guitars without GK-Vol: VG-99 auto mute if no 13pin is connected (sensed)

Started by matigrob, February 02, 2018, 06:10:45 PM

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matigrob

sorry if I repeat this but I could not find it on this forum, its pretty hard to find the key words

and its a pretty heavy and not easy to expect or correct:

the VG-99 watches whether an instrument is connected and mutes the output if it thinks there is none. nice idea, but the way it checks is that it watches whether there is a resistance at the vol control pin8.
so:::::
if you do not have a volume control on your instrument, you have to solder some resistor there. as far as I remember, 1MOhm to +7,5V pin12 does it.

not sure whether the GR-55 does the same, but its likely. older models do not have this feature so it took me quite a while to find why a guitar did work on the VG-8 but not on the VG-99!

admin

Quote from: matigrob on February 02, 2018, 06:10:45 PM
sorry if I repeat this but I could not find it on this forum, its pretty hard to find the key words

and its a pretty heavy and not easy to expect or correct:

the VG-99 watches whether an instrument is connected and mutes the output if it thinks there is none. nice idea, but the way it checks is that it watches whether there is a resistance at the vol control pin8.
so:::::
if you do not have a volume control on your instrument, you have to solder some resistor there. as far as I remember, 1MOhm to +7,5V pin12 does it.

not sure whether the GR-55 does the same, but its likely. older models do not have this feature so it took me quite a while to find why a guitar did work on the VG-8 but not on the VG-99!

Correct  - actually +6.3 VDC on GK 13 pin #8  = GK-VOL @ max level .

The Gibson Dark Fire ran into this issue of not considering the importance of  +DC Voltage  on GK 13 pin #8  to achieve Output Signal in most connected GK processors  - they had to build an adapter inside a custom cable described here:

Gibson RIP to GK13 Adapter Cable
https://www.vguitarforums.com/smf/index.php?action=downloads;sa=view;down=80

https://www.vguitarforums.com/smf/index.php?action=downloads;sa=downfile&id=80


cags12

Elantric or anyone else. I understand based on the pdf you attached that the Vol Pot can be excluded with that simple hack using a resistor like the darkfire. Fine!!I will need to do this as I will be using Cycfi pickups and the GK controls will not exist.

However, I am struggling to understand what is the purpose of the opamp section in the GK schematics that connect to the GK VOL section. What is it for if you can simply use a resistor or the variable resistor of the actual potentiometer?

Thanks!


Elantric

Its a buffer amp  used to provide more drive current for the GK-VOL pot DC Control voltage
common control voltage design stratgy
https://www.google.com/search?q=DC+control+with+op+amp&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj47O2J8JvZAhVNIqwKHZX6B-UQ_AUICygC&biw=1118&bih=598&dpr=1.25#imgrc=kG6o70iis8vC6M:

- adds stability to the GK Vol DC CONTROL VOLTAGE signal as it might be connected to a US-20 and become the sole drive DC Control voltage source for multiple connected GK processors


Compare to the GK-2A  - study the GK2A schematic and learn the basic functions driving each of the 13 pins pin the GK 13 cable


The big lesson is how the 3 way Guitar/Mix/ Synth switch works  - signals are not switched, instead, unwanted signals are muted by shunting to ground

cags12

Ohh great, that is what I suspected. Just needed final confirmation.

Yeah I go that about the 3 way switch by studying the GK3 schematics (even with my limited knowledge). Although by looking the GK-2A one is waaay clearer.

Many thanks!

Elantric

Quote from: cags12 on February 10, 2018, 10:24:59 AM
Ohh great, that is what I suspected. Just needed final confirmation.

Yeah I go that about the 3 way switch by studying the GK3 schematics (even with my limited knowledge). Although by looking the GK-2A one is waaay clearer.

Many thanks!

Bulk of the GK-3 added parts are focused on post 2005  compliance with FCC /CE RF emission, conducted emissions and ESD survivabilty

matigrob

a client just tested the 1MOhm resistor I suggested here with a GR-33 and it caused absurd new sound mixes, so neither disable as the VG-99 with open vol input nor volume down if the resistor was too big... I do not have a GR-33 to verify... sure the two resistors would work to adjust to 5V as admsustainiac suggested, but then those might be too much load when a real potentiometer is connected...

chacow

Yeah I go that about the World knowledge 3 way switch by studying the GK3  schematics (even with my limited knowledge).

Although by looking the GK-2A one is waaay clearer.