mic is
connected to a mixer with a single phantom power switch and other mics
need power) the prudent thing is to turn it off until the ribbon mic is
plugged in, and then turn it on.


> (Rob realizes that the more he knows the less he knows)
> > I guess I should have asked this earlier. I thought a transformer blocks
> > DC. But I guess it doesn't, right? Seeing as if you can have DC across
> > the secondary, you are saying that this will induce DC across the the
> > primary. Can I just clarify this? I guess it shows how little I know...

It blocks DC, but it passes AC (obviously - otherwise the microphone
wouldn't work). In reality, you don't have DC unless it's been on since
the beginning of time and is never turned off. So when you go from 0V
to 48V, until the voltage stabilizes at 48V, you have AC, and that's
what goes through the transformer.

Incidentally, Doug's useage of "primary" and "secondary" could be a
little confusing. Conventially, the input side of a transformer is
considered the primary. So, as he uses the term "primary" it's relative
to the microphone operating as a microphone. The windings connected to
the ribbon are indeed the primary. But when explaining what happens
when the mic is connected to some voltage souce, the OTHER winding
becomes the primary. Are you properly confused yet?

So what are you going to do?
Anonymous
September 11, 2005 2:11:25 AM

Archived from groups: rec.audio.pro (More info?)

Rob Reedijk <reedijk@hera.med.utoronto.ca> wrote:
> Mike Rivers <mrivers@d-and-d.com> wrote:

>> Rob Reedijk wrote:

>>> I am going to get into touch with Doug Walker and see what he has to
>>> say about this issue.

>> You don't believe me, or John, or Wes? Trust who you choose, but be
>> careful.

> I believe lots of people including you for many things.

> When it comes to microphones, I think Doug is at the top of the
> list of experts. He is one of three guys (Wes is also) when it
> comes to this in North America. The only problem is that now
> that Stephen Paul is no longer with us, there is so much demand for
> Doug's time in building and rebuilding condensor capsules that he
> does not have as much time for ribbons.

> Anyway, Doug has already sent me a response and I just am waiting for
> one clarification and his permission to post it.

> Rob R.

Below is the email that Doug sent me when I forwarded my questions to
him concerning worries about phantom powering ribbons. He appears to
follow a better-safe-than-sorry philosophy. I have also included my
follow up questions and his responses. I hope this is helpful:



(Doug's initial reply)
A ribbon can be badly stretched or destroyed when a current flows through
the secondary of the microphone's output transformer, and is then
inductively coupled to the primary side, causing a current to flow through
the ribbon. As you know, phantom power places 48 VDC on the audio pair (pin
2 and 3) with respect to ground (pin 1) through very closely matched
resitors. When phantom power is turned on, it is true that 48 volts will
appear at each terminal of the secondary of the transformer, but there
should be no potential difference between these terminals which would cause
a current to flow through the secondary. I note the comments below, but I
am not clear on why there would be a voltage imbalance between pins 2 and 3,
even momentarily. I suppose it could be argued that a capacitance exists
between each audio lead and ground, and that if this capacitance was not
exactly the same between each lead and ground, an imbalance could occur
while the RC circuit is charging, but I think this would be a reach.

Regarding ribbon microphones and phantom power, I just reviewed the
schematics for the 44BX, 77DX, and the BK5. From this examination, there
seems to be no indication, for these particular microphones, that having
the phantom power on would cause a problem, unless there was a fault causing
a short to ground in the secondary side of the circuit. Then current could
flow through the secondary causing possible ribbon damage.

Having said this, it seems to me that the prudent thing to do when using a
ribbon microphone is to ensure that phantom power is off. Some of my
clients use dedicated pre's for their ribbon mics, and these pre's either do
not have phantom power at all, or if the pre has phantom power, it is
permanently disabled.

(Rob clarifies the connecting hot to phantom fear)
> The reason that some people are worried about a voltage imbalance between
> pin 2 and pin 3 is if phantom power is already on, but the mic has not yet
> been connected, they worry that since both pins may not connect at the
> same time as the mic cable is hooked up to the mic there may be for a
> brief moment 48v on one side before the other pin goes live.
>
> Is this long enough for it to matter? Who knows.

(Doug's response)
In the situation described above, there would still need to be a current
path through the secondary to ground, and absent a grounded secondary centre
tap or a short somewhere in the secondary circuit to ground, the only thing
that I could think of that would cause a current flow in the secondary would
be the charging of stray capacitance within the secondary circuit to ground.
Depending on the values you assume for the equivalent circuit, we could be
talking about a pulse of a few milliamps, lasting for a fraction of a
microsecond. I doubt that this would cause much, if any, ribbon movement.

A greater concern when using ribbon microphones, I believe, is the likelihood
of a damaged cable, or a shorted or improperly wired connector, causing a
A greater concern when using ribbon microphones, I believe, is the likelihood
of a damaged cable, or a shorted or improperly wired connector, causing a
constant current flow in the secondary. This is much more likely to damage
the ribbon.

As I said earlier, it is prudent when using a ribbon microphone, to ensure
that phantom power is off, and never turned on.

(Rob realizes that the more he knows the less he knows)
> One more stupid question.
>
> I guess I should have asked this earlier. I thought a transformer blocks
> DC. But I guess it doesn't, right? Seeing as if you can have DC across
> the secondary, you are saying that this will induce DC across the the
> primary. Can I just clarify this? I guess it shows how little I know...

(Doug's response)
When I said that a current would flow in the primary, I certainly didn't
intend to imply that it would be a continuous current in one direction (as
in DC), but rather a momentary current, or pulse. A change from 0 volts to
some DC value applied to the secondary of a transformer won't induce a DC
current into the primary, but it can induce a momentary current flow in the
primary, the magnitude of which will depend on the rate of change and
magnitude of the current in the secondary, a host of other properties of
the transformer such as the turns ratio, and the impedance of the 'load' on
the primary, in this case, the ribbon.

(End of Doug's responses to Rob)
!