Thursday 13 April 2023

VCAs and Old Dutch Masters

 There's a saying out there, which is almost a truism:

    "you can never have too many VCAs".

Having some time on my hands today, I decided to knock up another of my takes on Yves Usson's 'simple VCA' circuit, which I have cast into Eurorack format. I made the VCA in an hour or so, with music ringing in my ears.

You can see the result in the pictures below, which show the front and back of the finished module as well as the PCB from the side which usually is obscured by the front panel.

My implementation pretty much follows Yves' words and music, only I drive each of the two outputs  actively in order to use the last of the four op-amps in the quad package you see above. 

Yves' circuit used a twin and a single op-amp and that's not very space efficient when you're squeezing chips onto a little board for Eurorack. I couldn't bear to see the last stage of my quad package sitting there doing nothing!

This is the fourth of these units I've made now (one is DC coupled, with linear controls, to use with CV signals) and they work like a charm. With the 4 other simpler CA3080-based VCAs already in my system (which were based on a MFOS design), I may not have too many, but I'm getting by for now.

As I said, I was building today "with music ringing in my ears". I wasn't listening to music - it was the memory of last evening, when I went to a wonderful gig at The Met, Bury, to hear Dutch "prog-rock" (and - I would say - "fusion") legends, FOCUS, who are on their 50th anniversary tour. I have been a fan since the 1973 UK release of "Moving Waves", so it's been 50 years for me too.

The band (who I've seen many times before) were superlative and the drummer, Pierre van der Linden, who played on that original album, was ON FIRE!

I was standing about six feet from another founder member, Thijs van Leer. Let's be clear - there was nothing synthetic last night - just real instruments. But the tonebars on Thijs' Hammond are often held up as an example of additive synthesis.

Talking about tonebars, when the good people at JLCPCB are finished with the pcb designs I sent them yesterday, I'll have something to say about adding and 'mixing' harmonics; watch this space.

I'm off to play with my new VCA and to revel in more music from "the most successful and the most appreciated of all the Dutch pop-rock exports" - and my favourite band of all time.


UPDATE (15/04/23) :

Design files for my Eurorack version of the YuSynth VCA 

have now been published on my github.


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