Yet another stereostim amp question

[stimekus]

Hi all,

I've been away from estim for several years, but I'm working on plans for a new DIY stereostim unit. I'd like to have independent hardware volume knobs for the two channels, rather than trying to adjust a balance slider or individual channel levels in the software audio player. Since I'm not finding amplifier boards with independent volume controls, I'm trying to figure out the options.

Option 1: Buy two of these 2x30watt boards and just use one channel on each amp.
https://www.parts-express.com/2-x-30W-H ... h-320-5030

Option 2: Buy a TPA3116D2 2x50W board and add two pots for individual channel control, using the board's volume pot as a master. But I would need help selecting the channel volume pots, and where best to insert them into the circuit. Could they be placed before the board's input, so I wouldn't have to try to insert them into the board's circuitry? This seems the easiest way. If so, what would be a suitable pot for volume adjustment to the line level signal?

I lean towards option 2 because it provides a physical master volume control as well. Nice to have a single control to adjust things once the balance has been set.

I don't remember exactly which design I used when I built my last unit, almost 8 years ago, but what I've seen after a quick look around now seems to be similar. I'm planning for the rest of the design to follow the typical schematics that have been around for years, UNLESS there's been something new and exciting developed in the last few years that I've missed. Trying to keep the cost and size reasonable, and the assembly as simple as possible.

Thanks for any suggestions!

[Bright_Sprinkler]

I used two of these, before passing the audio into the amp.
One for each channel (L/R).

This allows me to control the channels individually and also have the global volume on the amp itself.
So basically:
Aux -> Cinch-Splitter -> L -> Volume Knob -> L-Input Amp ---> ...
..........................\> R -> Volume Knob -> R-Input Amp /

[Phloxde]

I used these for individual volume control
https://www.mouser.com/ProductDetail/CT ... 1F1A%3D%3D
these were also on my shipping list
https://www.digikey.com/en/products/det ... A/10738638
wired in to the input before the amps volume control, per the max.v3 design. Just needs to be any decent10K Linear plastic pot.
Someone somewhere went the two amp route and was very happy with it, but they also used a very compact/cheap amp vs most builds, having the 2 amps took away some of the internal amp design concerns.

[stimekus]

Thank you @Bright_Sprinkler and @Phloxde!

This info is helpful! It seems putting a pot on each channel before the amp works just fine. That does make things easier.

[picofarad]

Good discussion.

My situation is a bit different. From the computer I feed my amp (Fosi Audio BT20A Pro Bluetooth Stereo Amplifier) via Bluetooth. This gives me isolation and fewer cables. It then goes into a box I built that has two audio transformers and a pair of current reducing 4 ohm resistors. viewtopic.php?p=361126#p361126

My question is: could I insert these volume controls after the transformers before the electrodes? Or would it be better to insert between the amp output and the transformer input?

Thanks!

may need to re-post in a new topic to get a response.