Doepfer

i noticed that cv2 input for vca 1 is way different to the other 3 cv2 inputs....

doesnt seem to be as sensitive as the other 3.  but there's no trimmer for this....

if it means anything i've removed jumpers so it acts as 4 separate vca's with no normaling and no summing...

this is weird no?

also just to be sure...- is this quad vca dc coupled?

cheers

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com
> [mailto:Doepfer_a100@yahoogroups.com]Im Auftrag von skp_pete
> Gesendet: Montag, 14. März 2011 11:48
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] a-132-4 help
>
>
> i noticed that cv2 input for vca 1 is way different to the other
> 3 cv2 inputs....
>
> doesnt seem to be as sensitive as the other 3.  but there's no
> trimmer for this....
>
> if it means anything i've removed jumpers so it acts as 4
> separate vca's with no normaling and no summing...
>
> this is weird no?
>
> also just to be sure...- is this quad vca dc coupled?
>
> cheers

The VCAs of the A-134-4 are DC coupled. CV2 of VCA1 should behave like CV1
with the trimming potentiometer for CV1 in it's max. position (i.e. no
attenuation) or like the CV2 of the other VCAs. If that's not true please
return the module for service to the dealer where you purchased the unit.
Which CV is used to control the A-134-4 ? As CV1 of VCA1 is normalled to the
other CV1 inputs the load is 4 times more than for the other inputs. Each
load is 220k or ~ 55k for CV1 of VCA1. Normally such a load should cause no
problems unless a control voltage source with high impedance output is used.

Best wishes
Dieter Doepfer

thanks for the reply

i've removed jumpers so it acts as 4 separate vca's with no normaling and no summing...

i did some tests 
this is what i get

-run 5.47 v into vca1 input
-run 3.85 v into vca1 cv2 input
- i get   0.61 v out of vca1 output

the same thing done with the other 3 vca's give's me 1.31v , 1.37v , and 1.34v respectively ....

i guess vca1 cv2 has a dud resister or something?

sending this back (only a few months old) is probably not an option because i'm in Australia and i purchased from analoguehaven with some other stuff.... elby didnt have stock at the time... i was impatient..

maybe an easy fix for me?

is there a resister that i can check maybe?

thanks

--- In Doepfer_a100@yahoogroups.com, <yahoo@...> wrote:

>
> > -----Ursprüngliche Nachricht-----
> > Von: Doepfer_a100@yahoogroups.com
> > [mailto:Doepfer_a100@yahoogroups.com]Im Auftrag von skp_pete
> > Gesendet: Montag, 14. März 2011 11:48
> > An: Doepfer_a100@yahoogroups.com
> > Betreff: [Doepfer_a100] a-132-4 help
> >
> >
> > i noticed that cv2 input for vca 1 is way different to the other
> > 3 cv2 inputs....
> >
> > doesnt seem to be as sensitive as the other 3.  but there's no
> > trimmer for this....
> >
> > if it means anything i've removed jumpers so it acts as 4
> > separate vca's with no normaling and no summing...
> >
> > this is weird no?
> >
> > also just to be sure...- is this quad vca dc coupled?
> >
> > cheers
> 
> The VCAs of the A-134-4 are DC coupled. CV2 of VCA1 should behave like CV1
> with the trimming potentiometer for CV1 in it's max. position (i.e. no
> attenuation) or like the CV2 of the other VCAs. If that's not true please
> return the module for service to the dealer where you purchased the unit.
> Which CV is used to control the A-134-4 ? As CV1 of VCA1 is normalled to the
> other CV1 inputs the load is 4 times more than for the other inputs. Each
> load is 220k or ~ 55k for CV1 of VCA1. Normally such a load should cause no
> problems unless a control voltage source with high impedance output is used.
> 
> Best wishes
> Dieter Doepfer
>

You find my answers written inline

Best wishes
Dieter Doepfer


> thanks for the reply
>
> i've removed jumpers so it acts as 4 separate vca's with no
> normaling and no summing...
>
> i did some tests
> this is what i get
>
> -run 5.47 v into vca1 input
> -run 3.85 v into vca1 cv2 input
> - i get   0.61 v out of vca1 output
>
> the same thing done with the other 3 vca's give's me 1.31v ,
> 1.37v , and 1.34v respectively ....
>
> i guess vca1 cv2 has a dud resister or something?

maybe. But to find out if this is true please check what I mentioned in my
last answer: CV2 of VCA1 should behave like CV1 with the trimming
potentiometer for CV1 in it's max. position (i.e. no attenuation). If the
CV1 and CV2 behave different it a problem with the VCA. Otherwise it's a
problem with the weighting resistor for CV2.

> sending this back (only a few months old) is probably not an
> option because i'm in Australia and i purchased from
> analoguehaven with some other stuff.... elby didnt have stock at
> the time... i was impatient..
>
> maybe an easy fix for me?
>
> is there a resister that i can check maybe?
>
> thanks

Please look if the resistors R8 and R9 are 220k (color code red-red-yellow
for 5% or red-red-black-orange for 1% types). These are located just behind
the trimming potentiometer for unit #1. These are the weighting resistors
for CV1 and CV2 of VCA #1.

If this is true I'd expect that CV1 and CV2 will behave in the same way
(provided that the trimming potentiometer is fully open). Please check then
if R11 is 100k. It defines the overall amplification of the VCA. R11 is the
next but one resistor behind R9. I can send you a silk screen overlay off
list if this helps.