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Impedance / level matching Desk to Mixer/Amp ??

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Anonymous
March 12, 2005 7:11:05 PM

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

Hi,

I am trying to get a mixing desk with 1 1V/600 ohm line out to connect
to a powered mixer with 35mV/68k ohms input. I already connect them
up like this, but the levels are all over the place and I have to get
the desk gains set to almost zero to avoid overdriving the powered
mixer.

How can I get this connected better ? Would it be as simple as
putting a resistor in the cable between them to reduce the levels ?
....or is it more complex than that ?

Many thanks for any replies !

Cheers,

Kev.
Anonymous
March 12, 2005 7:15:54 PM

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

....obviously that should read "a 1V / 600 ohm line out" (in case anyone
thought it was an eleven volt output ! ) :-)
Anonymous
March 12, 2005 8:02:07 PM

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

>What are the levels? Not the impedances, but the level ratings?

Sorry, but my knowledge of the subject isn't that good and I'm not sure
what you mean here.
I'm only quoting figures from the user manuals.

>Does the desk with the 600 ohm output have transformer balancing that
>requires a real 600 ohm load, or does it have a modern output stage?

Whooooosh ! <the sound of that one going right over my head !>

>The console with the 68k input.... is it really a mike level input
>that you're plugging into?

OK, I shall expand a little !..... I am in a band and we have a
powered mixer & speakers for our PA system. We have also recently
bought a mixing desk that has better EQ than the powered mixer. As we
have no separate amp yet, we are plugging the line level outputs from
the desk into the unbalanced 1/4" instrument inputs on the powered
mixer.

The desk is an Inkel MX-1410, the powered mixer is a Carlsbro GDX7. I
have manuals for both if more specs are required (but tell me what I'm
looking for first !).

Cheers,

Kev.
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Anonymous
March 12, 2005 10:30:05 PM

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

In article <1c948606.0503121611.58babf75@posting.google.com>,
<pcmangler@ntlworld.com> wrote:
>
>I am trying to get a mixing desk with 1 1V/600 ohm line out to connect
>to a powered mixer with 35mV/68k ohms input. I already connect them
>up like this, but the levels are all over the place and I have to get
>the desk gains set to almost zero to avoid overdriving the powered
>mixer.

What are the levels? Not the impedances, but the level ratings?

Does the desk with the 600 ohm output have transformer balancing that
requires a real 600 ohm load, or does it have a modern output stage?

The console with the 68k input.... is it really a mike level input
that you're plugging into?

>How can I get this connected better ? Would it be as simple as
>putting a resistor in the cable between them to reduce the levels ?
>...or is it more complex than that ?

A pad might be the solution, but since you haven't told us the operating
levels of the equipment we can't tell yet.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
March 13, 2005 3:12:42 AM

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

<pcmangler@ntlworld.com> wrote in message
news:1110675727.538500.279660@l41g2000cwc.googlegroups.com...
> >What are the levels? Not the impedances, but the level ratings?
>
> Sorry, but my knowledge of the subject isn't that good and I'm not sure
> what you mean here.
> I'm only quoting figures from the user manuals.
>
> >Does the desk with the 600 ohm output have transformer balancing that
> >requires a real 600 ohm load, or does it have a modern output stage?
>
> Whooooosh ! <the sound of that one going right over my head !>
>
> >The console with the 68k input.... is it really a mike level input
> >that you're plugging into?
>
> OK, I shall expand a little !..... I am in a band and we have a
> powered mixer & speakers for our PA system. We have also recently
> bought a mixing desk that has better EQ than the powered mixer. As we
> have no separate amp yet, we are plugging the line level outputs from
> the desk into the unbalanced 1/4" instrument inputs on the powered
> mixer.
>
> The desk is an Inkel MX-1410, the powered mixer is a Carlsbro GDX7. I
> have manuals for both if more specs are required (but tell me what I'm
> looking for first !).
>
> Cheers,
>
> Kev.
>

if you cannot adjust levels in a satisfactory manner and you really don't
want to build something, obtain a resistance mixer. one type can be seen
here http://www.dod.com/accessories/accessories.htm
Anonymous
March 13, 2005 3:19:05 AM

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

pcmangler@ntlworld.com wrote:
> I am trying to get a mixing desk with 1 1V/600 ohm line out to connect
> to a powered mixer with 35mV/68k ohms input.
>
> How can I get this connected better ? Would it be as simple as
> putting a resistor in the cable between them to reduce the levels ?
> ...or is it more complex than that ?

