[sdiy] Trueno

Neil Johnson neil.johnson71 at gmail.com
Wed Dec 13 10:44:17 CET 2017

Hi Roman,

> Here are more detailed pictures:
> http://www.synthdiy.eu/files/truenobottom.jpg
> http://www.synthdiy.eu/files/truenobottom2.jpg
> http://www.synthdiy.eu/files/truenobottom3.jpg
> http://www.synthdiy.eu/files/truenotop.jpg
> http://www.synthdiy.eu/files/truenotop2.jpg
> http://www.synthdiy.eu/files/truenotop3.jpg


> You were right, Neil, that's pair of LM4250 in the filter.

There aren't that many programmable op-amps these days, and while they
may be on lifetime buy, guys like this trueno outfit don't worry about
things like that.  A couple of reels would probably be enough for the
lifetime of this little thing.

> Also on the bottom side:
> 3rd VCO that was missing from yesterday's picture, with inevitable Kynar
> job, STM32F042C6 for the brains, ADC - AKM5720, and

Mmm.... yeah...

> silkscreen suggests
> analog part works at +/-3.5V supply.

So they're already operating the op-amps outside of their ratings (min
is spec'ed at +/- 5V).
Unless the circuit is designed with high impedances those poor old
TL074s will struggle to get any more than a couple of volts either
side of 0V.
They could have chosen better op-amps and got more headroom and/or SNR.


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