Guitar Reamping Question

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

Never mind, I answered my own question.

http://www.radialeng.com/di-xamp.htm


"Noise Farm" <tim@noisefarmstudio.com> wrote in message
news:41ba9b20$1_1@127.0.0.1...
>I have a question about electric guitar reamping. Given a guitar signal
>recorded through the signal chain below:
>
> Guitar -> DI Box -> Mic Preamp -> DAW
>
> How do I then take the track in the DAW and get it back to an
> instrument-level signal that I can plug into a guitar rig? Do I simply
> run it back through the same signal chain, going the opposite direction
> through the DI Box?
>
> And is the way I'm recording the dry signal the best way? Is there a
> better way to record and reamp for maximum fidelity?
>
> Thank you,
> Tim
>
>

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

Noise Farm wrote:
> How do I then take the track in the DAW and get it back to an
> instrument-level signal that I can plug into a guitar rig?

<http://reamp.com/>

Johann
--
Meiner Meinung nach ist ein Reply-To-Posting ohne Einleitungszeile wie
ein Ei ohne Gelb!
(Uwe Premer in <UwePremer@expires-2003-09-30.arcornews.de> )

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

In article <BDE0B741.29B39%kylesong@earthlink.net> kylesong@earthlink.net writes:

> > How do I then take the track in the DAW and get it back to an
> > instrument-level signal that I can plug into a guitar rig?
>
> Its a matter of level, and more importantly, impedance matching.

Level for sure, impedance matching isn't so critical. The console will
drive anytihng - the instrument amplifier directly, the mic side of a
DI, a small loudspeaker (you get the idea). The source impedance to an
instrument amplifier makes a little difference in the sound, but since
it's all artificial at this point anyway, it's not really a big deal.

What is a big deal is that the high impedance input of an instrument
amplifier makes it easy for a long cable to be a pretty good antenna,
so running 50 feet of cable from the console in the control room to
the amplifier in the studio will work, but it might be buzzy and
noisy. This is why it's standard practice to use a transformer to
provide a balanced input for the bulk of the cable run, with just a
short cable for the high-impedance run.

But if everything is in the same room, see what happens if you just
take an output from your console or DAW and connect it through a 10
foot or so cable to the amplifier input. Keep a hand on the playback
level control (fader on the console or track level on a DAW) and start
with it pretty low. It might work out just fine.

The reason why many passive DIs hooked up backwards don't work well in
this application is twofold. First, going in that direction, it's
somewhere between a 5:1 and 10:1 step-up transformer and you don't
want to boost the voltage going into the amplifer that much above
console level - in fact most of the time you want to reduce it some.
So you need to attenuate the signal going into the DI. And if you hit
it with the full console level you'll probably saturate the
transformer (though it might be just the sound you want out of the amp
- it never hurts to try).

An active DI won't work at all because it doesn't pass signal going
from the output to the input.

Spend money on gadgets if you're so inclined, but try the simple
approach first and see if you get something you can use, and like.

--
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

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

Noise Farm <tim@noisefarmstudio.com> wrote:
>Thanks for all your input, as usual you've all been tremendously helpful.
>Here's what I gather so far, please correct any mistakes you see:
>
>balanced mic level: 150 to 600 ohms, -60dB
>unbalanced mic level: 5k ohms, -60dB
>unbalanced instrument level: 10M ohms, -20dB
>line level (balanced): 200-800 ohms, +4dB
>line level (unbalanced): 200-800 ohms, -10dB

dB with respect to WHAT?

Note that whether something is balanced or not has nothing to do with the
operating level. Plenty of stuff works on consumer levels with balanced
lines, or professional levels with unbalanced lines.

>So far here are all the reamping devices that have been mentioned in this
>thread.
>
>http://www.radialeng.com/di-xamp.htm - $199
>http://www.reamp.com - $240
>http://www.littlelabs.com/redeye.html - $250
>http://www.littlelabs.com/ibp.html - $500
>
>So far I'm leaning towards the redeye as it's a DI box, a reamping tool, and
>a splitter.

