EH Deluxe Electric Mistress EH-5150 D (inverse green print version) problem

[The Groke]

Hi - I'm new to this list. I have a late 70s/early 80s Deluxe Electric Mistress which has never quite sounded right. My pedal is the deluxe version with the inverse green/black graphics. Basically, I can't get the unit to sound very effected, even after adjusting the feedback and trim. It sounds good as a light flanger effect, but sounds no where near as strong and rich as other old silver/black Mistresses that I have played. I searched through this site and read many of the posts, but no one seems to have mentioned my issue.

One potential wrench in the works for me trying to figure this out (with my limited knowledge) is that my board may have been modded at one point. Comparing my circuit board to the original and re-drawn schematics that are available on this site, I can note a number of differences:

1) C15 (.22uF off pin 7 of the LM324) has been removed (no jumper)

2) pin 3 of the 741 goes to a green 102k film cap and then the center pin of R4 (the color pot). Pin 4 goes to the other leg of this same film cap and then to C4

3) R13, the gain trim, has been removed. In its place is a 1.5k resistor

4) R31 has been removed. In it's place is a 1uF cap that connects the left lead to the right lead of R30.

5) the top two pins on the Gain trim have been bridged - but they are not like this on the schem.

Pics are here:

http://www-personal.umich.edu/~damont/EHMistressCase.JPG

http://www-personal.umich.edu/~damont/EHMistressCircuitSide.jpg

http://www-personal.umich.edu/~damont/EHMistressComponentSide.jpg

I have no idea which of these might simply be a product of the revision number of my unit (which I take to be "D" given the suffix) and which are the result of someone noodling around in here. There are quite a few lifted traces and solder bridge repairs, wiring looks new, and some caps look like they have been replaced. So it looks like someone may have done some work on it in the past.

Please help me identify which components I should try to restore and which I should leave be so that I can get this sounding good again (if it ever did). I appreciate any and all help... thanks! DT

[Govmnt_Lacky]

There is a bit too little information to make an informed suggestion HOWEVER.....

Here is a link to the Deluxe EM to use from JD's site:

http://www.generalguitargadgets.com/diagrams/dmistsc.gif

If I were you, I would restore the entire circuit to what you see in the schematic and go from there.

AND... for goodness sake.... DO NOT attempt to do ANYTHING without first removing the SAD1024 chip  Only install this chip if needed. If it fries.... it is gonna cost ya!

Good Luck 

[Thomeeque]

1) C15 (.22uF off pin 7 of the LM324) has been removed (no jumper)
4) ..a 1uF cap that connects the left lead to the right lead of R30.

IMO revision mod ("rounding" of sweep triangles moved from one place to another)

3) R13, the gain trim, has been removed. In its place is a 1.5k resistor

Veeery weird, IMO main cause of the weak effect (silent wet path), return 10k trim here (friend's working unit has cca 9k5 dialed here).

Have to leave now, good luck, T.

[StephenGiles]

5) the top two pins on the Gain trim have been bridged - but they are not like this on the schem.

This might indicate that the output of the balance trim (accross the 2 BBD outputs) is grounded!

[The Groke]

Thank you all for the comments. Following Thomeeque's advice, I will start by replacing that fixed resistor with a 10k variable trim pot. I'll be sure to report back on the outcome.

Stephen, is the grounding across the BBD pins a problem (if that is actually the situation)? Should I break this bridge?

Also, would you all suggest removing the SAD chip before I proceed, or is that actually a bit riskier than working on the unit with it in? I don't want to kill it with static.

Thanks again for your help.

[Govmnt_Lacky]

Stephen, is the grounding across the BBD pins a problem (if that is actually the situation)? Should I break this bridge?

If you look at the schematic that I provided the link for above, you will notice that the Gain trimmer has one of it's lugs (Lug 1??) tied to it's wiper (Lug 2) and both of those are going to GROUND. So, you SHOULD NOT break the bridge as it is needed in accordance with the schematic. Simply remove the 1.5K resistor and install the 10K trimmer in its place.

Also, would you all suggest removing the SAD chip before I proceed, or is that actually a bit riskier than working on the unit with it in? I don't want to kill it with static.

As long as you utilize PROPER HANDLING PROCEDURES... you will have a much greater chance of accidentally damaging the chip with power up/downs or stray voltages than you will with it sitting beside your work area in a static free piece of foam or baggie 

Good Luck 

[The Groke]

I have a static bracelet thing and will take your warning seriously (thanks for reminding me). Now I just need a trim pot... not so easy to get here in RadioShack free Sweden   I'll try out some resistors in series for now.

Thanks!

[Thomeeque]

Now I just need a trim pot... not so easy to get here in RadioShack free Sweden  I'll try out some resistors in series for now.

If you won't find trim-pot, start with 10k resistor there.

5) the top two pins on the Gain trim have been bridged - but they are not like this on the schem.

Clock Adjust Trim actually. That is normal, I've seen it on some EM schematics.

T.

[The Groke]

OK, I put in a resistor that was measuring under 10k (9.1ish), adjusted the feedback, gain, and clock (thanks for the correction on the gain trim)... and it now sounds *much* more like a spaceship taking off than before. Yay! (and thank you!) Tomorrow I'll get a proper 10k pot to put in (linear I guess, right?). I think it could use the full value (more rocket fuel), and I might as well just make it like in the schem.

I really appreciate everyone's help. Thanks again.