Two resistors if it's unbalanced: 33k in series and 1k across the desk
input.

Three if it's balanced, 15k in series with each leg and 1k across the input.

Switch the 1k for a higher value if the signal's too little, lower if
it's still too much.

Or buy a 30dB (approx) in line attenuator, but that's only a set of
resistors in a box with connectors...

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
March 13, 2005 7:05:20 AM

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

Phil Allison wrote:
> <pcmangler@ntlworld.com
> > Hi,
> >
> > I am trying to get a mixing desk with 1 1V/600 ohm line out to
connect
> > to a powered mixer with 35mV/68k ohms input. I already connect
them
> > up like this, but the levels are all over the place and I have to
get
> > the desk gains set to almost zero to avoid overdriving the powered
> > mixer.
> >
>
>
> ** Then set the channel input gains to zero - since that is
obviously
> the right setting. Seems you do not have real problem at all -
just an
> irrational aversion to seeing knobs set in positions that annoy.

What is it about Usenet and people getting wound up ? Chill out Phil !
I appreciate you offering advice but there's no need to start calling
people a 'posturing ass' for a misunderstanding. And I actually DO
have real problems, and it's not just an 'irrational aversion'.....

The problems are:-

The desk is a bit hissy and as I have to set the output so low in order
not to overdrive the powered mixer inputs, I'm just making it noisier.

I can't really utilise the meters on the desk properly, and as a novice
to mixing desks it would be helpful if I could.

The channel gain knobs (rotary) on the powered mixer have to be set
REALLY close to zero - i.e. to the point where the slightest touch can
result in no signal at all. I have so little leeway to adjust the
levels here, it's a right pain in the ass in a live situation.

Hence my desire to be able to set the Mains on the desk to zero dB and
have the channel gain knobs on the powered mixer set about halfway.
This at least will allow me to see the meters respond properly and also
get my channel gain pots more than 1mm away from the stops !

I am intrigued by Anahata's suggestion for using resistors (mainly 'cos
it's simple and very cheap ! :-) ). I can understand the 33k ohms in
series, but why the 1k ohms "across the inputs of the desk" ??? (I'm
presuming you meant across the inputs of the powered mixer, like this
..... ??

+ -------< 33k >---|------>
Output from desk : 1k Input to powered mixer
- -----------------|------>

Cheers,

Kev.
Anonymous
March 13, 2005 9:12:24 AM

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

In article <1110675727.538500.279660@l41g2000cwc.googlegroups.com> pcmangler@ntlworld.com writes:

> Sorry, but my knowledge of the subject isn't that good and I'm not sure
> what you mean here.

Well, you know, this really IS rocket science. You need to at least
know how to interpret what's in the manuals so you can explain your
problem. The 35 mV input sure doesn't sound like an input that's
designed for a line level source, which your other mixer is.

Thanks for naming names, but I haven't heard of either of them. You
can make it work by simply turning the master level of the mixer that
you're plugging into the powered mixer down. But if it has a meter,
you won't be able to depend on it. Just use your ears.



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
March 13, 2005 12:55:41 PM

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

Firstly,

Many thanks to Anahata for your advice. I'll give it a go - thanks
mate.


Now, lets get this out of the way....

