EML Electrocomp 400 and 401

[Jim Alfredson]

A local music store hired me to go through an EML Electrocomp 400 and 401 synth/sequencer. It's quite the piece of kit. 

 

 

The first order of business is to test the power supply and make sure it is outputting the correct voltages. According to the schematic, it supplies +/- 15vDC, pretty standard for synths of the era. It checked out just fine, so I moved on to turning the unit on and testing the audio output. 

 

Everything appears to be working but the sliders are super sticky and gunked up. Again, par for the course for old gear. Especially something like this that definitely lived in a smoker's house. 

 

Normally I would desolder the sliders, take them apart, manually clean them, lubricate, re-assemble, and re-solder. But I cannot figure out how to get these sliders open. They are riveted together with very small rivets. 

 

First I tried soaking them in 99% pure isopropyl alcohol for about 10 minutes. Then I flushed them with compressed air. And finally I used a paper towel inserted into the slot to further clean. This did an okay job, but several were still not conducting smoothly. 

 

So I decided to try a supersonic cleaner that I recently acquired in addition to the IPA soak. So far it is working really well! All the dirt is just flushed right out of the slider! I lubricate with Nyogel 767 grease that I load into a hyperdermic so I can squeeze it down into the slot. I test them with my analog Simpson 260 ohmmeter and I can see a nice, smooth movement of the meter after cleaning, whereas before the meter would jump around.

 

As I type this, the last batch of sliders from the 401 are in the supersonic cleaner. Once I dry them, lubricate, and re-install, I'll test that unit again and it should be fine. I'm making a video of all of this as well.

 

 

[Jim Alfredson]

 

 I still need to do the sequencer section. But it works.

Yes, all those faders on the sequencer need to be desoldered and cleaned. At least the ultrasonic cleaner is doing most of the hard work. 

 

 

 

[RABid]

Have fun with it while you can. I owned one for about 40 years. Sold it to help fund early retirement. It was a lot of fun. Unique sound, quite thin, almost digital. First instrument I owned with a built in quantizer. Not sure how they pulled that off being pure analog. Connected it to my MiniMoog for some nice A-tonal patterns. The Moog was 1v/oct. The ELM was 1.2v/oct. At the end mine had a few age related issues but I still got a really good price for it. I would really miss it but I built a Doepfer Modular system with most of the same functionality. It does not have that unique EML sound, but it is also not a vintage piece with vintage problems. I do prefer the sliders on the EML.

 

[Jim Alfredson]

It's a pretty wild system. I need to study the schematic to figure out how they did the quantizing. That was pretty radical at the time.

[Jim Alfredson]

I've been trying to track down an annoying issue with the trigger and envelope. system. If I insert a 1/4" connector into the EXT TRIGGER jack, thus breaking the normally closed connection (bottom left corner of this schematic), the internal trigger affects the envelopes. Without that connector in the jack, it doesn't trigger the envelopes. External triggers work but get combined with the internal.

 

I'm thinking it is probably a faulty JFET or two. I've tested all the E112s out of the circuit. One, possibly two of them have strange readings. They don't test 'bad' but their readings are quite different from the rest. Since there are three in the circuit acting as electronic switches, I'm thinking that's the issue. The one that reads funny is the one connected to the "B" terminal to the right of the one connected to the "A" terminal.

The unfortunate thing is that they are long out of production E112 JFET NPN transistors. I'm pretty sure I can substitute them for a general purpose JFET though.