MF101 - modification for separate audio signal to env.fol.
Posted: Mon Mar 22, 2010 1:29 pm
Hi everyone,
Sorry about the delay in getting this info up - I promised it several weeks ago.
The question was how to modify an MF101 to accept a second audio signal in to the envelope follower, so that the filtering of the main signal can be enveloped by a second audio signal.
I did this to my MF101 about 10 years ago, after sending a couple of e-mails to Big Briar, and receiving answers from Bob Moog himself with explicit directions. I no longer have the computer on which the e-mails were received, and I have no backups from that time. So the following is retyped from printouts of the e-mails. Points to note:
- these instructions apply to a Big Briar MF101, vintage 1999. I have no idea whether the board and circuit of the current version of the MF101 are the same.
- I haven't got around to taking photos of the guts of mine - sorry...
- these directions are provided under the motto "no responsibility taken" - if you wreck your MF101, that's your problem
- BUT I know that the instructions work - my MF101 has been doing this happily since 2000, when I made the modification.
First e-mail from Bob Moog, 2 March 2000:
"If you're adept at desoldering resistors on circuit board with plated-through holes, you can lift the end of R5 and connect your external signal to it. If you have access to shop equipment, you can drill an extra hole on the back panel of the MF-101, mount a bridging jack in that hole, and then wire the jack up to the R5 part of the circuit."
Several months later, when I finally got around to doing this, I asked for more explicit instructions:
Second e-mail from Bob Moog, 5th October 2000:
"1. DO NOT REMOVE THE CIRCUIT BOARD. Remove the bottom panel and face the jacks away from you. Identify U2 (LM324A).
2. Immediately to the left of U2, starting at the top, are a) two diodes, b) a 270K resistor, c) a 100K resistor, and d) four more resistors. That 100K, right below the 270K, is R5.
3. Carefully unsolder the left end of R5, that is, the end away from U2. Apply your signal to that end of the resistor."
So that's it, folks. It's actually quite easy, and it works like a charm. Like everyone else on this forum, I'm eternally indebted to Bob Moog (may he rest in peace) for his generosity and willingness to help - as well as for the great instruments!
So, have fun!
Cheers,
Jim F.
Sorry about the delay in getting this info up - I promised it several weeks ago.
The question was how to modify an MF101 to accept a second audio signal in to the envelope follower, so that the filtering of the main signal can be enveloped by a second audio signal.
I did this to my MF101 about 10 years ago, after sending a couple of e-mails to Big Briar, and receiving answers from Bob Moog himself with explicit directions. I no longer have the computer on which the e-mails were received, and I have no backups from that time. So the following is retyped from printouts of the e-mails. Points to note:
- these instructions apply to a Big Briar MF101, vintage 1999. I have no idea whether the board and circuit of the current version of the MF101 are the same.
- I haven't got around to taking photos of the guts of mine - sorry...
- these directions are provided under the motto "no responsibility taken" - if you wreck your MF101, that's your problem
- BUT I know that the instructions work - my MF101 has been doing this happily since 2000, when I made the modification.
First e-mail from Bob Moog, 2 March 2000:
"If you're adept at desoldering resistors on circuit board with plated-through holes, you can lift the end of R5 and connect your external signal to it. If you have access to shop equipment, you can drill an extra hole on the back panel of the MF-101, mount a bridging jack in that hole, and then wire the jack up to the R5 part of the circuit."
Several months later, when I finally got around to doing this, I asked for more explicit instructions:
Second e-mail from Bob Moog, 5th October 2000:
"1. DO NOT REMOVE THE CIRCUIT BOARD. Remove the bottom panel and face the jacks away from you. Identify U2 (LM324A).
2. Immediately to the left of U2, starting at the top, are a) two diodes, b) a 270K resistor, c) a 100K resistor, and d) four more resistors. That 100K, right below the 270K, is R5.
3. Carefully unsolder the left end of R5, that is, the end away from U2. Apply your signal to that end of the resistor."
So that's it, folks. It's actually quite easy, and it works like a charm. Like everyone else on this forum, I'm eternally indebted to Bob Moog (may he rest in peace) for his generosity and willingness to help - as well as for the great instruments!
So, have fun!
Cheers,
Jim F.