Tuner output circuit from Etherwave hotrodding manual

I'm thinking of adding the tuner output circuit to my Etherwave and was wondering if others here have built it and how well it worked for you.

http://www.suonoelettronico.com/downloads/HotRodEtherwav.pdf

I’ve built and installed that circuit several times as a kind of custom mod. Works without problems. Although the CA3080 has become obsolete, it’s still easy to find on eBay and similar platforms.

Thanks Thierry! Is there a replacement chip you'd recommend and any changes to the circuit?

No, unfortunately this kind of current controlled transconduction op-amp is definitively obsolete. The CA3080 had already a successor, the LM13700 which is used as VCA processor and for wave shaping in all Etherwaves (up to the Pro), the series 91, the Ethervox theremins, and most analog Moog synthesizers and analog pedals, is obsolete and out of production, too. But there is enough NOS (new old stock) of both for the years to come, so that the spare part and hobby builder market will not dry out, soon. Thus, you might buy this IC on ebay, ali express, or wherever and just be happy without worrying.

Why are they specifying a CA3080 in the first place?  The circuit doesn't appear to use / need electrically variable gain.

Or is it distortion harmonics they're looking for in pitch preview?  I'm confused.

With the actual fixed gain setting and dc offset, it does some nice soft clipping, transforming the raw U-formed wave into a nice rounded almost 50:50 square which can easily processed by an external instrument tuner.

Ah, I see, thanks!

Second, I think that we have to understand that in the 80ies and 90ies, these OTAs were Bob Moog's "daily bread" which he used in almost all his designs. So, he was for sure very familiar with these and preferred their use, even if other variants or choices would have been possible.

Great point. It would be nice to have a more up-to-date circuit design for adding a tuner output with modern parts. I'll go ahead and build this one though. Thanks for all the information!

Woah, that's awesome! Definitely worth the price for an experiment. Thanks!

Edit: they don't specify that it includes a pinout, but I could probably trace and figure that out.

I'm working on a little hack project using a Teensy+AudioSheild and the tuner routines from its audio library. I don't expect it to be super fast, but for my experiment, it might not need to be. I'll reveal more once I have a fully working prototype.