Xpantastic!

Hi Terje,
 
Nice work on the M12.  

--- On Wed, 4/14/10, Terje Winther <terje.winther@...> wrote:

>- I found a strange repeating ripple of approx. 100 - 150 mV from the 
>power supply. It looks (on the scope) like two ripples rather close, 
>then an interval, and then the two ripples repeat again, all 
>microseconds apart. I´ve read in the archives that this could be 
>enough to throw off the auto-tune process, so I better recap the power 
>supply, right? 

When I posted that, I should have stated low frequency (60 Hz) ripple
usually seen with a voltmeter. If you are using a scope you will see
lots of digital noise on the rails from the 30 Khz switching power supply 
output. ( 1/30 KHz = 30 uS ) I think this is what you are seeing. 
And it is normal and too high a frequency to be heard.
I would be willing to bet the tuning errors are caused by the 
Coupling Caps at the output of each voice. 2.2 uF 50VDC is the value
PC board reference number Cx49  ( x = Voice number).

Not that recaping the power supply is a bad idea. It would be good in the long run, however the coupling caps are the more likely culprit. 


>- The voice still missing puzzles me: I thought I traced the error to 
>a broken CEM3372 (the filter part works, but the VCA part seems to be 
>broken). So voice 6 is dead, but if I swap the CEM3372 between, say, 
>voice 5 and 6, then voice 5 becomes dead and voice 6 starts working. 
>So I got a fistful of CEM3372s (12 actually) from 
>Technologytransplan t, but they don´t work, or the M12 doesn´t like the 
>fact that the "new" CEM is from another date stamp. Any ideas?

That is strange. I do not know of anyone who has puchased from Tech Transplant, so I have no track record to work with there.

some thoughts:

Will a newly purchased 3372 work in one of the other voices? I supose there could still be something wrong with voice 6.

Did you try retuning VCF/VCA's after changing out the part? In theory
this would calibrate out any differences between individual chips.

It does not make any sense that a newer/different date chip would not work at all. More likly there would be tracking errors or offsets.

Best Luck

Karl Schmeer