Electro-Harmonix Stereo Memory Man (EH-7811)

The classic, basic, no-frills BBD delay. This is an EH-7811 revision, dating from around 1980 based on IC codes. This version is main powered (240V), runs at +/-15V internally, Panasonic MN3005. There is no LED, I think this was the last version without one. There is an Echo/Chorus switch which probably reduces delay times, and in-phase and out-of-phase outputs for a "stereo" effect.

This is another one that I have had a for a while, and later came back to. I bought this a couple of years ago and nearly got it working, then hit a dead-end.

It was pretty dirty on first inspection, and missing a knob for the blend control. The power cable had been shortened to a ridiculous length, about six inches, making it awkward to work on.

Before cleaning...

The original eBay picture shows this off:

 

The insides show that the PCB is complete with no obvious damage. It does anchor everything off of board-mounted pots which are only on one side of the large PCB - the other end floats and tends to cantilever.

PCB as received

The delay/chorus switch is almost entirely missing, just the frame left.

Interior of case, Echo/Chorus switch.

Closer inspection of the PCB found that the Blend potentiometer's pads had all craclked off. The pot was still hanging onto the board, but nothing was electrically connected. I ran some small jumpers from the pot back to the nearby traces. I also installed a new sliding switch. I referenced a schematic for the later EH-7811B at David Morrin's excellent site. The main difference (apart from the LED) seems to be that this version has an extra 741 opamp to invert the delay signal for the out-of-phase output.

At this point, I had some signal coming thorough, but hugely distorted. All output opamps were saturated, sitting at ~ 13 or -13 volts. I socketed and replaced some of the opamps with no change. There was a DC offset being introduced somewhere.

I had a few ideas:

1. dead opamp, or opamp feedback network. No changes when swapping opamps and measuring feedback resistors.
2. leaking AC-coupling capacitors. I replaced some 1uF caps of a type I had seen fail before with modern film caps, no changes
3. Missing ground node somewhere...

This went back into the "fix later" box for a while. I dug it out and went over some of schematics for other revisions and noticed that one side of the blend knob should be connected to ground. My blend knob had been cracked off the board, I could barely see a small track below the pot's pads that should have been connecting to ground.

I ran another jumper wire to ground, and now all the outputs were sitting at 0V.

I fitted a new mains cable so that is actually usable. There is no internal fuse, so I changed the cable fuse to a 3A part. I tried the original opamps in the sockets, but the outputs got noticeably more noisy. Maybe semiconductor processing has improved to the point where new 4558s and 741s are less hiss-y.

There was some serious clock whine, especially at long delay times. Fortunately I was able to completely trim this out.

PCB after repairs.

PCB after repairs, parts replacement.

I've said before I haven't noticed huge differences between analog delays based on BBD types. I had the Aqua Puss at hand for comparison between a V3205 and MN3005. The Memory Man sounds cleaner, if that makes sense? Less distortion on each repeat, a bit closer to the original signal. Still sounds like analog delay, just not as overblown.

Reassembled.

Digitech PDS 1700 Chorus/Flanger

I picked this up out of curiosity, I'm fond of the PDS series and the off-the-shelf design. This is a digital Chorus and Flanger, where the traditional BBD design has been replaced with an 8-bit digital delay line (i.e. not DSP or modelling) and the delayed signal mixed in the analog domain. This one worked but didn't switch very well.

PDS 1700

There aren't too many surprises when comparing the insides to the PDS delays. There is the same ADC (ADC0820) but instead of DRAM it uses a single 2k 6116 SRAM. This is probably because the required delay times for a Chorus and Flanger are much shorter (this pedal maxes out at 51 ms) they could spring for the more expensive SRAM. This also means all the DRAM refresh circuitry isn't needed, and there are fewer logic chips overall.

Guts

PCB Backside

The switches were pretty flaky. The mechanical design DOD/Digitech used at the time has a poor reputation for reliability. I find that if they are maintained they work well, but I don't think they stand up to force. The classic problem is that switches that won't switch on the first try get a harder stomp the second time, and things deteriorate.

PDS hardware. Input jack looks non-original.

The paddles press down on momentary push buttons on PCBs inside the pedal. The paddles bear against two bolts that pass through slightly oversized holes in the enclosure. There is a preloaded spring on the bolts on the insides to push them against the enclosure, with nuts holding the springs under tension. There is another return spring on the switch PCB to bounce the paddle back.

I replaced the switches, I'm using these. There was some play in the paddles, the bypass one would rotate slightly in place, meaning it would not always hit the button switch. I tightened down the nuts on the inside until this play was removed, then it switched every time. You need a 3/32" hex key and a 1/4" socket wrench to make the adjustment.

