MOTM

Hey fellas,

I have noticed in my two VCO system that when I use the transpose switch on 
my Roland M-181 keyboard or play higher up in scale thru my Kenton that the 
VCO's do start to sound flat or slightly off key. Especially one compared to 
the other. Could be my calibration (Unique problem to me) It is not a big 
difference, but in a live situation I would have to re-adjust the tuning of 
the 300's on the fly. Not very easy to do in an accurate fashion on stage 
right? Who out there plans to change these resistors and has anybody else 
had similar problems? Thanks loyal friends,

Thomas White

"MOTM 300", Still one thousand miles ahead of the competitors and a million 
miles ahead of the Moog VCO's! Has anybody ever thought about trying to get 
together some beautiful MOTM cheerleaders? JK


>From: "Paul Schreiber" <synth1@...>
>Reply-To: motm@egroups.com
>To: "MOTM listserv" <motm@egroups.com>
>Subject: [motm] MOTM-300 resistor change
>Date: Sun, 13 Aug 2000 21:23:21 -0500
>
>**NOTE**
>
>This is NOT a required change! Please read the following carefully!
>
>***************************************************************
>
>All new MOTM-300 kits will be shipped with R50 changed from 3M to 2M2 (also
>called 2.2M).
>
>Assembled MOTM-300s will have a 2M2 or a 1M8 depending on the particular
>performance
>of that circuit.
>
>This resistor adjusts the "High Frequency Track" of the VCO. Specifically,
>the tracking accuracy from 500Hz
>and up. No, I can't make it a pot because that causes more problems than it
>fixes.
>
>Newer batches of the MAT02EH NPN transistor used in the exponential
>converter show *improved* HFT
>when R50 is lowered.
>
>Now, should you immediated tear apart your MOTM-300 to replace this?
>NONONONONONONO!
>
>*ONLY IF* you think that in tracking multiple VCOs ABOVE 500Hz you have an
>issue, then you
>can change this resistor. You WILL HAVE TO RECALIBRATE THE VCO IF YOU DO
>THIS!!
>
>The following is the tracking of 1 VCO with R50 changed. Voltage source is
>Pro-2000. Errors in the Pro-2200
>are included in this (about 700uV over the range).
>
>Desired   Actual     With R50 = 3M
>25            24.97        24.91
>50            49.98        49.92
>100         100.01       100.2
>200         200.07        200.18
>400         400.06        399.97
>800         799.97        796.1
>1600        1599.5       1587.2
>3200        3197          3180
>6400        6386          6369
>
>This is an improved *average* error over 8 octaves of 0.065% Let's see
>anybody else top this!! :)
>
>You can see how the VCO "runs flat" in the upper octaves. Now, can you
>*hear* this? Probably NOT!
>But, if you are 'zero beating' VCOs without sync in lower octaves and want
>to maintain that in the upper
>ones, the lower value resistor will help.
>
>If you want a freebie 2M2 resistor(s), send me email.
>
>Paul S.
>
>
>
>
>
>
>

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