Tweaking a Deluxe Electric Mistress's Trimpots

[mipo]

I'm currently resurrecting a DEM I built a few years ago using the layout on GGG (http://www.generalguitargadgets.com/diagrams/dmistlo.gif ) - which I believe is exactly the same as the original DEM - but never got around to housing or building/acquiring a power supply for (currently I have it running on two 9Vs).  I found Stephen Giles' reply in this thread (http://www.diystompboxes.com/smfforum/index.php?action=printpage;topic=67766.0), but I don't have access to an oscilloscope or a signal generator.  The pots are labeled BIAS, FEEDBACK, CLOCK, BALANCE, and GAIN. The effect of the CLOCK trim is quite audible, and the BIAS trim appears to allow the unit to work in only a fairly narrow portion of its range; everything else is a bit of a mystery to me, though I assume GAIN affects output level?  I do have a multimeter with a Hz function, if that helps.  I should mention that the unit does appear to be working, but I'd like to get it as close to factory original in the settings department as I can.

Any assistance would be appreciated.  

[mipo]

bump

No ideas?

[dmc777]

I did this with my RI DEM. First I marked where everything was and then started tweaking. In the end I ended up just returning the pots to their original location because they really didn't do much "good" difference to the sound.

[mipo]

I wish I could do that myself, dmc777; unfortunately, as this is a home-made DEM, there ARE no original settings. BIAS and CLOCK seem pretty obvious, but I haven't a clue of how to optimize the others.

[blueduck577]

even if you don't have a signal generator and scope, these following instructions may be of some use to you.

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.
<
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.

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!

[mipo]

Thanks blueduck577; that's the information posted by Stephen Giles I mentioned in the first post. 

[StephenGiles]

But you can just as easily set up by ear.

[mipo]

I realize that I can do that to a degree, Stephen, but I don't even know what I should be shooting for on the FEEDBACK, BALANCE, and GAIN controls; and actually, what I hear from the CLOCK trim suggests that it could even be an external pot.   I'm assuming (?) that these controls are somewhat interactive, i.e., the setting on one will affect the settings on another.  I guess I'm just really looking for a good place to start; otherwise the possibilities are endless.

[Thomeeque]

Thanks blueduck577; that's the information posted by Stephen Giles I mentioned in the first post.  

And did you read it actually?

FEEDBACK - "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."

BALANCE - "Disconnect the input signal and set clock balance trim, (VR3) for minimum clock noise."

GAIN - "Connect a 200Hz sine wave to the input of the unit .. 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."

As you don't have signal generator GAIN could be tricky: this trimpot is there to adjust unity gain of BBD line (to make dry and wet signal equal for output mix as it makes most intense flange effect) - you have two choices, either you will adjust it by ear or you will get signal generator (build it , it's simple and very useful).

T.

[mipo]

I DID read it, but you really helped boil it down and isolate the stuff I was missing.   Thanks, Thomeeque.   

[Thomeeque]

I DID read it, but you really helped boil it down and isolate the stuff I was missing.   Thanks, Thomeeque.   

OK, my pleasure Good luck, T.

[DiscoVlad]

Is there an updated guide for the reissue DEMs? The trimpots and controls are all labelled Rxx instead of VRx, while the ICs are all Uxx

Board is EC1000 Rev-B, and uses a 24V DC wallwart, presumably given the 12V regulator an 18VDC supply is also fine.

ICs:

U1 = 78L12
U2 = 4558
U3 = RD5106A
U4 = LM324N
U5 = LM311
U6 = CD4013

Trimpots:
(all but R15 need verification as they're based on educated guesses)

R12 = Bias Trim
R13 = Wet/Dry mix
R15 = Regen. Trim
R34 = Delay Trim

Controls:

R26 = 10k Lin (Color)
R31 =  100k Lin (Range)
R24 =  10 Lin (Rate)