GM-800 with VG-99

[keitht]

I am planning to use both the GM-800 and VG-99 together. I have a Roland ready strat, so for now I'll stay with the 13pin guitar cable and use the GKC-AD to get the serial digital into the GM-800. I'm building a switch on the pin 8 volume lines to mute one or the other. That's simpler than switching the stereo audio outputs that I use for both.

It would be possible to use the serial output of the GM-800 and the GKC-DA to feed the VG-99 but that's pretty expensive all together. With 13pin into A/D, serial cable to 800, serial cable to D/A and another 13 cable to the VG-99. And I don't know how you would easily switch units unless you use a stereo mixer or just mono audio.

Instead I'll use the cheap 13pin Y cable and add a double pole switch to ground either of the two pin 8 volume output lines. With a center off switch an 800/99 mix could be done too. I'll use 4.7k resistors in series with each pin 8 output so that the volume op amp output from the guitar isn't shorted when output lines are grounded after the resistors. I've tested this muting idea and found it to be simple and clean with the VG-99, haven't received my GKC-AD but I'm confident it will also be fine. The Y adapter will go near both the 99 and AD inputs so noise pickup shouldn't be a problem on short wires.

Of course another approach would be to use the GK-5 pickup, the GKC-DA and then into the VG-99. That uses two serial cables and a 13pin cable and the switching problem remains. And it would be another guitar for me.

The Roland GKP-2 Splitter Cable is no longer available but this is https://www.ebay.com/itm/271164665960 I cracked open the splice box on mine to get access to the pin 8 volume wires. The power wires to pins 12 and 13 also need to be removed on one of the outputs. See this post https://www.vguitarforums.com/smf/index.php?topic=12621.0

[keitht]

Of course you can also use a Roland US-20 selector pedal and another 13pin cable if price is no concern.

[gumtown]

Can also use VG-99 guitar to midi as an option too, probably not the best option, but you can if you wanted to.

Is there such thing a stereo A/B mix Expression pedal ?
or if you use a midi controller for the VG-99, you could use allocate midi cc# to control the GM-800 mixing volume.

[keitht]

Here's a schematic of my selector.

[Elantric]

Is there such thing a stereo A/B mix Expression pedal ?

Boss  EV-30 connected to Expression pedal inputs on VG-99 and GM-800 with EV30 polarity invert switch enabled allows you to "Pan" between two processers
https://www.boss.info/us/products/ev-30/

[gumtown]

Actually I should have said stereo Volume pedal, where two sets of stereo device can input, and the analog stereo output can be a mix of either/both devices.

[keitht]

The EV-30 an interesting way to control the stereo audio mix and would be effective and reasonably priced. You still need a Y connection of some kind to get guitar signals to both the 99 and 800. It could be combined with my selector switch in the mix position.

I prefer not to have a lot of foot controls and wiring on the floor. I have the FC-300 foot controller but I rarely use it. I have my VG-99 on a stand so I can easily reach the controls and see the display while playing. The Y cable, selector switch and GKC AD will go up there too, while I am not yet sure whether I want the GM-800 up or down (wondering about a double male TRS instead of the serial cable between the AD and 800). But using the volume knob on the guitar means my overall level is always easy to adjust. A variable blend of synth and modeled guitar sounds seems like it would rarely be used, while having patches with some strings synth and some modeled could be nice with a preset fixed mix of levels.

The weakest part of my approach is that the S1 and S2 switches on the guitar always go to both outputs. So using those for changing up/down on one unit changes the other too. That might be fine once you have pairs that work together. But it will affect the ease of some back and forth sound selections. The US-20 selector would make the switch control follow the selection (I think?) but for me I'd need a long 13pin cable back up to the 99 so cost adds up. About 10x the cost of the cheap Y cable and a switch in a little box.

[gumtown]

Here's a schematic of my selector.

Only downside to this design from what I see of the schematic is there will be a large volume peak in the "both" position.
In the A or B position, the GK Vol is being weighted down by the opposite 4.7k ohm resistor.

[keitht]

Based on the GK-3 schematic, the pin 8 volume signal is buffered by an op amp with an output series resistor of 100 ohms. The voltage divider created with a 4700 ohm load gives a loss of 4700/4800 = 0.979 or about -0.18dB, not an audible volume shift compared to the mix levels.

