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Hi everyone. First off let me say that I am SO happy I found this place and I apologize for making my first thread about me needing help. I dodnt see an “introduce yourself” thread or sub-forum. My names Jackstand Johnny and Im a musician in Virginia USA who enjoys tonkering, circuit bending and Ive recently had my eyes opened to the world of building and using pedals after over a decade of using multi effects processors. Now that the pleasantries are out of the way…I really need yalls help.
So I got the seemingly very old EH Micro Synthesizer guitar pedal off Craigslist for cheap, knowing that it had a few issues. The input and output jacks were somehow switched so now the input goes to the amp and I plug my guitar into the output. A majority of the sliding pots are broken at the tip and fu ction, but are snapped off flush with the casing. The BIGGEST problem of all is the power cord. Its a small 2 prong plug soldered in and looks like it came off an old lamp.
So at first I thought it always had a permanently affixed power cord, but must have been a more robust 3 prong plug. Now…Im not sure of that at all. The pedal moraculously works, but not well. When I let a note or chord ring out it does so(poorly) and cuts out completely after about 2 seconds. Adjusting the levels do nothing to remedy or mitigate this, but doing so does make it cut off sooner sometimes. Could this be because it has the wrong power cord?
More importantly does this much older pedal(well before the name was changed to micro synth) use an AC power supply that plugs into the pedal itself? Am I basically operating this using DC since its soldered into the pedal and plugged into the wall? Please forgive me for my ignorance. I am here to resotre this pedal and learn from much more capable and experienced people. Heres a couple pics. Thank you very much in advance.
Well that was educational. I found that the power cable was basically ready to tear off of the sliding switch and I also think the reason the LED was so dim was because of a weak connection because both leads also snapped clean off. So after getting help on the BuildYourOwnClone pedal forum it looks like this power cord IS ok to use, but Id still rather replace it with one that has the 2 dofferent soze prongs so you always know which on is ground. Or can I not use one of those because this is wired for AC? Again please forgive my ignorance. Heres some more pics now that its opened up:
So these are the parts I really want to replace along with the cord. Im having a hard time finding this exact style seitch, but 3 of the terminals arent even used. So can I get away with another switch to the same specs but with only 3 points instead of 6 or does it need the other 3 not being used for whatever reason? Ive already found these sliding pots on SmallBearElec.com as well as its caps so Im good there.
UPDATE: I learned that the switch currently installed is a Master Switch double pole double throw but I really only need a double pole single throw(or is it a single pole double throw?). I was gonna get a dofferent style switch with only 3 terminals but I was told if this is the original switch that potential future buyers might be scared off if its different. Is this power switch I have the original? Theres clear evidence that people have tried to repair this pedal over the years so I have no idea what is the correct original part and whats not. Thank you in advance for your help.
Okay, that’s a lot to read through but I think I can narrow it down.
Yes the switch is original, it’s a DPDT slide switch, you can use another DPDT or SPDT (it doesn’t matter which) this one is fine http://smallbear-electronics.mybigcommerce.com/alpha-dpdt-slide/
If the power cord is dodgy by all means replace it, with 2 prongs you don’t have to worry about ground, the pedal gets AC and the transformer in there (the metal thing with yellow electrical tape) plus some circuitry converts it to the DC the pedal uses. However, putting a 3 prong cord on there would certainly be a good idea for safety and isn’t invasive regarding originality as it can easily be undone.
To do so, wire the power cables to the switch as normal then you can add a solderable washer (like this, check for screw size http://smallbear-electronics.mybigcommerce.com/solder-lug-angled/ ) to the earth cable and anchor it to the enclosure. I like to stick them between the transformer and enclosure, just stick the transformer screw through the washer and bolt it in tight with the existing screw and bolt, you want a good secure connection.
For the input and outputs being switched it’ll be a simple case of switching the jack tip wires around on those 2 jacks
Regarding its decay issues, could be a set up issue (there’s 2 trimmers, read the manual of the micro synth on the main site for an explanation of them) could be just your expectation of the pedal or it could be a fault.
If the pedal seems to work for the most part a simple servicing of replacing all the electrolytic and tantalum capacitors can sometimes help reduce noise and rectify issues and give the pedal a fresh bill of health, both types of capacitor have a limited life span and at this point they’re already at about 35 years old and probably drying up, just one less thing to worry about going wrong down the line, just remember they have a polarity which must be observed when replacing them.
I realise that goes against keeping the pedal totally original (something I am a proponent of) but it’s just one of those jobs that will have to be done sooner or later and wont effect if functionally other than extending its life, you can always save the original parts in a baggy and include them if you sell it on.
Edit: Oh and the reason your power cable was probably loose on the switch is that there should be a plastic bushing in that metal hole to hold the cable securely, you should be able to find a replacement once you’ve got the measurements of the hole and your new power cable.
A quick check of the schematic and there should only be ~15 to replace, not too bad.
Well if you want to do a full debug rather than just replacing the caps you can post up the voltages of ALL the IC pins but I think it’ll be easier and more sensible just replacing them, if the problem remains after though that is what you will have to do.
The old EHX PCBs are a bit delicate though so make sure you have some solder wick and a good pump action solder sucker (not one of those squeezy ball ones) on hand to do the job or you’ll be making up a lot of jumpers to fix broken traces!
Get that earth sorted first though for safety and good luck! I’m a little jealous, looks like a fun project
Oh and one more thing, inspecting the board for any suspect joints is worthwhile, old EHX pedals can vary a lot depending on who did the soldering on it the day it was made and bad joints can be an issue which could also be causing your problem if something is working intermittently.
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