From Ken's site, see schematic on page
On the first (yellow) run of PCBs, the grid bias resistor (330k) goes to the negative rail. In this position, it causes some distortion of the signal. This can be a good thing. I prefer the resistor in this position when using the unit as a timbral gate. This is shown in BLUE on the schematic. An alternative is to bias the grid to around 1.2V with respect to the negative rail - in other words, to the other end of the heater/cathode. This is shown in RED on the schematic. Doing so will reduce the distortion at low input levels. Do not put in both red and blue options at the same time or you will short out the heater. It may be appropriate to connect pin 4 of the tube to pin 1 of the tube instead of pin 2 as well, if making this modification.
On the first (yellow) run of PCBs, the grid bias resistor (330k) goes to the negative rail. In this position, it causes some distortion of the signal. This can be a good thing. I prefer the resistor in this position when using the unit as a timbral gate. This is shown in BLUE on the schematic. An alternative is to bias the grid to around 1.2V with respect to the negative rail - in other words, to the other end of the heater/cathode. This is shown in RED on the schematic. Doing so will reduce the distortion at low input levels. Do not put in both red and blue options at the same time or you will short out the heater. It may be appropriate to connect pin 4 of the tube to pin 1 of the tube instead of pin 2 as well, if making this modification.
----- Original Message -----
From: squidb0i
To: cgs_synth@yahoogroups.com
Sent: Wednesday, August 01, 2007 8:16 PM
Subject: [cgs_synth] Re: Tube VCA revision question
Sounds interesting and I do have that board in the cue.. what does
this mod do exactly?
~!J!
--- In cgs_synth@yahoogroups.com, "thealisonproject" <alison@...> wrote:
>
> I finished my Dual Tube VCA today, this thing is great. I added the
> DPDT switch like mentioned in this topic and there is no pop at the
> output when switched, works perfectly... Adding feedback is where I
> really like this thing, pure crunch...
[Non-text portions of this message have been removed]