SV: Re: SV: [sdiy] SCI Pro-One problem (audio leaks to CV or something)

[karl dalen]

The pro one has a blasting gain , reffered as very hot output.
Which means that if you lower the gain (adjusting r1122) the 
magnitude of errors would decrease (i.e offsets and leakages etc).

Instead of having the Volume knob at 9 o' clock  and blasting gain
you get blasting gain at 4 o' clock.

if you look at the schematics you will see that the volume knob
are actually a voltage divider to the current converter of the VCA
which is not a regular volume knob.

The problem are most notified when full resonance are set at the VCF,
it has a constant tone in the background depending on cutoff even if
Volume are at zero. You could try to increase r1142 to 30K.

Wait a minute now!!

Have you checked the potential at u115 pin 14, it should not be to 
much positive.

KD

Yes i have the beer please! But i skip the sauna! :-)



ofte
--- Matti Kari <maza at maza.fi> skrev:

> Hola
> 
> karl dalen wrote:
> > Some Pro one's are known to leak *audio* signals trough the VCA,
> > trim R138 and/or decrease r1122 in value.
> 
> Yeah, it definetely is a VCA problem! Now that I started to twiddle with 
> the synth more, I just understood that somehow when any of the CV's is 
> on some specific value, the VCA leaks. And after a while I noticed that 
> at certain volume setting, the problem is practically unnoticeable - I 
> just have to compensate that on my mixer.
> 
> However, adjusting VCA balance and that resistor you mentioned didn't 
> help that much.
> 
> More ideas?
> 
> Ps. I already owe you sauna and beer if you happen to visit Helsinki. ;)
> 
> -- 
> Matti Kari   ||   Vesalantie 38a, FI-00940 Helsinki
> maza at maza.fi || http://maza.fi/ || +358 40 838 6607
> hammondleslierhodestubeanalogsynthlinuxinternetetc.
> 



      
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