I'm hoping someone here might be able to help me out a little with this
project I'm working on. I have a Left and Right RCA Audio output that's fed
directly into a speaker amp, unfortunately, the speaker amp does not have
volume control. I'm hoping I could build something to go between the output
and input to control the volume. Is it simply a matter of just inserting a
variable resister (potentiometer)? Is that all there is to controlling
volume on an RCA audio signal? If so, what are the ohm ranges? Obviously 0
ohms for full volume, but how many do I need to make it silent? Also should
I use a linear pot or logarithmic pot?

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead of
making it.

Thanks,
Harry

In article , Harry Muscle
wrote:

I'm hoping someone here might be able to help me out a little with this
project I'm working on. I have a Left and Right RCA Audio output that's fed
directly into a speaker amp, unfortunately, the speaker amp does not have
volume control. I'm hoping I could build something to go between the output
and input to control the volume. Is it simply a matter of just inserting a
variable resister (potentiometer)? Is that all there is to controlling
volume on an RCA audio signal? If so, what are the ohm ranges? Obviously 0
ohms for full volume, but how many do I need to make it silent? Also should
I use a linear pot or logarithmic pot?

You can do a google search to come up with ideas. Any larger sized
pot would do, anything from 50K ohm to 100K ohm would do the trick.
Most folks prefer the action of a log taper, but in practice, the
log taper varies from pot to pot, so the right and left might be
different volume at some spots. Using a linear pot taper avoids
that problem.

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead of
making it.

You can buy cheap stereo receivers with remote control via E-bay
or one of the discount on-line sites. You need one that has
pre-amp out/power amp in jacks. A remote control per-amp would be
even better.

-john-

--
================================================== ==================
John A. Weeks III 952-432-2708
Newave Communications http://www.johnweeks.com
================================================== ==================

Harry Muscle wrote:

I'm hoping someone here might be able to help me out a little with this
project I'm working on. I have a Left and Right RCA Audio output that's fed
directly into a speaker amp, unfortunately, the speaker amp does not have
volume control. I'm hoping I could build something to go between the output
and input to control the volume. Is it simply a matter of just inserting a
variable resister (potentiometer)? Is that all there is to controlling
volume on an RCA audio signal? If so, what are the ohm ranges? Obviously 0
ohms for full volume, but how many do I need to make it silent? Also should
I use a linear pot or logarithmic pot?

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead of
making it.

Thanks,
Harry



You could do that, but it's likely to affect frequency response unless
it's compensated. A better solution might be a cheap pre-amp if
fidelity matters. Or you could put something together with a dual
op-amp, in a way that lets the feedback loop take care of the response.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"CJT" wrote in message
...
Harry Muscle wrote:

I'm hoping someone here might be able to help me out a little with this
project I'm working on. I have a Left and Right RCA Audio output that's
fed
directly into a speaker amp, unfortunately, the speaker amp does not
have
volume control. I'm hoping I could build something to go between the
output
and input to control the volume. Is it simply a matter of just
inserting a
variable resister (potentiometer)? Is that all there is to controlling
volume on an RCA audio signal? If so, what are the ohm ranges?
Obviously 0
ohms for full volume, but how many do I need to make it silent? Also
should
I use a linear pot or logarithmic pot?

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead
of
making it.

Thanks,
Harry



You could do that, but it's likely to affect frequency response unless
it's compensated. A better solution might be a cheap pre-amp if
fidelity matters. Or you could put something together with a dual
op-amp, in a way that lets the feedback loop take care of the response.

--
The e-mail address in our reply-to line is reversed in an at to
minimize spam. Our true address is of the form .

Just curious, how cheap of a pre-amp would do the job? I've never really
looked at pre-amps, so I have no clue as to prices for them.

Thanks,
Harry

Harry Muscle wrote:

I'm hoping someone here might be able to help me out a little with
this project I'm working on. I have a Left and Right RCA Audio
output that's fed directly into a speaker amp, unfortunately, the
speaker amp does not have volume control. I'm hoping I could build
something to go between the output and input to control the volume.

Probably. Tell us something about the source of this signal.

