Showing posts with label DIY. Show all posts
Showing posts with label DIY. Show all posts

Thursday, 19 February 2015

Korg (Keio) MiniPops 1

This is a odd one to categorize as it has no official name.
She looks like a minipops 5 (MP5). It's shape indicates that it was meant to sit under an organ or piano.
The MP5 was manufactured in 1966 as was the MP 7

Prior to the Mini Pops, Korg or Keio as it was known then, were famous for their Donca Matics.
So maybe this this could be called the Keio - Doncamatic Minipops. ???
Or shall it just be named "The Unnumbered MiniPop".????


And to make matters more confusing the MiniPop numbering system was not cronological.
The MP 5 & 7 came out in 1966.
The MP3 was manufactured in 1967.



Anyway, I think it's safe to assume that this drum was the first in the line of MiniPops, and was produced
in 1966 or before.

Temp, Cymbal & Switch-Volume dials. The Cymbal dial sets the volume level of the cymbal .... so you can cancel this sound completely if you like.


I really like the preset buttons which look like fake toy piano keys.
We have 16 patterns:
Waltz, Samba, Cha-Cha, Mambo, Rumba, Beguine, Habanera, Tango, Blues, Rock-Beat, Bossanova, Rock-a-Ballard, Swing, Six Eight, Fox Trot & March-Polka.

And you can combine up to 3 patterns at the one time.... creating some crazy rhythms


 The bottom cover slides off to reveal the inner PCBs.


We have 3 separate PCBs. The top is for the power supply.
The second (lower) PCB is the pattern generator. Notice the diodes.
The 3rd & largest PCB holds the voice circuits.


Well what does it sound like. It sounds nothing like a real drum. It's distorted . That bass drum is malformed beyond recognition. The snare and toms ... are they really toms ??? OMG.....well everything is twisted & misshaped. In other words I love this drum.


What was probably considered a mistake my the manufacturer makes this one a real find.

I'm seriously tempted to mod this one. The pattern board is at the top. I love the layout of these Japanese boards. They are logical & well thought out. It should be very easy to bypass the pattern PCB and trigger the voices directly.


I'll sit on that thought for a while. This drum is uber rare. It is good to sometimes leave things in virgin condition.

Modding ??? would be nice but maybe if I found a second one ....


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

Sunday, 15 February 2015

Ace Tone (Roland) FR-4

The MultiVox FR-4 is basically a Roland Rhythm Ace from 1967.
It's all very confusing at this period as Roland was yet to be born.


 The parent company was called AceTone and it was still licencing its products to companies around the world. In the USA, the FR-4 was sold under the name MultiVox.

There are 8 sounds available on the FR-4.

It looks very similar to the FR-6 which came out in 1972. I don't think there was ever a FR-5.
The FR-6 and FR 4 have the same patterns except for one.
The second last (from left to right) on the FR-4 is DISCO.
ON the FR-6 this is now SLOW ROCK



There are 20 Presets: waltz, disco, ballad, rock'n roll, rumba, beguine, mambo, bossa nova, cha-cha, tango, samba, fox trot 1, fox trot 2, swing 1, swing 2, swing 3, march, haba-nera, bass snare, bass.
 Pretty basic mixing of patterns. The preset rhythms include 2-beat and 4-beat variations with the sounds accented on certain beats. This helps to reinforce the rhythms.
You can play more than one preset pattern at once. Combining these with the two Beat buttons opens up lots of variation in pattern.



These old machines are beautifully constructed & rock solid pieces of hardware.
The balance control adjusts the balance between the base drum and cymbal sounds.

 The diode matrix for pattern generation ??? I don't have the schematics for this drum. If anyone out there does I'd be eternally grateful if you'd contact me.

As this is a very an early machine, inductor coils & tuned tanks are used to create the drum sounds.
Thus cloning would be very difficult. Some of the individual sounds can only be isolated by messing around inside the machine. I plan to try to get individual outs first, and maybe bypass the diode matrix rhythm selector and trigger the voices separately.

