Minimoog D Pitch Bend modification (solved)

[chris j]

thanks Alain, capacitor yes,( condensateur in french, I translated to condenser ).

you wouldn't happen to know about the Voltage on the PBend's ground/wiper at center position when there's no mod?

[chris j]

Pitch Bend : One of the many manuals I have say there should be 15.3Kohm at center position when the connector is unplugged.
trouble is it says between the green and orange wires, orange I have, but no green.
Was the green wire the 10V or ground ? I get very different values on each side.

[thealien666]

Probably just a question of creating a slight offset to bring the voltage coming out of the circuit to 4.3 Volts when in the dead zone. Probably what the resistor shown on Rudi's photo does...

Probably that I don't know bleep about it anyway ?

EDIT: to measure the resistance on the pot at notch position, just unplug the mod wheel assembly from the synth and measure directly on the pot legs between ground and wiper. Simplest way to do it. That, I know.

[chris j]

EDIT: to measure the resistance on the pot at notch position, just unplug the mod wheel assembly from the synth and measure directly on the pot legs. Simplest way to do it. That, I know.

yes but between wiper and ground or wiper and 10V ? I get very different values depending on where I test

[thealien666]

I edited my last message to specify, just before you've asked...

Between ground and wiper. Ground being the wire that also goes to one side of the pot for the modulation wheel, and the ground of the two connectors (jacks). It's usually white.

[chris j]

thanks man !
yes for the colours I'd followed Rudy's photo, but thanks again!

If i set the pitch bend as it should be, will I have to do a complete retuning of the oscillators (scale, octave, hi end, shift)
or (most preferably) just shift ?

[thealien666]

Sorry, I wouldn't know about that, since I'm not familiar with the tuning procédure, euh, procedure of the new oscillator board. I have the old one which doesn't have a shift trimpot. Only range and scale.

[chris j]

ha! OK I'll try and see, merci!

[chris j]

I found this thread http://forum.moogmusic.com/viewtopic.php?f=1&t=11541

Rudy's pic can be seen bigger, I still can't work out the colors of his resistor though

To counter balance the pitch change due to the mod, there's talk of a 619k precise resistor "added from +10V to the summing node of the VCO common CV " for the newer boards, or 332K for the older boards.

The 2 resistors I removed yesterday were 200K +150K = 350K, and my board, although sold to me as "old" is a new one, the mod was probably done with the old board in, so I probably should get a 619K resistor, although I'm not sure where to put it : "the summing node of the VCO common CV ", where is that ?
cheers!

[chris j]

Alain, you said you have a different zero band mod, which is it ?
Where can we get them ?
cheers

[thealien666]

Sorry if I might have involuntarily implied, in an earlier message, that I have such a mod on my Mini, I do not.
In fact, I just love how sensitive and expressive the original pitch bend is. I often use it as a manual vibrato.

I do have a couple of mods on my Mini, but not this one.

And before you ask, out of curiosity, which are they ? The first, and more important one, is the optical detection system for the keyboard keys, replacing the mechanical contacts that were often dirty or oxidized and causing all sorts of problems. And the second is the oscillators synchronization option.

[chris j]

ha OK!
I could live without it if the zero point was always the same, but it fluctuates so much it's never in tune.

I've been looking for hours on the net the schematics to insert the right value resistor, to no avail. Lots of people mention they have the mod, but nothing more.
The article on wikipedia mentions "Moog later recommended adding a deadband mod and published this mod in their factory service notes"
I've downloaded tens of factory service notes and manuals but nothing about that.

Maybe I should post a new thread just asking about it, as the length of this one may discourage the people who'd know

Optical, yes I've seen that, sold by Kevin, indeed my keyboard suffers from bad contacts.
OSC in sync, yes I've seen the schematics to this mod yesterday

cheers Alain!

[chris j]

you remember I told you there was no ground on my pitch bend but instead -10V ?

I found this post by MC:
You can add a deadzone to a Minimoog pitch wheel but it's a bit more work than just adding deadband diodes. The pitch wheel pot is tied to (+)10VDC and ground - the ground connection has to be replaced with (-)10VDC. Then the bias voltage needs to be changed on the oscillator board or all of the VCOs will be off by half an octave. This involves replacing three resistors on the VCO board, and you have to play around to find the correct bias resistor value.

So maybe the mod I had was supposed to work...

[thealien666]

... This involves replacing three resistors on the VCO board, and you have to play around to find the correct bias resistor value...

That sounds like a lot of efforts (and guess work) just to get a dead band.

You do know that the mechanical tension of the notch on the pitch bend wheel is adjustable, right ? Maybe yours is not tight enough ? When I got my Mini, I had to put just a tad more tension on it, because it had lost a bit of stiffness after some 36 years...

[CZ Rider]

I've been looking for hours on the net the schematics to insert the right value resistor, to no avail. Lots of people mention they have the mod, but nothing more.

I have the Moog modification outlined here. Shows a diagram of the resistor locations and values.
Hope that helps a bit.
Moog factory service bulletin 830 pitch wheel mod.

Seem to remember a similar mod published in Keyboard magazine years ago with the added opamp.