[sdiy] Ripple on a Metasonix R60 MIDI 2 CV

[Adam Inglis]

I'm probably way off base here, but this thing looks like a monophonic  
version of "computune" (there were several other names for it) that  
exists in my Jupiter 8. The CPU puts out a CV via a DAC and a Sample  
and Hold circuit, then something like a PLL detects the actual VCO  
frequency for the CPU, which then computes the scale - yes?
Anyway, when I had a similar pitch wobble on one of my JP8 VCOs, it  
only ocurred when the VCO had been "computuned", and the problem  
turned out to be in the S&H circuit - the op-amp I recall.

Of course ICBSC


regards
Adam Inglis
http://www.adambaby.com

On 30/01/2012, at 4:56 PM, David Ingebretsen wrote:

> I wanted to build a MIDI 2 CV into my Synthasystem and bought a  
> Metasonix
> R60 self tuning module. I put it behind a custom panel to match, and
> therefore voided my warranty. I know, I know, but I'm used to this  
> SDIY
> thing.
>
> It completes its tuning cycle, but then there is some serious ripple  
> on the
> CV output. As the CV increases, there is an increasing magnitude  
> ripple at
> about 200 to 400 Hz. At a 4 volt CV, the ripple is about 200 to 300  
> mV and
> distorts the sound terribly. There is a scope grab on the Electro- 
> Music
> forum:
>
> http://www.electro-music.com/forum/viewtopic.php?t=51817
>
> I've tried with 3 different VCOs: JH Living VCO, MOTO Ultra 300 VCO,  
> and the
> Steiner VCO. I've tried 4 different MIDI controllers.
>
> I wrote Metasonix, told them I mounted it behind a different panel
> understanding that likely voided the warranty and offered to pay in  
> advance
> to have them take a look at the problem, but was basically told to  
> trouble
> shoot it myself; except a little more bluntly...
>
> I don't have the schematic or source code for the processor, so any  
> ideas
> where to start? It looks like a pretty simple PCB, however, I  
> suspect it is
> something other than a bad OpAmp.
>
> Otherwise, I've got a $350.00 paper weight...
>
> David
>
>
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