Sorry for silence - I've been away. I half thought I might get thread replies in email, but no.
Opamps - 741's are old hat. There are much better modern opamps, as people have said. I'd use duals. TL082 would do in a +/-9 environment (and that's pretty old now too). LM6132 I'm fond of these days. Rail-to-rail, fast, low power. Not as cheap as some, but if you're just making a few of something it doesn't matter much what it costs. Time is money too.
Given new opamps I'd get the input impedance up to 1M or more. Also there are places where the 100nF coupling caps form an HPF that rolls off too high. They need rooting out. Also in the LFO the integrator capacitor could be reduced by an order of magnitude, which reduces ticking currents. Just increase the resistor driving the integrator by the same factor.
Any old FET WILL do. I use J112 or J113 these days. But remember that the Vgs(off) is all over the shop with JFETs, even within the same batch. Use the bias control to get round this variation. J112, for example, is somewhere between 1 and 5 volts. Such precision and repeatability!
A LED to mirror the LFO is good, like Chris Carter added. A LED to show effect in/out is also good. Millenium Bypass is the answer to that. A cracking design!
I started the 2009 reissue in Feb this year thinking I'd just revamp it for modern stuff. Op-amps on a single 9V rail would be much cleaner than two batteries or switching negative converters. But, as with many things I start, it grew into more than I'd expected. It is now sufficiently different to justify having both. I redid the filter with three bandpass sections because I've been playing around with voice formants. It sounds really nice on rock organ/gritty Hammond tones. The deal with the LFO is that I think the original is a bit of a bugger to play along with. You have to let it take the lead on timing. You follow it, it doesn't follow you. What I wanted was an LFO with sync from an envelope follower. And that led me into AVR because I've got most of the software components written already for another project. All the waveshaping stuff and that cumbersome rotary switch get subsumed into software.
You're right - it does need to be future-proofed. The object code as a free download on the web in several places at the least. I'm not going to put the source code out there - that's my job and I need to earn money out of it.
I'm not ready to publish on the 2009 reissue anyway, so don't hold your breath. Full steam ahead on the PCB's I would say - and could I have one or two please? I'll build it up and pot comments.
I'm STILL waiting for a Gristleizer from Endangered Audio. Ho Hum.
Roy
