Passive Volume Knob - Can this be that hard?

[Erik Korte]

Hi folks.
I'm looking into (hopefully making) a passive volume attenuator
between my Balanced Out interface and an Unbalanced Adcom 535.

Any advice for a novice with decent soldering skills? A parts list
perhaps?

Or is this more involved than I'm giving it credit for?


Thanks!

[Scott Dorsey]

Erik Korte > wrote:
>Hi folks.
>I'm looking into (hopefully making) a passive volume attenuator
>between my Balanced Out interface and an Unbalanced Adcom 535.
>
>Any advice for a novice with decent soldering skills? A parts list
>perhaps?

Get a 10K dual audio-taper pot (and get a nice one that tracks well so both
volumes will be the same). Input goes into the top of the pot, output
comes off the wiper, bottom of the pot is grounded.

Or trade it in for the 535 model with the gain control... 535S or something?
--scott

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

[Mike Rivers]

Erik Korte wrote:
> Hi folks.
> I'm looking into (hopefully making) a passive volume attenuator
> between my Balanced Out interface and an Unbalanced Adcom 535.
>
> Any advice for a novice with decent soldering skills? A parts list
> perhaps?

It's really not that hard, but people who want to do this
keep asking for a schematic or parts list. If you need
someone to do that for you, then you're not ready to do it
all yourself. This is as simple as it gets.

However, you threw a monkey wrench into the "simple" works
because now you have two things to deal with, the volume
control, and connecting a balanced output to an unbalanced
input. Any time you do that, you have an unbalanced
connection. That's normally nothing to worry about when
you're dealing with line levels and short cables, and in
fact it simplifies the major part that you need because you
need only a two-section pot for left and right rather than a
four section one, for tip and ring left and right. But you
need to know how the balanced output is configured so you'll
know how to connect it to the unbalanced input of a pot.

Now, it really is simple. You need a dual pot, enough of the
right connectors for the cabling you're using, a box to put
it all in, and a bunch of holes. Making the holes is really
the hardest part of this project.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[William Sommerwerck]

We haven't asked the OP how long the cable run will be. A long run of
high-capacitance cable can cause problems, especially when the control is at
its electrical midpoint.

[Mike Rivers]

William Sommerwerck wrote:
> We haven't asked the OP how long the cable run will be.

I read his mind that this was for a tabletop setup.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[Erik Korte]

On Jul 30, 4:39*pm, "Soundhaspriority" > wrote:
> "Mike Rivers" > wrote in message
>
> ...> William Sommerwerck wrote:
> >> We haven't asked the OP how long the cable run will be.
>
> > I read his mind that this was for a tabletop setup.
>
> Erik,
> * * *Keep your output cable really short, like three feet, or any advantage
> you might think a passive setup has will definitely not be there.
>
> Bob Morein
> (310) 237-6511




Mike you did read my mind...... 3' to the knob & 3' back.

[Mike Rivers]

Soundhaspriority wrote:

> Keep your output cable really short, like three feet, or any advantage
> you might think a passive setup has will definitely not be there.

You mean if he had a long cable, he might not be able to
turn off the sound when something craps out? Did you really
get the sense that this request came from an audiophile
sound snob? Nope, he just needs an on/off switch, or an easy
way to turn down playback when the phone rings.

Trust me on this.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[William Sommerwerck]

> Trust me on this.

I thought he was asking for a volume control.

[Mike Rivers]

William Sommerwerck wrote:

> I thought he was asking for a volume control.

He did. But it's better to actually solve his unpredictable
volume problem at the source, and put in a switch for
emergencies.

If he wanted to adjust the volume, that would be a fair
requirement for a volume control. But in this case he
described a problem where some unpredictable sound would
come out, sometimes at a dangerous volume. Isn't it better
to simply see that this doesn't happen?