There isn't all THAT much going on inside these boxes. I keep saying that
I am going to do a DIY project article on building one. Any of the above
will work just fine, although some of them are more convenient than others
(in part, it's very nice to have wide level controls on the box so that you
can use the amp at whatever gain setting it sounds best at without spending
a lot of time fiddling with gains on the console).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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

>>balanced mic level: 150 to 600 ohms, -60dB
>>unbalanced mic level: 5k ohms, -60dB
>>unbalanced instrument level: 10M ohms, -20dB
>>line level (balanced): 200-800 ohms, +4dB
>>line level (unbalanced): 200-800 ohms, -10dB
>
> dB with respect to WHAT?

Whatever hypothetical "0 dB" they relate to when one comes across them in
user manuals is beyond me - maybe you can help here. I'm trying to get a
general idea of what kind of conversion has to be done to reamp a guitar
signal. From what I've gathered so far, given unity gain signal paths (from
the electric guitar through the DI box through the mixer through the
converter and into the DAW, and back out through the converter and the
Reamping device into the amp) it'd be somewhere in the neighborhood of
a -24dB drop in signal and a change of impedance from roughtly 200 ohms to
10M ohms. Is this a reasonable estimate?

Scott, what is a good reference to get the basics of what is actually
happening in microphone, instrument, and line-level cables? How does the
line level relate to voltage relate to impedance, the difference between
balanced and unbalanced, etc. There must be an audio cable 101 FAQ online
or some kind of seminal reference work indispensable to electronics-impaired
novices like me.

> There isn't all THAT much going on inside these boxes. I keep saying that
> I am going to do a DIY project article on building one.

That would be absolutely wonderful as I'm sure the components required to
build one are far less than $199.

Thanks again,
Tim

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

The schematic and circuit description for the Reamp box
can be viewed here.
http://patft.uspto.gov/netacgi/nph [...] PN/6005950

If anyone has a source for the 500ohm to 30K ohm
UTC-0-10 transformer let us know.

Goober

"Scott Dorsey" <kludge@panix.com> wrote in message
news:cpg6nr$1cl$1@panix3.panix.com...
: Noise Farm <tim@noisefarmstudio.com> wrote:
: >Thanks for all your input, as usual you've all been
tremendously helpful.
: >Here's what I gather so far, please correct any
mistakes you see:
: >
: >balanced mic level: 150 to 600 ohms, -60dB
: >unbalanced mic level: 5k ohms, -60dB
: >unbalanced instrument level: 10M ohms, -20dB
: >line level (balanced): 200-800 ohms, +4dB
: >line level (unbalanced): 200-800 ohms, -10dB
:
: dB with respect to WHAT?
:
: Note that whether something is balanced or not has
nothing to do with the
: operating level. Plenty of stuff works on consumer
levels with balanced
: lines, or professional levels with unbalanced lines.
:
: >So far here are all the reamping devices that have
been mentioned in this
: >thread.
: >
: >http://www.radialeng.com/di-xamp.htm - $199
: >http://www.reamp.com - $240
: >http://www.littlelabs.com/redeye.html - $250
: >http://www.littlelabs.com/ibp.html - $500
: >
: >So far I'm leaning towards the redeye as it's a DI
box, a reamping tool, and
: >a splitter.
:
: There isn't all THAT much going on inside these
boxes. I keep saying that
: I am going to do a DIY project article on building
one. Any of the above
: will work just fine, although some of them are more
convenient than others
: (in part, it's very nice to have wide level controls
on the box so that you
: can use the amp at whatever gain setting it sounds
best at without spending
: a lot of time fiddling with gains on the console).
: --scott
: --
: "C'est un Nagra. C'est suisse, et tres, tres
precis."

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

KyleSong wrote:

> Noise Farm wrote:
>
>> How do I then take the track in the DAW and get it back to an
>> instrument-level signal that I can plug into a guitar rig?
>
> Its a matter of level, and more importantly, impedance matching.


