AC-Coupled module inputs

[Martin Czech]

> > Sometimes it is difficult to avoid dc offset for outputs at all operation
> > points and over the whole temperature range. E.g. ota.
> > 
> 	These modules (e.g. a 3080 based state-var filter that I find always
> gives me offset problems) should have ac coupling at the final output...
> 
Well, I said it is not that easy..., I'd like to enable my vca
to controll "controll" voltages as well as audio voltages,
which is not possible with a cap at the output....
I mean, mixing controll and audio is part of the fun of a modular....
You really can't tell which is which...

> > Sometimes a source controlls severall modules, some may need dc bias,
> > others won't like that. A ac/dc switch at all inputs would allow this
> > to be possible.
> > 
> 	Agreed, but I would think this would be a rare circumstance, and
> even rarer is (for example) an lfo that allows the addition of a dc offset
> *at the lfo*. Usually you add the offset in somewhere by summing a dc and ac
> control signal - in that case you still have the original ac source
> available by itself.

E.g. up vibrato, voltage controlled:
Strings can only get pulled, so the vibrato gets only up, and down
to mormal tension again. A symmetrical lfo thus needs some dc offset
to make an all positive signal which is fed into a vca and then to the
vco...
Wouldn't be too hard to find dozends of other examples...

> > -lower end of audio (30Hz)?
> > At least. Even Lower ?
> > 
> 	Another good question for friendly debate! - Regardless of whether
> you think the filter should be on the input of some modules or the output of
> others! :) I'm definitely a fan of a lower frequency - 10Hz or so.
> 

Here we are.
1Hz was no joke, this case could be usefull for slow modulation and excluding
any offset. I guess this is the beginning of a new module, a anti-slew-unit:
highpass instead of lowpass (1st order, not voltage controlled).

m.c.