Sunday, 16 November 2014

Univox/Korg SR-55 Analog Rhythm Drum Machine - 1967

Some pics of my vintage Univox SR-55 Analog Rhythm Drum Machine. This machine dates from 1967.

It's almost half a century old & is also known as the Korg MiniPops 3. 

A confusing thing about these early Korg machines is their numbering system. The MiniPops 5 & 7 arrived on the scene in 1966. The MP3 was produced in 1967. So this machine should have much in common with the MiniPops 7. The sloping face is shared by both the MP7 & MP3 and they are very similiar sounding machines, but the 7's got that awesome quijada/Guiro sound. They were both designed to sit on top of the organ/table

The MiniPops 5 was in comparison a different beast -- designed to sit under a organ, like the Keio MiniPops-Doncamatic.

Depeche Mode used this drumbox. It's all over Jarre's Magnetic Fields album though this may also have been the MP7 ??? . Kraftwork may have also used this???

Anyway, we have solid construction.  Nice big clunky switches.
The shiny aluminium knobs belong in the 1960s. Certainly well built.

These two knobs are a great way to combine different patterns for the swing & foxtrot.

This is the circuit board taken from the underside of the machine.

 Inductors ??? 

I don't have a MiniPops3 service manual or schematics but the MiniPops 7 schematics is available online and it has inductors all over it. It seems logical to suppose that Korg would have used similar technology in both machines. If anyone has a MP3 service manual, please email me. I would be eternally grateful.

I suspect this a RLC circuit or "tuned resonant circuit" - using inductors, caps & resistors.

The RLC circuits form harmonic oscillators.
Inductors are passive devices used in electronic circuits to store energy in the form of a magnetic field. They are basically coils of wire. They are the compliment of capacitors, which store energy in the form of an electric field. 

The pot on the right is the tempo control.
This looks like a good place to start your search for a sync in. The lack of a way to syncronise the 55 is one serious limitation.

The diode matrix/pattern section.

For more info on the history of Korg Drum Machines Click Here


  1. any infoes for this Keio Mini Pops MP-7

    many thanks in advance

    1. Hello, What sort of info are you looking for Mohamed?

  2. Hi, my one has a bit of buzz on the output, does your one too? Do you know if normal or can be fix? Thanks

    1. Hello, mine doesn't have any buzz at the output. I'm not sure what the problem is. Bets to have a technician have a look. Good luck. J

  3. Hey Jon, I'm trying to bring a univox sr55 back to life and it's missing one of it's inductors, If it's upside down with the knobs facing you it's the second one from the right. Can you tell me if that is marked 100 or 4000? What the value is? Any help would be greatly appreciated, also did you end up find a service manual? many thanks for your time. Nate

  4. Hey Jon! I just bought one of these, but both "Snare/Kick" and "Brush/Cymbals" pots are fully un-wired inside. Do you have a clear picture of how to connect these or any document that would help? Thanks!!

  5. How do you compare the univox sr55 with the ace tone FR3 . Im taking a long time to decide, any thoughs / recommendations ?