[Govmnt_Lacky]

OK, I put in a resistor that was measuring under 10k (9.1ish), adjusted the feedback, gain, and clock (thanks for the correction on the gain trim)... and it now sounds *much* more like a spaceship taking off than before. Yay! (and thank you!) Tomorrow I'll get a proper 10k pot to put in (linear I guess, right?). I think it could use the full value (more rocket fuel), and I might as well just make it like in the schem.

The 10K pot is LINEAR. I don't know if you meant a 10K "trimmer" or not but either way.... all trimmers are linear.

If you search the archives, I believe that Fender3D posted a thread or comment about how to PROPERLY adjust the trimmers on the EM. If I were you, I would definitely look that up!

Good Luck 

[The Groke]

Sorry, yes, I meant trimmer. I did not know that they were all linear.  I did find and download the procedure when I first found this site, and I will go through it more carefully at some point. Right now, I'm just excited to play.... Thanks!

[StephenGiles]

Surely grounding output of balance trim = no delayed signal.

What I suggest you do is make a probe with a length of coax lead. Connect one end to a jack plug as normal. The other end should be opened up, then solder two lengths of wire say 6" long to each of the hot and ground wires, and then solder a crocodile clip to the other end of the 6" wires.

Now turn your amp volume down, connect the ground wire clip to ground ( ) and the hot wire clip to the balance trim output. Let us know what you hear apart from a lot of hiss.

[The Groke]

Thanks Stephen - I actually had (more on this in a second) a light effect before I touched anything (at the start of this thread). With the addition of the 10k resistor (measuring just over 9K), it was sounding quite good. I played it for at least an hour with no issues.

Then today, I brilliantly decided to pick up a 10k trimmer and put it in place of the fixed resistor. I used a static bracelet and was careful with the board etc. But after putting in the trimmer, everything went awry. Now, I can hear the clock ticking away (responsive to the rate button) over a loud static buzz, but no effect apart from a loud flangey sounding squelch when I first power it all up.

Putting the 10k resistor in does not help the problem. I checked all trace continuity, checked the ESR of the caps, and made sure that all of the wires had proper connections and had not come loose, but it still sounds broken. I don't know how, but I'm afraid I zapped the SAD IC.  I know you are all shaking your heads at my stupidity right now... but I truly was careful! And I only touched that one resistor that was in place of where a gain trimmer was supposed to be.

Is there a way that I can check the functionality of my BBD? (some voltages values that I should check for)? I'll look through the archives for this answer on my own as well...

[tiges_ tendres]

If you've got flanging, there's a good chance your chip is fine.  Must be something else.

[Govmnt_Lacky]

Check for solder bridges near or around the "recently re-worked" trimmer area.

Also, the high-pitch squeel and static buzz leads me to believe that you might have a grounding issue. Possibly induced by the trimmer change itself OR from the moving about of the internals whilst performing the trimmer swap.

Good Luck and let us know if you find anything 

P.S. Pictures of the circuit would possibly help as well. Post 'em! 

[The Groke]

I initially only hit three solder points. Everything is clean in that area. The flangey squeal and the buzz are only present when I engage the effect. The switch itself seems to test out OK. But many of the wires running to the mounted case hardware are quite brittle. Your suggestion makes sense (thanks).... I'm going to go through them again to make sure something didn't go wrong when I removed the circuit board.

Here is the schematic:

http://www.diystompboxes.com/pedals/EHmistress_deluxe.jpg


Additional pictures of my actual unit are in my first post. here are the links:

http://www-personal.umich.edu/~damont/EHMistressCase.JPG

http://www-personal.umich.edu/~damont/EHMistressCircuitSide.jpg

http://www-personal.umich.edu/~damont/EHMistressComponentSide.jpg

[The Groke]

Just following up on this repair. I did manage to fix it, and the issue was a grounding fault as StephenGiles suggested. I recapped it for the heck of it to save future pain.

Since my board is a revision D, and there doesn't seem to be any info on this online, I will summarize the differences that I noted (I found more),  I'm not sure which are factory and which are from some mad tweaker from long ago, but here they are:

1)   C15 (.22uF off pin 7 of the LM324) has been removed (no jumper)
2)   pin 3 of the 741 goes to a green 102k film cap and then the center pin of R4 (the color pot). Pin 4 goes to the other leg of this same film cap and then to C4
3)   R13, the gain trim, has been removed. In its place is a 8.5k resistor
4)   R31 has been removed. In it's place is a 1uF cap that connects the left lead to the right lead of R30.
5)   R15 is 100K instead of 47k
6)   R17 is 22k instead of 68k
7)     it uses a 78L15 (the small package regulator) instead of a 7815

There was one other resistor that was different, but I forgot to write it down...

I replaced the fixed resistor in R13 with a 10k and am now getting a good deal of flange. Does anyone have any thoughts as how I can get even more (I know... I'm asking for trouble)? I guess what I'm missing are the scoops from really low to really high - it just sort of whirls about in the middle frequencies.  I tried replacing R15 with a 47k (like in the earlier revisions). Not sure if it is my imagination, but it seems to make the flange a bit deeper.

Thanks again for all your help... this is a great list!

[Thomeeque]

 Hi,

it would be much easier for others to help if you would take existing schematic which you are refering to, draw all those changes distinctly into this schematic and post it here. Your way we have to do the same thing mentally and it hurts (plus it's not clear which schematic you are refering to /not the last one you linked/ and this forces us to dig in history to try to find out - it is discouraging too)

Another useful thing you could do would be to post sound sample (slow rate, maximal range, no color), so we could tell if "missing scoops from really low to really high" is bug or feature.

R13 = 10k or 8.5k?

T.

[oldschoolanalog]

You want more flange?
Build this.