Is it simply a matter of just inserting a variable resister
(potentiometer)?

Could be.

Is that all there is to controlling volume on an RCA audio signal?

In many cases, yes.

If so, what are the ohm ranges?

Depends on the source and the load. If I was going to pick a number for
most modern applications, say 5 K ohms.

Obviously 0 ohms for full volume, but how many do I need to make it
silent?

Potentiometers are typically hooked across full signal and ground, and the
slider selects a voltage at either extreme, and those in-between.

Also should I use a linear pot or logarithmic pot?

Logrithmic.

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it
instead of making it.

The "already exists" device is called a passive controller, and generally
ain't cheap unless you built it for yourself.

John A. Weeks III wrote:

In article , Harry Muscle
wrote:


I'm hoping someone here might be able to help me out a little with this
project I'm working on. I have a Left and Right RCA Audio output that's fed
directly into a speaker amp, unfortunately, the speaker amp does not have
volume control. I'm hoping I could build something to go between the output
and input to control the volume. Is it simply a matter of just inserting a
variable resister (potentiometer)? Is that all there is to controlling
volume on an RCA audio signal? If so, what are the ohm ranges? Obviously 0
ohms for full volume, but how many do I need to make it silent? Also should
I use a linear pot or logarithmic pot?


You can do a google search to come up with ideas. Any larger sized
pot would do, anything from 50K ohm to 100K ohm would do the trick.

It depends on the situation. Too low a value will load the source.
Too high a value will be more susceptible to parasitic capacitance
effects on the frequency response, and noise.

Most folks prefer the action of a log taper, but in practice, the
log taper varies from pot to pot, so the right and left might be
different volume at some spots. Using a linear pot taper avoids
that problem.


Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead of
making it.


You can buy cheap stereo receivers with remote control via E-bay
or one of the discount on-line sites. You need one that has
pre-amp out/power amp in jacks. A remote control per-amp would be
even better.

-john-



--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Harry Muscle wrote:

"CJT" wrote in message
...

Harry Muscle wrote:


I'm hoping someone here might be able to help me out a little with this
project I'm working on. I have a Left and Right RCA Audio output that's

fed

directly into a speaker amp, unfortunately, the speaker amp does not

have

volume control. I'm hoping I could build something to go between the

output

and input to control the volume. Is it simply a matter of just

inserting a

variable resister (potentiometer)? Is that all there is to controlling
volume on an RCA audio signal? If so, what are the ohm ranges?

Obviously 0

ohms for full volume, but how many do I need to make it silent? Also

should

I use a linear pot or logarithmic pot?

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead

of

making it.

Thanks,
Harry



You could do that, but it's likely to affect frequency response unless
it's compensated. A better solution might be a cheap pre-amp if
fidelity matters. Or you could put something together with a dual
op-amp, in a way that lets the feedback loop take care of the response.

--
The e-mail address in our reply-to line is reversed in an at to
minimize spam. Our true address is of the form .


Just curious, how cheap of a pre-amp would do the job? I've never really
looked at pre-amps, so I have no clue as to prices for them.

Thanks,
Harry



I haven't looked lately, but I wouldn't be surprised if something
acceptable could be found for under 50 bucks.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Mouser.com part number 313-2420-x Dual Ganged Audio taper potentiometer
(where x is the value - 1k, 10k, etc.)


"Harry Muscle" wrote in message
...
I'm hoping someone here might be able to help me out a little with this
project I'm working on. I have a Left and Right RCA Audio output that's
fed
directly into a speaker amp, unfortunately, the speaker amp does not have
volume control. I'm hoping I could build something to go between the
output
and input to control the volume. Is it simply a matter of just inserting
a
variable resister (potentiometer)? Is that all there is to controlling
volume on an RCA audio signal? If so, what are the ohm ranges? Obviously
0
ohms for full volume, but how many do I need to make it silent? Also
should
I use a linear pot or logarithmic pot?

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead of
making it.

Thanks,
Harry

Harry Muscle wrote:
Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead
of
making it.

"CJT" wrote ...
You could do that, but it's likely to affect frequency response unless
it's compensated. A better solution might be a cheap pre-amp if
fidelity matters. Or you could put something together with a dual
op-amp, in a way that lets the feedback loop take care of the response.

