Hello,
indeed the VCAs used in the A-135-2 tend to close not fully with 0V CV. But actually we have added a small negative offset voltage in the circuitry to each VCA CV to avoid this flaw (resistors R3, R7, R11, R15, all 10MOhm). If you are familiar with electronics you may reduce the values of these resistors a bit to increase the negative offset (e.g. by soldering another 10M resistor in parallel). The four resistors are all at the upper rim of the pc board.
Otherwise please return the module for modification/repair to the dealer where you purchased it.
Best wishes
Dieter Doepfer
> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com [mailto:Doepfer_a100@yahoogroups.com]
> Gesendet: Montag, 15. Juli 2019 12:34
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] A-135-2 as quad VCA
>
> Hello,
>
> I got an A-135-2 a few months ago to use as a quad VCA. I notice that with
> all the knobs turned completely to the left and no CV signal plugged in, if I
> connect a signal to an IN socket on any one of the VCAs, the signal is still
> present at the output for that individual VCA, albeit very quietly. (I'm
> using a sawtooth from a Dixie VCO as a test signal. If I connect the output
> of the VCA to my RME Fireface UCX with no extra gain on the soundcard input,
> the signal is present at roughly -84 db and can clearly be seen and scoped in
> the mixer channel of Ableton Live.)
>
> This surprised me, as with all the other Doepfer VCAs I own, the output is
> fully closed when the knobs are turned all the way down and there is no
> control signal.
>
> Is this a problem with my unit, or have I misunderstood the module? Is it
> possible to adjust some trimmers on the unit to fully close the VCA in this
> situation?
>
> Thanks in advance for any help!
>
> All the best
> CB
Message
Re: [Doepfer_a100] A-135-2 as quad VCA
2019-08-03 by Chris Bassett
Hi Dieter,
thanks for the information! However, it wasn't clear to me in your reply if the VCA should be closed with no control voltage, or if the current behaviour is intended.
I finally had the opportunity to do the soldering today thanks to the kind help of a friend. As you suggested, I soldered four 10M resistors in parallel. Now the signal which passes through with no control voltage is between -96db and -102db. I notice my "new" edition A-132-1 also lets the signal through at -102db with no control signal, so after the modification the behaviour of the A-135-2 is the same as that.
I tested my "old" edition A-132-1 and there is only noise at -120db when there is no control signal. It seems that the new higher quality VCA components just behave in this way. It is certainly nothing which could be heard in a mix anyway.
Are there plans to reduce the resistance in future editions of the A-135-2? I may get another one at some point, as it's one of my favourite modules, but would rather not have to solder again.
All the best,
CB
On Mon, Jul 22, 2019 at 1:27 PM yahoo@doepfer.de [Doepfer_a100] <Doepfer_a100@yahoogroups.com> wrote: