Hello,
I've bought an old (but working...) EHX Electric Mistress (from '90-'92), but the seller told me that he'd played a lot with the trimpots.
The effect it's sounding almost right, but i think that on some settings it sound strange.
Sometime ago I found on this forum (if i remember well) a long procedure to adjust the trimpots using a signal generator and an oscilloscope, but i forgot where :D
I use the "Search" button, but no luck...
Please help me!
???
patience may bring you set up notes if I can find them!
OK....thx a lot Stephen!!!
???
part 1
DELUXE ELECTRIC MISTRESS ALIGNMENT PROCEDURE.
Set RATE and COLOR (feedback) controls to minimum (CCW) and mode switch to the FILTER MATRIX position.
The clock waveform is now an unmodulated square wave whose frequency is determined by the RANGE control.
Set the RANGE control to maximum (CW) .
Adjust clock frequency trim (VR4) for approx. 35kHz, (28.6 micro-second period), at pin 1 of 1C 4.
.
Connect a 200Hz sine wave to the input of the unit and set bias trim, (VR1) for the maximum undipped waveform at VR3 wiper. This should be at least 1.6V p/p. Set input level to 1.0V p/p at pin 6 of 1C 1 and set gain trim (VR2) for the same level, (unity pain), at VR3 wiper.
Disconnect the input sipnal and set clock balance trim, (VR3) for minimum
clock noise. "
Reconnect input and recheck unity pain.
Vary RANGE control over its full travel and adjust bias trim, (VR1) for maximum undipped s'ignal at VR3 wiper.
Set input to 0.5V p/p and 3kHz. The signal level at VR3 wiper should now be approx. 0.9V p/p due to the pre-emphasis, but the output of the unit should remain at approx. 0.5V p/p due to the de-emphasis.
Set mode switch to FLANGE and examine the clock waveform at pin 1 of IC4. This should be a square wave whose frequency is being swept at a rate determined by the position of the RATE control. Varying the RANGE control adjusts the width of the sweep, the maximum frequency of the sweep remaining constant.
Set input to 0.2V p/p at 400Hz and set COLOR and RANGE controls to maximum, (CW), and RATE control to minimum (CCW)..
Switch mode to FLANGE and observe the output.
If the unit oscillates, adjust feedback trim, (VR5) until the oscillation just ceases, ensuring that the oscillation does not occur at any point of the sweep. The oscillation can easily he recognized by bursts of a large amplitude waveform at a higher frequency than the output waveform itself. This can be heard as a very loud screeching sound at the output.
part 2 - from different notes:
DELUXE ELECTRIC MISTRESS ALIGNMENT.-
(FOR UNITS SHIPPED UP TO 3/15/79)
Set RATE and FEEDBACK controls to min(CCW); set mode switch to FILTER , -MATRIX. The clock frequency is now fixed(not modulated) and its frequency is determined by the RANGE control.
Set the RANGE control fully CW. Set the clock frequency trimpot(lOOK) for approx. 20KHZ at pin 1 or 5 of the CD 4013A. This is a square wave with a period of approx. 50 usec. Feed in a 200 HZ signal and set the bias adj. for an unclipped sig of 1V p-p min. at the output of the balance adj.
Set the gain adj. for unity gain between the bal. adj. output and pin 6 of the 741. Set the bal. adj. for minimum clock freq. with no audio sin., and make sure the unity gain is still OK.
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Vary the RANGE control over its full range, and trim the bias adj. for max undipped p-p signal through the SAD 1024A. Recheck the bal. adj. with no signal.
Decrease the input to .5V p-p and increase the frequency to about 3KHZ. The output level from the 1024A should go up about 5db (almost X2, or to about .9V p-p) due to the pre-emphasis, but the output from the unit should not due to the de-emphasis.
Look at the clock (pin 1 or 5 of 4013A) and switch to the FLANGE mode. Check for proper freq. modulation and action of RATE and RANGE controls.
With RATE at midpoint and RANGE at max(CW), set the F. B. trim so that with the FEEDBACK control at max (CW) the unit cannot oscillate but has sufficient feedback effect.
WOOOOOOOOOWWW...amazing....thx a lot Stephen...thx a lotttt...
DELUXE ELECTRIC MISTRESS ALIGNMENT
(FOR UNITS SHIPPED AFTER 3/1V79)
OBSOLETES PREVIOUS PROCEDURE. MUST BE DONE AS WRITTEN HERE.
Set RATE and COLOR (feedback) to min (CCW), set mode switch to FILTER MATRIX. The clock frequency is now unmodulated and determined by the RANGE control.
.Set RANGE fully CW. Set the clock freq trim (100K) for approx. 35KHZ(a 28:6 microsec. period) square wave at pin 1&5 of the 4013B. Connect a 200HZ sine wave sig. to the input and set the bias trim for the max. possible unclipped sig. at the balance trim wiper; this should bo 1.6V p-p or more. Set input level for l.OVp-p at pin 6 of the 741 and set gain trim for same level (unit gain) at bal. trim wiper. Disconnect the input and set bal. trim for min. clock noise, and
recheck unity gain when sig. reconnected.
Vary RANGE control over its full travel and trim the bias for max. unclipped signal through the SAD 1024A over the range.
Set input to 0.5Vp-p at 3KHZ. The gain through to the bal.trim wiper should
go almost to X2(about 0.9Vp-p) due to the pre-emphasis, but the output should
remain at about 0.5Vp-p due to the de-emphasis.
Look at the clock(pin 1 or 5 of 4013B) and switch to FLANGE mode. Check for proper freq. modulation and action of RATE & RANGE controls; at higher RANGE
settings the freq. should sweep to a lower minimum.
Set input to 0.20Vp-p 400HZ and COLOR at max. Switch to FILTER MATRIX and look at output. If unit oscillates, adjust F.B. trim to stop it. Set RANGE to a point where output is maximum(about 2/3 of way CW). Set F.B. trim for an output of 0.70Vp-p.
That's it.
Scanned and OCR to Word, then hopefully corrected the rubbish!
Thx a lot again!!!
You're fantastic!!!