Vintage Synth Repair

Update:

changed the Pot! Works fine! Unit now behaves like it should, with 
the Reverse characteristics...

Sound is good, only some tuning to do... this will finish the job.
Thanks! 


--- In vintagesynthrepair@yahoogroups.com, "ambrosia800" 
<s_carter@...> wrote:
>
> Thanks! 
> 
> Great explanation. In the meantime I managed to find a suitable 
pot. 
> I was a little bit hesitating because I always thought, that there 
is 
> a special "Audio" type with better characteristics. But now I 
learned 
> that the revlog one is this sort of Audio type...  I will try to 
> evaluate this with the high quality one I found.
> 
> The pot has to be used not with an Minimoog (which I own also) but 
on 
> an old russian synth, an Altair 231 (which is an almost perfect 
> Minimoog clone).
> The problem in the filter Emphasis (Resonance) control is that the 
> Russians had no Reverse Logarithmic pots. So they used standard 
ones.
> Due to that, there is happening almost nothing from 8h to 15h, and 
> then, if you turn the pot for 1 mm more, it goes directly into self-
> oscillation. As you described it.... 
> 
> So I will change the pot with the same value as on the Mini. This 
> should solve the problem.
> We will see.... (Should be interesting to hear how it sounds 
> afterwards). 
> 
> Ambrosia
> 
> 
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, "duncan" <ferrograph@> 
> wrote:
> >
> > generally speaking, "audio" in the context of a variable resistor
> > means "logarithmic taper". "rev" is an additional indication that 
> the
> > taper should be reversed.
> > there's no harm in substituting a standard log taper pot or a 
linear
> > pot of the same value in such circuits, but the behaviour of the 
pot
> > once one starts to use it will be incorrect.
> > 
> > if you attach a resistance meter to a normal "audio taper" pot & 
> watch
> > the value as you move the pot, you'll see that all the action 
seems 
> to
> > be piled up at one end of the travel of the pot. 
> > 
> > now, in the context of adjusting the feedback of a filter 
circuit, 
> you
> > can see why you'd want the low-end of the pot's travel (working 
from
> > fully ccw, or the bottom of a slider's travel) to make a lot of
> > difference, & for the control to be of a higher resolution 
towards 
> the
> > critical part where the circuit begins to self-oscillate.
> > 
> > with a linear control, the fine-control as the filter goes into
> > oscillation isn't so good. with a regular log pot, the control is
> > almost unusable.
> > 
> > hth-
> > duncan.
> >
>