PRIMOVA - GKMX-42 Project – Box with 4 GK/4 Jacks in 2 GK out

Started by CodeSmart, August 03, 2013, 10:47:23 AM

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CodeSmart

I started this project about a year ago because I have three guitars of different character (2 with GK and one without), and needed a stage switch to quickly shift guitar between songs. I could have bought a SW-41 but that wouldn't allow me connect my LP using a regular jack.  Also I might buy a VG-99 or a GR-S someday and that would require also a US-20, and that's a lot of footprint.

So I decided to make a switch box for 4 guitars IN and two synths OUT covering my needs and what else more I could read about in this great forum.

I hand-wired my first prototype in August 2012 and it's been working fine at the gigs since, but this summer I designed a proper circuit board.  :)

Next step will be to try to squeeze everything into a Hammond enclosure (172x122x55 mm). I hope it fits as planned.

If this project sounds interesting I keep you posted about the progress.


But I got more gear than I need...and I like it!

whippinpost91850


bassman4d521


gumbo

Great stuff!!  I really look forward to seeing your progress on this!   :)
Read slower!!!   ....I'm typing as fast as I can...

CodeSmart

OK  thanks :D Here's the features of the Guitar/Unit Selector (what can be attached to the board in a maximized configuration):



  • 4 Inputs - Each with one GK connector and one buffered guitar jack. Both signals independently mixed together
  • 2 Outputs - Two GK connectors A and B for up to two synthesizers (GR-55, VG-99,GR-D,GR-S etc). A powers the unit.
  • 1 Send/master output jack. Allows for regular guitar stomp boxes before the sound of regular pickups gets to the GR-55.
  • 1 Receive/input jack. Buffered. Allows for regular guitar stomp boxes, or taking the clean hex pickup modeled guitar sound from GR-55 output and feed it back to the synth as it was coming from regular guitar pickups for further COSM effects in the GR-55.
  • SEL footswitch. This switch will cycle through the input channels when engaged.
  • 3-way toggle switch Selecting maximum number of inputs for SEL cycling: 2, 3 or 4 guitars.
  • A/B footswitch. Enables sound on unit A or B and directs guitar S1/S2 signals to it.
  • BOTH footswitch. Enables sound on both A and B (but guitar S1/S2 signal only routed to A or B)
  • S1 and S2 footswitches. Momentary type.
  • S1/S2 mode selector. 3 position rotary switch A, B and A/B. When A is selected the pedal S1/S2 is hard routed to A.  When B is selected the pedal S1/S2 is hard routed to B, when A/B is selected S1 and S2 is routed according to the current setting of the A/B footswitch (regardless of BOTH footswitch setting).
  • VOL A Stereo jack for optional EV-5 volume pedal acting on output A.
  • VOL A MAX/GTR 2-way toggle switch. In pos. MAX the volume of VOL A pedal is independent of guitar volume. In pos GTR the volume is derived from guitar volume.
  • VOL B Stereo jack for optional EV-5 volume pedal acting on output B
  • VOL B MAX/GTR 2-way toggle switch. In pos. MAX the volume of VOL B pedal is independent of guitar volume. In pos. GTR the volume is derived from guitar volume.
Furthermore:
- The guitar S1/S2 switches is always routed to the actual setting of A/B footswitch regardless of BOTH footswitch setting.
- The future pin 9 signal is also switched in this unit (input 1-4) and feed to both A and B simultaneously.
- The regular guitar signal is always feed to both A and B simultaneously.
- Buffered inputs and Receive jack input resistance = 100kohms
But I got more gear than I need...and I like it!

Elantric

#5
Looks great. But one caution. I see no external power source. Remember Roland VG/GR processors typically only supply 200mA on the +7v/-7v power , yet I see provisons for 2 13pin guitars. If both are RMC XTSA type I suspect you may exceed the available supply current.

CodeSmart

Thanks Elantric. It's actually worse as there might be up to four (4) GK guitars to power. It looks there will be a second round with PCB if I want to do the board perfect due to problem with header holes too small and a couple of other mechanical issues. So I could add voltage regulators... Do you have some circuit recommendation? Also should I have improved from US-20 and multiplexed STR1-STR6 to A and B units (i.e putting strings at GND when the unit is disabled in case VOL is not volume)?
But I got more gear than I need...and I like it!

CodeSmart

AND IT WORKS GREAT!!!  :D
No noice, no hum, silent guitar switching and great sound on both regular guitars and GK guitars.
Tested with my Ibanez, Fender strat and Gibson LP Traditional all connected. Just grab a new axe hit the switch and off you go!

