Message 314
From: "Steve Ridley"
Date: Tue Sep 2, 2003 12:09 am
Subject: Re: [resergence] 4 trans use (was Re: 6 trans. use?)

More constructively, I built a 101A VCA stage during
by lunch break at work today. If there's time next
week, I'll measure it's performance and report back.
I have a Quad Pan board (not mine) to test too.

I got my 101A VCA running today. I used very roughly matched BC549s and BC559s, and a TL072 because I didn'thave an LF353. It was built on veroboard and measured in a partially screened environment, so a real one in an enclosure should be quieter.

Gain:
Pot fully up (0v), no CV applied - gain 0.35dB (i.e. unity)
Pot at "12 O-clock", (-6v) no CV applied - gain -73dB (i.e. fully attenuated)
Pot below "12 O-clock", no CV applied - no further reduction.

Main CV input: +20dB/volt

AM CV input: +8dB/volt

Noise:
unity gain: -67dBu (unwtd)
minimum gain: -87dBu (unwtd)

Distortion
Less than 0.2%
Output clips hard at around +20dBu.

I think that's quite respectable in the circumstances. I was surprised by the +20dB/v, as the later ones quote +12dB/volt in the catalogue. I also noted that this held true over a wide range - no obvious sign of the range being restricted at the top like Serge quotes in the later catalogues.

I've been having a long think about how equal power panning was carried out in the 100 series boards, but I still need to play with the quad pan board and maybe lash up a stereo panner to see if I've got it right.

Is anyone finding this interesting? Does anyone else have any thoughts on how Serge worked his equal powermagic? I think I understand it, but I'd like to hear someone else "piss on my bonfire".


Cheers
Steve