Costeffective digitally controlled analog signal mixing circuit. How?

Hi,

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
cheers

K-Mix?

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.

@Jensu:
Thanks.
So vca or ota is the best way to go?

I’d like to avoid the 2164 though.

edit:
@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

Yes.

> 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 ?
http://www.princeton.com.tw/en-us/products/multimediaaudioic/electronicvolumecontroller(6channels).aspx

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!

@Jules974
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, (http://www.njr.com/semicon/audio_video/audio_signal_processing_all.php) but they are almost all smd, and the only DIP one (NJW1159D) is only available as 1000 units at mouser…