Building a simple speaker volume control

[pingles]

We've just got a new hi-fi setup in the office here, and want to get 2 speakers wired up. One set will be near my desk, the others towards the other side of the office.

It'd be nice if both could have their own volume control so that the two sides can control the volume when necessary (i.e. making phone calls etc.).

I've not done any audio electronics other than simply assembling some MINT and PIMETAs and was wondering how complicated it had to be? Is it simply a case of putting some resistors and a pot together with the speaker cable in and out? If so, what kind of values would I be looking at for the resistors to control the volume reasonably?

Thanks for any suggestions.

Paul

 

[tangent]

If you put resistance inline with the speaker cable, that will indeed let you reduce the speakers' volumes, but it will reduce the amplifier's control of the speakers. The sound could get sloppy, smudged, etc.

Ideally, you want two separate amplifiers here. Two small integrated amps would work fine for the relatively low volume level and fidelity you're probably asking the system to put out.

 

[pingles]

Would a CMOY-based amplifier be suitable? What kind of adjustments would need to be made? I'm just thinking that the tutorials on your site would be a good way to go.

 

[amb]

Quote:

Originally Posted by pingles Would a CMOY-based amplifier be suitable? What kind of adjustments would need to be made? I'm just thinking that the tutorials on your site would be a good way to go.

A Cmoy-like design will not be able to drive speakers directly because op amps cannot handle the low impedance load. You need power amps intended for speakers. To make a Cmoy drive speakers you need to add a high current output buffer stage with some voltage gain running off separate, higher voltage power supply rails. That is non trivial and if you're going to be doing that much you might as well start with a speaker amp design in the first place (instead of Cmoy).

That said, if you don't care too much about the sound quality, you can use L-pads on each speaker to control the volume. An L-pad is basically a volume control pot for speakers, except it has dual elements wired in such a way to present an approximately constant impedance load as seen by the amplifier (regardless of the setting of the control shaft). Also they are constructed to handle more power than small-signal pots. Radio Shack carries L-pads.

Another alternative is to use self-amplified speakers with its own built-in volume control, like some of those for computer use. You won't find too many high-end speakers in this category but I don't know what your requirements are. This may be the easiest solution to your problem.

-Ti

 

[Budgie]

Cheapest way is to use stereo L-pads to control each set of speakers.