Phil.... I really think you need to seek some help mate. You have an
awful lot of anger in you that is obviously coming from somewhere else.
I'm not going to engage you in a war of words, because that's just a
coward's way - hiding behind your screen and being abusive to people
from your keyboard, when in reality, you wouldn't have the courage to
say it to my face. ...Well, not if you had any sense you wouldn't.
You need professional psychiatric help, and I really am being sincere.

Moving on.....

Re Mike's suggestion to use a different input; Yes, that would work, I
do have a tape-in more suited to the levels from the desk but, I want
to use two channels on the powered mixer - one with some reverb from
the built-in processor and another one dry for my guitar (and I use my
own external effects). So, unless I dispense with my twin channel
plan, then I have to use the instrument inputs on the powered mixer -
and therefore attenuate the signals coming in.

>This may also be a situation of "connector of convenience" or someone
>who thinks that if you don't have matching connectors for the source
>and destination it won't work because "the impedance is off."

Would you care to elaborate on what makes you think such a situation
would apply to my question ? I never mentioned connectors, or
impedance !

Re: Laurence's question;
No - it's not a input trim. What I mean (and possibly using the wrong
terminology) is the master fader gain on the mixing desk.
I am connecting our instruments to the mixing desk, then the mixing
desk outputs to the instrument inputs on a powered mixer.
The line-level signals from the mixing desk are too strong for the
instrument level inputs on the powered mixer.
That's why I'm trying to attenuate the outputs from the mixing desk.

Thanks to everyone who took the time to reply.

Cheers,

Kev.

p.s. - Phil..... save your 'Mr Angry' reply for someone else,
preferably someone who can offer you counselling and / or medication.
Anonymous
March 13, 2005 12:59:51 PM

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

<pcmangler@ntlworld.com> wrote:
>>What are the levels? Not the impedances, but the level ratings?
>
>Sorry, but my knowledge of the subject isn't that good and I'm not sure
>what you mean here.
>I'm only quoting figures from the user manuals.

Okay, it sounds to me like you're going into a mike input. But that
"68 mV" isn't referenced to anything.

>>Does the desk with the 600 ohm output have transformer balancing that
>>requires a real 600 ohm load, or does it have a modern output stage?
>
>Whooooosh ! <the sound of that one going right over my head !>

Okay, what kind of console is it? Is this a Mackie that is all electronic,
or is it an old Collins broadcast console or something that actually cares
about the load?

>>The console with the 68k input.... is it really a mike level input
>>that you're plugging into?
>
>OK, I shall expand a little !..... I am in a band and we have a
>powered mixer & speakers for our PA system. We have also recently
>bought a mixing desk that has better EQ than the powered mixer. As we
>have no separate amp yet, we are plugging the line level outputs from
>the desk into the unbalanced 1/4" instrument inputs on the powered
>mixer.
>
>The desk is an Inkel MX-1410, the powered mixer is a Carlsbro GDX7. I
>have manuals for both if more specs are required (but tell me what I'm
>looking for first !).

Okay, this stuff doesn't really care about impedance. Your problem is
signal levels. You're trying to run a line output into an instrument level
input.

You need a 30 dB pad or a 40 dB pad, something in that range. I know Shure
makes XLR pads, but if you want a 1/4" phone pad you may have to look
around a bit or use some XLR-to-1/4" adaptors.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
March 13, 2005 2:00:53 PM

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

pcmangler@ntlworld.com wrote:


> The line-level signals from the mixing desk are too strong for the
> instrument level inputs on the powered mixer.
> That's why I'm trying to attenuate the outputs from the mixing desk.


One point about instrument inputs on a powered mixer: sometimes these
also contain fixed EQ to sort-of simulate the tone shaping of a guitar
amp; ie, a midrange notch. You may want to check that when you get this
all set up, if it doesn't sound quite like what you expect. If this is
a switched feature (and you are using the inst position because the mic
position makes the distortion worse), you may want to experiment with
even more attenuation and try the mic position.
Anonymous
March 13, 2005 2:58:15 PM

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

>One point about instrument inputs on a powered mixer: sometimes these
>also contain fixed EQ to sort-of simulate the tone shaping of a guitar

>amp; ie, a midrange notch. You may want to check that when you get
this
>all set up, if it doesn't sound quite like what you expect. If this
is
>a switched feature (and you are using the inst position because the
mic
>position makes the distortion worse), you may want to experiment with
>even more attenuation and try the mic position

Hmm... now you've got me thinking :-) Each channel on the powered
mixer has a balanced XLR mic socket (at 3.5mV / 6K8 ohms) as well
as an unbalanced 1/4" socket (at 35mV / 68K ohms).

