Doepfer

> According to the response I got from Dieter, the A150 User's Manual 
> has been UPDATED to describe the -8V - +8V restriction. I guess if a 
> product doesn't meet it's prospectus, update the prospectus ;)

Ah ha - I hadn't realised that there was a version in existence which
*didn't* describe this problem, as my manual entry does!!

> I'm wondering if it's possible to mod only half of the dual switch.

Almost certainly: I don't have the full PCB diagram with me, but there
must be a suitable point at which to cut the +8V and -8V tracks
between both halves of the 150 circuit, and then strap the appropriate
one (of the now isolated rails) to +12V and the other to ground. You
would really also need to place new 10uF and 100nF capacitors between
the new 12V rail and ground.

BUT if you are going to go to this extent, it's not really such a
great step to sorting the problem out properly (if I'm right about
it's cause I must add!!!), and then the whole module would work with
+/- 8V *and* 0 - 12 V (although the switched gate/trigger would no
longer be 0 - 12V, but I've seen nothing in any circuit so far to
suggest that this would be a problem). The problem as I see it is
because the diodes 'protecting' the chip won't conduct until the
inputs are around 8.7V: this voltage is then greater than the supply
to the chip (8V), which is what (I'm assuming) is causing it to
misbehave. A solution would be to lower the +8V to the diodes to, say,
+7V: then nothing above 7.7V would reach the chip, which being less
than 8V would (hopefully!) mean it behaves properly. This could be
achieved with another regulator of appropriate rating, but would
require quite a few straps and cuts to tracks because of the way the
diodes and chips hang off the +8V rail. In fairness, the FAQ solution
is described as 'simple' - perhaps you could persuade Dieter to post a
more 'Rolls-Royce' solution (after checking the above 'theory' out of
course)?

Tim

[The views expressed above are entirely those of the writer and do not
represent the views, policy or understanding of any other person or
official body.]