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[William Sommerwerck]

> If he wanted to adjust the volume, that would be a fair
> requirement for a volume control. But in this case he
> described a problem where some unpredictable sound
> would come out, sometimes at a dangerous volume.
> Isn't it better to simply see that this doesn't happen?

Yup. Makes sense.

[William Sommerwerck]

> I don't think I'm way-out-there if I assert that driving cable
> with a 10K output impedance will cause loss of highs.

It depends on the cable capacitance. I had this happen when I used long,
high-C Neumann cables with a Shure 5000-series surround processor (which a
Zout of around 5K).

But a "high" output impedance, in and of itself, will not cause loss of
highs. What's the cable capacitance?

By the way, a 10K pot would have a maximum output impedance of only 2.5K
(assuming the source impedance were close to zero).

[Mike Rivers]

Soundhaspriority wrote:

> Mike, I once had an opportunity to purchase a highly reviewed Adcom preamp
> that had a single-ended hexfet output with a high output impedance. It
> literally could not drive more than three feet of cable without dulling of
> the highs.

Same with most electric guitars. But in this case, the
output device is something balanced (unspecified) and the
Adcom amplifier is the input. And he's not making high
fidelity music, he's making odd noises which occasionally
come out at high volume because he doesn't have good control
of what's creating the sound.

> I don't think I'm way-out-there if I assert that driving cable with a 10K
> output impedance will cause loss of highs.

Let's say he has 10 feet of cable with a capacitance of 35
pF per foot. That represents a capacitive load of about 30K
Ohms at 15 kHz. Make a voltage divider out of that with 10K
as the input (it'll likely be less than that since it's
coming off the tap of the pot, which he'll likely have
turned down if he has any sense) and you get about 2.5 dB
loss at 15 kHz. Hardly anything to worry about.

> In fact, I am not in favor of passive volume controls,
but if Erik wants to do it, I feel he should know
> the one definite downside.

And now he does.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[Scott Dorsey]

Mike Rivers > wrote:
>Soundhaspriority wrote:
>
>> I don't think I'm way-out-there if I assert that driving cable with a 10K
>> output impedance will cause loss of highs.
>
>Let's say he has 10 feet of cable with a capacitance of 35
>pF per foot. That represents a capacitive load of about 30K
>Ohms at 15 kHz. Make a voltage divider out of that with 10K
>as the input (it'll likely be less than that since it's
>coming off the tap of the pot, which he'll likely have
>turned down if he has any sense) and you get about 2.5 dB
>loss at 15 kHz. Hardly anything to worry about.

It's actually not even this bad since there is some series inductance
that helps you out.

Incidentally if you want to do a lot of this, Gepco makes a "siamese" cable
designed for S-Video... it's two mini 75 ohm coaxes joined side-by-side like
zip cord, it's less than twenty cents a foot, and it has very low capacitance
per unit length.

I have about a thirty-foot run from the mastering mixer to the old Citation
II monitor amp here. The measured top end rolloff is (unfortunately) all due
to the resonant pole on the Magnepan tweeters.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Erik Korte]

......But in this case, the
output device is something balanced (unspecified) and the
Adcom amplifier is the input. And he's not making high
fidelity music, he's making odd noises which occasionally
come out at high volume because he doesn't have good control
of what's creating the sound.

The output is coming from an Echo Audiofire 12 interface (no physical
volume knob for "control room" output).
Up till now that 2 mix output went into my Sound Workshop 1280 and
that mixer of course provided a volume knob.

Now, I'm using separate pre's feeding the same interface and coming
out as always..... but straight to the Adcom.
I miss the knob. Sure I can control the volume in the software console
app, but that's a bit clunky.

I see folks like TC Electronic make a product for this purpose. But
It's $70+ and I'm sure it could be built for a fraction of that.
The hitch? I'm not an EE by a long shot. All the same, I can solder
and buy parts from Mouser. I just don't know which ones.
The box I can drill no problem.

I am proudly creating mid-fi music that tens of people occasionally
tolerate.

Thanks for any & all help.

[Mike Rivers]

On 7/31/2010 8:06 PM, Erik Korte wrote:

> I see folks like TC Electronic make a product for this purpose. But
> It's $70+ and I'm sure it could be built for a fraction of that.
> The hitch? I'm not an EE by a long shot. All the same, I can solder
> and buy parts from Mouser. I just don't know which ones.

That's why it costs $70 - they know and you don't. They also probably
had a custom pot made for the job. Go to the Mouser catalog and see if
you can find a 10K ohm quad (4 gang) audio taper pot with the sections
matched closely enough so the left/right image won't shift when you
change the volume, and also the tip/ring balance won't change either.
It's easier (and less expensive) to make an unbalanced one, and it'll
work just as well as long as you don't have long cable runs, which you
aren't likely to have in your case. But you'll never make one as neat
looking as the Level Pilot.


--
"Today's production equipment is IT based and cannot be operated without
a passing knowledge of computing, although it seems that it can be
operated without a passing knowledge of audio" - John Watkinson

[Mike Rivers]

Erik Korte wrote:

> I think I'll just pop for one of those.

This is one of those kind of projects that I'd tackle in a
minute because I have the tools and the parts junkbox so
that it's not a big deal to get started. And of course I
know how to connect a pot as a variable attenuator. But if
you aren't already equipped, it's really too simple a
project to do as a one-off and you're better off buying one
ready made. Several years back, I wrote an article in
Recording Magazine that was about creating your own
do-it-yourself projects. Since at the time, the "monitor
controller" didn't exist and there was a common need for
one, for the same purpose as you want one now, I used it as
an example, developing in complexity from a pot in a box to
one with switching to mix playback with the input source for
overdubbing, and including a headphone amplifier. I don't
know how many readers I started on a path of sin with that
article, but I didn't get many questions about it so
probably not many.

> Are you still doing any work for Mackie?
> What do you know about their new line of FW interfaces.
> The last batch really came and went fast.

No, Mackie hasn't asked me to do anything for them for
several years, so I really don't have any inside
information. I noticed that they have a couple of new
interfaces, looks like scaled down versions of the 1200F and
Satellite, both of which were discontinued after a short
while. They keep shifting their engineering department
around and I don't know how much in-house software expertise
they have now. Probably still not enough to be fully
supporting a lot of software-based products, which is why
they're cutting their line way back.

> I love my Echo stuff a lot and if I heard correctly they had an
> agreement some time back no?

Echo stuff is fine. As long as it still works for you,
there's no reason to look for an upgrade. Echo did the
Firewire parts and drivers for the 1200F and 400F, but it
was a contract job and when the contract was over, it was
over. There was no continuing contract for updates and support.

> Also, do any of you have any recommendations for a 8 channel mic pre?
> Any that you've heard that actual sound decent for under $1K?

8 channels of decent mic preamp for $1000 is probably not
hard to do these days, but it's kind of like the passive
volume control - not much to the circuitry but the packaging
is expensive. 8 channels of exceptional (as in worth haveing
a few channels of) mic preamp for $1K is probably still not
happening. I'm perfectly satisfied with what I have for
inputs (nothing exotic except for 2 channels of Great River
from 10 years ago) that I don't follow those things closely.
Maybe Focusrite would be a good place to start looking.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[[email protected]]

