Electro-Harmonix Deluxe Electric Mistress

I really like these big box EHX pedals. I understand why trends have moved away from huge pedals but I love the look of them even if they are unpractical.

This is a 90s Deluxe Electric Mistress reissue (EC 1000 Rev B) that I was asked to look at. It passed a clean signal, but no effect. You could sort of hear something happening when power was cut to the pedal but it was very weak. This seemed like a positive, it meant the BBD was still able to do something.

Going through this pedal was pretty easy thanks to Ralf Metzger's fantastic Electric Mistress site (presumably inspired by Kit Rae's Big Muff shrine). Ralf has info on identifying different versions & reissues, theory of operation, full schematic and repair & aligning instructions. This version (V4) has a Reticon RD5106A BBD and 24V DC input. Oddly enough there is no bypass indicator LED, this is usually a good way to tell old EH pedals from the reissues.

Walking through the alignment procedure for the V4 I found that I couldn't adjust the clock signal to get as low as the specified 40 kHz. I had some clock signals at the BBD but I couldn't see any modulation on them in any switch or knob settings (the modulation of BBD delay time produces the flanging effect). After buzzing out the circuit it turned out that there was no continuity across any of the terminals of the Filter Matrix switch. As far as I can tell the switch wafer was removed or disappeared somewhere, sliding the switch didn't bring anything in contact with the terminals. I wired in a spare DPDT switch in parallel and had a working flanger.

Temporary eplacement switch added across the original.

I did a quick alignment following Ralf's guide to correct any adjustments I made when it was working incorrectly. The only diversion was setting feedback, I always feel that any pedal with a feedback control should be just about oscillating at the extreme end. It will get a replacement slide switch, they are easy to source but I didn't have one at hand. The switch doesn't effect calibration so it can be swapped out later.

This is the first through-hole pedal I've written up here. I suppose not having any SMD parts makes it the least false.

Cheers to Ralf.

Klon KTR

Another quick one. Another pedal that's a lot fancier than I normally get to play with. This is the reissue/sequel Klon that "inspired" the EHX Soul Food and dozens of other klones.

Not of Bill's making, but it probably helps.

The build quality is pretty high, everything is board mounted and the footswitch is on it's own small board with a ribbon cable and snap-in connectors providing strain relief. The only wires are for the battery snap. Despite the "essential" diodes, there are no exotic or outrageously expensive parts. It looks like surface mount film counts are used throughout.

 

The circuit seems to be similar to Centaur traces found online, and pretty close to the Soul Food except for the magic diodes. The 7660 doing voltage doubling and inversion seems to add a lot more ultrasonic switching noise (~26-27 kHz) to the power rails than I remember seeing in the Soul Food.

This one had a bad TL072 opamp (U2). I would guess that someone used a power supply above 9V and the charge pump supplied a voltage above +18V (the upper limit for the TL072) and popped it. The pedal works after replacing it, so an easy enough fix once the problem had been found (I just guessed when everything else around the opamp measured OK). I forgot to take many pictures of this one, the noisy one above is an "after" shot, you can tell the alignment of U2 is a little off.

Side-by-side it's very close to the Soul Food in sound. Connecting to a signal generator and scope, both can do ridiculous 25+ Vpp output with the right input settings and signals, which should overdrive the shit out of pretty much anything.

Revisiting the Ibanez Echo Shifter

After repairing the second Echo Shifter, the PCB sat on the bench for a few days before I re-assembled it. When I did, I found that it had stopped working again. It would light up, but there was no signal in either effected or bypass modes. When I played with the controls I found I could still get it to oscillate by changing delay times with the oscillation switch on, so I knew the delay and output circuits were good.

I opened it up, connected a signal to the input jack and started tracing to see where it died. It wasn't getting past the input jack. Measuring continuity, I found that the jack tip and sleeve were shorted together. I desoldered the jack and it tested fine out of circuit. There is another choke/filter at the input jack, presumably to keep any high-frequency digital noise out of guitar cables, and it looks just like the failed one on the power input. I took it off, and the jack was no longer shorted, but no signal was getting through. Shorting across the pads as before and everything works again. I measured the part out of circuit and the pins were shorted together in a way that doesn't make sense to me at all. It seems like they fail both as open circuits and as shorts.

L6 removed and pads shorted

This is probably totally fine as a fix, and I couldn't see any clock noise or similar on the input jack. I decided to replace the jumpers with some ferrite beads to help cut any high frequency crap. 0805 parts will just about fit, the ones I had are 1 kOhm at 100 MHz.

L6 populated with ferrites

There is another one of these filters at the output jack, I replaced this part at the same time.

L7 replaced wit ferrites as well

Technically these parts have a 500 mA rating but I decided not to add them to the power supply input, as I worried about reliability.

After re-assembling and punishing the switches and jacks for a little while all seems good. This should make the ES-2 closer to bulletproof. Hopefully some more dead units can be revived as well.

Line6 DL4/MM4/FM4 firmware images

Here is my collection of firmware dumps for this series. The DL4 and MM4 are from pedals I've owned or repaired, the FM4 image I found online.

Stickers on the EEPROMs and text data in the images refer to version numbers but I've never actually seen any different revisions.


DL4 1.3:
https://drive.google.com/file/d/0ByVCt2OFhXnyVF9kZnRXTDJTNEk/view?usp=sharing&resourcekey=0-86887qF7KuqQq77nf4Vd7A

MM4 1.0:
https://drive.google.com/file/d/0ByVCt2OFhXnyNURXckFJUTlJYmc/view?usp=sharing&resourcekey=0-DM-HZXCfQB50_p-1awD_cg

FM4 1.0:
https://drive.google.com/file/d/0ByVCt2OFhXnyZUx2R0RSQTBzc00/view?usp=sharing&resourcekey=0-1ak_q2Ip8ABL4MlzcFJE2g

I am still hoping to do a mod to switch between different firmware images. I was hoping that I could find larger pin-compatible EEPROM and toggle some address pins but the larger chips seem to have different pin-outs. Making an adapter board to go in place of the socket is probably the way to go but I haven't really had the time.

Once again, if there are copies of the firmware from the AM-4 and DM-4 please get in touch.