How to trigger COSM/PCM/MIDI without a GK

Started by Elantric, October 22, 2011, 09:03:06 AM

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Elantric

QuoteMy specific issue is I want to trigger COSM/PCM without a GK even connected to the 13 pin connector.

This post will provide one solution.

If you build a cable with a 1/4" phone plug at one end and 13 pin male circular DIN plug at the other.

The Tip connection of the 1/4" phone plug feeds Pin#6 (Low E string Input) on the 13 pin male circular DIN plug. The Shields get connected to the shells at each end.

On the GR-55, if you program a custom patch with "GK VOL = OFF" , you are almost done.

But most older Roland Gear requires the GK-3 to be connected and "GK Vol" or "Synth Volume" to have just below +5VDC on pin# 8 for max volume. The GK-3 pickup typically feeds pin #8 a 0VDC (min) to +4.7VDC (max) control voltage.

If you are clever, you may incorporate 2 small resistors inside the 13 pin male circular DIN plug, and this will fix the GK-VOL on the connected to gear to max volume, thus enabling you to trigger GR-55's COSM/PCM without a GK and without programming custom patches.



The resistors may seem to be odd, but these are typical values for the 1% resistors.

R7 = 121 ohms
R8 = 243 ohms

These establish a circuit known as a voltage divider. The source voltage is +7 Volts DC from pin #12.

So +7 Volts DC feeds R7 (121 ohms) which is connected to R8 (243 ohms) and the other side of R8 is connected to Ground.

The voltage at the junction of R7 and R8 in +4.67 volts, and this DC voltage feeds pin #8, the voltage controlled "Synth Volume" pin. If pin #8 is left unconnected, there will be Zero volts at the voltage controlled "Synth Volume" pin, and this will effectively "mute" the connected Roland processor.   


This circuit idea was developed for the Gibson Dark Fire to feed Roland 13 pin gear, after they discovered the GK-Vol sense line required a DC voltage before any sound could be heard from the Roland processor.

For reference, I attached a PDF of the complete Gibson Dark Fire cable, the added 121 ohm resistors to GND on each string signal act as attenuators for the active (hot) Gibson RIP signal output) and are not needed.


Using this custom cable described above, you may feed your normal guitar to any 13 pin processor or MIDI convertor. Of course if you play chords it may suffer mis-tracking, but the COSM guitar processing should work and get more flexibility to use your normal guitars. Also  - I encourage use of an active buffer between the guitar and this cable, or use a guitar with active electronics or active PUs. So use a guitar with EMG PU's, or a Strat with an Alembic Strato-Blaster, or an acoustic with an onboard active piezo preamp. In general, if it uses a battery, you are OK. 
.


Also - If the Tip connection of the 1/4" phone plug feeds Pin#7 (Normal Guitar Input) on the 13 pin male circular DIN plug. This is would allow your Normal guitars to use the the GR-55 COSM Amp processing - but you MUST insert an active buffer between your passive PU guitar's output and GR-55 input. I use  a Boss Floor tuner or any Boss pedal in bypass mode. Of course you may engage the boss pedal upstream of the GR-55 for added signal processing power.  Boss CS-3 compressor might be handy. 

Bill Ruppert

Warning
The Male 13 pin connector above is viewed from the OUTSIDE of the plug.
Be aware of this as the numbers will be different from the inside.

Elantric

#2
Correct!

this why it says: "EXTERNAL END VIEW OF PLUG " in the middle of the diagram


Bill Ruppert

Just wanted to make it VERY clear.
I missed it the first time.

Dany_Lane