Custom Volume Control Modules for Power Amplifiers

Looking at the design of some custom step attenuator based volume control modules that can be used in power amplifiers.

I've used the PGA2311 from TI. A controller is also required, this is based around an ESP32 and TFT display.

With the hardware built and tested, modules are fitted to my valve power amplifiers.

Finishing up, a little Blink mobile app is created that allows control of the volume as well as monitor the valve bias.

[bigalhudson]

Just found your site after pulling out my Cyrus collection after 5 years in storage. I had a nasty addiction with about 15 units. Bi/mono amped in a surround sound system. Mainly older stuff. Apa7.5 etc. Anyway now no space for it. I’ve learned so much from your posts.

[ashleycox]

Brilliant work, I really like the bias monitoring and the app. One of the best attenuator implementations I've seen.

[clifffinn]

Just found your site as I'm trying to build an ESP based Graphic Equaliser with automatic setup for each band so was looking for a digital volume control to set ref level. This was really informative and well described and a great help. Are you able to post the Arduino code you used as this would save me such a lot of time as I am very new to coding? Thanks again ether way for publishing the video.

[paulstubbs]

Nice, I have bought a kit based on that IC, it was in 'Silicon Chip' (Australia) so that solves PCB problems (offloaded it to someone else), However I do like your phone app idea, what are you using there, or did you write that yourself?
One Idea I had was a circuit to monitor the amp and if something like a overload, or excessive clipping occurs it would automatically wind back the volume.

[a-job]

Great, I'll keep it as a reference.
When using DB9 connectors, is the communication TTL or CMOS as is? RS232? Have you thought about using RS485? With a 120 ohm twisted pair shielded cable and many meters without problems.
Something I would put is a rotary encoder and some push buttons.
Using a wifi app to control it is very good.

[SatyajitRoy]

It's a really fascinating product you've made. However, you might consider removing U1 for two reasons. Firstly, a balanced output from any source will typically have its own driver, so there's no need to worry about its output impedance. Adding an extra op-amp not only increases the BOM cost but also introduces a bit of noise. Secondly, I'm not a fan of directly connecting an op-amp's input pin to the external world without any current-limiting series resistor. In today's environment, where numerous gadgets with switching power supplies can cause sudden spikes on the wiring lines, this might damage the op-amp. While this op-amp does have back-to-back diodes, they are only between the input lines.

[rjwestland]

Very nice, can you share building details please?