Elektronika EM-25 (Электроника ЭМ-25) SYNTHESIZER


Purchased from eBay December 16.

These synths are very well built and look really cool.

Electronically they are not the most reliable. Built in military production plants in the former Soviet Union. My particular synth was made in 1989.




The EM-25 is considered a string synthesizer but it has organ and brass. It also has quite an aggressive filter which screams when over driven. Nice. It sounds the buisness with a small stone phaser.

The synth is fully polyphonic, paraphonic really. except for the 16' bass ranges which seem to be monophonic.

Synths built in the USSR tend to scare people away as they seem hard to repair and deemed to be full of exotic components.

In reality many are just Russian equivalents of western components, such as 40 logic IC's

The hassle can be working out what the alternatives are..

To be fair there are some nice features on this synth, One is the handy hinged keyboard assembly, that lifts for voice board access.

Please note: A lot of this information on this site has been gather by me and may not be 100% accurate. It's hard to get information on these synths in English. Please email me with any corrections or pertinent information at: quad303 AT ntlworld DOT com



First check the Power supply and adjust +15 and -15 rails using R25/24

Watch when de-soldering components that you don't lift the PCB tracks. They are pretty fragile on this synth.

Get yourself the schematics. They are in Russian but will at least throw some light on the internals


Of course this synth had a few problems with it when I got it.

One of the upper 'B' notes was stuck on. On upper voice registers 2 and 4.

This turned out to be a bad diode KP521. I used a DIY audio probe to trace this down to voice area Z11 on the PCB.

This diode was replaced with a 1N4148 and the upper 4' voice issue was fixed.

The bender range was way off, so adjusted with these two trimmers:



Although my synth was ok, many EM-25's have keys that do not release. This can be down to a bad capacitor which sits under the corresponding key.

Another issue was some bad solder dry joints. A dry resistor solder joint was responsible for range upper 2' not working.

The EM-25 has a 'slide' control with interval. On my synth this doesn't work. I assume it's the same as the 'glide' found

on western synths. I have the transposer board out and I think it's a faulty logic IC.

K561TM2 IC = 4013A Dual Flip Flop

or one of the other 3 IC's in the area.

K554SA3 = LM311 DIP14

K553UD2 = LM201 DIP14

K561LA7 = 4011A


Update - I actually found out that these controls only affect pedal operation and were not faulty after all. DOH! It was fun to decode the IC's though. Thanks go to Karolis for confirming this.


some PCB images




EM-25 transposer PCB



EM-25 voice resistors and transistors (one of these diodes was faulty)



EM-25 audio board, notice the DIN sockets instead of qtr inch jacks



EM-25 voice boards raised position


EM-25 analogue delay line chip KA528BR2

Some info: 2 channels of 512 steps, manufactured Borzna, Chernigov region, Ukraine

Datasheet here and rough English translation here


It's worth repairing this solder bridge between boards.