GK-3 - Blend Pot. One control replaces three

Started by MusicOverGear, July 30, 2014, 11:57:32 AM

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MusicOverGear

I just switched over to a GK setup after using tube amps my whole life (I'm 42 years old). I really need reliability, so I'm going to have to do something about the cable situation. Which in turn is leading me toward an internal GK installation.

I was looking at my guitar, thinking about how I would lay out the controls, and I just know from experience it would be too much to have all that *stuff* down there on the interface with my existing guitar controls - for my simple mind I need to thin it out. So I starting thinking about which controls I could omit and it hit me: three of the interface elements I was considering would work better for me if they were rolled into one. Here is what I mean.

I have a Guitar (Mag Pickups) volume, A GK Volume, and a Pickup Selector Switch. Currently I use them as follows: Guitar volume is just that, GK volume is for Modeling Volume globally, and the GK Switch selects Guitar, Both, or Modeling. If I used a Blend pot with appropriate values and a center detent, I could have one control that did the job of all three controls, moving me smoothly between all the settings that are possible with the three controls.

I'm thinking that if I do switch to an internal installation, I will replace my regular guitar volume pot with a blend pot, forget about the GK Pickup Selector Switch, and also forget about GK SW1 and SW2 - the GP-10 has plenty of per-patch control for me already. That way the interface of the guitar keeps the same approximate density as my normal guitar.

The only real catch I can think of is that I would probably have to buy a 500k blend pot and a 50k from the same product line and swap out the tracks on one side. Either that or see if I could run the magnetic pickup signal through the blend pot between the main PCB and pin 7 on the GK jack - i.e. using the buffer that's already there so it would work well with the 50k blend pot. Doing it that way I would have to add a 500k resistor to ground in place of the original guitar volume pot to load the pickups appropriately. Also there is the problem of sifting through pan pots labeled as blend pots...   

I found this post where apparently someone did something similar, although he seems to have used a 250k blend with a resistor parallel to the track of one pot to make it 50k. https://www.vguitarforums.com/smf/index.php?topic=359.msg3600#msg3600  Telengard, if you're still around I'd appreciate any pointers/insights.

Also I'm thinking I would use a switching jack on the regular guitar output to disconnect it from the GK circuit when using a regular cable.

Right now I'm just brainstorming, and I'm wondering what kinds of problems I'm going to run into with this approach. I would appreciate anyone's anecdotes or input.

mbenigni

#1
QuoteI would appreciate anyone's anecdotes or input.

I've only just skimmed your post (trying to cram in my VGuitar catch-up before the work day runs out) but I am generally sympathetic to the aim of simplifying the controls and making things more intuitive.  One thing I would recommend as a zero-cost proof of concept, before you invest too heavily in mods etc:  reassign the GK Volume from COSM tone volume to crossfade, with the magnetic pickup input assigned heel, the COSM tones assigned to toe (or vice-versa) and everything else* off (disassociated from crossfade).  Then make sure both mags and COSM are on and routed appropriately (e.g. on my GR55 these would head to the amp/MOD block), set your guitar/synth/mix switch to mix, and dime your mag. volume.  See how much mileage you get just using the GK Vol as a crossfade.  You might find that the job is already done.


* Note "everything else" may be moot on a GP-10.

MusicOverGear

#2
OMG genius! Yes this could totally work for me.

For an internal installation, tell me if this would work:

Assuming I'm using this schematic: http://s412.photobucket.com/user/elantric/media/GK-3_zps389eff64.png.html

Can I make these mods (attached)?

Basically I want to use a dual gang pot where side A is the normal GK VOL control and side B both loads the pickup and feeds the 1/4" output on the guitar, so I could still use the guitar with an old-school rig if I wanted. My (very dim) understanding is that when the GK circuit is unpowered (off - no GK cable present) the GUITAR IN would be inert to the circuit at the 1/4" output in my mod.

Elantric

#3
MusicOverGear,

Yes a ganged Dual Vol pot that controls both the that would work (many others already have done this too)

GK Vol pot = 50K "B" ("B" is a linear taper)

Normal Mag PU Vol pot = 500K "A" ("A" is a Audio (Log) taper) (However most Strats employ 250K Audio taper Vol pots)


- But you must employ the "Roland Ready / GC-1" circuit for your internal kit, as this adds a switching output jack that removes the Normal Mag PU passive Vol / Tone electronics away from the Active GK Internal circuit. 

See these threads for details (schematics)
https://www.vguitarforums.com/smf/index.php?topic=73.0



mbenigni

That's one for Elantric, I think - every time I assume I know something about the GK3 circuitry, I'm wrong.

But if I understand your basic design correctly, the only distinction between this and my proposal for using the GK Vol as crossfade (excepting the physical detent of course) is that you have silence in the middle of the knob's range (5) with increasing volume of COSM only from 5-10 and increasing volume of mags only from 5-0 (or, again, vice versa.)  I would say you could achieve the very same thing by applying two Assigns to the GK Volume, one targeting COSM tone volume, one targeting mag volume, e.g.

Assign1
Momentary
From: GK Volume
To: COSM tone volume
Range: 0-100 (full range)
Input Range: 64-127

Assign2
Momentary
From: GK Volume
To: magnetic pickup volume
Range: 100-0 (full range, reverse)
Input Range: 0-63 (or whatever the halfway point is)

Kind of shooting from the hip here - no GR55 in sight - so some trial and error may be required.  But you get the idea.  Solution with no hardware mods: faster, cheaper and easier to resell than with hardware mods.