The effects are cool. There is interesting play between the delay time and depth controls, the flanger side can go from covering high to lower-frequency ranges, kind of like the difference between a Boss BF-2 and a HF-2. The chorus does odd (cool) detuning effects at high delay times, modulated chorus in the middle and traditional chorus at minimum delay.

I have this one listed on Reverb if anyone is interested.

Another Electro-Harmonix Freeze

I got another Electro-Harmonix Freeze fairly cheap, it sounded like it had been killed by an incorrect wrong power supply. I took it apart and found that it was a newer revision than I had seen before, the board was EC-D68 Rev C (the last one was Rev B). The main difference I notice was an AK4558 codec instead of PCM3052A.

Freeze Rev C PCB, flash ROM temporarily removed.

Main PCB, LM317 temporarily removed.

There was no sign of life, I found that the series Schottky diode at the 9V input had failed open-circuit and that the LM317 had an internal short between it's input and output pins. The fast/slow/latch mode switch also fell to pieces when the board came out of the enclosure.

I replaced the bad diode with an SS14L (it was the correct size and I already had some at hand) and installed a new LM317. I thought that the LM317 was supplying 3.3V to the DSP and this would fix everything. Instead, the pedal would pass a clean signal but with a clicking sound once or twice per second. I found out that LM317 is actually used as a 1.25V regulator, which is only used for the analog VCC of the DSP56374.

I thought the clicking may be the DSP watchdog timer firing, possibly because it was missing program code, so I removed the flash memory and dumped it. It was a perfect match for the dump I made of the first pedal I repaired, so no problem there.

Measuring power at every IC I found that the 5V rail was high at around 5.9V and the 3.3V supply was sitting at 3.9V. I thought that U5 and U8 (both SOT-89 packages) were also voltage regulators and that maybe they had been damaged as well. I also noticed that U6 is connected to the reset pin of the DSP, and it was resetting the DSP every second or so. My guess is that U6 (also connected to the 3.3V supply) is some kind of voltage supervisor and it is resetting the DSP because of an incorrect 3.9V at VCC.

I found a great picture at freestompboxes (thanks to Steven_M!) showing that on previous version, U5 was 78L05 (5V regulator) and U8 was BA932 (who knows, but from context it has to be a 3.3V regulator).

U5 & U8 on another revision.

The Rev C board in front of me had "BA420" on both chips. Possibly EHX decided to run all 5V parts off of 3.3V, and doubled up on regulators? I don't know.an

To test this out, I decided to remove both chips and apply 5V and 3.3V from  external power supplies.

U5 & U8 removed, external power applied

This set up was a little awkward, but everything work correctly. Current draw looked totally reasonable, 19mA from the 5V supply and 21mA from the 3.3V. No resetting, no clicking, and the pedal could freeze audio in all 3 modes.

Current draw on 5V and 3.3V supplies.

I ordered L78L05ABUTR and MCP1804T-3302I/MB as replacement 5V and 3.3V SOT-89 regulators. I also used 2MD3T2B2M2RE as a replacement switch. This replacement is not threaded for a nut, but recent version of the Freeze don't look like they are threaded either. Pedal works like new.

Ibanez DDL10 Delay II

This is another early digital delay pedal, I am guessing it was built in 1986 from some of the IC date codes. I don't know if the 10 series included the first Ibanez/Maxon digital delay. Obviously this is the "Delay II", but the DDL Delay I and Delay III were also released in the same series of pedals,  each with different delay times. The max delay time of 900ms of the Delay II put it in a similar league to the Boss DD-2.

Inside, there is a two PCB construction with a hard-wired ribbon cable. The top board has unpopulated parts, I would guess that a DML10 (modulated delay) could be built on this same board by populating an opamp LFO and adding the two extra pots.

DDL10 internals

The bottom PCB has two 4164 DRAMs, an NE571 compoundor, LM311 comparator (most likely used as part of an ADC as in the DD-2 and PDS delays) and a bunch of opamps. The SIL (single in-line) package chips are M5218L low-noise preamplifiers, used in lots of Japanese pedals. There are only 2 4164 64kb DRAMs, the DD-2 has 3. Either the DD-3 has higher sampling rates, or the Ibanez uses 8-bit samples instead of 12-bit. This is still more than the single 64k seen in Digitech PDS 1 second delays.

Main PCB, component side

The back side of the lower board just has a main controller MC4101F IC. I can't find any info on this, it's almost certainly a custom controller for digital delays (like the Boss/Roland RDD63H101).

Main PCB, back-side.

This unit looked mostly dead, it passed no effected signal and LED didn't respond to the footswitch. I thought the back of the larger board looked a bit crusty so I clean it with 99% IPA, afterwards I saw the LED blink with the footswitch. Still no signal.

