[sdiy] Moog 911A dual Trigger Delay

[Carsten Toensmann]

Hi David,

I can highly recommend using a Spice simulation software like LTSpice or 
something like that. I did this for my own Moog module clones and checked 
the circuits for proper operation before heating up the soldering iron. In 
one case I found a bug / not working part in the Moog service maunal.
Another point is that you can fix side effects of using new components 
instead of the originals, like I had to do for my 914 Fixed Filter Bank 
clone. You can find more details here:

http://www.analog-monster.de/mmclone_en.html

I've not simulated the trigger delay yet, so I can't say anything about it 
now. Perhaps LTSpice is an option for you.

Regards

Carsten

-----Ursprüngliche Nachricht----- 
From: David Ingebretsen
Sent: Friday, April 26, 2013 5:53 AM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Moog 911A dual Trigger Delay

Hi everyone! Long time lurking :)

I would like to beg for some ideas, please. I am trying my hand at a Moog
911A Dual Trigger delay. The original Moog schematic, the data sheet for an
E203 FET, and my schematic capture are at:

ftp://ftp.xmission.com/pub/users/d/dingebre/outgoing/E203.pdf
ftp://ftp.xmission.com/pub/users/d/dingebre/outgoing/TriggerDelay.pdf
ftp://ftp.xmission.com/pub/users/d/dingebre/outgoing/Moog911A1.1.pdf

I'm pretty sure I have the circuit properly entered into Eagle, and I'm
think this Moog schematic should work as it is shown.

The initial stage up to the FET, Q3, works fine. The problem is Q6 never
turns off, so something is happening between the FET and Q6.

I removed the FET in case it wasn't turning off, which means (assuming I
understand the circuit, which is a reach) means Q4 is off, Q5 is on, Q6 is
off and the output floats, like a good S-Trigger should. However, even
removing the FET, which I think should make sure there is no trigger output,
Q6 is still on. I'm assuming the transistors are operating as switches given
this module is dealing with triggers and not audio signals.

If I short Q6 base to ground, it turns off and the trigger is off.

Does anyone have a suggestion on how to trouble shoot this thing? I'd like
to think I can make something this simple work, but maybe that's too much to
expect :)

I'm enclosing the FET data in the hopes someone can help me find a
substitute. I'm trying a NTE466 which the NTE site recommended, but I'm open
for ideas.

Thanks everyone.

For fun, here is the latest info on my Synthasystem:
http://analoguerealities.blogspot.com/

David

David M. Ingebresten
dingebre at 3dphysics.net
dingebre at CFandE.com


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