I will try both, just in case. I presume that I would just need
resistors of 270K and 1K ohms to attenuate the signal down to the
3.5mV mic level, following Anahata's potential divider suggestion ?
(ten times the value of the ones for the 35mV instrument level).
Anonymous
March 13, 2005 4:40:25 PM

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

"Scott Dorsey"
> In article

>>
>>I am trying to get a mixing desk with 1 1V/600 ohm line out to connect
>>to a powered mixer with 35mV/68k ohms input. I already connect them
>>up like this, but the levels are all over the place and I have to get
>>the desk gains set to almost zero to avoid overdriving the powered
>>mixer.
>
> What are the levels? Not the impedances, but the level ratings?


** The OP says 1 volt and 35 mV - have you gone blind ??


>
> The console with the 68k input.... is it really a mike level input
> that you're plugging into?


** It's clearly an instrument level input.



> A pad might be the solution, but since you haven't told us the operating
> levels of the equipment we can't tell yet.


** He did - you posturing ass.




............ Phil
Anonymous
March 13, 2005 4:44:00 PM

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

<pcmangler@ntlworld.com
> Hi,
>
> I am trying to get a mixing desk with 1 1V/600 ohm line out to connect
> to a powered mixer with 35mV/68k ohms input. I already connect them
> up like this, but the levels are all over the place and I have to get
> the desk gains set to almost zero to avoid overdriving the powered
> mixer.
>


** Then set the channel input gains to zero - since that is obviously
the right setting. Seems you do not have real problem at all - just an
irrational aversion to seeing knobs set in positions that annoy.





............... Phil
Anonymous
March 13, 2005 4:44:01 PM

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

In article <39hnndF620cvjU1@individual.net> philallison@tpg.com.au writes:

> ** Then set the channel input gains to zero - since that is obviously
> the right setting. Seems you do not have real problem at all - just an
> irrational aversion to seeing knobs set in positions that annoy.

Well put! I don't know how many times I've read that someone doesn't
"want" to turn the knobs all the way up or all the way down.

However, as I'm sure you realize, there may be a problem with turning
the knobs all the way down. If there's enough gain ahead of the knob
so that the input signal clips, while the output won't be to loud with
the knob all the way down, it will be distorted. And guessing from the
post that the original poster doesn't have much experience, he may not
recognize the distortion.

Better to turn down the output level of what he's feeding to the
powered mixer, or find a different input to use - an effect return, a
tape playback input, something. Unless you want to call a guitar
amplifier with more than one input a "mixer" there aren't too many
powered mixers that have only instrument level inputs.

This may also be a situation of "connector of convenience" or someone
who thinks that if you don't have matching connectors for the source
and destination it won't work because "the impedance is off."


--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
March 13, 2005 4:46:57 PM

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

On 12 Mar 2005 16:11:05 -0800, pcmangler@ntlworld.com wrote:

>I am trying to get a mixing desk with 1 1V/600 ohm line out to connect
>to a powered mixer with 35mV/68k ohms input. I already connect them
>up like this, but the levels are all over the place and I have to get
>the desk gains set to almost zero to avoid overdriving the powered
>mixer.

Is this "desk gain" an input trim control? If so, perhaps fully
down is the right setting for a line input, but there's gain available
to suit a 35mV input if required. You need to have it right down.

