Doepfer

Hi all, hi Dieter (if you're listening :^),

I'm new to modular synthesis and got my hands on a used Doepfer A-100 base system which worked fine until this year's scorching summer, or at least I didn't notice any issues before; not sure if there's a connection with the high temperatures we've been experiencing.

I know the A-110 VCO's tuning/tracking is often discussed to death on forums, but I appear to be stuck with a pair of untunable A-110's.

The two A-110 VCOs in my kit (rev.3, > 15 years old?) have both drifted WAY out of tune. I followed the calibration procedure on Doepfer's website, but after 4 attempts, I've given up: both VCOs barely track over 1 octave, and the scaling pots on both (P7) are at their limits. But get this: they are at opposite ends of their respective limits, i.e. the tracking of these VCOs is actually divergent. I find that pretty weird.

Just to make sure, I've calibrated the A-190 MIDI-CV interface accurate to 1mV, and checked that the supply voltages are within spec too. I even checked the relative values of the critical resistors R1, R1', R2, R3, R3'; they are all within 0.1% as required.

I'm at the end of my rope. Is it time to replace the aged opamps, or should I just replace both modules outright?

Many thanks,

--GT

I'm sorry about your problems with the A-110. Please contact our A-110 specialist directly: Matthias Marass (keyboards@doepfer.de).
He has tested more than 10000 A-110 over the last 20 years and is responsible for the service of the A-110. Maybe the internal
transistor heaters are defective and the CA3046 have to be replaced. But that's only a guess.

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com [mailto:Doepfer_a100@yahoogroups.com]
> Gesendet: Freitag, 21. August 2015 10:39
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] The untunable A-110s
>
>
>
>
>
>
> Hi all, hi Dieter (if you're listening :^),
>
> I'm new to modular synthesis and got my hands on a used Doepfer A-100 base system which worked fine until this year's
> scorching summer, or at least I didn't notice any issues before; not sure if there's a connection with the high
> temperatures we've been experiencing.
>
> I know the A-110 VCO's tuning/tracking is often discussed to death on forums, but I appear to be stuck with a pair of
> untunable A-110's.
>
> The two A-110 VCOs in my kit (rev.3, > 15 years old?) have both drifted WAY out of tune. I followed the calibration
> procedure on Doepfer's website, but after 4 attempts, I've given up: both VCOs barely track over 1 octave, and the
> scaling pots on both (P7) are at their limits. But get this: they are at opposite ends of their respective limits, i.e.
> the tracking of these VCOs is actually divergent. I find that pretty weird.
>
> Just to make sure, I've calibrated the A-190 MIDI-CV interface accurate to 1mV, and checked that the supply voltages are
> within spec too. I even checked the relative values of the critical resistors R1, R1', R2, R3, R3'; they are all within
> 0.1% as required.
>
> I'm at the end of my rope. Is it time to replace the aged opamps, or should I just replace both modules outright?
>
> Many thanks,
>

On Fri, 21 Aug 2015 10:46:05 +0200, yahoo@doepfer.de [Doepfer_a100]  
<Doepfer_a100@yahoogroups.com> wrote:

> I'm sorry about your problems with the A-110. Please contact our A-110  
> specialist directly: Matthias Marass (keyboards@doepfer.de).
> He has tested more than 10000 A-110 over the last 20 years and is  
> responsible for the service of the A-110. Maybe the internal
> transistor heaters are defective and the CA3046 have to be replaced. But  
> that's only a guess.

Thanks for referring to Matthias, Dieter.

FYI, I tried swapping the CA3046's, but that made no difference. I also  
checked the tempco voltage, and it was at around 0.63V as per the  
calibration requirements.

I hope Matthias can drop me a hint. Many thanks,

--Roland


-- 
"END OF LINE" [MCP, 1982]