Doepfer

--- In Doepfer_a100@yahoogroups.com, <yahoo@...> wrote:
>
> > Two of my A-131 log VCAs from 1999 have the same problem:
> > The initial gain control (top pot) barely works at all. I have swapped
> > the modules for other working VCAs to isolate the problem to the
> > module itself and not the bus or rack. I even swapped the IC1 and IC3
> > from one to another without any luck.
> >
> > The modules are the CEM version I believe, and there is no sign of any
> > component having failed. All  the other features work, but when you
> > apply a CV to CV1-in or CV2-in then the initial gain control does have
> > an effect.
> >
> > I am wondering whether this is a common problem with the CEM chip or
> > if anybody else has had similar problems.
> >
> > sean
> 
> You have to consider that the A-131 has an exponential control
scale, i.e.
> the manual control has only little effect in the lower range of the
initial
> gain control because of the exponential control scale. But if you
turn the
> control fully clockwise  the gain should increase clearly and reach an
> amplification close to 1 in the fully clockwise position.
> 
> Best wishes
> Dieter Doepfer
>

I understand the log scaling, but I have 3 other identical A-131 VCAs
purchased at the same time - same version - which still work properly.
The initial gain control, when fully open, in the two faulty modules
barely allows any signal through at all - closer to 0.05 than to 1.0.

I am hoping it is not the CEM chip since I assume that it is not
possible to buy these anymore.