[sdiy] Jp-8 head scratcher

The Laboratory of Sound info at labofsound.com
Thu Nov 7 15:12:42 CET 2013

On 2013-11-07 14:17, Jack Jackson wrote:
> Slight thread hijack...Are the Jupiter 8 knob caps exactly the same
> part as the ones on the Juno 60?

Yes they are (I’m looking at a JP8 and Juno 60 while I am writing 
this). Technology Transplant sells remakes.

Cheers, the other Jack

> ----------------------------------------
>> From: diy at artefacts.nl
>> To: synth-diy at dropmix.xs4all.nl
>> Date: Thu, 7 Nov 2013 12:14:45 +0100
>> Subject: Re: [sdiy] Jp-8 head scratcher
>> Hello All.
>>> So you have *only* the KCV input driving the VCO pitch ?
>>> Even after it leaves auto-tune ?
>>> And it still has an error, even if you move the voice card to a 
>>> different
>>> location ?
>> Yes I disconnected all modulation sources and the problem still 
>> persists!
>> Moving the card moves the problem, so this rules out wiring, module
>> controller board, interface board and cpu board. I moved the board 
>> serveral
>> times because the problem I am having points more to these boards 
>> than to
>> the voice board. I also replaced the tuning multiplexers, cv summing 
>> amp,
>> transistor array.
>>> Could there be some kind of HF oscillation coming from somewhere 
>>> that's
>>> affecting the tuning ?
>> I looked with my scope at the cv summing amp, tuning output of the
>> oscillator but I don't see any oscillations nor on other places in 
>> the
>> tuning circuit (sample&holds multiplexers etc).
>> When I look at the output of the comparator which goes to the counter 
>> I see
>> no difference between working and bad channels. I also compared the 
>> output
>> of the cv summing amp of the channels but the slew rate is the same. 
>> I stop
>> the repair for now because I keep running in circles and keep testing 
>> the
>> same things. But suggestions are still more than welcome.
>> Best,
>> Maarten
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