Electro-Harmonix Graphic Equalizer

Another EHX big box pedal, a mains powered 10 band graphic eq. I'm guessing this one is a late 70s/early 80s vintage. Google finds at least two versions, this one and a more modern looking black-and-yellow version with a power switch and LED/lamp. Oddly enough, none have a knob in the lower left corner instead of a stomp switch, so this may be a less common variant or someone's science project. It doesn't work - moving the sliders just brings in some noise, the knob in the corners seems to attenuate this.

A few things are apparent once the lid is off. The "master volume" is not stock, it's someone's mod in place of a bypass switch. The jacks are probably replacements, as EHX didn't use those isolated plastic jacks. There is a third jack that has been added, probably for a remote footswitch for bypass. The PCB is also broken! It's held in place to stand-offs with screws and washers and one corner has broken off. Some of the plastic sliders of the potentiometers are sheared off, it's clear that someone stamped over the sliders hard and managed to break the PCB as well. There is a pair of washers and a screw holding the board in that corner, and it actually seems stable mechanically.

A schematic was easy enough to find, the model name is the same as on the PCB art and the circuit seems to match. It's 9 notch filters (using single opamp gyrators) in parallel with different centre frequencies plus a passive 16 kHz filter. This seems to be a common design for guitar EQ. Power supplies are approximately +-13.5V using a centre tapped transformer and zener regulators.

Schematic found online

I took the board out of the box to take a lot at the pots. Date codes are from 1979. Some black foam was attached at some point, probably to keep dirt out, and over the decades it has perished and turned to sticky fluffs of black shite that are now all over the PCB and inside the pots. I cleaned these with contact cleaner and cotton buds until the pots slid smoothly. Also washed the enclosure while I had it gutted, removed the plastic jacks, installed some new metal open-frame 1/4" jacks and pulled out the volume knob and wiring.

Some of the pots have broken sliders, so it's possible that they have broken tracks or the wipers have disconnected from the tracks. I tried to measure the resistance of the left-most pot from the backside and it didn't seem to reading correctly. All the pots extremes should be wired together in parallel, and it turned out that left hand one had no continuity to it's neighbour. I tried to desolder it to measure out of circuit, and the pad and track lifted right away. The pad on the next pot also started to lift as soon as it was heated. Usually I don't see any lifted traces or pads when desoldering. It turned out that these tracks were physically broken, when the PCB corner was broken the pots must have been pulled away from the board. The left-side sliders were completely disconnected, the ones on the far right were fine and the middle were a bit flaky. I ran a piece of bus wire across the top pads to connect them, much like how the pot cases are grounded together.

Cracked pads

Pots jumpered with bus bar

At this point I clipped a test signal to the board and fired it up. Power supplies were OK. The signal didn't get any further the first opamp stage, so after checking the feedback network looked good I replaced it with a new 4558 opamp. Everything works afterward, all bands boost and cut and none have any noise or crackling.

I added a new switch and wired for true-bypass, and then managed to confuse myself when I saw a huge 50 Hz hum on the output. I thought the power supplies had gone bad and replaced the filter caps with new Nichicons. It turned out that although the enclosure is grounded, and the PCB is bolted to the enclosure, the PCB is not grounded through these bolts. Running a wire from the input jack fixed this up. At least I know this won't need new filter caps any time soon.

The extra hole in the enclosure is a decent fit for a large LED bezel and some spare hardware, I've added this as a bypass indicator.

Repaired and cleaned up.

It sounds exactly like a 10-band EQ sounds. The +-13.5V supplies mean that this has huge headroom, and it can be used to filter high amplitude signals without distorting as soon as a 9V or 18V unit.

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.

Ibanez ES2 Echo Shifter

1 second analog delay with modulation, an oscillation switch and tap-temp from Ibanez. I really like this delay. Opinion tends to be split on these, they sound great and and have a very nice feature set but are very prone to dying. Online reviews are split between gushing praise and reports of the things crapping out:
http://www.musiciansfriend.com/amplifiers-effects/ibanez-echo-shifter-analog-delay-with-modulation-guitar-effects-pedal#reviews

https://www.amazon.com/Ibanez-ES2-Shifter-Analog-Guitar/dp/B00BFWIZGI/ref=sr_1_1?ie=UTF8&qid=1473597444&sr=8-1&keywords=ibanez+es2#customerReviews

I wanted to look at these to figure out why, I ended up with two with different faults. These seem to match the most common complaints.

Broken Sliders

This first unit was sent to me already repaired and modded. The previous owner had had someone swap out the footswitches for nicer soft-touch switches. The originals are actuators that press microswitches on the PCB. The new switches worked, but tap-tempo and bypass had been swapped functions. The slider for delay time had also been sheared off and the battery snap had been cut off.

 

The backside has some opamps (TL072) and some 74HC4040 ripple counters. I don't know what the counters are doing. The toggle switches are wired to the PCB and mounted through the PCB in rectangular cut-outs - I like this, it prevents form turning when the nut is tightened and they are strain-relieved from the rest of the board. J6 has two pins soldered together. The trimpot on the right hand side looks like a mod but may be done at the factory, it looks pretty clean.

