Doepfer

Hi Zoran

The reason for the noise is quite simple to explain. The old A-130/131 
used Curtis CEM-VCA-Chips (which is out of production as far as I know), 
which had low noise. The new 130/131 uses CA3080 OTAs (like the 132 
always did). To my knowledge there is no difference between the Audio 
circuit of the new 130 and the 132. The new 131 is noisier, because its 
logarithmic behaviour requires a higher amplification. More 
amplification -> more noise.

> This noise disappears when using A-109 VCA.
This is clear, because the A-109 uses again another Curtis CEM-Chip (but 
a different from the one in the old A131).

If you have an old 131, you should think about an extension as it is 
mentioned in the service manual of the module. The CEM VCA-chip in the 
A131 contains two(!) VCAs but only one is used. The pcb of the A-131 
offers the possiblity to access the second VCA, you need a second A-131 
pcb and frontplate, but without the second CEM-chip.

It should be possible also to implement this as a quite simple diy project.


Florian
-- 
Florian Anwander                  |ConSol
Tel.   +49(89)45841-133           |Consulting&Solutions Software GmbH
Fax    +49(89)45841-111           |Franziskanerstr. 38, D-81669 München
email: florian.anwander@consol.de |http://www.consol.de