compressor

[Haible Juergen]

Hi,

built a little compressor / preamp to replace the original preamp of
my HiFli Clone. It might be interesting as a standalone tool, too, 
because it's cheap, opto electronic, ultra low noise, and even has 
symmetrical inputs.
It's built around an SSM2017, with a 5k -log pot to set the gain, 
two 10k resistors from the input jack to the two SSM2017 inputs,
and the LDR of a VTL 5C4 directly across the SSM chip inputs.
The LED of the vactrol is driven from an extra opamp (741) over
a bridge rectifier, and I have put 100uF across the LED, too.
That's all.
The concept isn't new (I remember how excited I was when
Gene brought this up on the list many moons ago!), but using
this cheap microphone amp chip has great advantages. A lot
of gain, and almost no noise, even when the compressor sees
no input signal. I spent a few hours just playing guitar sounds
from the VL7 thru this compressor, complete with echoes and
reverb (from the VL7, i.e. before compressing) - much fun.
It's not a "precision" tool,  more like a typical guitar compressor
(i.e. leaving some attack overshot in the sound), but what sets
it apart from my previous experiments (NE570, opamp + LDR,
LM13700 etc.) is that it's so absolutely quiet. 

If you're interested, I 'll include the schemos in my next web 
page update.

JH.