MIke Rivers writes:
>> I see folks like TC Electronic make a product for this purpose.
>>But It's $70+ and I'm sure it could be built for a fraction of
>>that. The hitch? I'm not an EE by a long shot. All the same, I
>>can solder and buy parts from Mouser. I just don't know which
>ones.
>That's why it costs $70 - they know and you don't. They also
>probably had a custom pot made for the job. Go to the Mouser
>catalog and see if you can find a 10K ohm quad (4 gang) audio taper
>pot with the sections matched closely enough so the left/right
>image won't shift when you change the volume, and also the tip/ring
>balance won't change either. It's easier (and less expensive) to
>make an unbalanced one, and it'll work just as well as long as you
>don't have long cable runs, which you aren't likely to have in your
>case. But you'll never make one as neat looking as the Level Pilot.
True, and you also have to figure what your time is worth to
you. By the time you've researched the parts you need,
wired, and tested of course, this level control box before
you trust it to doing a session you'll have enough time
invested in it that just getting the box will be as cost
effective for you. ESpecially if you're really more
interested in creating in your studio, or bringing in paying
clients. Either way, you trade something.

YEs one way you learn a bit, maybe have some fun, and get a
device you can use. But, if you're thinking of building the
device just to save a few bucks and you will find the layout
and the drilling and the soldering a bit tedious, you're
probably ahead of the game to spend the seventy bucks and
get back to making music. That's a judgment call the rest
of us can't make for you, but chances are pretty good that
in my case I"d just spend the seventy bucks.

I've had to work with a colleague to design a device to do
what I wanted, or build one from plans elsewhere, as in
blind man's vu metering. Yah i can get a nice 4 channel
blind man's vu meter box that has nice preset steps from -25
to +4, with increments for the usual -10 and +4, all the way
to +8. Trouble is, the damned thing is $900. SO, we built
one.

IS the science products device a good unit? YEs. IT worked
well for me for many years. A state rehab grant bought it
for me back in the late '80's early '90's. Katrina, or the
after Katrina fire took it from me.

THe unit we built works as well, probably isn't as pretty
when you take its clothes off and look inside it for sure,
but, it works.

Regards,





Richard webb,

replace anything before at with elspider
Remote audio in the southland: see www.gatasound.com

[Sean Conolly]

"Erik Korte" > wrote in message
...
> Also, do any of you have any recommendations for a 8 channel mic pre?
> Any that you've heard that actual sound decent for under $1K?

I've been looking at the stuff from Seventh Circle Audio:
http://www.seventhcircleaudio.com/

It's a kit you assemble, which sounds like something you might like to
dabble with. If you price it out with 8 of the T15 modules it comes out a
little over $1K. The T15 is based on the latest round of That Corp preamp
chips, so it's a good general purpose preamp. They also have kits for more
esoteric preamps with discrete op-amps and transformer inputs, and you can
mix any combination of modules in the chassis.

Might be worth taking a look at, anyway.

Sean

[Mark]

You don't need to use 2 pots for each balanced line (4 total for
stereo).

A single pot (2 for stereo) will work fine to control a balanced line,
connect the pot as you normally would except instead of hot to ground,
the pot goes acrosss + and - with no connection to ground.



Mark

[Mike Rivers]

Mark wrote:
>
> You don't need to use 2 pots for each balanced line (4 total for
> stereo).
>
> A single pot (2 for stereo) will work fine to control a balanced line,
> connect the pot as you normally would except instead of hot to ground,
> the pot goes acrosss + and - with no connection to ground.

That might sort of work for an output that's not
differential, but with an output where both legs have signal
on them, you'll get an unbalanced output (to ground - you
must have SOME point of reference for that voltage) that, at
the center of the pot's rotation, changes polarity and
starts increasing again.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[Mark K]

>
> That might sort of work for an output that's not
> differential, but with an output where both legs have signal
> on them, you'll get an unbalanced output (to ground - you
> must have SOME point of reference for that voltage) that, at
> the center of the pot's rotation, changes polarity and
> starts increasing again.
>
>
Yes good point..I stand corrected...

mark

[Mark]

On Aug 2, 2:47*pm, Mark K > wrote:
> > That might sort of work for an output that's not
> > differential, but with an output where both legs have signal
> > on them, you'll get an unbalanced output (to ground - you
> > must have SOME point of reference for that voltage) that, at
> > the center of the pot's rotation, changes polarity and
> > starts increasing again.
>
> Yes good point..I stand corrected...
>
> mark

whoops. on second (or is it third) thought, it will work...

