Author Topic: How to use external expression pedal with GR-55  (Read 6593 times)

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Offline Gastric

How to use external expression pedal with GR-55
« on: October 01, 2011, 02:59:08 PM »
OK, I've hacked a mono normal pickup send/return into my GR-55. I've yet to tackle the GK VOL though some simple resistor application was provided to me to lock it to GK VOL = MAX all of the time. However, what would be more useful is having a stereo 1/4" jack and being able to connect an external expression pedal to that to control GK VOL. Something like a BOSS FV-500H since I already own one of those.

Can any of the electronics gurus provide the necessary schematic to accomplish that?  From what I've read the FV-500L is a little odd in that it's reverse from some other expressions and output 8.5k ohms in the heel down position, and 0 ohms in the toe down position. I'm assuming I can modify polarity in the pedal itself, or better yet, in whatever little GR-55 mod I have to implement. Or I can use some other pedal if it's easier.

I'm good at following directions and soldering and have completed a variety of DIY projects. However, not educated enough to construct electronics schematics on my own.

Offline gumtown

Re: How to use external expression pedal with GR-55
« Reply #1 on: October 01, 2011, 07:32:32 PM »
I am not familar with that particular pedal, but would assume it uses 3 pins (TRS plug)?
Probably the 500L would work better as a 5 volt divider.
Might be worth giving a thought if the FV pedal curve is linear or log.
Free "GR-55 FloorBoard" editor software from http://sourceforge.net/projects/grfloorboard/

Offline Gastric

Re: How to use external expression pedal with GR-55
« Reply #2 on: October 07, 2011, 03:55:52 PM »
Yes, the BOSS FV-500H is TRS for the expression output. From what I can gather it's a 10K pot on the expression, similar to the EV-5.  I've never used the actual volume side of the pedal, only as an expression for which there's a dedicated jack. I'd be happy to buy some other pedal if someone could tell me which would work by installing an external TRS and wiring it up to the GK VOL controls.

Offline Elantric

Re: How to use external expression pedal with GR-55
« Reply #3 on: October 07, 2011, 04:32:20 PM »
The Gk-3 Vol pot feeds a Control Voltage to the GR-55 using Pin #8 on the GK 13 cable.

Refer to the Gk-2A Schematic - (essentially the same as the GK-3 GK Volume circuit)




 GK Volume is a  50 K pot (VR1), feeding the opamp GK Volume driver(IC1A).

Referring to the Circuit above:

VR1- pin 1 = Ground

VR1- pin 2 = Wiper (feeding R18 3.3K resistor)

VR1- pin 3 = (Hot) connected to SW3 & R20 18K pull up resistor)

Clone the above circuit - but swap VR1 for a Volume Pedal with a 50K pot wired to a TRS cable.

VR1- pin 1 = Ground

VR1- pin 2 = Ring

VR1- pin 3 = Tip

« Last Edit: October 07, 2011, 04:35:40 PM by Elantric »

Offline Gastric

Re: How to use external expression pedal with GR-55
« Reply #4 on: October 07, 2011, 05:34:32 PM »
Is there some way in electronics to use a lower value pot as the source, but scale it's resistance?  10K pot seen as a 50k pot to make the full range of the GK VOL available, but still let it roll down to 0?

Offline Elantric

Re: How to use external expression pedal with GR-55
« Reply #5 on: October 07, 2011, 05:44:32 PM »
The goal is to achieve a voltage range of 0 to +5VDC at pin #8 on the 13pin connection.
0 V = mute
+5V DC = max volume.


Take a 10K linear pot. Lets call it "VR".

VR- pin 1 = Ground

VR- pin 2 (wiper) = GK13 pin #8

VR- pin 3 = +5VDC
« Last Edit: October 07, 2011, 05:48:11 PM by Elantric »

Offline Poparad

Re: How to use external expression pedal with GR-55
« Reply #6 on: October 14, 2011, 11:50:04 PM »
The goal is to achieve a voltage range of 0 to +5VDC at pin #8 on the 13pin connection.
0 V = mute
+5V DC = max volume.


Take a 10K linear pot. Lets call it "VR".

VR- pin 1 = Ground

VR- pin 2 (wiper) = GK13 pin #8

VR- pin 3 = +5VDC

So is that a 'yes' to using a 10k expression pedal?  I'm looking to do the same kind of mod, by inserting a stereo switching jack to use with an EV-5.

Offline Elantric

Re: How to use external expression pedal with GR-55
« Reply #7 on: October 15, 2011, 03:57:34 AM »
yes if you use the circuit below
Quote
The goal is to achieve a voltage range of 0 to +5VDC at pin #8 on the 13pin connection.
0 V = mute
+5V DC = max volume.


Take a 10K linear pot. Lets call it "VR".

