Monday, 8 April 2024

Circuitbenders CB55 - drum machine build notes.

These are my build notes for the circuit benders clone of the Roland/- Boss Dr 55 drum.
The clone is called the CB-55.
The original is a really simple and great sounding machine. It's definitely a classic.
I think where it falls short is it's limited sequencer, and that its tricky to sync to external gear. 
I loved the first DR-55 I bought so much, that I purchased a second one with the intention to mod it.
But I just couldn't vandalize  it .
Mods to overcome this are out there but I think its a shame to need to mod vintage gear. 
These relics are getting harder to find as the years go by and in the future, the ones that will
retain their value will be those in original condition.

So from a practical level, get an original to admire & treasure and build the clone to 
mod to your hearts content.


Links:


I'll install the trigger conditioning circuit.... connected to TRIG_IN1 connector.
This allows you to connect 5V triggers that last longer than 10ms





The build looks easy. all through hole with standard parts that i probably already have in my store.


Resistors first.

Caps 


fairly straight forward build so far.

D1 1N4001 Rectifier diode
D2, D3, D4, D5, D6, D7, D8, D9 1N4148 or 1N914
D1 is a larger 1N4001
rectifier diode that provides polarity protection for the power input, but all the others can be general purpose
small signal diodes such as 1N4148's or 1N914'




Jumper wires:
The jumper wires at J3-J7 connect the output of each voice circuit to the main mix bus.
These links are designed as 
jumpers for easy mods to provide individual outputs, but at this point it would probably be better to just install 
them. You can always change things at a later date.


the voltage regulators and transistors. 

REG1 is a 78L06 regulator that supplies the 6v power to the 
voice circuits. REG2 is a 78L09 that supplies 9v to the trigger conditioning circuit
ebay ... ordered



There is just one IC
IC1 - LM324 Quad opamp



T1, T2, T3, T4, T5, T6, T7, T8, T9, T10 2SC945 Or similar transistor
Its a  Bipolar (BJT)

"T1 to T10 are general purpose NPN transistors. Roland/Boss used 2SC945's is virtually everything they produced 
during this era, so this is what we've specified here, but you could probably get away with using any number of 
transistors with similar specs. We haven't actually tried it, but we would imagine it'd also work fine with the 
common 2N3904 or 2SC1815"

I'll use 2n3904s

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Q1 in the accent circuit should be a JFET transistor with a DSG pinout. A few different types will fit here. We've
tried the J201, MPF102 and 2N5457, and they all seem to work okay.

I installed a J201

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L1 --- 47mH inductor Original DR55 uses 45mH **
mouser







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