if you wire the pot across the + and - leads of a diff pair, when the
pot is set to 0, you will get 0 volts across the diff pair.. (the two
outputs are connected together in that case and the DIFF output can be
nothing but 0.... Granted there will still be a common mode output in
this case but if the input is true differential , it won't matter...
If you set it to 1/2 you will get 1/2 the voltage.. the output will
never reverse polarity... don't think about ground at all, no part
of this circuit is connected to ground.... think only about the
voltage between the two wires...

I guess the answer to the original question is YES it can be that
hard... :-)


Mark

[Mike Rivers]

Mark wrote:

> if you wire the pot across the + and - leads of a diff pair, when the
> pot is set to 0, you will get 0 volts across the diff pair.. (the two
> outputs are connected together in that case and the DIFF output can be
> nothing but 0.... Granted there will still be a common mode output in
> this case but if the input is true differential , it won't matter...
> If you set it to 1/2 you will get 1/2 the voltage.. the output will
> never reverse polarity...

I don't understand how you're doing this. Where do you take
the output in this configuration? Between the pot wiper and
what? You can't mesure voltage at a single point, you need a
reference.

> don't think about ground at all, no part
> of this circuit is connected to ground.... think only about the
> voltage between the two wires...

If the ends of the pot are connected to the two hot wires,
the voltage between the wires won't change regardless of the
position of the wiper. What am I missing here?







--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[John Williamson]

Mike Rivers wrote:
> Mark wrote:
>
>> if you wire the pot across the + and - leads of a diff pair, when the
>> pot is set to 0, you will get 0 volts across the diff pair.. (the two
>> outputs are connected together in that case and the DIFF output can be
>> nothing but 0.... Granted there will still be a common mode output in
>> this case but if the input is true differential , it won't matter...
>> If you set it to 1/2 you will get 1/2 the voltage.. the output will
>> never reverse polarity...
>
> I don't understand how you're doing this. Where do you take the output
> in this configuration? Between the pot wiper and what? You can't mesure
> voltage at a single point, you need a reference.
>
> > don't think about ground at all, no part
>> of this circuit is connected to ground.... think only about the
>> voltage between the two wires...
>
> If the ends of the pot are connected to the two hot wires, the voltage
> between the wires won't change regardless of the position of the wiper.
> What am I missing here?
>
I can see a couple of possible circuits here. In one, the two input
wires connect to the output wire via a pair of resistors with the
variable resistor shunting across the two output wires. As the
resistance varies from high to zero, so the output drops. Not in a
linear manner, and the impedance shown to both source and sink reduce as
the level reduces. Parallel the whole VR with a switch for an instant
"kill" for the output signal.

In another, the -ve input and output are both connected to the "earthy"
terminal on the VR, the input +ve is connected to the other end of the
strip, while the +ve output is connected to the wiper. Nothing is
grounded, and the signal remains balanced. Impedance shown to the source
and sink reduce as the output level increases. It's a normal volume
control, but with a virtual ground point at the ground end of the strip
instead of a real one. Again, a switch between the wiper and the
"earthy" end will kill the signal immediately.

Both configurations do horrible things to the impedances seen by the
source and sink as the wiper is moved.
--
Tciao for Now!

John.

[Arny Krueger]

"Mike Rivers" > wrote in message

> On 7/31/2010 8:06 PM, Erik Korte wrote:
>
>> I see folks like TC Electronic make a product for this
>> purpose. But It's $70+ and I'm sure it could be built
>> for a fraction of that. The hitch? I'm not an EE by a
>> long shot. All the same, I can solder and buy parts from
>> Mouser. I just don't know which ones.
>
> That's why it costs $70 - they know and you don't. They
> also probably had a custom pot made for the job.

