Doepfer

One of my A-111 VCOs has suddenly developed an issue. I noticed some note sound fluctations in a sequence I was running and after checking my quantiser I then checked the oscillator's tuning (normally tuning is pretty rock solid on the A111s).

I plugged the output of the A111 into a tuner and the A111 won't hold its frequency/note pitch...it shifts randomly (plus and minus) around whatever note/frequency I dial in. The shift isn't huge, but its relatively large enough that the shift is very noticeable (around +/- 20-35 cents, sometimes a little more).

I'm assuming a component has failed or something which is destabilising the module. I've switched the unit between racks (same issue) and tried my other A111s on the same rail and in the same rack as the affected unit and there is no problem, so the issue is isolated to the one A111.

Any ideas?

Season's greetings to all !

Steve

Am 28.12.2016 um 06:42 schrieb sj230962@gmail.com [Doepfer_a100]:
> the A111 won't hold its frequency/note pitch...it shifts randomly 
> (plus and minus) around whatever note/frequency I dial in. The shift 
> isn't huge, but its relatively large enough that the shift is very 
> noticeable (around +/- 20-35 cents, sometime

How fast is the frequency changing? Is it a slow change, not noticable 
in individual short notes, or is the frequency jumping suddenly?

Florian

An audio example would be good.

If you say the changes are sudden random changes, then I assume, that 
you have a noisy octave switch or pitch potentiometer.

Florian

Am 09.01.2017 um 10:57 schrieb sj230962@gmail.com [Doepfer_a100]:

>
>
> I can record some audio and some oscilloscope video to show the 
> problem if that would help...
>
>

make sure you have the internal CV jumper disconnected. If it isn't then 
any stray voltage on the busboard can leak in to the VCO

Best Regards
Laurie Biddulph
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Happy New Year

On 9/01/2017 8:55 PM, sj230962@gmail.com [Doepfer_a100] wrote:
>
>
> Hi Florian - its not a slow periodical swing in pitch, its much more 
> of a random walk within limits, sometimes small increments, sometimes 
> slightly larger increments...but its plus/minus around the root note.
>
>

I was on holidays until yesterday. That's why I did not answer so far.

I'd agree to Florians diagnosis. Only in the worst case it could be the
CEM3340. But I think it's a faulty potentiometer or trimming potentiometer
or rotary switch. It's impossible to estimate the repair charges in advance
because all depends upon the required working time and spare parts.

You may send in the module to our address for repair (see ABOUT US on our
website). In this case please follow the repair notes on the FAQ page of our
website (as the procedure depends upon your home country and the purchase
date). The A-111-1 modules are serviced by Matthias Marass
(keyboards@doepfer.de).

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com [mailto:Doepfer_a100@yahoogroups.com]
> Gesendet: Montag, 9. Januar 2017 04:41
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] Re: A111-1 VCO problem - won't hold pitch
>
> I there's no suggestion on what the problem is, perhaps I can
> send it back to Germany for analysis/repair ?   Is there a cost
> associated with Doepfer fixing a faulty module ?