[sdiy] Memorymoog VCO trim

[Luís Marka]

Hi folks,
When servicing my Memorymoog a few years ago I observed the instability 
in pitch was not always originated on the VCOs themselves, but from 
fluctuations in the CV feeding the VCOs. New connectors, IC sockets and 
trimpots across *all* boards sure helped stabilizing it. I would say it 
is a good idea to get the schematics and track the CV path from, say, 
the AM6012 IC and its associated S&H circuits all the way to the VCO 
ICs, replacing or cleaning connectors and such. It is also a good idea 
to replace +15V/-15V/GND connectors on the boards and associated wiring: 
at times, *touching* these connectors was enough to introduce pitch 
fluctuations!

dragon.servicing wrote:
> Hi,
> I think I read a while ago that the trimpots in the Memorymoog ( and 
> some other older synths ) can wear out causing unpredictable 
> performance. I did find this with a Minimoog I worked on a couple of 
> years ago. ( but the trim pots are probably a different type ).
> I think it was on the Memorymoog that the power supply trims were not 
> ten turn pots but had to be set very accurately ?
>  hopefully someone else can confirm this....
> regards Peter
>
>
> Barry Klein wrote:
>> Hi all,
>> I have been occasionally working on the MM+ I just purchased.
>> Trying to get 6 tuned oscillators but only get 5.  When I go back to 
>> check
>> usually I find one that is off by >2 digits from 7F.  Is that what would
>> cause the tune failure or something else?  The oscillator that is off 
>> is not
>> consistantly the same.  I also see a problem where every 6th note 
>> does not
>> play in this test state. 
>> This is the 3rd MM I have worked on and (as before) the trimpot 
>> adjustments
>> are damn touchy.  So much so that I wouldn't want to even bump one 
>> that was
>> tuned....
>> Is this due to old trimpots - do new ones make life much easier here?
>> Anyone tried installing digital pot IC's?
>> What improvements have you made to your MM's to either make calibration
>> easier and more stable or even just mods you have made to increase
>> capabilities?
>>
>> Barry
>>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>