Alps makes several. The rub is that they want you to order big lots. Every
once in a while someone bites the bullet and orders up a bunch, and sells
them for a big markup.

If you can find one for sale, the NHT Pro PVC is basically one of these in a
box with the usual XLR/TRS jacks.

http://www.nhthifi.com/s.nl/it.A/id.827/.f?sc=12&category=1213



> Go to
> the Mouser catalog and see if you can find a 10K ohm quad
> (4 gang) audio taper pot with the sections matched
> closely enough so the left/right image won't shift when
> you change the volume, and also the tip/ring balance
> won't change either.

Last time I looked, there was nothing for sale.


> It's easier (and less expensive) to
> make an unbalanced one, and it'll work just as well as
> long as you don't have long cable runs, which you aren't
> likely to have in your case. But you'll never make one as
> neat looking as the Level Pilot.

That is a bit of an artsy looking thing, isn't it. Price isn't bad,
considering that it comes with cabling.

[Arny Krueger]

"Mike Rivers" > wrote in message

> Mark wrote:
>>
>> You don't need to use 2 pots for each balanced line (4
>> total for stereo).
>>
>> A single pot (2 for stereo) will work fine to control a
>> balanced line, connect the pot as you normally would
>> except instead of hot to ground, the pot goes acrosss +
>> and - with no connection to ground.
>
> That might sort of work for an output that's not
> differential, but with an output where both legs have
> signal on them, you'll get an unbalanced output (to
> ground - you must have SOME point of reference for that
> voltage) that, at the center of the pot's rotation,
> changes polarity and starts increasing again.

Put a 5K or so resistor in series with each source leg.

As you rotate the pot you increase the resistance across the source and the
output voltage increases.

Only disadvantage is that it won't give you unity gain.

[Mark]

On Aug 2, 4:17*pm, Mike Rivers > wrote:
> Mark wrote:
> > if you wire the pot across the + and - leads of a diff pair, when the
> > pot is set to 0, you will get 0 volts across the diff pair.. (the two
> > outputs are connected together in that case and the DIFF output can be
> > nothing but 0.... *Granted there will still be a common mode output in
> > this case but if the input is true differential , it won't matter...
> > If you set it to 1/2 you will get 1/2 the voltage.. * the output will
> > never reverse polarity... *
>
> I don't understand how you're doing this. Where do you take
> the output in this configuration? Between the pot wiper and
> what? You can't mesure voltage at a single point, you need a
> reference.
>
> *> don't think about ground at all, no part
>
> > of this circuit is connected to ground.... *think only about the
> > voltage between the two wires...
>
> If the ends of the pot are connected to the two hot wires,
> the voltage between the wires won't change regardless of the
> position of the wiper. What am I missing here?
>
> --
>

amp out + goes to the top of the pot
amp out - goes to the bottom of the pot
(the differential output of the amp is applied ot the ends of the pot)

amp in + goes to the wiper of the pot
amp in - goes to the bottom of the pot

a fraction of the differential signal is tapped off the pot and sent
to the next stage

nothing goes to ground



Mark

[Mike Rivers]

Arny Krueger wrote:

> Alps makes several. The rub is that they want you to order big lots. Every
> once in a while someone bites the bullet and orders up a bunch, and sells
> them for a big markup.

You can still buy a pretty well matched dual Alps pot from
Radio Shack, but it's 100K, not 10K ohms. It works OK for a
volume control, however.

> If you can find one for sale, the NHT Pro PVC is basically one of these in a
> box with the usual XLR/TRS jacks.

