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:

Wednesday, 11 February 2015

Roland Rhythm 55 - TR-55 Drum machine

Roland's Transistor Rhythm 55 (TR 55) drum machine came out in 1972.
Internally & sonically, its very similar to the Acetone FR6.
Controls: volume, balance, tempo, up tempo, power on-off, touch start 
Dimension: 130 (H) x 380 (W) x 235 (D) mm (5.1" x 15.0" x 9.3")

In that year (1972), Roland also released the TR-33 & TR-77
She weighs about 4 kg  (8.8 pounds) & has 13 buttons & 4 knobs.

The Start-stop Electro-static touch sensitive switch is a great feature.
You will see these on the Roland TR-77 also.
The diode above the on/off switch flashes in time with the beat.

The Up-tempo button is a double-time switch

There are 10 voices (split into 6 channels) & 10 patterns: Bossa Nova, Samba, Mambo, Cha-Cha, Rhumba, Beguine, Rock N' Roll, Ballard, Slow Rock, Waltz.
The variation knob splits the rhythms into two parts.: 2 Beat & 4 beat
- 2 BEAT: bass drum, bass + snare, foxtrot1, swing1, march and parade
- 4 BEAT: bass drum, bass + snare, foxtrot2, swing2, swing3 and tango


The 10 voices are : bass drum, low conga, high conga, cowbell, rim-shot, claves, snare drum, high-hat, cymbal, maracas

Sadly, there is no real way to mix the voices, however, the BALANCE knob does alter the balance between  bass/snare & hi hats/maracas.It allows you to cancel the HH sounds on every pattern - or to mix them to the pattern as loud as you want.

This is the base of the TR-55. It's quite portable. and comes with a carry handle.


bass/snare and hahats/maracas
Sadly there is no way to sync the drum externally.
Back panel jacks: main out low & high, plus a start/stop pedal switch.
This is ripe for modding. It's all analog with tons of  trimpots begging to be tweaked

If you pull off the backplate and tweak the trimpots you can get  that 808 bass and it's decay can be set to last forever !!!!
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For more info on the history of Roland Drum Machines click here

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

Roland CR-8000 CompuRhythm Drum Machine - Description.

The Roland CompuRhythm CR-8000 came out in 1981.
It's without a doubt one of Roland's classic drum machines with roots that go back to the  famous CR-78 (produced in 1978) & the TR-808 (which came out just one year before in 1980).
The 8000 & 5000 also look a lot like the Korg KR-55 which came out in 1979. There must have been  intense rivalry between these two Japanese corporations and I suspect the CR5000/8000 was a response to Korg's KR-33/55.

The unmodified CR-8000 weighs in at 3.2Kg, with 12 knobs & 32 buttons.
I really like the the digital tempo display. It's very accurate at giving a precise BPM reading.


The digital display was not a feature on the slightly earlier CR-5000 
The CR 8000 also adds the user programmable presets and fills.

Unmodified, the CR-8000 has a trigger out (+5V pulses) so you can clock external gear.
Sadly there is just one audio output, but unlike the CR-5000, the 8000 has DinSync (24ppqm).
dinsync I/O at 24PPQ

DRUM (weight: 3.8Kg) Main panel features a display, a data encoder, 11 knobs and 32 buttons.
- See more at: http://www.polynominal.com/site/studio/gear/drum/roland-cr-8000/roland-cr-8000.html#sthash.bPBX691N.dpuf
DRUM (weight: 3.8Kg) Main panel features a display, a data encoder, 11 knobs and 32 buttons.
- See more at: http://www.polynominal.com/site/studio/gear/drum/roland-cr-8000/roland-cr-8000.html#sthash.bPBX691N.dpuf
Another advantage the CR-8000 had over the 5000 was the "Programmable Rhythm Section".
Here you can program your own beats, one instrument at a time,  in step time. 
The drum uses two 1.5V batteries to store your patterns in 8 slots when the machine is turned off.
The CPU used is a 8-bit micro-controller - a 8049/8048 chip. (40 pins)
CPU NEC D8049C232

There is a knob above that allows you to pick the instrument you wish to program.

To the right of the Program section is the "Voice Level". This essentially is a 6 channel mixer. The Cr8000 has in total 13 sounds so compromises had to me made with the mixer. The channels are:
1. Bass Drum
2. Tom Tom /Rim Shot /Snare
3. Conga
4. Claves/ Cowbell,
5. Cymbal/ High Hat. (the HH is unique...and one of the strengths in this machine)
6. Hand Clap.

Another advantage the CR-8000 has is the "accent" dial.

I think the unmodded CR-8000 sounds like a cross between the CR-78 & TR-808. It's often referred to a the poor man's 808. Though it really shines when you start to mod it.
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For more info on the history of Roland Drum Machines click here

Sunday, 8 February 2015

Korg SQ-1 Vs monotribe.

A few test videos using the Korg SQ-1.
Sorry for the poor audio - this was recorded on a smart phone.








And a link to a trial sq-1 & monotribe video - demo 1

Saturday, 7 February 2015

Amer Fort - Rajasthan - India

The Amer Fort & palace was built in the 16th century by the Rajput Maharajas.
The Palace & castle are divided into 4 sections or courtyards, each with it's own gate, style and history. It's just 11kms from Jaipur.

Lattice window.

The Jaleb Chowk (Main Courtyard).
This is where returning armies would display their war booty to the populace ... parading around the courtyard. Women would often view this area from the veiled windows of the palace above the crowds.



Diwan- E- Aam or The Hall of Public Audience.

These 40 pillars were erected by Mirza Raja Jai Singh between 1631-40. It's an assembly hall built of red sandstone and white shell plaster - looks like marble. Each  column is topped by a capital in the shape of an elephant.
 
Suraj Pol (Sun Gate) - on the right.
To the left (not in view) is the Moon Gate

Diwan- E- Aam or The Hall of Public Audience
 The Maharajahs used to receive the public here, listening to their problems regarding the kingdom.
This space is significant as it combines both Hindu and Muslim architecture.


Maota Lake and Garden


The Jai Mandir (Hall of Victory) or the Mirror Palace is noted for its inlaid panels and multi-mirrored ceiling. The painted glass & mirrors was imported from Belguim.

  A carved marble relief panel. These can be see all over the hall. So delicate.

Baradhari pavilion at Man Singh I Palace Square.