VR- pin 1 = Ground

VR- pin 2 (wiper) = GK13 pin #8

VR- pin 3 = +5VDC

Offline Poparad

Re: How to use external expression pedal with GR-55
« Reply #8 on: October 15, 2011, 07:06:33 AM »
yes if you use the circuit below

So if I were to simply take lead #8 that connects to the GR-55 board (synth volume), and splice the incoming part to the ring of a stereo switching jack, the out to the tip, and then ground the sleeve, that would work?  Or is there somewhere else that the +5v comes from that needs to be added into the mix?

Offline Elantric

Re: How to use external expression pedal with GR-55
« Reply #9 on: October 15, 2011, 07:18:28 AM »
You need a source of +5V DC

+/- 7VDC is on the 13 pin jack, and used to power the the GK-3.

But if you are new to building electronic gear, I would use much caution, its very possible to short the GR-55 internal DC power to ground if you wire things wrong, and then you WILL have a dead GR-55.
Frankly all these GR-55 user mods of drilling holes for new jacks and cutting / splicing internal wires are the wrong approach IMHO.
Its very possible that your LCD may loose a line of pixels in 9 months, then you will have the Roland Service Center refuse to fix your GR-55 because its been "modified by the user" and you will be left with a nice large Blue Doorstop. 

In 1997 i modified my Boss GT-5 with a few new jacks, but in 2004 when I wanted to sell it, i had to accept way less than going rate because very few buyers want modified gear.

Instead, we need to explore REVERSIBLE MODS!

For example the RMC OPT-01 filter mod is designed to be completely reversible for a good reason.

I'm an advocate for fabricating a replacement plate for the USB thumb drive door, that would house all the additional jacks required ( 1/4" jacks for Guitar Input, S1/S2 remote switching and EV-5 type expression pedal for GK-3 Synth Volume, along with a USB Host jack for a thumb drive and a small interface PC board.  If / when the GR-55 breaks and needs to go to the Roland Factory service center  - you simply remove the "mod plate" and revert it back to stock by reinstalling the original  USB thumb drive door before you show your broken GR-55 to the Roland Service technician.

« Last Edit: October 15, 2011, 02:29:15 PM by Elantric »

Offline paults

Re: How to use external expression pedal with GR-55
« Reply #10 on: October 15, 2011, 02:20:30 PM »
I'm with Elantric- any modifications to the inputs (S1-2, volume, normal guitar in) could also be put into an external box, with a 13 pin output from the box.

 

Offline Poparad

Re: How to use external expression pedal with GR-55
« Reply #11 on: October 15, 2011, 06:39:29 PM »
I suppose another option would be to buy a MIDI Solutions Pedal Controller box and plug the EV-5 into that.

Offline gumbo

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Re: How to use external expression pedal with GR-55
« Reply #12 on: October 15, 2011, 10:07:48 PM »
Quote
I'm with Elantric- any modifications to the inputs (S1-2, volume, normal guitar in) could also be put into an external box, with a 13 pin output from the box.

Another vote for a separate box.. ;)

..something I've been thinking about for a while also..
« Last Edit: October 15, 2011, 11:36:58 PM by Elantric »
Read slower!!!   ....I'm typing as fast as I can...

Offline Gastric

Re: How to use external expression pedal with GR-55
« Reply #13 on: October 16, 2011, 07:11:44 AM »
I've added the FX S/R jacks to my GR-55 and I can also say the separate box is the way to go. No because I'm concerned about hacking my box and warranty issues. But because it would simply be an easier work environment. I now want external volume, S1/S2, I'd like to be able to swap which GK pin I'm sending a mono PCM trigger to. It's annoying to have to keep opening the chassis and screw with the wires on the tiny loom.

Note the warranty is only 1 year parts 90 day labor to my knowledge.

Offline Elantric

Re: How to use external expression pedal with GR-55
« Reply #14 on: October 16, 2011, 07:36:00 AM »
Quote
Note the warranty is only 1 year parts 90 day labor to my knowledge.
That is USA warranty

In other countries its much longer. Roland warranty is three years in the UK if you register the product.

http://www.roland.co.uk/articles/default.aspx?c=187

Warranty

In addition to a 12 month standard manufacturer’s warranty, all Roland Registered Users receive:
Additional two year warranty on Roland/Boss/Edirol/Cakewalk hardware products (accessories excluded) covering parts and labour.
Additional four-year warranty on Boss Compacts.
Free telephone technical support
Free online technical support
Free regular e-newsletters informing you of the latest product releases
Access to MyRoland which enables you to check which products you've registered with us - or register a new one - and also manage your communications preferences and personal info. All this is available 24 hours a day, seven days a week: you don't have to call during office hours.


