[sdiy] Simple VCA schematic, anyone?

[Andre Majorel]

On 2007-01-09 03:05 +0100, René Schmitz wrote:
> Andre Majorel wrote:
> 
> >Ah yes, one of 'em vertual grownds. Like this ?
> 
> Looks good. Maybe you should even take out the 1k resistor, to make this 
> really into a current input. (virtual GND, transimpedance configuration)

I put the resistor in front of the inverting input so as to set
the gain to 100. I don't know how to compute the gain of an
inverting amplifier when there is no resistor between the source
and the inverting input. I'll experiment. In the PS-3200, they
appear to use 10 k (I think "R21~32" in the schematic should be
"R25~32").

> Also I think it is needed to give the Emitter a DC path to GND. (Like 
> R21 in the PS3200 schemo Jürgen posted.)

100 k to ground between the emitter and the 1 µF cap then.

> Or leave out the 1µ, and tie the Emitter directly to the
> inverting input. There's lots of room for experimentation. Like
> which transistors are best in this circuit, what are the optimum
> levels and so on.

Noted. Thanks for the help, everyone.

Oh, one more stupid question : the BC550 data sheet gives the
following maximum values :

  V_CBO : 50 V
  V_CEO : 45 V
  V_EBO :  5 V

If the control voltage drops down to -15 V, will it damage the
transistor ?

-- 
André Majorel <URL:http://www.teaser.fr/~amajorel/>
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