CubaseFAQ www.laurencepayne.co.uk/CubaseFAQ.htm
"Possibly the world's least impressive web site": George Perfect
Anonymous
March 13, 2005 5:38:43 PM

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

In article <1110715520.819647.114240@f14g2000cwb.googlegroups.com> pcmangler@ntlworld.com writes:

> The desk is a bit hissy and as I have to set the output so low in order
> not to overdrive the powered mixer inputs, I'm just making it noisier.

In that case, by lowering the output (at the mix output, not by setting
all the channels low) you're probably ahead of the game.

> I can't really utilise the meters on the desk properly, and as a novice
> to mixing desks it would be helpful if I could.

Actually, the way you're using it, the meters probably wouldn't be
very useful. In fact, if you use them as a guide to when you're about
to overdrive the input of the powered mixer, that's the best use you
could put them to.

> The channel gain knobs (rotary) on the powered mixer have to be set
> REALLY close to zero - i.e. to the point where the slightest touch can
> result in no signal at all.

That's why I suggest turning down the ouptut of the non-powered mixer.

> Hence my desire to be able to set the Mains on the desk to zero dB and
> have the channel gain knobs on the powered mixer set about halfway.

For that you need an attenuator, or you need to find a different input
on the powered mixer. Are there any alternatives? An effect return? A
tape input? A stacking input (that goes straight into the power
amplifier?)

> I am intrigued by Anahata's suggestion for using resistors (mainly 'cos
> it's simple and very cheap ! :-) ). I can understand the 33k ohms in
> series, but why the 1k ohms "across the inputs of the desk" ??? (I'm
> presuming you meant across the inputs of the powered mixer, like this
> .... ??
>
> + -------< 33k >---|------>
> Output from desk : 1k Input to powered mixer
> - -----------------|------>

That makes a voltage divider. The voltage from the "desk" is applied
across the series combination of 33K + 1K ohms. The voltage to the
powered mixer is taken across the 1K resistor. The ratio of the
voltage out of the netword to the voltage into the network is

1K
--------- = 0.029
33K + 1K

So if you have 1V coming out of the desk, you'll get 29 mV going into
the powered mixer, just about what you want.

John's suggestion of using the headphone output is good, too. But
unless you have some test equipment, you'll have to cut-and-try.


--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
March 13, 2005 6:18:59 PM

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

pcmangler@ntlworld.com wrote:
> I am intrigued by Anahata's suggestion for using resistors (mainly 'cos
> it's simple and very cheap ! :-) ). I can understand the 33k ohms in
> series, but why the 1k ohms "across the inputs of the desk" ??? (I'm
> presuming you meant across the inputs of the powered mixer, like this
> .... ??
>
> + -------< 33k >---|------>
> Output from desk : 1k Input to powered mixer
> - -----------------|------>

Exactly like that. The combined resistors make a potential divider - the
output will be 1/34th of the input. Actually a 27k instead of the 33k
would be be closer to what you want, but you have a huge range of
adjustment anyway.

The advantage of using the 1k is that there's still a fairly low
impedance source driving the mixer (translation: less susceptible to
noise pickup). In theory if the mixer's input is really 68k you could
just use a series resistor of 1.8M but that would be so prone to noise
pickup and possibly capacitive loss of treble it would be horrible.

By the way, for similar reasons it is best to put the attenuator at the
powered mixer end, not at the desk end.

As you say it's a cheap solution to try - if it doesn't work it didn't
cost you much and either you or I didn't really understand the problem.

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
March 13, 2005 8:08:02 PM

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

In article <1110736541.769466.4640@g14g2000cwa.googlegroups.com> pcmangler@ntlworld.com writes:

> Phil.... I really think you need to seek some help mate.

He's had that advice before. He reacts to it in a predictable way.
Best thing to do is simply ignore his posts. Your blood pressure will
stay closer to normal that way.

> Re Mike's suggestion to use a different input; Yes, that would work, I
> do have a tape-in more suited to the levels from the desk but, I want
> to use two channels on the powered mixer - one with some reverb from
> the built-in processor and another one dry for my guitar (and I use my
> own external effects). So, unless I dispense with my twin channel
> plan, then I have to use the instrument inputs on the powered mixer -
> and therefore attenuate the signals coming in.

