Costeffective digitally controlled analog signal mixing circuit. How?


I’d like to have some kind of digitally controlled mixer for mixing 6 analog signals with the ability to store and recall the settings.
It would have to have a gain range from mute to 0dB. Gain resolution is not that important, 4bits/16 steps would be sufficient.
I’ve looked into programmable gain ampliliers and digital potientometers, but haven’t found anything usable that was not unreasonably expensive for this project.
Looking for some inspiration :slight_smile:

thank you


Oh, sorry I should’ve mentioned that this is about a diy synth design.

I’m looking for a circuit for mixing oscillator signals into a VCF.
So I hoping for some kind of IC circuit for a few bucks per channel.

Frames does this, although with 4 channels. For the four channels it uses a ssm2164, four tlc072, a 4 channel DAC, which you could possibly omit, and a arm processer, but that could be anything. I’m sure that’s a couple of bucks per channel.

Trade-off between price and number of steps/clicks when changing gain.

2x1.5 + 2.0€ / 1000. A pair of (non-linearized) 2164 controlled by an 8-channel 8-bit DAC like the DAC088S085. If your definition of “mute” is -100dB, then you can adjust things by steps of 0.4dB. Uses a complete VCA, so adds a tiny bit of noise/distortion/offset. Deals with full range signals. With filtering of the 6 CVs, the transition between steps can be silky-smooth.

2x1.0€ / 1000. A pair of quad digipots, like the MCP4341. Caveat: can only handle unipolar voltages in the 0V…5V range. Audible stepping.

6x 0.2€ / 1000. One 4051 per channel, switching 8 resistors (only 8 gain steps though). Even more stepping. Tolerates bipolar signals.

So vca or ota is the best way to go?

I’d like to avoid the 2164 though.

@pichenettes :
Great food for thought.
With “2x1.5 + 2.0€ / 1000” you mean for example 5€ for 6 channels, when bought in quantities of 1000, right?

I don’t mind stepping at all since it’s not meant to be modulated, just for total recall.
8 steps should be usable. Haven’t thought about using analog mux ics + resistors, but they’re really cheap. Might be the path i choose.

Thank you!

> I’d like to avoid the 2164 though.

Why so? Absolute transparency required? I wouldn’t worry about noise/distortion if this goes into a ladder or OTA VCF :slight_smile:

> you mean for example 5€ for 6 channels when bought in quantities of 1000


> Why so? Absolute transparency required? I wouldn’t worry about noise/distortion if this goes into a ladder or OTA VCF :slight_smile:

Haha, not because of transparency. In fact I wouldn’t mind a little distortion/noise at this stage at all, since it’s pre filter/pre vca and a monophonic signal, so no IMD. It’ll probably just add some nice character :slight_smile:

No, it’s mainly because it’s not exactly cheap (at least for this application), afaik there’s only one manufacturer (coolaudio) and for a hobbyist (low quantities) not the easiest to source + prices vary all over the place + relatively high shipping costs.

The chip itself is great :wink:

PT2258 ?

6 channels, can be found on eBay or Aliexpress for less than 1$.
It’s a multimedia volume controller with I2C interface.
Cheaper than 2164 for sure. I don’t know about quality though.

O_O good catch!

Wow, cool! Seems to be exactly what I want. Thanks!

If more information is needed :
An Arduino library found on internet

To find the full datasheet with i2c protocol, remove “-s” at the end of the download link the manufacturer put on his website.
The normal link (ending with “PT2258-s.pdf”)give access to a datasheet with some pages missing.

I once tried to do a “DCF” out of this, which never succeded, or even a vca, but it lacks a zero crossing feature, hence it makes lots of audio clicks. So do not expect to modulate it! (But that was not your goal)

Some JRC equivalent chips have these features, ( but they are almost all smd, and the only DIP one (NJW1159D) is only available as 1000 units at mouser…