Impedence may not be as big a deal as it seems. Since (at least) the early
80s, most stomp box pedals have had low impedence outputs (at least
substantially lower than a typical guitar pickup). I'm looking at the
original literature that came with a Tube Screamer & a Boss CE-2 chourus.
(Yes, I'm one of those obsessive/compulsive types who never throws away any
product documentation.) Both of these units are designed to feed inputs of
10K ohms or higher. In the modern world, that's what we call consumer line
level.

Since we don't see many guitarists patching reamp devices between their
pedalboards & their amps, we can assume that most guitar amps are perfectly
happy with the lower impedence output from the pedals. And, since it's
common practice to string several boxes serially, we can assume that the
boxes themselves are also happy with the lower impedence.

As always, there are exceptions. Old germanium fuzz boxes & inductor based
wahs will sound substantially different with a lower impedence input. Then
again (speaking as a guitarist), I can't imagine trying to add wah to a
part after the fact. The passive volume & tone controls on the guitar are
also affect the loading of the pickups & have a big effect on the sound.
If you're dealing with a guitarist who uses the knobs while playing, you
won't be able to duplicate that with the controls on your DAW or mixer.

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

Mike Rivers wrote:
> In article <89Zud.8688$yr1.8282@newsread3.news.pas.earthlink.net> dashes-@mindspring.com writes:
>>The schematic and circuit description for the Reamp box
>>can be viewed here.

> I give up. What kind of smartass web page is this?

I suppose you are looking at the images? They are in TIFF format.
IrfanView [1] displays TIFF files, among others.

[1] <http://irfanview.com/>

Johann
--
Eigentlich hast Du ein Verstaendnis ueber Plonken, welches mich auch als
Real-FAQ ueberhaupt nicht interessiert wuerde. Who cares?
(*Tönnes in <3bf061d2$0$332$9b622d9e@news.freenet.de> )

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

agent86 wrote:

> I can't imagine trying to add wah to a
> part after the fact.

Of course you're right if you're talking about playing a Wah part. There are
other applications too, like an edgy filter, which might not move during the
part. That would be something you might do while reamping?

I know I'm splitting hairs, but since i got nailed on the impedance
question, I'm grasping

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

Much appreciated Mike, you and Scott both recommended the Yamaha Sound
Reinforcement book and I acted on that. Cheers!
Tim

