Balanced Volume Control

zingo

I am POSSIBLY going to be building an integrated amp, and am looking for a good option of balanced volume control. I would prefer it to be remote control as I don't like to get off the couch . I've done a few unbalanced, stereo pots before which were easy enough, and it seems like wiring up a quad attenuator for balanced (one option) would also be fairly easy. I'm also not against digital volume control, but again, remote control is the preference. Thanks in advance to anyone who's dealt with the issue before and can lend any advice.

megasat16

If I am reading right, you want to use 4 gangs POT as a balanced volume pot and use each gang for + and - for L and R channels?

If so, I think you should explore a bit more into the balanced designs. Most balanced pre-amps summed the balanced signals at input before passing the signal through the Volume POT and then to the line amp stage and then convert back to balanced circuit at the pre-out. But some preamps put the POT after the line amp before signal is converted back to the balanced circuit again.

A few variations exists for sure but I don't know if there is any manufacturer using a 4 gang pot as a Balanced Volume POT without signal summing first coz it's going to have inaccuracies between - and + signal levels due to small resistance variations between gangs (even for step attenuator with high precision resistors). You need to add the + and - lines from the balanced anyway. You can add before amplifier stage or at the amp output stage but the latter requires a lot of component matching to very high degree and most DIY can't probably do it easily or cheaply.

It's probably doable but may not be a great idea. Since you are building an integrated, the volume pot is best placed after the balanced summation point at the pre-amp stage. There is no need to convert anything back to balanced after the POT since it's an integrated amp. And you can use any regular Remote Controlled Volume Pot offered from HongKong sellers on eBay.

zingo

I completely agree with you, but let me illustrate my specific situation without completely tipping my hand. As you can see, a balanced signal (or unbalanced with shortening) gets inputted and the amplification process concludes at the speaker output; not leaving the option of attenuation between the two. Obviously the below module would work perfect for a power amplifier whether mono or stereo, but I do like the ease of integrated, and was trying to go that route if it was reasonable.

megasat16

Jake,

I think you are building one of these Class D module amps? :biggrin:

If so, everything is most likely built in the module and all you need is the power supply section and volume control. I now understand why you want the quad gang volume POT.

I was thinking you are going to build Regular Class A or A/B integrated.

I don't know if you stumbled upon this thread but looks like it's what you intend to do?

http://www.diyaudio.com/forums/pass-labs/5790-balanced-volume-control.html

zingo

It is a class D module, and should be pretty fun to play around with. :biggrin:

Instead of placing the pot between output and ground (4 needed) place the pot between positive and negative output of each balanced channel (2 needed), so one stereo pot would work. This way, depending on impedance of the pot, positive and negative output will cancel each other without connecting to ground. You can find this setup implemented by Nelson Pass on his D1 DAC.

This sounds like an intriguing idea after reading through the DIYaudio thread (thanks). I'm trying to figure out how it would compare to a correctly wired 4 gang attenuator...

zingo

I just emailed Scott Endler from Endler Audio (made famous for his inline attenuators) about a balanced attenuator, and here is what he sent back:

Hi Jake,
I can make a raw stereo attenuator (no connectors) for balanced sources in 4k or 20k ohms for $100 plus $7.50 shipping to US addresses. To keep the cost down (the Elma switches are ridiculous) they are true balanced using only one switch deck per channel so they won't attenuate correctly with a single ended signal.
Scott



Even though it wouldn't be powered, it's a great price for a shunt style, resistor based attenuator with a true balanced signal path for each left and right channel.