Doepfer

hello zoran,

i mostly use 2 old a131, but i also have two newer a131 and
i don't have that problem you mentioned. the newer a131 are a bit
more noisy, but they do not distort the signal like you described,
it is just a bit of hum and you can barely notice it.
i believe you, don't get me wrong. i just don't understand
how different our modules can be. maybe i'm too much
on the lofi side these days ;-)

i also have a blacet vca and i like it very much, but you have to
notice that the blacet needs a voltage of +10v to open completely,
which is not common with doepfer modules.

best wishes

ingo



--- In Doepfer_a100@yahoogroups.com, "Zoran Bosnjak" <dj_allin@h...> 
wrote:
> Hi, thanks for the post. Unfortunatelly, I don't have any old A-131 
VCAs! 
> Both units I had problems with are 2 to 7 months old. Please don't 
get me 
> wrong, but what I am experiencing on both of these A-131s is not 
occasional 
> distortion at the loudest points, but pitched hum that follows the 
melody. I 
> have samples to illustrate this for both VCAs I owned (returning 
second one 
> today, first one was returned already).
> So what is my solution than? First, I tested all three available 
VCAs (A131, 
> A132, A109) last night little bit more, to confirm results. And 
here it is:
> - A-131 - cannot use it (pitched hum)
> - A-109 - barely noticable distortion on loudest notes in bass line 
(your 
> "normal" distortion) - I am keeping this module, because VCA on  it 
can do 
> the task, and filter is very good
> 
> So you might be asking: look at this guy! He says both A-131 and A-
109 are 
> at least imperfect but he still takes one anyway. And this is my 
point 
> exactly: imperfection between two is very different in character 
and 
> loudness (I am looking for the right word - while you really have 
to try 
> hard to notice distortion on A109, on A131 it is more like a second 
voice 
> :-).
> 
> - I also checked A-132 - no noise whatsoever. But dynamics (volume 
changes) 
> were slightly different than what I am used to (I guess because it 
is linear 
> VCA).
> 
> So, my choice is A-109 for audio. What would have happened if A-109 
was not 
> good enough? I would play more with A-132, and if they were not 
> satisfactory, I could always use them for CV duties. And than I 
would have 
> ordered Blacet VCA and see where that takes me.
> 
> Regards
> 
> Zoran
> 
> 
> >From: Florian Anwander <Florian.Anwander@c...>
> >Reply-To: Doepfer_a100@yahoogroups.com
> >To: Doepfer_a100@yahoogroups.com
> >Subject: Re: [Doepfer_a100] Noisy A-131 VCA
> >Date: Wed, 04 Feb 2004 11:29:05 +0100
> >
> >Hi Zoran
> >
> >The reason for the noise is quite simple to explain. The old A-
130/131
> >used Curtis CEM-VCA-Chips (which is out of production as far as I 
know),
> >which had low noise. The new 130/131 uses CA3080 OTAs (like the 132
> >always did). To my knowledge there is no difference between the 
Audio
> >circuit of the new 130 and the 132. The new 131 is noisier, 
because its
> >logarithmic behaviour requires a higher amplification. More
> >amplification -> more noise.
> >
> > > This noise disappears when using A-109 VCA.
> >This is clear, because the A-109 uses again another Curtis CEM-
Chip (but
> >a different from the one in the old A131).
> >
> >If you have an old 131, you should think about an extension as it 
is
> >mentioned in the service manual of the module. The CEM VCA-chip in 
the
> >A131 contains two(!) VCAs but only one is used. The pcb of the A-
131
> >offers the possiblity to access the second VCA, you need a second 
A-131
> >pcb and frontplate, but without the second CEM-chip.
> >
> >It should be possible also to implement this as a quite simple diy 
project.
> >
> >
> >Florian
> >--
> >Florian Anwander                  |ConSol
> >Tel.   +49(89)45841-133           |Consulting&Solutions Software 
GmbH
> >Fax    +49(89)45841-111           |Franziskanerstr. 38, D-81669 
München
> >email: florian.anwander@c... |http://www.consol.de
> >
> 
> _________________________________________________________________
> STOP MORE SPAM with the new MSN 8 and get 2 months FREE*   
> http://join.msn.com/?page=dept/bcomm&pgmarket=en-ca&RU=http%3a%2f%
2fjoin.msn.com%2f%3fpage%3dmisc%2fspecialoffers%26pgmarket%3den-ca