Sadly there is no way to sync this to external gear without moddification.

The plan is to mod this in the future. I love the old Roland drums. That's the voice board on the top.

This is the rear section of the faceplate with the red lamp in the centre. The voice board is in the foreground.


This is the power supply part of the drum. Do be careful ... 
high & lethal voltages that can kill are here

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For more info on the history of  Roland Drum Machines click here

Thursday, 12 February 2015

SYNTHACON VCF - CGS 35 build notes

These are some build notes for the Cat Girl Synth (CGS) tribute module
of the Steiner-Parker synth VCF. (CGS module # 35).
My thanks to Ken Stone & Nyle Parker for making this possible.


This filter is so very different from all the other filters that I've used. I first heard this on my Arturia Minibrute.  According to Vintage Synth, it can self-oscillate like the Minimoog, but has an opposite polarity so it doesn't lose any volume when resonance is increased as do the Minimoog and Odyssey's filters.

If I'm not mistaken, the original multimode synthacon filter had a knob to change between high, band and lowpass filtering.
The 4 toggle switches at the bottom allow the VCF to be controlled by Keyboard, Envelope 2, Sample and Hold, and VCO3.To the left the toggle switches select inputs for VCO1, VCO2, VCO3 and Noise. There are 3 knobs for frequency, filter type and Resonance(Q).

Ken's version allows all three to be used simultaneously.

The simplicity & elegance of  this filter always amazes me. The circuit seems to be based on your standard non-inverting amp LP / Sallen Key type filter design

 Sallen Key filter
 If the resistors (R1 & R2) are voltage controlled (eg with vactrols or OTAs), then we have a voltage controlled filter. (OTAs = operational transconductance amplifiers can be found in Korg MS-20 type filters & vactrols can be seen in many Buchla filters).

In the Steiner- Parker VCF, a string of eight (1N4148) diodes morphs into this voltage controlled resistor. How ???

And all 3 filters (BP, LP, HP) are obtained simply by injecting the audio signal into different parts of the circuit.

Take the LP filter as an example.
The LP filter is obtained by injecting the audio into the 47k resistor at the top. There it enters the diode string (1N4148) and the 2n2F capacitors.

Those three 2n2F caps are v important.
Also notice the two 2n2222 transistors that sit on either ends of the diode string. They form a voltage differential across the diodes.
The diodes need to be fed current if they are to act like a resistor......
By varying the voltage we can produce different effective resistances in the diode string as we force current through them.
The whole idea of the diode string is based on Ohm's Law & the equation R=V/ I   (R= resistance, V= volatge & I= current )

I've chosen to use 3 x 2N2222 trannies.(Mouser). 

 The pic to the left is the view of a NPN 2n2222 from the underside.
 I didn't match these. I wonder if you can use any standard NPN transistors?
 Maybe BC 547s ???

In Nyle Steiner's 1972 article it looks like he used 2N5174 transistors instead of the 2N2222 . On Analogue Realitie's site, they use two monolythic matched SSM2210 pairs.

The PNP Transistor 2N2907 - mouser Part No.
 Alternatives ??? - 2N5138 or BC 557 - I might try these in future versions of the filter

"Original transistors as per Nyle Steiner's schematic are 2N5138 and 2N5172"

Hope I've got their orientation right.

Simple = Beautiful 
8 diodes, 3 caps & 2 transistors = a multi-mode VCF.

Some more Links:

Monday, 9 February 2015

Roland CR-8000 CompuRhythm - mods

The Roland CompuRhythm CR-8000 came out in 1981 & is without a doubt one of  Roland's finest drum machines. Often referred to as the "poor man's 808" I think it has its own unique character that is neither TR-808 nor CR-78.... but something in between. It's high hats are legendary and that bass drum certainly has a kick to it, but it has a few flaws. A lack of individual outs, and its very basic programmability are some of the limitations.



Moddifying the drum will help this instrument reach its true potential.
My friend Paul A (aka: Cobramatic), has given me permission to document some of his mods.