 
A bit more involved, but member "a2dconverter" crafted this doc and looks ideal:



more of a2dconverter's good ideas here:
http://www.vguitarforums.com/smf/index.php?action=profile;area=showposts;u=3500
« Last Edit: October 16, 2011, 07:56:25 AM by Elantric »

Offline Poparad

Re: How to use external expression pedal with GR-55
« Reply #15 on: October 16, 2011, 12:39:09 PM »
I have a keyboard controller on hand with a volume pedal, so I ran the MIDI out into the GR-55 and assigned the PCM1 and PCM2 patch volume to be controlled by CC7 on the MIDI in, and it worked like a charm.  I went ahead and ordered the MIDI Solutions Pedal Controller, which should work exactly the same, sans the giant 88 key keyboard.

Offline Gastric

Re: How to use external expression pedal with GR-55
« Reply #16 on: October 21, 2011, 09:29:19 PM »
I have a keyboard controller on hand with a volume pedal, so I ran the MIDI out into the GR-55 and assigned the PCM1 and PCM2 patch volume to be controlled by CC7 on the MIDI in, and it worked like a charm.  I went ahead and ordered the MIDI Solutions Pedal Controller, which should work exactly the same, sans the giant 88 key keyboard.


My specific issue is I want to trigger COSM/PCM without a GK even connected to the 13 pin connector. I wired the FX S/R jack to GK PIN6 internally and it accepts a mono signal and triggers pretty well. What it doesn't do is make any sound unless a GK controller is plugged in. :)  Apparently due to the GK VOL which is why I desired to connect an external expression.  It's easy enough to slap a switched TRS jack in the chassis and plug a 50k expression.

But not so easy to just "clone the circuit above" when you don't really know enough to be able to take a schematic and envision precisely how to do that. There's at least two ICs used, the pesky GK 3-way switch which wouldn't physically be needed... well, it might, I'd personally just set it to "both" and use patches and assigns to decide which tones are on/off. And it's late and I'm too tired to think about it any further. :)
« Last Edit: October 21, 2011, 09:35:17 PM by Gastric »

Offline Elantric

Re: How to use external expression pedal with GR-55
« Reply #17 on: October 22, 2011, 09:17:11 AM »
Quote
My 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. 

   
« Last Edit: October 22, 2011, 10:19:43 AM by Elantric »

Offline jonathanf106

Re: How to use external expression pedal with GR-55
« Reply #18 on: July 09, 2016, 06:40:36 AM »
There got to be a easier way of doing this? Buying all that equipment and have all those pedals sitting on your floor just to use external fx pedals??

what about doing a SEND and RETURN between the two output ports and using PHONE/LINE port to connect to the amp?

Would that work? I know a problem I had from trying to plug up the external pedal from the guitar out port and from the pedal to the amp, when it is in bypass mode, i hear completely nothing, but in latched mode it was more of effect or no sound at all, and in unlatched mode was the same when pressed down upon. With that being said there needs to be a send and return in order for this external  loop to work correctly, of course its easy on the GT-8,10,100, but I'm not using that lol, Im using a Behringer UV300 Ultra Vibrato Pedal and the GR-55. 

My objective here is to use external fxs on COSM guitars, not your normal PU guitar.
« Last Edit: July 09, 2016, 07:00:26 AM by jonathanf106 »

Offline gumtown

Re: How to use external expression pedal with GR-55
« Reply #19 on: July 09, 2016, 04:05:04 PM »
The GR-55 L/R output jacks are soldered directly on to the GR-55 circuit board, so modifying those is near impossible.
You could use the 'Guitar out' and route your COSM guitars through external effects, and use a micro mixer to mix the FX return and the GR-55 together.
Free "GR-55 FloorBoard" editor software from http://sourceforge.net/projects/grfloorboard/

Offline jonathanf106

Re: How to use external expression pedal with GR-55
« Reply #20 on: July 10, 2016, 04:00:15 AM »
The GR-55 L/R output jacks are soldered directly on to the GR-55 circuit board, so modifying those is near impossible.
You could use the 'Guitar out' and route your COSM guitars through external effects, and use a micro mixer to mix the FX return and the GR-55 together.

I wasn't planning on hard modding my gr55 anyways lol but the micro mixer for $40 sounds like the best option for this solution thanks,  I gotta another question what if you got an amp with send and receive port and fx switch on board for a external amp switch,  could I use those ports to kinda do same thing?  I'm using a "marshall valvestate 8080" amp , it's half solid and half valve. 

Oh wait I just remembered I hooked up the guitar like this:

Guitar>pedal>audio speaker/sub woofer,  and the sound came out while the pedal fx was on or off, so I don't even need a mixer now lol, thanks for your help tho,  this was after I changed the AC adapters to reduce noise level. 
So Guitar(GK3)> GR-55> Phone/Lines>UV300 FX> Amp,  should work fine if the pedal operates as a bypass while not in use, so I still hear the COSM tone through my amp.

I saw on YouTube this guy hooked the pedal up to a keyboard and a speaker,  and the sound bypassed while the pedal wasn't actively pressed down, so I think I had to change my AC adapter because the other I was using had too much wattage or volts.   

« Last Edit: July 10, 2016, 04:38:45 AM by jonathanf106 »

 

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