[sdiy] Minimoog tuning woes, Op-amp swaps?

[Tom Arnold]

On Tue, Feb 01, 2011 at 03:31:59PM -0500, Eric Frampton wrote:
> Second, I'm wondering what I can do to get the keybed itself linear. For instance, the tuning between high A and lowest A requires a different scaling than, say, the middle two C's. It's like it's a perfect 1V/Oct on the ends but not in the middle. Do I just have to go through and replace all the resistors on the keybed, or am I missing something else? The bus bar contacts are clean.
> 

Remember that the Minimoog is not 1v/oct, its 1.2v/octave or something odd.

A long while back I got a response on this list on how to rescale the
keyboard for 1v/oct and I happen to still have it:
----
	From: 	analoguediehard at att.net
	Subject: 	Re: [sdiy] MiniMoog Scaling
	Date: 	February 18, 2004 9:11:11 AM PST

Very early RA Moog Minimoogs *DID* have a keyboard scale trimpot, yet it
does not appear on RAM schematics.  I have serial #1053 and it is there.

On circuit board #2 Contour Generator and Keyboard (figure 9-7 of late
service manual), the junction of R20 and R22 are tied to the base of Q11.
Replace this junction with a 100 ohm wirewound and tie the wiper to the base
of Q11.  I don't know if it will bring the scaling to 1v/oct but it is a
start.

MC
----

I did this very mod and it worked spiffy and allowed me to rescale my Mini
so that it works normally with a midi/cv, assuming I tell the midi/cv to
start at F instead of C.

Yeah, won't fix your problem if you have an end to end scaling issue on the
divider, but it helps to know that you shouldn't expect to see 1v/oct out of
the keyboard circuitry.

A quick check down the ladder with an ohm meter should determine if you have
a problem there, or on circuit board #2.

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