Yes, that's another good one. A-Designs has one as well. Not
all that hard to find, but not $20 either. The Behringher
C-Console (or is it C-Control) is about $100 and does a lot
of useful stuff. Seems like that's about the buy-in point
for an off-the-shelf product. Any cheaper and it's not worth
while building commercially.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

[GregS[_3_]]

In article >, Mark > wrote:
>On Aug 2, 4:17=A0pm, Mike Rivers > wrote:
>> Mark wrote:
>> > if you wire the pot across the + and - leads of a diff pair, when the
>> > pot is set to 0, you will get 0 volts across the diff pair.. (the two
>> > outputs are connected together in that case and the DIFF output can be
>> > nothing but 0.... =A0Granted there will still be a common mode output i=
>n
>> > this case but if the input is true differential , it won't matter...
>> > If you set it to 1/2 you will get 1/2 the voltage.. =A0 the output will
>> > never reverse polarity... =A0
>>
>> I don't understand how you're doing this. Where do you take
>> the output in this configuration? Between the pot wiper and
>> what? You can't mesure voltage at a single point, you need a
>> reference.
>>
>> =A0> don't think about ground at all, no part
>>
>> > of this circuit is connected to ground.... =A0think only about the
>> > voltage between the two wires...
>>
>> If the ends of the pot are connected to the two hot wires,
>> the voltage between the wires won't change regardless of the
>> position of the wiper. What am I missing here?
>>
>> --
>>
>
>amp out + goes to the top of the pot
>amp out - goes to the bottom of the pot
>(the differential output of the amp is applied ot the ends of the pot)
>
>amp in + goes to the wiper of the pot
>amp in - goes to the bottom of the pot
>
>a fraction of the differential signal is tapped off the pot and sent
>to the next stage
>
>nothing goes to ground

including the next stage, and its output. A differential input stage should work. Maybe a transformer.

greg

[Scott Dorsey]

>>amp out + goes to the top of the pot
>>amp out - goes to the bottom of the pot
>>(the differential output of the amp is applied ot the ends of the pot)
>>
>>amp in + goes to the wiper of the pot
>>amp in - goes to the bottom of the pot
>>
>>a fraction of the differential signal is tapped off the pot and sent
>>to the next stage
>>
>>nothing goes to ground

This is using the output impedance of the source as half of a voltage
divider. It kind of works, although it doesn't do wonders for your noise
rejection.

If you do it, you MAY need to add breakout resistors (say 1K or so) in
series with each leg of the output, because some equipment won't like having
both legs of the balanced signal shorted together. The Entech DACs are some
of those things. Others will already have breakout resistors on the outputs
anyway.

Incidentally, if you are building a volume control box, and you're already
including breakout resistors, you might as well also add a switch to sum
both channels to mono, and a switch or button to mute the signal. They
both turn out to be very handy.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Frank Stearns]

(Scott Dorsey) writes:

-snips-

>Incidentally, if you are building a volume control box, and you're already
>including breakout resistors, you might as well also add a switch to sum
>both channels to mono, and a switch or button to mute the signal. They
>both turn out to be very handy.

And if you really want to get fancy, a "dim" switch. Throw the switch, the level
goes way down, but not completely off.

The mono switch is critical, however. Even if you don't have a direct need to check
for mono compatibility, summing to mono can tell you about problems in your
monitoring environment, as well as problems with your source material.

Frank
Mobile Audio
--

[GregS[_3_]]

In article >, (Scott Dorsey) wrote:
>Erik Korte > wrote:
>>Hi folks.
>>I'm looking into (hopefully making) a passive volume attenuator
>>between my Balanced Out interface and an Unbalanced Adcom 535.
>>
>>Any advice for a novice with decent soldering skills? A parts list
>>perhaps?
>
>Get a 10K dual audio-taper pot (and get a nice one that tracks well so both
>volumes will be the same). Input goes into the top of the pot, output
>comes off the wiper, bottom of the pot is grounded.
>
>Or trade it in for the 535 model with the gain control... 535S or something?
>--scott
>

I was reading through the posts. Wow. he above will work just fine.

