Doepfer

The amplification range of my A-138c is not -1 to +1, but something 
like -0.9 to +0.9. According to the manual, the range can be changed by 
replacing a resistor. I wonder, if it would be difficult to get very 
accurately -1 to +1?

I am routing keyboard CV through the A-138c and precision is needed. As 
it is now, I need to add (and tweak) an extra amplification module to 
compensate.

Does anyone know, how accurate the Serge 3p is?
http://www.analoguehaven.com/bananalogue/3p/


Best regards
Jari Jokinen

> The amplification range of my A-138c is not -1 to +1, but something
> like -0.9 to +0.9. According to the manual, the range can be changed by
> replacing a resistor. I wonder, if it would be difficult to get very
> accurately -1 to +1?
>
> I am routing keyboard CV through the A-138c and precision is needed. As
> it is now, I need to add (and tweak) an extra amplification module to
> compensate.
>
> Does anyone know, how accurate the Serge 3p is?
> http://www.analoguehaven.com/bananalogue/3p/
>
> Best regards
> Jari Jokinen

From the theory the amplification should be +/-1 as all resistors in the
circuit are 100k. Probably the actual amplification differs from +/-1 due to
the tolerances of the resistors. Another reason maybe the 1k output
protection resistor (R16). You could short this resistor to try if it helps.
It is located just behind the output control.

To obtain exactly +/-1.0 amplification all 100k resistors of the module have
to be selected. We can arrange that but additional charges for the manual
selection of the resistors (each resistor has to be measured before
assembly) and the manual assembly/soldering arise.

Best wishes
Dieter Doepfer

I got a custom A-138c with hand picked resistors. Excellent service 
by Doepfer!

Best regards
Jari Jokinen

--- In Doepfer_a100@yahoogroups.com, <hardware@...> wrote:
>
> > The amplification range of my A-138c is not -1 to +1, but 
something
> > like -0.9 to +0.9. According to the manual, the range can be 
changed by
> > replacing a resistor. I wonder, if it would be difficult to get 
very
> > accurately -1 to +1?
> >
> > I am routing keyboard CV through the A-138c and precision is 
needed. As
> > it is now, I need to add (and tweak) an extra amplification 
module to
> > compensate.
> >
> > Does anyone know, how accurate the Serge 3p is?
> > http://www.analoguehaven.com/bananalogue/3p/
> >
> > Best regards
> > Jari Jokinen
> 
> From the theory the amplification should be +/-1 as all resistors 
in the
> circuit are 100k. Probably the actual amplification differs from +/-
1 due to
> the tolerances of the resistors. Another reason maybe the 1k output
> protection resistor (R16). You could short this resistor to try if 
it helps.
> It is located just behind the output control.
> 
> To obtain exactly +/-1.0 amplification all 100k resistors of the 
module have
> to be selected. We can arrange that but additional charges for the 
manual

> selection of the resistors (each resistor has to be measured before
> assembly) and the manual assembly/soldering arise.
> 
> Best wishes
> Dieter Doepfer
>