Tested the US-20 A/B + S1/S2 feature also and it works fine. I only have one synth so I needed to open the box and move two jumpers to get power from output B instead of A while testing output B features.

Could use some nice paint and a print on the box, we'll se about that...




Regarding the power consumption discussion:
No GK-3 guitar connected: 36mA on +7V and 7mA on -7V
2 GK-3 guitars connected: 62mA on +7V and 20mA on -7V
This indicates that each connected GK-3 guitar draws  13mA on +7V and 6.5mA on -7V
For four connected GK-3 guitars this would be 36+(13*4)=88 mA on +7V and 7+(4x6.5=33 mA
Totally = 88+33=121 mA

My guitars don't have LED's.
If we assume 4 additional LED's at max 15mA the grand total would be: 181 mA

If the maximum current we can take from the GR-55 is 200mA I say we are close but not over the limit with four GK-3 equipped guitars.
The unit satesfies my needs but as Elantric noted other guitars may consume more power.

I might investigate possibility for connecting an external 18V AC/DC adapter to the unit if there's an interest getting a device like this on the market.

Do you think there's an interest?
But I got more gear than I need...and I like it!

gumbo

Yep!
...put one in your baggage next month for me...   ;D
Read slower!!!   ....I'm typing as fast as I can...

cell7


CodeSmart

Quote from: gumbo on August 05, 2013, 03:33:04 PM
Yep!
...put one in your baggage next month for me...   ;D

Mucho thanks for the support amigos. Two out of 10000 members at this forum has an interest  :P I probably need a little bit more before ordering components for the first batch of 10 units. What do you guys figure the street value is?

What is the most valuable feature? Is it the guitar switching or the synth switching or the fact that it does it all?

Should there be two versions, also one cheaper 3 GK+3 jacks in and 1 synth out as a complement?
But I got more gear than I need...and I like it!

billbax

Hi CodeSmart,

Good job.

Price point? umm, that looks like a fair bit of fabrication with the pcb and punching out all those 17.5mm holes.  £200.00GB would be a good starting point, considering the unit would probably take about 20 hours to complete + parts of £20-25.  Works out at around £8.75ph - just my guess looking at the unit.  How about a really nicely labelled sticker on top?

Bill


whippinpost91850

I have interest ,I don't know that I need that many options, but would need to have an idea on price. Thanks

gumbo

...most valuable feature for me at the present would be multiple GK in to singular GR out...for stage work.

Bill is on the money, BTW...
...if that doesn't work or cut it for you, maybe you could consider kit sales..


Cheers,
gumbo
Read slower!!!   ....I'm typing as fast as I can...

CodeSmart

Quote from: gumbo on August 07, 2013, 07:22:58 AM
...most valuable feature for me at the present would be multiple GK in to singular GR out...for stage work.

Bill is on the money, BTW...
...if that doesn't work or cut it for you, maybe you could consider kit sales..


Cheers,
gumbo

Hi Gumbo, yes having multiple GK in and also a "normal" guitar possibility was my own primarily "stage" need. But then after investigating this forum and many people where referring to the US-20 an its clones (but they were perhaps not a typical guitar guys  ;) , I thought why not embedd a pimped US-20 thingy as well while doing the PCB. The extra components on the board required was just a few dollars more.

However the the extra hardware on the Box: S1/S2 three-pole switches, rotary switch+knob, special VOL jacks with embedded switches, two extra footswitches (A/B + BOTH), extra LED's added up CONSIDERABLY and especially the soldering TIME of these components was essential. However to make this long story shorter, the board is designed so you can take the board as is, put a few jumpers in the connectors and it will operate as a 4 guitar(GK or regular) to 1 synth multiplexer. If you want more features you just connect hardware to the flat cable connectors. I have user's guide for this procedure.

I'm very dedicated and quality thinking guy (self employed senior C++ software developer), so before I release anything I would like to produce a second version of the PCB where I fix a couple of flaws. And if I can squeeze in a external power supply option for the piezo guys I will do that. Then I know I have reached perfection of the board.

Marketwise for me this is just hobby work. I can never earn what I earn in software with this unit. I'm just doing this because its fun. But my hope is that I can get back the money spent and some for the design time.

I foresee three levels (prices are PRELIMINARY ESTIMATES):
Item 1. GKMX-42: Full small footprint box /w 4 in and 2 out (i.e SW-41+reg. guitar + US-20 /w incl. S1/S2 and VOL A/VOL B)
Price abt. 330 euro (func. as US-20 at www.Thomann.de at 237 Euro + SW41 (if available) at 199 Euro).

Item 2. GKMX-31 3 in (3 GK+ 3 buffered reg. jacks) with 1 synth out. No S1/S2, no VOL jacks etc. