[sdiy] Small and simple vca details desired (oh, and a voltageinvertor too)

[harrybissell]

Hi Antti

Antti Huovilainen wrote:

> On Wed, 2 Mar 2005, Harry Bissell Jr wrote:
>
> > you might want to try adding a 15K resistor to the +15
> > and the linearizing diode terminal, and add a divider
> > and DC offset pot to the unused input terminal. Make
> > the input divider like a 30K : 1K.  This will make the
>
> How should these values be adjusted if some other supply voltage is used,
> say +- 8V?

I use 1mA for the linearizing diodes, so that would be 8K for your supply.
The audio
divider should be the smallest series resistor that will prevent clipping at
max gain.
The values I suggested are for pretty large signals... like maybe 15V pk-pk

> > Downside... lower input impedance, and the need to use
> > the DC offset adjust. You 'might' like the soft
>
> Do linearizing diodes increase the offset voltage?
> I'd think that using hotter input signal would result in smaller relative
> offset error.

In the LM13600,13700... yes.  They increase the offset a huge amount (that
can then
be trimmed out).  Once trimmed it works quite well.   I always use equal
shunt resistors so it can't be bias current error... I think its the diodes.

H^) harry

>
>
> Antti
>
> "No boom today. Boom tomorrow. There's always a boom tomorrow"
>    -- Lt. Cmdr. Ivanova