[sdiy] ARP 2600 VCA - 4019 module

[Dave Manley]

In an off-list email, I suggested he use a 100K pot for the linear gain 
setting instead
of 50K.  He said it fixed the problem.  The 2600 service manual shows a 
100K pot,
while the 4019 module schematic shows a 50K.

-Dave

rob wrote:
> Hi
> I have cloned the ARP 4019 using the original ARP blueprints - which match
> the Arptech ones.
> I am finishing off the testing today, so will let you know..
>
> http://www.emulatorarchive.com/Amplifiers/AM8019/am8019.html
>
>
> Regards
> Rob
> www.emulatorarchive.com
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Dave Leith
> Sent: 26 June 2009 05:44
> To: SDIY
> Subject: [sdiy] ARP 2600 VCA - 4019 module
>
>
> Has anyone built this circuit from the ARP schematics from
> http://www.arptech.synth.net/modmain.htm ?
>
> I can't get the signal out to match the signal in (unless I change some
> resistor values.) It's about half the level out compared to the input. I
> have double checked resistor values, transistor orientation/polarity and
> have used the circuit layout from the schematic package, and messed with the
> trim pots. I've also measured voltages and they seem about right except the
> current swing is too small....
>
> Oakley makes a similar module as do some of the boutique repair shops so it
> should work correctly unless I'm missing something really obvious (quite
> possible especially after the number of hours staring at it :-) or I wonder
> if the parts values are correct as shown.
>
> Any suggestions?
>
> Thanks Dave
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