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[mrpumpkin]

I have a multi moog but the lower registers have gone out of tune. I have not been able to find a solution for a fix. any help would be greatly appreciated.

Also i have heard that there is a modification to extend the base on the multi moog, make it more like the mini at the bottom. has anyone heard of this?

Thx

[kt_over_q]

The following is a link for a simple mod that improves the Multimoog bass frequency response: http://www.physicsenterprises.andrews.edu/diy_archive/manuals/moog/micromoog/vcfmod.html

The tuning is a little more involved.....do you have a good digital voltmeter (3 1/2 digit is minimum....4 1/2 digit is better) and a tuning reference?

Craig

[Guest]

I have a yamaha clavinova. As for the voltmeter,I am sure a friend of mine has one. He has access to oscilloscopes and other goodies.

[mrpumpkin]

that's me above, I forgot to log in

[kt_over_q]

I have not found an online manual for the Multimoog.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=1289&item=2565520983 is the factory service manual for the micro/multimoog and a "buy it now" price of $16 is a bargain.

The tuning procedure for the Multi is longer because of the two oscillators.

The clavinova will work fine for the tuning reference. Use a sound that has little or no animation and if your model has a chorus control turn the chorus off.


A quick tune of the Main oscillator may be done by the following procedure. Be sure to hold the keys down while adjusting so that the KBD CV is active from the keyboard. I will use a comb to gently "wedge" a key down to free up both hands.

1. Oscillator should be set to Drone and the Octave to 2' with the fine tune control in the rear vertical at the 12 o'clock position. Compare the Multimoog pitch to the reference (F above Hi C). If the tuning is close, just adjust the fine tune control, if it is significantly off then adjust the OSC RANGE trimpot on the back to "Zero Beat" to the reference device.

2. Switch the Oscillator back to Normal from Drone, set the Octave to 8', and depress and hold the Low F key. While listening to the same reference as step one, adjust the FINE TUNE control so the Multi sounds a perfect 2 octaves lower than the reference. Depress and hold the HI F on the Multi and turn the OSC SCALE until the Multi and reference device "Zero Beat".

3. With the Oscillator still in Normal mode, switch the Octave control to 2' and depress and hold LO F and "Zero Beat" with th reference device with the Fine Tune control. Now depress and hold HI F and adjust the OSC HI trimpot for "Zero Beats" with the reference.

There is some interaction with the HI and SCALE OSC controls. You made need to repeat steps 2 through 3 again.

4. Set the Oscillator to Drone, and the Octave to 2' and "Zero Beat" with the reference device with F key. Switch Octave to 16' and adjust OSC OCT for "Zero Beats". You may get some interaction between the OCT and OSC HI. Just work carefully and repeat steps 2 through 4 if necessary.


For the second oscillator, center the Interval control, turn on the 2nd OSC audio only, and follow the steps above for the 2nd oscillator.


This is a quick and dirty tuning. To really do it correctly you should follow the manual procedures for Power Supply adjustments and tune the Filter and set the VCA offset if necessary.

Work slowly and carefully, it is an art and you will learn to do it quickly with practice. The other oscillator adjustments that maintain the temperature trim should NOT be done as they are almost never required unless the tempco heated pair "3046" IC is replaced.

The other common failure in a Multi/Micro is the 3080 transconductance amplifier IC(s). You can figure these out fairly simply from the schematics.
One word of warning on the 3080 OTA IC(s), If you short (Iabc line) PIN 5 to ground, it's a goner. Be careful when probing the 3080 OTA IC(s) with a Voltmeter.

Craig

[mrpumpkin]

Thanks, the synth was not used that much so I'm hoping that the
3080 transconductance amplifier is sound, unless it can go bad from sitting.