Author Topic: How to adjust EHX Electric Mistress's trimpots?  (Read 7819 times)

gigimarga

How to adjust EHX Electric Mistress's trimpots?
« on: May 10, 2008, 01:05:32 PM »
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!

gigimarga

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #1 on: May 10, 2008, 05:34:38 PM »
 ???

StephenGiles

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #2 on: May 11, 2008, 05:04:21 AM »
patience  may bring you set up notes if I can find them!
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

gigimarga

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #3 on: May 11, 2008, 10:37:32 AM »
OK....thx a lot Stephen!!!

gigimarga

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #4 on: May 12, 2008, 09:40:49 AM »
 ???

StephenGiles

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #5 on: May 12, 2008, 04:35:11 PM »
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.
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

StephenGiles

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #6 on: May 12, 2008, 04:42:21 PM »
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.
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

gigimarga

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #7 on: May 12, 2008, 04:44:39 PM »
WOOOOOOOOOWWW...amazing....thx a lot Stephen...thx a lotttt...

StephenGiles

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #8 on: May 12, 2008, 04:52:01 PM »
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!
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

gigimarga

Re: How to adjust EHX Electric Mistress's trimpots?
« Reply #9 on: May 12, 2008, 05:37:17 PM »
Thx a lot again!!!
You're fantastic!!!