I am building this now. I've added a second switch to lift the ground going to the selector switch. With a center on selector switch, that add a "Both" mode regardless of the selector position and gives a convenient center mute choice when Both is off. The Both switch makes this design equivalent to the US-20 switches except they are hand height toggles instead of floor buttons. I'll have my GKC AD soon and will report here on its real world performance.

[Best_Peasant]

Kind of related, but can the GM800 connect to a vg88 or 99 and utilize the alternate tuning function? Or even the sy1000.

[Bluesbird]

Kind of related, but can the GM800 connect to a vg88 or 99 and utilize the alternate tuning function? Or even the sy1000.

Yes, using the GKC-DA.  Go GK out from the GM-800 to GK in of the GKC-DA and then GK 13-pin out on GKC-DA to 13-pin input to SY-1000, VG-99, etc.

You cannot view this attachment.

[Best_Peasant]

Yes, using the GKC-DA.  Go GK out from the GM-800 to GK in of the GKC-DA and then GK 13-pin out on GKC-DA to 13-pin input to SY-1000, VG-99, etc.

You cannot view this attachment.

And sorry, I'm wrapping my head around it...does that mean my alt tuning feeds the gm800 sounds?

[BROCKSTAR]

Kind of related, but can the GM800 connect to a vg88 or 99 and utilize the alternate tuning function? Or even the sy1000.

The gm-800 can do alt-tunings too. So you can turn any of the synth stuff into whatever tuning you want, or to match your other systems etc.

[Best_Peasant]

The gm-800 can do alt-tunings too. So you can turn any of the synth stuff into whatever tuning you want, or to match your other systems etc.

Yes, they feel weak, for example I keep a guitar in DgCgCD for some Zep stuff, but when I alt tuned on the gm800 it just sounded....off.
Of course, I'm happy to be informed I'm doing something wrong.

[Elantric]

And sorry, I'm wrapping my head around it...does that mean my alt tuning feeds the gm800 sounds?

No.

Traditional method would be to employ an equivalent to the Roland US20 GK A/B/Y selector- feed Any GK 13 pin VGuitar processor ( SY-1000) in parallel with a GKC-AD> GM-800. Outputs from both feed a stereo mixer to PA.

Program Alt tuning patches for both SY-1000 and GM-800, and use a MIDI Footcontroller to control synchronized Alt Tuned patches on SY-1000 and GM-800

[Elantric]

Yes, they feel weak, for example I keep a guitar in DgCgCD for some Zep stuff, but when I alt tuned on the gm800 it just sounded....off.
Of course, I'm happy to be informed I'm doing something wrong.

Explain- if your actual guitar strings are tuned DgCgCD with GM-800 in guitar mode, you run into hitting the brickwall cutoff frequencies of the 6 internal  individual bandpass filters inside the GM-800, which expects EADGBE tuning at A4 = 440Hz . To insure best tracking there is a low frequency limit on each string , and essentially bulk of your strings are  a whole step flat and right on the lower frequency threshold of functional GM-800 performance

As a test,  retune guitar to standard pitch (EADGBE tuning at A4 = 440Hz), and use the GM-800 Alt tuning function to create your desired DgCgCD tuning

https://www.nist.gov/pml/time-and-frequency-division/popular-links/time-frequency-z

[Bluesbird]

Explain- if your actual guitar strings are tuned DgCgCD with GM-800 in guitar mode, you run into hitting the brickwall cutoff frequencies of the 6 internal  individual bandpass filters inside the GM-800, which expects EADGBE tuning at A4 = 440Hz . To insure best tracking there is a low frequency limit on each string , and essentially bulk of your strings are  a whole step flat and right on the lower frequency threshold of functional GM-800 performance

As a test,  retune guitar to standard pitch (EADGBE tuning at A4 = 440Hz), and use the GM-800 Alt tuning function to create your desired DgCgCD tuning

https://www.nist.gov/pml/time-and-frequency-division/popular-links/time-frequency-z

Elantric,

You can do special tunings on your guitar which can be set within the GM-800. As I pointed out a couple weeks ago, you could use a physically tuned Nashville guitar to get faster pitch to midi response. This is unique to the GM-800. No other Roland/Boss product does this. The band pass filters will be adjusted according to the tuning. From the parameter guide:

You cannot view this attachment.

