PCB for MAT-04 VCA

[gstopp at fibermux.com]

     Good job Chris.
     
     Well in the time between my last response and now I've tried a few 
     more things. First of all it looks like it's best to keep the input 
     signal at 4V p-p or lower, because of what appears to be a long-term 
     minor DC drift in the input electrolytic cap. Second, on a whim I 
     swapped out the MAT-01 matched transistor pairs and put in four 
     randomly-chosen 2N2222A transistors instead. No change in behaviour! 
     Absolutely identical performance. So - no expensive parts at all, just 
     six cheapo transistors and two TL082's. You can keep the layout the 
     same, Chris, as far as I can tell you can still stick four NPN's in a 
     14-pin DIP footprint if you don't want to buy MAT-04's.
     
     Maybe I should point a heat gun at it next, and see if anything drifts 
     over temperature?
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: PCB for MAT-04 VCA
Author:  Chris Crosskey <chrisc at zetnet.co.uk> at ccrelayout
Date:    2/24/97 3:27 PM


Hi All,
 I've just finished laying out a PCB for the MAT-04 VCA. It has 
the complete circuit as listed in the AD data book, plus an IP buffer 
for the CV that also has a voltage divider and shifter incorporated 
plus an audio input divider and output buffer to cope with the 3V RMS 
(what's that P-P, something like 2V isn't it? The buffers are based on 
a quad op-amp, I'd suggest a TL074 or better.
Unless I get a lot of <NO's> fired at
     
chrisc at metrics.co.uk 
     
tommorrow then I'll send a .GIF of the PCB and a .GIF of the datasheet 
to the list sometime tommorrow early evening GMT.
     
     
chrisc