I did not see anthing on using.... the pos leg out to a 5K-10K resistor, and
after that, a 100K or less, pot to ground. Signal goes straight through. The output
Z remains 5K or lower for longer lines. Basically a two resistor attenuator for each channel,
or one dual pot. I'm not sure how the taper would work out. Max volume is max pot resistance.

greg

[Mark]

On Aug 3, 3:58*pm, (GregS) wrote:
> In article >, (Scott Dorsey) wrote:
> >Erik Korte > wrote:
> >>Hi folks.
> >>I'm looking into (hopefully making) a passive volume attenuator
> >>between my Balanced Out interface and an Unbalanced Adcom 535.
>
> >>Any advice for a novice with decent soldering skills? A parts list
> >>perhaps?
>
> >Get a 10K dual audio-taper pot (and get a nice one that tracks well so both
> >volumes will be the same). * Input goes into the top of the pot, output
> >comes off the wiper, bottom of the pot is grounded.
>
> >Or trade it in for the 535 model with the gain control... 535S or something?
> >--scott
>
> I was reading through the posts. Wow. he above will work just fine.
>
> I did not see anthing on using.... the pos leg out to a 5K-10K resistor, and
> after that, a 100K or less, pot to ground. Signal goes straight through. The output
> Z remains 5K or lower for longer lines. Basically a two resistor attenuator for each channel,
> or one dual pot. I'm not sure how the taper would work out. Max volume is max pot resistance.
>
> greg

well the interesting part is that apparently for the balanced case
anyway.. it's NOT that simple... :-) proving the theory that
nothing is ever easy..
Mark

[PStamler]

Mike's last post basically just takes one leg of the balanced output
and pretends it's an unbalanced output. Since the cables are a big 3'
apiece that should work just fine. Run a resistor from the other (-)
leg to ground that's equal to the value of the pot, plus buildout
resistor if you use one.

Use a dual 10k audio taper pot with 2k as the resistor (between the
input jack's positive terminal and the top of the pot), connect a SPDT
switch to connect the tops of the two pots for mono, hang 12k from the
- terminal to ground, and Bob's your uncle.

Peace,
Paul

[alex]

Il 04/08/2010 4.44, Mark ha scritto:
> On Aug 3, 3:58 pm, (GregS) wrote:
>> In >, (Scott Dorsey) wrote:
>>> Erik > wrote:
>>>> Hi folks.
>>>> I'm looking into (hopefully making) a passive volume attenuator
>>>> between my Balanced Out interface and an Unbalanced Adcom 535.
>>
>>>> Any advice for a novice with decent soldering skills? A parts list
>>>> perhaps?
>>
>>> Get a 10K dual audio-taper pot (and get a nice one that tracks well so both
>>> volumes will be the same). Input goes into the top of the pot, output
>>> comes off the wiper, bottom of the pot is grounded.
>>
>>> Or trade it in for the 535 model with the gain control... 535S or something?
>>> --scott
>>
>> I was reading through the posts. Wow. he above will work just fine.
>>
>> I did not see anthing on using.... the pos leg out to a 5K-10K resistor, and
>> after that, a 100K or less, pot to ground. Signal goes straight through. The output
>> Z remains 5K or lower for longer lines. Basically a two resistor attenuator for each channel,
>> or one dual pot. I'm not sure how the taper would work out. Max volume is max pot resistance.
>>
>> greg
>
> well the interesting part is that apparently for the balanced case
> anyway.. it's NOT that simple... :-) proving the theory that
> nothing is ever easy..
> Mark

As far i know Scott said right.
In a unbalanced line, ground carries the "cold" part of the signal.
So ground needs to be involved in order to attenuate the incoming voltage.
In a balanced line the cold part is carried by the (-) wire so there's
no need to involve ground in the attenuation process.
for balaced lines simply use (-) as ground in the scott explanation and
let ground do his job.

(G) will go straight from IN to OUT;
(-) will go from IN to the bottom of the pot and then to OUT
(+) IN will go to the top of the pot;
(+) OUT is connected to the wiper.