I couldn't find any schematics for this model online, but someone has scanned and uploaded an Ibanez factory schematic for the DFL10 flanger from the same series, which uses the same controller IC. There is a full pinout.

DFL10 schematic page 1.

DFL10 schematic page 2.

From the schematic, the clock signal for the controller looked like it was coming from a VCO to pin 26 ("2F"). I probed my board and found that I did have a clock signal, it could be varied by turning the Delay knob, and I also had what looked like communication between the controller and the RAM chips.

At this point I got really lucky. There was a 100uF electrolytic capacitor near the LM311 comparator that was a little discoloured. While taking measurements I noticed it was getting warm. I pulled it from the circuit, and the pedal started passing a delayed signal. This cap is connected from 5V to ground right next to the comparator input, if the cap was leaky then it would effectively mute the comparator. Everything worked without this capacitor, I replaced it anyway with a new low profile 100uF for peace of mind.

Faulty capacitor pulled.

The LED turned out to be a bad solder joint - it would light sometimes if it was held in a certain position. Reflowing the joints fixed it.

Way Huge Aqua Puss MK II

I don't think I've ever looked at anything by Way Huge before. This is a modern version of the Aqua-Puss, and Jim Dunlop acquired Way Huge in 2006, so I expect it to be similar to the current Dunlop and MXR stuff.

This one would light it's LED when switched on but wouldn't pass a signal.

The insides are really nice, and very easy to disassemble. There are three PCBs - one just breaking out the switch contacts, one SMD board for input/output and switching and one through-hole board with the effect guts. They probably re-use the two smaller PCBs for all of the pedals in this size of enclosure.

Interior

The upper board has a CD4013 dual flip-flop, a CD4093B quad NAND gate and a relay to handle the bypass. The manual says the pedal has "AC protection", I don't know if this is just a series Shottky diode or something more sophisticated. There are some opamps and what looks like a IRF7606 Mosfet in a micro-8 package, that could be doing some power switching in case of reverse polarity or an AC supply connected. Relay is a EA2-5SNJ, similar to what's in a DL4.

I/O & switching board component side

Jack side

The delay board a V3205 BBD and BL3102 clock generator, SA571 compoundor and LF353 opamp for input and output buffering. Freestompboxes.org has the full schematic, it's not too complex a delay and similar to a DM-2/DM-3.

Pinout of the 8-pin connector is as follows (taking the pin with square PCB footprint as pin 1)

1. 9V
2. Ground
3. LED
4. Bypass switch
5. Input signal
6. Output signal
7. Relay coil
8. Relay coil 

The relay coil contacts are probably only broken out so the small PCB can be connected to a test jig, the main board doesn't route them anywhere.

Delay board component side

Delay board back side

I couldn't tell if the relay was actually switching, as it was hard to hear it click over the sound of the footswitch. When I disconnected the foot switch board and triggered the switch with some wire I could hear the relay clicking, so the switching logic was probably good.

After hooking up a test signal and oscilloscope I could see that the input signal was reaching the first opamp stage but there was nothing at the output pin. I desoldered the LF353 and replaced it with a socket and a TL072 for now.

Removed LF353

Now I had a clean signal in bypassed mode, but no delay. No switching waveforms on the BBD on the oscilloscope. No power at either the clock generator or BBD either. The schematic shows an NPN transistor/diode voltage regulator for these chips, I found that the 2N3904 transistor was blown to shit! After replacing with a new 2N3904 it regulator to around 7.4 volts. I'm not totally sure why this is needed as the BL3102 & V3205 should be happy to run on 9V, this may be a holdover from using older BBD chips. (Update: it turns out that there are multiple V3205 datasheets online, with conflicting information. According to Coolaudio, the max Vdd for a V3205SD is 8V).

Epoxy case blown off voltage regulator pass transistor. I don't know how I missed this.

I could now see clock signal at the BBD which varied with the delay knob as expected, but still no delay. I could see an input signal at pin 11 of the SA571 but nothing at the output on pin 10. I borrowed an SA570 from PDS delay pedal and this brought back the delay effect. Sounds great but not too different from other analog delays I have.

So: dead 2N3904 regulator, dead LF353 and dead SA571. I'm guessing this was fed too high a voltage from the wrong power supply. It's running happily 24 hours later with a new SA571 so this will probably go up for sale on Reverb pretty soon.

Silvertone Bass 35

This is a cool little solid state bass amp, I'm guessing dating to the 60s. No idea if Silvertone manufactured this, or if it was a rebrand, as there is very little information about this model online.

Solid State Bass 35

No output signal. Only 5 transistors, so surely this would be easy? Instead of getting through this quickly I had it for several months, only looking at it when I had a few minutes to spare. If I had more space to work with this could have been much faster and easier. This has been a trend with physically large gear, I should really think about learning a lesson and getting a wide bench and keep it clean somehow.

