[sdiy] Ele4Music (EFM) VCA 6b issues...

[Matthias.Herrmann at jeppesen.com]

you may find some information here:
http://www.modular.fonik.de/files/EFMforum/VCA%206B%20forum.pdf

i did not read carefully thru it, though. just a guess.

cheers,
matthias
___
www.modular.fonik.de


synth-diy-bounces at dropmix.xs4all.nl wrote on 01/25/2009 11:44:47 PM:
> Hello,
> 
> I know its a bit late in the day, but i actually still have a stack 
> of Tom's boards left to go...
> 
> Todays one is the VCA 6b.
> 
> Supprisingly it seems to work, pretty much, without issue, with a 
> couple of exceptions - a 100k resistor has to be added to the AC 
> input, as the board is not actually as per the schematic, and there 
> is no resistor between the capacitor and opamp.  Without this 
> resistor, the AC and DC input levels are very different.
> 
> So, thats that bit, but, where im having issue is the gain.
> 
> What im wanting is, with no additional voltage at the CV jacks, the 
> gain to be simply controlled by the VCA level pot, such that, at 
> minimum, there is no signal, and, at maximum, there is unity gain.
> 
> This isnt the case though, and, unless ive made an error that i 
> havent spotted, theres nowhere near unity gain (the output level is 
> a fraction of the input), and im wondering where would be best to 
> alter the values.
> 
> Ive just uploaded the schematics to here -
> 
>  http://www.zen9084.zen.co.uk/vca_6b.pdf
> 
> 
> Should i do R17 / R34, or R7, R24 (or indeed somthing else), and is 
> there any real reason why one, rather than the other?
> 
> Thanks, Julian 
> 
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