The risk of audible anomolies is significantly greater from a
"cheap pre-amp" than from a conventional passive potentiometer.

The risk of spending too much to solve the problem is definitly
greater using a "cheap pre-amp" than assembling a passive
potentiometer in a metal box with two pair of RCA connectors.

The circuit is literally trivial and can be found in any number of
sources, both conventional and online.

Richard Crowley wrote:

Harry Muscle wrote:

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead

of

making it.


"CJT" wrote ...

You could do that, but it's likely to affect frequency response unless
it's compensated. A better solution might be a cheap pre-amp if
fidelity matters. Or you could put something together with a dual
op-amp, in a way that lets the feedback loop take care of the response.


The risk of audible anomolies is significantly greater from a
"cheap pre-amp" than from a conventional passive potentiometer.

It's true that the shortcomings of a passive potentiometer are
not anomalous -- they're well known and fairly easy to characterize.
But that wasn't my point.


The risk of spending too much to solve the problem is definitly
greater using a "cheap pre-amp" than assembling a passive
potentiometer in a metal box with two pair of RCA connectors.


Yes, pots are cheap.

The circuit is literally trivial and can be found in any number of
sources, both conventional and online.



And the circuit is trivial. That doesn't mean it's good.


--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Yes, pots are cheap.

The circuit is literally trivial and can be found in any number of
sources, both conventional and online.

And the circuit is trivial. That doesn't mean it's good.

Huh? It is precisely the same circuit used equipment of every
possible description from $3 radios to $3,000,000 audio systems.

The same circuit used in "passive preamps" costing hundreds
(even thousands) of dollars.

Richard Crowley wrote:

Yes, pots are cheap.


The circuit is literally trivial and can be found in any number of
sources, both conventional and online.

And the circuit is trivial. That doesn't mean it's good.


Huh? It is precisely the same circuit used equipment of every
possible description from $3 radios to $3,000,000 audio systems.

The same circuit used in "passive preamps" costing hundreds
(even thousands) of dollars.


I assume you're being deliberately dense on this for some reason unknown
to me. My point was simply that a simple potentiometer, in conjunction
with parasitic capacitance, is a filter. As such, it can affect
fidelity. Of course, the devil is in the details. But an earlier post
in this thread suggested, as I recall, pots in the 100K ohm range.

In a pre-amp, the designer has some control over the impedances involved
and the circuit configuration, and can compensate for these effects.
That's not to say all do, of course, and perhaps the really cheap ones
don't. If that's your point, then maybe we're not far from agreement.
But that's why my original post in this thread was worded the way it
was.

Tell me why you disagree. But I'm not impressed by arguments based on
"passive preamps" unless accompanied by significant detail about the
circuits involved. Nor am I convinced by your apparent claim that every
audio system simply ignores the issue and uses the precise same circuit.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"CJT" wrote in message
...
Richard Crowley wrote:

Yes, pots are cheap.


The circuit is literally trivial and can be found in any number of
sources, both conventional and online.

And the circuit is trivial. That doesn't mean it's good.


Huh? It is precisely the same circuit used equipment of every
possible description from $3 radios to $3,000,000 audio systems.

The same circuit used in "passive preamps" costing hundreds
(even thousands) of dollars.


I assume you're being deliberately dense on this for some reason unknown
to me. My point was simply that a simple potentiometer, in conjunction
with parasitic capacitance, is a filter. As such, it can affect
fidelity. Of course, the devil is in the details. But an earlier post
in this thread suggested, as I recall, pots in the 100K ohm range.

We agree that recommending something like a 100K pot for what
would appear to be conventional consumer line-level use is not
appropriate. My assumption of consumer line-levels is ~1K source
impedance and ~10K input impedances.

I would wager a nice dinner that it would be impossible for the OP
to detect any difference between a reasonable-quality 10K passive
pot in a simple shielded enclosure and the most expensive solution
you could suggest.