Can you describe the mixer further, or is there a manufacturer's web
page I could look at? How many inputs are there, and are they (with
the excpetion of the tape input) all at the "guitar" level? Do you
plug your guitar into two inputs of the powred mixer? What do you
connect to the "outboard" mixer?

> >This may also be a situation of "connector of convenience" or someone
> >who thinks that if you don't have matching connectors for the source
> >and destination it won't work because "the impedance is off."
>
> Would you care to elaborate on what makes you think such a situation
> would apply to my question ? I never mentioned connectors, or
> impedance !

No, but it was a guess. There may be other inputs on different types
of connectors that you aren't using because you don't have mating
plugs, or the connectors aren't of the same typs as the output of your
"outboard" mixer. It's very common for novices to think that they
can't make things with different connector types work.

> I am connecting our instruments to the mixing desk, then the mixing
> desk outputs to the instrument inputs on a powered mixer.
> The line-level signals from the mixing desk are too strong for the
> instrument level inputs on the powered mixer.
> That's why I'm trying to attenuate the outputs from the mixing desk.

I think that in order to fully understand your problem (and yes, we
all understand your description) we need to know more about the
mixers, and apparently nobody here knows what you have. The answer
might be right in front of you. Or it may be that what you're trying
to do doesn't really make good sense.

For instance, if "conncting our instruments" means plugging guitar
pickups into 1/4" jacks on the mixer, then I'm surprised that you're
having a problem with the output level. If it means connecting
keyboards, that's a different story. But the real problem is that
you're trying to connect a line (high level) output to a low level
(high gain) input. There's a simple solution to this - use a pad, as
you understand. I'm just floored that this powered mixer has no inputs
other than instrument level inputs.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
March 13, 2005 10:08:26 PM

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

pcmangler@ntlworld.com wrote:


> Hmm... now you've got me thinking :-) Each channel on the powered
> mixer has a balanced XLR mic socket (at 3.5mV / 6K8 ohms) as well
> as an unbalanced 1/4" socket (at 35mV / 68K ohms).


> I will try both, just in case. I presume that I would just need
> resistors of 270K and 1K ohms to attenuate the signal down to the
> 3.5mV mic level, following Anahata's potential divider suggestion ?
> (ten times the value of the ones for the 35mV instrument level).


You're definitely on the right track, but since the mic inputs are
balanced, you may want something like this:


tip--------- 120K ---+----XLR 2
|
1000
|
sleeve---+-- 120K ---+----XLR 3
|
+----------------XLR 1


The two 120k's are basically in series with your signal to add up to
something near your 270 k unbalanced attenuator. And using your version
would be just fine, too; just connect pin 3 to pin 1 in that case.
Anonymous
March 15, 2005 3:01:53 PM

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

OK, I've done some searching and found an audio shop that recommends
using a value for R2 (the one across the tip & sleeve) that's one tenth
(or less) of the input impedance of the unit you are trying to drive.
Would you agree with that ? (I don't know the reasoning behind it, so
I'm asking !).

If so, then I could use values of 560 ohms for R2 (1/12 of the input
impedance) and 82K for R1 & R3 (the ones in series with the tip &
sleeve).

Using V2 = (R2 / (R1 + R2 + R3)) * V1 this would give me an output of
3.4mV for a 1V input.

Do these figures look good ?

Cheers - and thanks again to everyone taking the trouble to help me
here :-)

Kev.


