[sdiy] VCA troubles, NE5517

[Fredrik Carlqvist]

Tim, 

Yes the voltage drops are double that of the 3080. In my application, the
useful voltage drops are 1.0 V and up. At 1.15 V, the Iabc maximum of 1mA is
flowing. If I understand the function of the circuit correctly, this would
imply that all the current mirrors has approximately the same drop, so I was
hoping for about 2 volts of signal. Since the filter circuit works ok, I
have not bothered to check the voltages, I just assume there is some
headroom. So there is not so much weirdness, only this VCA feed thru thing.

Fredrik C

PS Of course, all these voltages are at room temperature, what did you
expect? ;-)



-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Fredrik Carlqvist
Sent: Wednesday, April 14, 2004 16:56
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] VCA troubles, NE5517



Hello all you brilliant people!

I am very sorry to attach the image, but I have trouble with my ISP today,
so I cannot put it on the internet. At least it is very small.

I have truble with what I thought would be a simple VCA circuit. I use half 
a NE5517. The trouble is that the control current feeds thru to the output 
in a very distinct manner. Sometimes the feedthrough is even stronger than 
the actual signal. 

Vdd is 5 volts. Vdd/2 is 2.5V. I didn't use the buffer since I 
am using a single +5V supply, and I didn't want the 1.2V drop over the 
darlington.

Can someone please help me remove the control current feedthrough?


Thanks,
Fredrik C