Paul used a combination of mods from Josh Gumi's excellent site GumiElectronic and some
Analogue Solutions mods but he also came up with a couple of mods to the mods on his own.
Most of the mods involve replacing fixed resistors with pots. The mod for the bass decay is awesome and uses just a cap and a few more resistors.

Gumi's site describes dozens of mods but Paul wanted to keep everything within the original case. So due to the lack of room a choice had to be made re the ones that appealed the most.

With this many mods there is just enough room to get 24 mini pots and switches in the top cover
(maybe a few more if you are brave) but closing all up afterwards is a real challenge with all those wires.

Obviously a breakout box is another way to go for those with the skill and patience to use ribbon cables and connectors. Plus you could also add switches to everything & even some "tone pre-sets" using fixed resistors if you are really game.

Paul did the 6 main individual outs - a must-do in his opinion. It's also theoretically possible to take out all 13 drums but this involves much more wiring. And beware, that steel plate on the back is 2mm thick and needs some careful and rigorous drilling to get through.

Paul doesn't like the suggestion of utilising the existing footswitch and sync jacks
because then you loose that valuable functionality. (especially the sync pulse outs). They are invaluable with CV/gate synths and modular's. He also uses it to sync up his modded Bentley Rhythm Ace for even more analog goodness.

 Josh's suggested voice swap to get the Tom's on a different output is a very good idea which will possibly be a future mod. For now Paul has left it out ... you know, you can't do everything.

"The sound bending is way way greater than a normal machine of course - going from crazy tuning to booming decays (open up decay all the way) and overdriven sounds". Paul now has tuneable bass drums, hats, cowbells, toms, snares and to top it off, "the worlds snappiest clap".

At the last minute he added the snare boost circuit and mounted that next to the on off switch
(so he didn't have to open her up again!).


Final thoughts
"There are an amazing set of tones now available. the Bass Drum (make sure you also do the separate decay mod circuit), Snare, Clap and Tom's are really worth doing. Hats are great too - I did my own hats mod to switch between  808 style and noise/sizzle maracas sounds which also gives the ride cymbal a fantastic harder metallic strike. The cowbell is cool if you love it but I notice it did  introduce a slight noise hum into the snare channel - no idea why, but it is not critical  and can be turned down when not using the Cow Bell"..

"Be very careful when you open her up - there is a high voltage power section that you must be very careful with while testing the mods". Paul taped plastic over this section so he wouldn't accidently touch it.
It's good to play safe. Electricity can KILL YOU

"I (Paul) also blew the fuses because I accidently let the voices board slip onto the programming board while powered up - ooopps, this could have blown the whole project and I did it twice!!! Be a lot more careful than I was and don't even try it if you cant identify the High Voltage power zone from the rest. You have been warned!"

(Sorry that the pic is upside down)

Some people say that the CR8000 is a poor mans 808 - but with these mods Paul say's he will take it any day of the week  Plus at way way way less than an 808 price even if you add $100 of pots, components, knobs and wires, you can get for yourself a highly customisable & awesome sounding analog drum machine with dinsync in and out (get a dinsync / midi swing convertor and you are set).
This coupled with the amazing "Register and Arranger" section which are not available on any other machine.
make this one brilliant piece of kit.


It's great for jamming. Plus you get to have 8 programmable 2 bar presets and 4 programmable fills which you can mix with the other presets at will. Programming it is easy once you get the hang of it (but yeah, obviously not as good as on a 808 style machine).

"This baby is definitely my favourite drum machine now - hands down.(thanks again to Josh Gumiela for the well documented mods and info on his site)".

Many thanks to Paul for his efforts. May it encourage others to get out their soldering irons and have a go.

More Links:
1. CR-8000 description & features.
2. Roland CR-8000 :: GumiElectronic
3. Roland CR 8000 with mods mov - YouTube
4. Roland cr 8000 analogue solutions tonal mod video


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For more info on the history of Roland Drum Machines click here