>You're definitely on the right track, but since the mic inputs are
>balanced, you may want something like this:
>
>tip--------- 120K ---+----XLR 2
> |
> 1000
> |
>sleeve---+-- 120K ---+----XLR 3
> |
> +----------------XLR 1
>
>
>The two 120k's are basically in series with your signal to add up to
>something near your 270 k unbalanced attenuator. And using your
version
>would be just fine, too; just connect pin 3 to pin 1 in that case.
Anonymous
March 15, 2005 5:59:37 PM

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

pcmangler@ntlworld.com wrote:

> OK, I've done some searching and found an audio shop that recommends
> using a value for R2 (the one across the tip & sleeve) that's one tenth
> (or less) of the input impedance of the unit you are trying to drive.
> Would you agree with that ? (I don't know the reasoning behind it, so
> I'm asking !).


That way the effect of input resistance of the driven unit on the
attenuation is negligible. Remember the input R is actually in parallel
with your 560-ohm resistor.


> If so, then I could use values of 560 ohms for R2 (1/12 of the input
> impedance) and 82K for R1 & R3 (the ones in series with the tip &
> sleeve).
>
> Using V2 = (R2 / (R1 + R2 + R3)) * V1 this would give me an output of
> 3.4mV for a 1V input.
>
> Do these figures look good ?


Most excellent; I assume your math is correct. All I'd suggest is maybe
using 75k instead of 82k, giving you a little more signal. Since you're
attenuating almost 50 dB anyway, you're a good way toward where you want
to be, and it's easier to turn down a slightly hot signal than to have
to max out a slightly weak one. IOW, fudge it a little; you wouldn't
want to build it and then decide you'd gone too far.
Anonymous
March 15, 2005 11:19:35 PM

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

pcmangler@ntlworld.com wrote:
> I could use values of 560 ohms for R2 (1/12 of the input
> impedance) and 82K for R1 & R3 (the ones in series with the tip &
> sleeve).
>
> Using V2 = (R2 / (R1 + R2 + R3)) * V1 this would give me an output of
> 3.4mV for a 1V input.
>
> Do these figures look good ?

Yes, they're fine. The general idea is to have the load presented to the
driving end significantly less that its source impedance and the shunt
resistor significantly less than the input impedance its driving. If you
don't do that nothing will break but you'll have to include the source
and input impedances in your calculations or you'll find you're getting
more attenuation than you expected.

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
March 15, 2005 11:21:40 PM

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

anahata wrote:
> The general idea is to have the load presented to the
> driving end significantly less that its source impedance

Duh! I meant greater than, of course

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
March 19, 2005 6:06:14 AM

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

Well, I made up the cables using your suggested values of 75k & 560R
and they are spot-on ! It works like a dream !!! I now have all the
meters behaving on the desk, and my gain knobs on the powered mixer are
no longer 1mm from the stops. I even managed to get the circuit built
inside the XLR connectors.

MANY thanks to everyone who helped :-)

Another satisfied customer :-)

Cheers,

Kev.


S O'Neill wrote:
> pcmangler@ntlworld.com wrote:
>
> > OK, I've done some searching and found an audio shop that
recommends
> > using a value for R2 (the one across the tip & sleeve) that's one
tenth
> > (or less) of the input impedance of the unit you are trying to
drive.
> > Would you agree with that ? (I don't know the reasoning behind it,
so
> > I'm asking !).
>
>
> That way the effect of input resistance of the driven unit on the
> attenuation is negligible. Remember the input R is actually in
parallel
> with your 560-ohm resistor.
>
>
> > If so, then I could use values of 560 ohms for R2 (1/12 of the
input
> > impedance) and 82K for R1 & R3 (the ones in series with the tip &
> > sleeve).
> >
> > Using V2 = (R2 / (R1 + R2 + R3)) * V1 this would give me an output
of
> > 3.4mV for a 1V input.
> >
> > Do these figures look good ?
>
>
> Most excellent; I assume your math is correct. All I'd suggest is
maybe
> using 75k instead of 82k, giving you a little more signal. Since
you're
> attenuating almost 50 dB anyway, you're a good way toward where you
want
> to be, and it's easier to turn down a slightly hot signal than to
have
> to max out a slightly weak one. IOW, fudge it a little; you wouldn't

> want to build it and then decide you'd gone too far.
!