Doepfer

Hi Zoran,

> Why? Because I have just returned noisy A-131 (creates distortion 
on any 
> setting, not only above 7), just to receive brand new A-131 that 
behaves 
> almost the same (noise not as loud, but STILL there).

Florian has already pointed out the differences in the chips from old 
to new - there are other things that affect the behaviour here too.

Assuming the component values in the A-131 are still the same as mine 
(it's marked v2, 2001), then the resistor values around the CA3080 
which set the gains in the 131 and the 132 are quite different, 
making it much easier to drive the 3080 in the 131 into its non-
linear area of operation, causing distortion, which is also likely to 
be contributing to what you hear. (If I remember from previous posts 
on this topic, Dieter has said this is deliberate.)

You seem to have tried reducing the level of the input, which should 
reduce these effects - are you also aware that 'In2' is more 
sensitive than 'In1'? That is (if you haven't already tried it), if 
you are using In2, try it on In1 instead (and vary the setting) to 
see if this makes much difference.

In theory it should be a relatively simple matter to replace about 3 
or 4 resistors in the 131 to make it more like the 132 (albeit with 
the log scaling), which has the potential to reduce this distortion 
effect. I'll have a more detailed look at this tonight (I have more 
resources at my disposal now compared to when I looked at this last, 
18 months or so ago.)

Also if you are driving the 131 from a 140, if the CV2 setting is too 
high (above about 6 or 7) you don't get the full 'range' of the 
envelope, the top gets flattened off (this shouldn't cause distortion 
at all, but will affect the overall shape of the sound). 

Tim