[keitht]

When I get my AD I'll try this tuning stuff. My box is done and working fine with the VG-99

[Elantric]

Elantric,

You can do special tunings on your guitar which can bet set within the GM-800. As I pointed out a couple weeks ago, you could use a physically tuned Nashville guitar to get faster pitch to midi response. This is unique to the GM-800. No other Roland/Boss product does this. The band pass filters will be adjusted according to the tuning. From the parameter guide:

You cannot view this attachment.

I suspect we all must try these new settings.

I know in the past Baritone Guitars tuned B1–E2–A2–D3–F♯3–B3 struggled with any GK Processor.

[keitht]

https://www.vguitarforums.com/smf/index.php?msg=86415 "Also observe the two added 1N914 Switching DIODES  - wired in series on the "Unit B" DIN 13 pins #10 and #11, these provide voltage isolation  / protection to the 2nd connected 13 pin processor's GPIO lines used for Gk-3 S1 & S2 Momentary Switches "

I'm not planning to add those two diodes on the S1 and S2 lines. As far as I can tell, they have no purpose when both connected units are listening to the GK switches from a guitar. There may be some other 13pin connections that send on those pins and the diodes would make sense for that case. But a true diode OR connection would require four diodes, two for each switch signal line, and would be used on both connectors. The switches pull these lines down to ground when pressed. The input pull ups from the two connected units should not mind being connected in parallel and will be easily pulled down by the 1k series resistors on the switches. I'm a EE, I asked a friend also a EE and we don't see how these two diodes make sense.

Am I missing something? https://electronics.stackexchange.com/questions/37158/sharing-a-pull-up-resistor

GK-3 schematic https://www.vguitarforums.com/smf/index.php?msg=115

[Elantric]

Review the typical destination for S1, S2

https://www.synthxl.com/wp-content/uploads/2020/03/Roland-GR-33-Service-Manual.pdf

[keitht]

I understand the connection and know input characteristics of that type of chip. One way this might make sense is if the second unit is turned off. In that case, since it has no supply voltage, its inputs might pull down the switch lines falsely and the diodes would prevent that. That's the only case I can imagine that justifies inserting them.

[keitht]

If I squint I think I can see that the GR-33 schematic shows discrete pnp transistor bases on those lines, with diode protection to supply and ground. The upper diode would pull down the switch line if the second unit is off. Since the GM-800 has no power switch, I'm not concerned, I will set it to stay on and it will be powered whenever my VG-99 is powered. So no diodes for me. I am now convinced that is the reason for them. If there is no power on the first unit, the GK won't work. No power on the second unit could cause user confusion like unwanted patch changes so they added the diodes for that reason.

[gumtown]

The clamping diodes are for protection of the units inputs and back-fed voltages if the other unit is off.

It can be damaging to chips if the input voltage exceeds the chip rail voltage by more than 0.7 volts,
 so any voltage above 0.7v feed into an input pin can potentially damage the unit if it were powered off. 

[keitht]

That is correct, a voltage outside the supply range is damaging to inputs. However, this will not occur on the S1 S2 lines with two connected devices under any power conditions. That's because the pull ups are very low current and that current cannot generate enough voltage to do harm. The purpose of those Y connector diodes is to prevent an error in logic levels caused by a powered down second unit. The switch logic is active low, they go to ground when a switch is pressed, and the protection diodes internal to a powered down second unit will create a logic low on these lines. That will not cause damage, it is the same as pressing both switches on the guitar. However, Roland decided that preventing this logic error was worth the cost of adding diodes.

The clue to understanding this is the asymmetry of the diode placements. Why are they only on the second unit and not both? That's because the logic error is irrelevant when the unit sourcing power to the GK-3 is turned off. There will be no sound, switch logic does not matter. So, they add diodes for the second unit only, for the sole purpose of preventing it from sending switch pressed logic signals to the first unit when the second is powered off. Anyone who doubts this can install the diodes, they won't be in my version.