revised 292c LPG PCB layout...

fonik · Posted: Thu Oct 23, 2008 3:04 pm Post subject:

the advance orders in this thread are a little bit missleading.
this thread is about my PCB layout for the 292c LPG. thomas started from this point and asked don buchla for permission to do a PCB run for us DIYers. and don said yes, great! Very Happy

during the design of the new PCB thomas incorporated several improvements, as discussed in his thread.
meanwhile i incorporated the improvements concerning the resonance modification to my press'n'peel layout, too.
the professional manufactured PCB by thomas will be top notch quality boards. they provide two onboard mixers (one for audio, one for control voltages), footprints for several pot types and a "deep switch mod" that you won't find on my layout. the main difference is the use of two single vactrols instead of one double vactrol, as on my layout.
anyways, i ordered thomas PCBs for me, too.

simmeau · Posted: Fri Jan 23, 2009 6:03 pm Post subject:

I've just done a dual of Fonik's layout with the res mod and I have a couple of questions:
In vcf mode, as you turn the offset up (with no external cv input) the filter cutoff very quickly reaches it's maximum. Basically, the vcf goes through it's entire range in the first 1/10 turn of the pot. Is this normal? Under cv control it sounds pretty much like the demos I've heard, except for one of the Thomas White youtubes where he seems to have much finer control over vcf cutoff than I do.

I'm also confused about the trimmer. The voltage at the anode of the vactrol goes very quickly from 0 to 3.2V and the trimmer doesn't seem to change things.
It sounds pretty damn cool the way it is though. It's just that having never messed with an LPG, I'm not sure how its supposed to behave.

fonik · Posted: Fri Jul 10, 2009 3:59 am Post subject:

after a long time and many professional boards available, it has been discovered by a DIY fellow that there is a little bug in my the revised p'n'p layout:
C5 and the trimmer are NOT connected to pin 9 of U1 Shocked

i wonder how some guys could build it this way and be happy with it.

anyways, i believe this issue can easily be solved. since you etch these boards yourself: you can easily connect C5 and T1 to the trace leading to pin 9. it's just .05 inches away...

i will update the layout next week. i just wanted you to be informed. thanks.

softfin · Posted: Fri Jul 10, 2009 4:29 am Post subject:

Thanks for the info. Your remark came at a good time as I'm about to start building a pair of these. too much coffee

andrewF · Posted: Wed Jul 15, 2009 7:45 am Post subject:

I have two of the early PnP boards, but added the 33pF caps on the Res mod.
They both still break into screeching oscillation too easily, my ears are sore.
Has anybody else fund this?
have I missed some update?
I see the feedback path from pro run of PCBs starts from the output of the opamp rather than the non-inv input, is this the fix?
Or alter the resistor values to reduce the gain of the Res mod subcircuit?
cheers
A

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

oh wow
ive etched so many of these pcbs for poeple
might have to do a mail out to them all about the fix

fonik · Posted: Thu Jul 16, 2009 12:49 am Post subject:

fonik · Posted: Thu Jul 16, 2009 12:53 am Post subject:

andrewF · Posted: Thu Jul 16, 2009 1:21 am Post subject:

simmeau · Posted: Sun Jul 19, 2009 8:11 pm Post subject:

I just saw this today and put in the fix. I want some more. Thanks for the update. Very Happy