"Mike Rivers" <mrivers@d-and-d.com> wrote in message
news:znr1102857714k@trad...
>
> In article <41bbc31a$1_1@127.0.0.1> tim@noisefarmstudio.com writes:
>
>> > dB with respect to WHAT?
>>
>> Whatever hypothetical "0 dB" they relate to when one comes across them in
>> user manuals is beyond me - maybe you can help here.
>
> In general, with audio equipment, when they leave off the reference
> from the "dB" it's dBV if it's -10 and dBu if it's +4. Those are about
> the only numbers you see when it comes to line levels. If you see a
> number like -60 dB it's usually referring to the sensitivity of a
> microphone input. For that, you really need to know how the
> manufactuer does his specsmanship.
>
> Note: All errors of a factor of ten or 1.4 are attributable to the fact
> that I wrote this .5 BC (half an hour before coffee). Please accept
> them in the spirit of the newsgroup and only argue about the big
> stuff.
>
> dB without a reference is gain, so "-60 dB" could mean that the mic
> input has 60 dB of gain: 1V out for 1 mV (.001 V) in, or a ration of
> 1000/1. If the mic preamp has a nominal output level of +4 dBu (1.2 V)
> and 60 dB of gain, it would require .0012V coming out of the mic to
> reach that nominal level. If the preamp has a nominal output level of
> -10 dBV (0.31 V) and 60 dB of gain, it would require only 0.00031 V
> coming out of the mic to reach the nominal output level.
>
> Which is "better?" It depends on what operating voltage the next stage
> requires. But that's a different story.
>
>> I'm trying to get a
>> general idea of what kind of conversion has to be done to reamp a guitar
>> signal. From what I've gathered so far, given unity gain signal paths
>> (from
>> the electric guitar through the DI box through the mixer through the
>> converter and into the DAW, and back out through the converter and the
>> Reamping device into the amp) it'd be somewhere in the neighborhood of
>> a -24dB drop in signal and a change of impedance from roughtly 200 ohms
>> to
>> 10M ohms. Is this a reasonable estimate?
>
> You probably don't have to drop the level by 24 dB. Guitars can be
> pretty hot when you're playing hard, upwards of a couple of volts out.
> But since the source impedance is quite high, if you try to connect
> a guitar pickup directly to a conventional line level input which
> might have an impedance of 5K to 20K ohms, you end up dropping much of
> the voltage across the pickup itself, leaving maybe 20% to go to the
> console (about a 14 dB loss). But the output impedance of a console or
> DAW audio interface is low and will not be affected by connecting it
> to a guitar amplifier input. So all you really have to be concerned
> with is:
>
> - Dropping the level down to the point where the guitar amplifier
> input either doesn't clip or clips the way you would like it to if
> the actual guitar was connected to it.
>
> and
>
> - Getting the signal from the control room equipment to the
> amplifier without picking up too much hum along the way.
>
> A secondary (and probably minor, but you're the guitar player, not me)
> consideration is how the amplifier reacts to being fed from a low
> impedance source rather than a high impedance source. In the Millenia
> Media Twin Direct, there are two taps on the DI output transformer so
> that you have a choice of source impedances to drive the amplifier.
> Throw a switch and see if it makes a difference that you care about.
>
>> Scott, what is a good reference to get the basics of what is actually
>> happening in microphone, instrument, and line-level cables? How does the
>> line level relate to voltage relate to impedance, the difference between
>> balanced and unbalanced, etc. There must be an audio cable 101 FAQ
>> online
>> or some kind of seminal reference work indispensable to
>> electronics-impaired
>> novices like me.
>
> I wrote an article in Recording about this several years back and the
> editor says it's time to recycle that thought, so if you can hold out
> until late Spring you'll probably be able to read it there. The Yamaha
> Sound Reinforcement Handbook (I think it's still available) has a
> pretty good explanation of voltage, current and impedance
> relationships (Ohm's Law) and of how dB is used in audio. Somebody
> probably has written all of this up and put it on line, but there's
> also probably _something_ wrong or incomplete in any one place.
>
>> > There isn't all THAT much going on inside these boxes. I keep saying
>> > that
>> > I am going to do a DIY project article on building one.
>
> The first step in creating a DIY project (and I wrote another article
> in Recording about this subject) is to figure out what problem you
> need to solve. Connect your recorded source to your instrument
> amplifier with a cable, play with the knobs, and see what happens.
> Play with it (source output level and amplifier gain) for a while and
> see what you can conclude. If you have too much hum, experiment with
> grounding to see if you can make it go away by eliminating a ground
> loop. Experiment. Learn. Ask questions about what you've learned.
>
>
>
> --
> 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
>

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

Scott, I've got my hands on the Yamaha sound reinforcement handbook as we
speak.

Thanks again,
Tim


"Scott Dorsey" <kludge@panix.com> wrote in message
news:cphin9$soe$1@panix2.panix.com...

> The Yamaha Sound Reinforcement Handbook is probably a good place to start,
> but the FAQ for this newsgroup has a nice introduction to some of this
> stuff.
> And I bet the Rane website has some info also, and their discussion on
> interconnecting cables is worth reading.
> --scott
>
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."
>

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

a good thing to look into is the Millennia Media TD-1. It's an HV-3
mic pre with high and low eq, plus re-amp features and other stuff. A
great tote-around one channel box of truly professional specs.