 

The other side has two Coolaudio V3205 4096 stage BBDs, and 2 BL3102 clock drivers. The clock frequencies for the BBDs goes as low as ~3.5 kHz, which is ~500 ms for a 4096 stage delay, so if both BBDs are cascaded then a 1 second analog delay is achieved with a bandwidth in the region of 1-1.5 kHz. This is dark but still sounds very nice for long delays for guitar.

U9 is an Analog Devices ADAU1701 DSP. This device has 2 ADCs and 4 DACs but very little memory, so it seems very unlikely that it is providing any digital delay. I am guessing that this is only handling tap-tempo, bypass, generating the modulation signal and maybe doing filtering and/or compression of the delay signal before and after it hits the BBDs. U13 is 24AA128 EEPROM for the program code.Analog Devices make a visual drag-and-drop programming environment for these DSPs (SigmaStudio) but unfortunately it will not load binary ROM dumps so I can't see what exactly what this chip is doing. I can probably dump this if anyone needs it.

 

These sliders are a standard 45mm footprint.

 The delay slider is a 10K linear 45mm potentiometer, I used a Bourns part (PTA4543-2015DPB103) as a replacement.

Added a connector to footswitch wiring so I could take the board in and out of the case.

I also re-did some wiring to swap the footswitches back.

Power Failures

This seems to be the most common problem. I came across a second unit that refused to power up at all. This one had a piece of foam between the battery bracket and the back of the board, and had the original switch PCB and actuators. There was no trimpot with hot-glue this time, but otherwise identical.

L1 looking worse for wear.

 I started measuring for power at the 9V jack. No current was drawn, and L1 looked a bit dodgy. This looks like a common-mode choke on the power input, filtering noise along with C7 and C70. The top of the ceramic broke off when touched with a tweezers. I guess this part wasn't rated for the current draw of the pedal, or doesn't handle vibration or shock well.

L1 bridged.

 As this is just a choke, we can jumper straight across it and restore power to the rest of the pedal. I lifted it off with hot-air and used some bus bar to bridge the pads.

Working again, and sounds just like the other one.

Current draw is less than 60 mA on these, which is surprisingly low.

I haven't seen any problems with noise or interference since removing this choke, so I will probably go back to the first pedal and do the same as a preventative measure. It is likely that this filter is need for EMC compliance to stop power cabling radiating the ADAU clock signal. This is a simple enough repair, and only needs the back casing taken off, the board can stay in place inside the pedal.

2 More DL4s

Big Green Delays, again.

I had a couple of these Line 6 DL4s handed over for repairs and each had a different problem from what I have seen before, so I'm holding out that this will be interesting to someone.

Silver-Taped Green Delay

By now I have something of a checklist of problems for these pedals. This one had all power supplies present, and none had any strange ripple or noise superimposed. Next step is to look at the test pads - there was no clock signal anywhere. Since the MCU generates the clock, and the MCU is responsible for resetting and waking the DSP (which produces the sampling clocks) nothing will work without this master clock.

U7. Oscillator and caps swapped at this point.

I know the problem is likely to be in the area of the MCU (U7). I replaced the oscillator crystal and capacitors with parts from the scrap board to see if I got a clock signal, as that's an easy place to start. No luck. I took off the MCU with hot air and replaced it with the one from the scrapper and everything worked again. Fantastic.

After removal and wicking of U7.

Alignment of the replacement is not great, but solder joints look good and function perfectly.

These MCU are a cheap 8051 core in a "ROMless" configuration, meaning that they have no ability to be programmed and only load code from external memory. This is a Good Thing for repairs, as it means that a scrap unit isn't really necessary, any new IC of this model should work, and all the code is in the one socketed EEPROM. In practice, I have found that "ROMless" is sometimes a misnomer. MCUs often have fuses or configuration bits that need to be programmed, or even have a small area of programmable memory for a bootloader, so a straight swap isn't always possible. More on this to come.

Normally I use a Kester flux pen for surface mount work, but this was the first time I used a syringe of tacky flux paste. It is really amazing stuff and I am completely won over. It made this job much faster and cleaner (I used it again for the Whammy repair, but unfortunately I'm getting to write about these out-of-order).

The owner had cover this pedal in silver gaffer tape. I think it looks cool.

A New Power Issue

This unit didn't get as far along before something look wrong. It had a working 3.3V supply, but all other power supplies voltages were low.

Another Rev 6 board.

The 6.6V voltage doubler (MAX660, U20) follows the 3.3V supply, so I started there and removed the output cap (C48) and IC. Measuring resistance across the output cap pads (6.6V to ground) gave 29 ohms, so there is still a problem.

U20 & C48 pulled.

The 5V regulator is next (U21, LM3480) so that was pulled, and the 29 ohm to ground was gone. I pulled U21 from the scrap board and replaced it, then repopulated U20 and C48. All power supplies returned and relays clicked, worked again.

Poor focus, but U21 has been replaced.

LEDs and relays are working after C48 and U20 are back.

At this point the scrap board I have is looking pretty bare. Between the 3 pedals I have written about and another personal unit that hasn't been fixed yet I've removed pretty much every IC. This is fine though, as I found out that very little (if anything) on these pedals is pre-programmed. In nearly every case new parts will work perfectly, having a donor just means avoiding waiting a day for replacements to be delivered. This shouldn't really be surprising as these are consumer goods made in large quantities, it makes sense to keep any custom, selected or programmed parts to a minimum to keep costs down.