From: "Tim Stinchcombe <timothy@t...>" <timothy@t...>
Date: Thu Jan 9, 2003 11:02 pm
Subject: Re: It's sounds like there's nothing wrong with my VCA's!!

Hi Tim,

Thanks for the explanations.
Yes, your right about when I bought my basic systeem 2.
Yes, the chips have must have an influence on the sound.
When I still had the Alpha Juno 1, I read that the sound
was a bit colder and harsher then the juno's, due to the
the new chip which they put into the machine!
And yes it sounded colder dan the juno's and that's why
I sold it. Though, I miss it no very much and want
it back.

I knew about the VCA not being a real amplifier, but I it's
hard for me to hold on to that fact, if the name implys, it is
an amplifier!!

About the manual. Yes, I have seen this picks many times and
I understand them I think, only I want to understand it soundwise!
What's the difference in sound when you compare the two
There I lose it, it's all to abstract for me.
By the way. I hear several people from England and the States,
complaining they can't read a german manual.
I must be a lucky bastard then, mine is in english!!!
Mind you, if it were in german, I would have no problems with that
either.
I am asking you why Music House in the Netherlands could deliver
me a english manual and you guys and to struggle with german
ones

Dual VCA's, I will check it out, but since their cost effective,
they lose on options!

Roel



Tim wrote:

Hi Roel,
First I went back and checked your original post - I note you bought
your system about 2 years ago. As far as I'm aware, the new version
of the A-131 came out in the autumn of 2001 - thus I suspect yours
*is* one of the originals. This would use the PA382 chip , the
exponential version of the PA381, which is linear and used in the A-
130. New A-131's use a different chip - a CA3080. Thus most of what I
said before doesn't apply, and the fact that you have confirmed the
outputs sound roughly the same at full gain ties in with what Florian
said.

The VCAs don't really 'amplify' - they give you voltage controlled
gain, which at its *maximum* is about 'times 1'. This should explain
why your patch sounds louder directly to the 138, rather than through
the 130/131: generally the output of a 130/(old)131 is less than the
input!

As for the difference between lin and exp, this is not so easy to
explain in words! For the linear VCA, the gain you get is directly
proportional to the gain knob setting (or the CV in) - equal
increments in the gain setting change the gain by the same
increments. for the exp VCA, starting at gain = 0, large changes of
knob setting give small changes in gain, then gradual you work up to
where smaller changes of knob setting give bigger changes of gain. If
you can think of an 'x squared' curve you'll get the idea (it's not
quite right, but good enough to give the idea). The way the circuitry
works out between the two, it appears the exp curve is virtually
always 'below' the linear one, and comes up to meet it near the max
gain setting. This is not the case for the newer A131, where the exp
curve finally overtakes the linear one, hence why it is louder! (I'll
check the PCB of my A-130 to see how the values changed for the old A-
131, and see if I can do some calcs to back all this up...)

After thought: if you have the manual check out pikkies on page 3 of
the A130/131 entry!!!!!

The difference between the 138's is just the potentiometers, being
either 'linear' or 'logarithmic' (which is just the inverse of
exponential - again if you have the manual, in the figures, 'mirror'
the curve line to be the other side of the straight one). Basically
you get a different 'feel' between how much the knob turns for the
effect on the signal. Because of the way the ear hears, things
following the a log or exp relationship should sound more natural
than a linear one.

As for more VCAs, some people find the A132 dual VCA to be very
handy - check out some of the past discussions on this!

Tim