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

"Mike Rivers" <mrivers@d-and-d.com> wrote in message
news:znr1102867783k@trad...
:
: In article
<89Zud.8688$yr1.8282@newsread3.news.pas.earthlink.net>
dashes-@mindspring.com writes:
:
: > The schematic and circuit description for the Reamp
box
: > can be viewed here.
: > http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PT
: > O1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm
: >
&r=1&f=G&l=50&s1=6005950.WKU.&OS=PN/6005950&RS=PN/60059
50
:
: I give up. What kind of smartass web page is this?
Initially I got a
: broken QuickTime icon and a note that I had to
download Quicktime
: Image. So I did. Now I still get a broken QuickTime
icon and a message
: saying that there's no need to download new software,
it's already
: installed. Same in Netscape and Explorer. Is there a
PDF? Or a link
: directly to a file that I can download and play with?

It is the US patent office web page. There is a link in
the page that tells you to download a TIFF viewer plug
in for your browser. With that viewer you can see the
diagrams in much the same way you navigate a PDF.

It took some searching but it is genuine, I guarantee
it.

Goober

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

Noise Farm:

You can put your ohm meter into the output of your
passive guitar output jack and see directly what it's
output impedance with different volume control
settings.

You can put your ohm meter into the input of most amps
and stomp boxes and read directly what the input
impedance is. Try with amp on and off it may change.

Watch out trying to measure output impedance of
something active like a preamp out connected to an op
amp. It may not work as well as the above passive
inputs. Usually this is just really low z line out.

Goober

"Noise Farm" <tim@noisefarmstudio.com> wrote in message
news:41bcd734$1_2@127.0.0.1...
: Is there some kind of a relatively inexpensive
measuring device that can
: tell you what the voltage and impedance of an analog
audio signal is? If
: you could read that from the source signal of the
electric guitar and from
: the output of your reamping device, it might aid in
assuring that the source
: signal from your guitar pickups and the output of
your reamping box are as
: matched as you can get them, barring A/D - D/A
conversion and some extra
: signal noise.
:
: I realize I'm probably being a bit silly about this
when the obvious answer
: is "take the output from your converter and plug it
into your amp" but I'd
: also be able to at least know how to get as close a
match as possible and
: understand what's actually happening in the process.

A match is not necessarily what you want for the best
tone. Actually you will need to screw around and find
what you want just like anything else.

And don't forget that an EE will tell you a good match
is having the input z about 10x higher than the driving
output z. This again is not necessarily what you want
for the best tone.

Goober
:

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

GoobAudio <philsaudio-remove this and the dashes-@mindspring.com> wrote:
>The schematic and circuit description for the Reamp box
>can be viewed here.
>http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=6005950.WKU.&OS=PN/6005950&RS=PN/6005950
>
>If anyone has a source for the 500ohm to 30K ohm
>UTC-0-10 transformer let us know.

The O-10 was probably selected because it was the cheapest transformer with
the right ratio available. The Triad or Tamura equivalents will be fine. I
will say that this schematic is not necessarily what Reamp is currently using,
though.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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

In article <41bcd734$1_2@127.0.0.1> tim@noisefarmstudio.com writes:

> Is there some kind of a relatively inexpensive measuring device that can
> tell you what the voltage and impedance of an analog audio signal is?

A voltmeter is a relatively inexpensive measuring device that can tell
you what the voltage coming from a source is. A signal, as such,
doesn't have an impedance, but a source or a load has an impedance.
When you understand Ohm's Law, you can use a voltmeter and a resistor
to get a pretty good idea of the magnitude of the impedance.

> If
> you could read that from the source signal of the electric guitar and from
> the output of your reamping device, it might aid in assuring that the source
> signal from your guitar pickups and the output of your reamping box are as
> matched as you can get them

That's a little harder. A voltmeter is essentially for measuring
steady voltages, and unless you play an electric guitar with a bow,
the output voltage will be far from steady. An oscilloscope and an
eyeball (for observing the peak voltage and taking an eyeball average)
is a better tool for this. Oscilloscopes suitable for measuring audio
voltages and frequencies, if you have space for a fairly large
cabinet, can be very inexpensive, though very old. Hewlett Packard 130
scopes can be had at hamfests for $10 or so (and are frequently
purchased by people who sell them on eBay for $50 or so). However, as
has been pointed out here, nominal values are good enough to get what
you need. You really don't have to measure YOUR guitar other than out
of curiosity.


--
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

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

In article <eygvd.9566$yr1.5193@newsread3.news.pas.earthlink.net> dashes-@mindspring.com writes:

> There is a link in
> the page that tells you to download a TIFF viewer plug
> in for your browser. With that viewer you can see the
> diagrams in much the same way you navigate a PDF.

Found it (before your reply), downloaded it, installed it, still get
the same result. I guess the group doesn't get the benefit of my
wisdom on this one, unless I can get the benefit of someone else's
wisdom on how to properly view the TIFF images on the Patent Office
web site. But I know how difficult remote troubleshooting can be, and
that goes double for a remote computer that you don't know intimately.

--
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

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

It is basically an H pad feeding a series RC in
parallel with the transformer 500 ohm side ( not center
tapped as previously stated in error) It has 2x 175
ohms on the input side, 2x 113 ohms on the output and
the center of the H is bridged by 338 ohms. The RC on
the input side is 100 ohms and 96 pf.

The transformer output goes across a 50 K pot with the
wiper being the output hot.

goober
----- Original
"Mike Rivers" <mrivers@d-and-d.com> wrote in message
news:znr1102949802k@trad...
:
: In article
<eygvd.9566$yr1.5193@newsread3.news.pas.earthlink.net>
dashes-@mindspring.com writes:
:
: > There is a link in
: > the page that tells you to download a TIFF viewer
plug
: > in for your browser. With that viewer you can see
the
: > diagrams in much the same way you navigate a PDF.
:
: Found it (before your reply), downloaded it,
installed it, still get
: the same result. I guess the group doesn't get the
benefit of my
: wisdom on this one, unless I can get the benefit of
someone else's
: wisdom on how to properly view the TIFF images on the
Patent Office
: web site. But I know how difficult remote
troubleshooting can be, and
: that goes double for a remote computer that you don't
know intimately.
:
: --
: 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

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

::
: That's a little harder. A voltmeter is essentially
for measuring
: steady voltages, and unless you play an electric
guitar with a bow,
: the output voltage will be far from steady. An
oscilloscope and an
: eyeball (for observing the peak voltage and taking an
eyeball average)
: is a better tool for this. Oscilloscopes suitable for
measuring audio
: voltages and frequencies, if you have space for a
fairly large
: cabinet, can be very inexpensive, though very old.
Hewlett Packard 130
: scopes can be had at hamfests for $10 or so (and are
frequently
: purchased by people who sell them on eBay for $50 or
so). However, as
: has been pointed out here, nominal values are good
enough to get what
: you need. You really don't have to measure YOUR
guitar other than out
: of curiosity.

A channel on the DAW makes an excellent voltage level
storage scope. You could record your playing voltage on
the output of the guitar and across a resistor in
series with your guitar and amp input into two channels
on the DAW. Then you can use a signal generator to
match the recorded voltages. You can solve for the
unknown input impedance using a voltage divider
equation or substitute the series resistor ( read
adjust a pot) until the voltage across the series
resistor ( pot ) is the same as the voltage across the
amp. At this point the input impedance of the amp is
the same as the voltage.

But this aint simple.

goober

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

In article <8rmvd.10090$0r.919@newsread1.news.pas.earthlink.net> dashes-@mindspring.com writes:

> It is basically an H pad feeding a series RC in
> parallel with the transformer 500 ohm side ( not center
> tapped as previously stated in error) It has 2x 175
> ohms on the input side, 2x 113 ohms on the output and
> the center of the H is bridged by 338 ohms. The RC on
> the input side is 100 ohms and 96 pf.
>
> The transformer output goes across a 50 K pot with the
> wiper being the output hot.

Doesn't sound like any big secrets there. A transformer in a box, with
a level control. The RC is probably to flatten out the transformer.

--
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