Single sided phenolic PCB

Full of cracks and mild corrosion

This amp has been worked on in the past, and has some of the electrolytics replaced. It was also dropped on it's faceplate at some point in the past, and the phenolic PCB has cracked. The ground pour is broken in a few places and it has been bridged with solder.

Original output transistors.

Most of the transistors appear to be branded with house-markings, as I can't find any references to their part numbers. I initially though output transistors were bad. They are marked "761" and "CG121", no info on these. One seemed to have a very low Vbe when measured with a DMM diode mode, which looked like a shorted junction. The TO-3 pinout is fairly standard for transistors, so I was assuming all cases were collectors. Collectors voltages were +35V and 0V, so I made guesses as to which output transistors were NPN and PNP types and then replaced with new 2N3055 and MJ2955 in TO-3 packages, new mica washers and new thermal grease.

Dead bass control/driver transistor

After tracing the signal through the amp with a scope I found that nothing was getting to the output transistor bases. Nothing was passing the third transistor that drives the output transistors and implements the bass control. It was marked "5981 274 S6721", no idea. I desoldered this part and found that it was dead, completely shorted leads. I replaced this with a BD139. Based on a guess of the polarity of the original and the size of that package I thought this should handle the current requirements. With the BD139 I got some life, there was an output signal sometimes. Turning power on and off would sometimes get it working, sometimes it would stop. I found that there was a high-frequency oscillation at the output stage, if it drifted in and out of oscillation then things would work. Capacitors from collectors to base pins fixed this, values were just picked experimentally.

It still didn't sound right. There was an odd overtone riding on top of the signal that couldn't really be dialed out, though it sounded better at higher volumes. Another parasitic oscillation? Bias issue?

Around this time I bought a Peak Atlas DCA 55 Semiconductor tester. This is a very useful tool for testing transistors and diodes, and will also attempt to identify parts based on I/V characteristics. I still had the original TO3 power transistors, so I tried them out. One read a Vbe of 0.19V but was identified as PNP germanium, and working. I had assumed Vbe this low was a problem. After putting the old transistors back into the amp with new grease it sounded great, not very clean but not totally distorted either. The replacement silicon part wasn't biased correctly, the odd sound was probably some crossover distortion.

There is a diode from the base of CG121 which is probably used for biasing, I would guess that this is also germanium and modifying the amp to use new silicon transistors would involve replacing this as well.

The replacement BD139 runs quite warm, but not so much that I would worry about heatsinking it yet.

Here are measurements of the originals, they are surprisingly mismatched. This may not be a push-pull design at all.

7671
NPN silicon
hfe 108 @ Ic 2.5 ma
Vbe 0.643V

cg121
PNP germanium
hfe 59 @ Ic 2.5 mA
Vbe 0.190V
Ib 4.781 mA

Hopefully this is good for another 40 years.

Red Panda Particle

It's been a while. I have been doing repair jobs and not posting them, so I will try to clear the backlog.

I bought a non-working Red Panda Particle granular delay for a decent price. This is fairly well documented as a Spin FV-1 design, but the granular delay programs and pitch-shifting & randomised modes really drew my interest.

The insides are fairly simple - the FV-1, a 24LC32a serial EEPROM, a 74HC148 priority encoder (to decode the rotary switch and select which program to run) and a quad OPA4134 opamp. The "chop", "delay/pitch" and "param" pots are read by the FV-1, the blend and feedback controls appear to be done in the analog domain. This looks more or less like a reference FV-1 design, all the magic is in the program code.

The PCB layout is nice, pots and jacks are board-mounted and the DC jack is on a connector so the entire board can be removed or tested before installing in an enclosure. They use a PCB mounted spring to ground the enclosure, like the modern EHX designs, but this one seems to be contacting an oversprayed section.

Interior layout.

This pedal passed no signal in effected mode. I probed the OPA4134 and the first opamp that drives the mix control was stuck at near ~8V DC. After replacing the chip everything worked.

IC10 removed.

This is a really cool design, in that it's very different to nearly every delay I've used before. It is quite difficult to predict how the different modes will sound, and I think this would need some significant playtime to learn. Unfortunately this one came along at a time when I didn't have a lot of free time or desire to keep amassing pedals, so I have sold it on.

I did dump the EEPROM. Looking at it briefly with the excellent online FV-1 decompiler, each program looks to have disassembled correctly and makes some sense. I'm reluctant to share this, as this is really the only unique part of the pedal, and AFAIK it hasn't been cloned. If you have a genuine repair need (pedal with dead ROM) then get in touch, maybe I'll help. I may also revisit this and get it running on a different FV-1 board at some point in the future.