Interesting video showing a tone control based on a TDA1524 ( 10 pieces for about 2.5 USD at aliexpress)
Given that the controlling pots (they are linear according to the data sheet) use a reference voltage from inside the chip itself, those could easily be replaced by CV-inputs.
Note, the text at the switch says ‘contour’ and ‘linear’.
Is there a better quality image that you can post? I’m interested in the project
Last buy 2009-09-31 so usual caveats apply; might be recycled, might be something entirely different.
Given the video description says that the chips were cheap off AliExpress, I’m happy to take a punt on some cheap chips to see if I can get a similar response 
just under £3 for 10 (including Brexit tax) from a seller I’ve used dozens of times in the past without any problems. I imagine they’re clones that don’t quite match the datasheet but do a good enough job for one-off projects.
I ordered a few as well.
A quick follow up - my chips arrived this morning. I did a check of them; there’s a few different date codes from 1991 to 2000, the pins are clean and even and wiping across the tops with isopropyl didn’t revel any signs of them having been painted over. Looks like they’re probably NOS parts.
The datasheet isn’t the greatest detailed datasheet I’ve seen - no physical pinout etc - so I’m trying to cobble together a test circuit. My Long COVID has flared up again 
so I’m not sure how long it’s going to take me…
I got a message that my order has arrived in my country. So far it has taken between 3 and 24 days before I received anything former orders have learned. So … still waiting. But I’m very curious what your experiments will bring. And obviously I hope you get well soon!
Another follow-up. I put together a really simple test circuit with some potentiometers, but I don’t have all the capacitor values on hand to match the circuit above. I could probably run some in parallel but my head’s hurting too much at the moment to be bothered digging through things. The bad substitute values I put in did nothing for the filters, regardless of the levels I attempted to set (at least as far as I could tell with the test audio I was pushing through) so I’ll have to come back to that in a week or two.
On the upside, the balance control and, more importantly, volume control worked exactly as you’d hope. Connecting the output from my ADSR module to the volume CV input made a nice enough VCA for me to consider using these chips to make some properly. I have a homemade power supply that gives me +5V as well as +/-12V; as long as you’re running the TDA1524 on more than 10.8V you can connect pin 17 (used for the potentiometer reference) to 5V and that makes voltage control from other circuitry nice and easy.
I’m rather pleased with these chips. I’ll get some decent capacitors next time I’m doing an RS order and make something on a perfboard.
Follow-up III time!
While pottering around I found the blog posts that accompany the project in the video that started this all off (for me at least). Tyler has provided schematics for his first test rig (which is what is in that video) and the follow-up, a proper module with integrated noise source.
His schematics are well labelled and fill the gaps that I thought were in the datasheet - pins are clearly named and he’s included documentation on the schematic itself. Having different filter configurations for the left and right channels and using the built-in balance control to mix them is the sort of obvious thing to do that I’m kicking myself for not thinking about using stereo circuits like that before!
Edit: it seems Tyler is one of us - @koko, this is you right?