In a pre-amp, the designer has some control over the impedances involved
and the circuit configuration, and can compensate for these effects.
That's not to say all do, of course, and perhaps the really cheap ones
don't. If that's your point, then maybe we're not far from agreement.
But that's why my original post in this thread was worded the way it
was.

Tell me why you disagree.

I don't disagree. But IMHO you are significantly overblowing the
level of the original question. Everything you wrote was true, but
seems to offer little of practical value to the OP.

Richard Crowley wrote:

"CJT" wrote in message
...

Richard Crowley wrote:


Yes, pots are cheap.



The circuit is literally trivial and can be found in any number of
sources, both conventional and online.

And the circuit is trivial. That doesn't mean it's good.


Huh? It is precisely the same circuit used equipment of every
possible description from $3 radios to $3,000,000 audio systems.

The same circuit used in "passive preamps" costing hundreds
(even thousands) of dollars.



I assume you're being deliberately dense on this for some reason unknown
to me. My point was simply that a simple potentiometer, in conjunction
with parasitic capacitance, is a filter. As such, it can affect
fidelity. Of course, the devil is in the details. But an earlier post
in this thread suggested, as I recall, pots in the 100K ohm range.


We agree that recommending something like a 100K pot for what
would appear to be conventional consumer line-level use is not
appropriate. My assumption of consumer line-levels is ~1K source
impedance and ~10K input impedances.

I would wager a nice dinner that it would be impossible for the OP
to detect any difference between a reasonable-quality 10K passive
pot in a simple shielded enclosure and the most expensive solution
you could suggest.


In a pre-amp, the designer has some control over the impedances involved
and the circuit configuration, and can compensate for these effects.
That's not to say all do, of course, and perhaps the really cheap ones
don't. If that's your point, then maybe we're not far from agreement.
But that's why my original post in this thread was worded the way it
was.

Tell me why you disagree.


I don't disagree. But IMHO you are significantly overblowing the
level of the original question. Everything you wrote was true, but
seems to offer little of practical value to the OP.


Fair enough. I'm not sure how we seem to have got crosswise, but it
might relate to the context in which I first posted, at which time the
only reply on the board was suggesting a 100k pot. That probably
colored my thinking toward a more consumer failsafe option.

Of course, we don't really know much about the OP's "project," either
....

:-)


--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

In article , CJT wrote:
Harry Muscle wrote:

"CJT" wrote in message
...

Harry Muscle wrote:


I'm hoping someone here might be able to help me out a little with this
project I'm working on. I have a Left and Right RCA Audio output that's

fed

directly into a speaker amp, unfortunately, the speaker amp does not

have

volume control. I'm hoping I could build something to go between the

output

and input to control the volume. Is it simply a matter of just

inserting a

variable resister (potentiometer)? Is that all there is to controlling
volume on an RCA audio signal? If so, what are the ohm ranges?

Obviously 0

ohms for full volume, but how many do I need to make it silent? Also

should

I use a linear pot or logarithmic pot?

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead

of

making it.

Thanks,
Harry



You could do that, but it's likely to affect frequency response unless
it's compensated. A better solution might be a cheap pre-amp if
fidelity matters. Or you could put something together with a dual
op-amp, in a way that lets the feedback loop take care of the response.

--
The e-mail address in our reply-to line is reversed in an at to
minimize spam. Our true address is of the form .


Just curious, how cheap of a pre-amp would do the job? I've never really
looked at pre-amps, so I have no clue as to prices for them.

Thanks,
Harry



I haven't looked lately, but I wouldn't be surprised if something
acceptable could be found for under 50 bucks.

Just get on ebay one of those elcheapo audio/video mixer boxes

Harry Muscle wrote:

Or, if something like this already exists (and has a remote control to
control the volume), please let me know, cause I'll just buy it instead of
making it.

Adcom SLC-505 (no remote control).

Also, I know that there a manufacture making a passive pre-amp with a
remote volume control: I dog-eared the page of a magazine recently --
now if I could only remember which one!

--
Len Moskowitz PDAudio, Binaural Mics, Cables, DPA, M-Audio
Core Sound http://www.stealthmicrophones.com
Teaneck, New Jersey USA http://www.core-sound.com
Tel: 201-801-0812, FAX: 201-801-0912