MusicOverGear

#5
Maybe this is clearer.

When GK cable is plugged in VR1A works as normal with the GP-10. Nothing is plugged into the 1/4" output on the guitar. VR1B loads the normal guitar pickups but the movement of the wiper has no effect.

When the GK cable is absent but the 1/4" output is plugged into a fuzz pedal, VR1B functions as a normal guitar volume control. All the GK circuitry has no effect.

EDIT: whoops missed responses while I was typing.

I was thinking of converting a GK-2a pickup. I was thinking that the wiper on the 500k pot wouldn't hurt the GK functionality because the wiper isn't tied to anything the GK input "sees" ??? Hope that makes sense I usually only hack my own stuff and don't usually try to communicate this type of stuff - I don't really know the vocabulary.

mbenigni

I think in my skimming your first post I may have confused your intentions.  Obviously the GK Vol. is no substitute for a concentric dual pot; I thought you mentioned a center detent, and I assumed you wanted to map half the range of one pot to COSM, the other half to mags.  So anyway... don't mind me.  :)

MusicOverGear

Quote from: mbenigni on July 30, 2014, 01:57:29 PM
I think in my skimming your first post I may have confused your intentions.  Obviously the GK Vol. is no substitute for a concentric dual pot; I thought you mentioned a center detent, and I assumed you wanted to map half the range of one pot to COSM, the other half to mags.  So anyway... don't mind me.  :)

No your advice was perfect because I hadn't thought to use crossfade on the GP-10. I think this is the way to go

MusicOverGear

#8
Elantric, what if I used a Normally Closed switching 1/4" jack to break the connection with R14 when I plug in a 1/4" cable? Would that make my mod work?

I like the way my guitar sounds and feels now going into the GP-10, with all the passive controls going from the guitar to the GK-3. I would like to retain the same values in the old-school circuit if I can.

BTW where I drew just one pickup in the mod, I'm actually assuming there are two pickups, a switch, and tone control. Just trying to keep it simple to figure out the correct approach.

Elantric

#9
QuoteElantric, what if I used a Normally Closed switching 1/4" jack to break the connection with R14 when I plug in a 1/4" cable? Would that make my mod work?

Exactly - thats what they use in Fender Roland Ready and GC-1 Strats

The wire diagram is here:



(pay attention to these references in above diagram!)

* "Black Wire From Output Jack" = Ground /Earth connection.


* "White Wire From Output Jack" = Passive Mag PU Electronics Output connection


as these wire go here to the Normally closed 1/4" "Switching Jack :


As seen here:
https://www.vguitarforums.com/smf/index.php?topic=1099.msg59088#msg59088



QuoteOutput Jack

Its a switching type jack  - actually the same type used as an Input jack on old vintage Fender Twin reverb amp

When this Jack's switching elements go bad, the Roland Ready Strat's mini three way toggle may act non-functional.


This arrangement of using a switching output jack is unique to the the Fender Roland Ready  / GC-1 Strats  - and different than Roland Gk Internal kits.

The goal of the switching Output Jack is when the 1/4" Guitar cord is connected, this will  completely remove the entire Roland GK circuit from the normal guitar output path. 

* Remove the Jackplate and verify the contacts are clean on the SWITCHING OUTPUT JACK. If these contacts become dirty, much noise can be introduced or worse, complete failure of the normal guitar sound passing thru the 13 pin cable. Most Roland Ready Strats older than 5 years will suffer contact failure on this unique 1/4" switching jack. (Hint: This is the same switchcraft type switching jack as used on a 1960's Blackface Fender Twin Reverb Input Jack

LIKE THIS


MusicOverGear

Fantastic - thank you so much!

I owe you another "Applaud" (won't let me click again until an hour passes) :)

Elantric

#11
LIKE THIS (PDF is attached)

MusicOverGear

Okay I hacked together a pot using salvage parts. I would REALLY like to find something more robust/confidence-inspiring.


I need 3/8" (or longer) bushing and relatively small body (<= 24mm) because this is going in a Dot (335, semi-hollow). Any pointers on sourcing a better quality pot would be appreciated. I want "stereo"/dual-gang/dual/whatever, a B50k track and a B500k track. I know it's traditional to use an audio taper on guitar volume, but I use linear for volume and Dimarzio taper for tone. Anyway, I'm thinking that if can find a suitable line of dual pots, I can just buy two and DIY like I did with the one I hacked already - I can just swap the side tha'ts easiest to get to. E.g. a retail source for CTS 270 series with the 3/8" bushing http://www.ctscorp.com/components/Datasheets/270.pdf  Or anything adequate quality really. I've spent a lot of time searching where I know to look.

BTW for anyone else trying to do a custom interface, this is very handy. This is my mule guitar I use to compare pickups quickly w/o slacking strings or soldering. Now I am using it to try GK interface ideas. It's a very fast, direct, easy way to try things out before you hack up that cherished, handmade guitar.


I started building another one - finished a from-scratch walnut/rw neck even - where the cutout is in the bottom and it looks tidy enough to take out and use IRL. I lost interest tho. Wish I had it now

Elantric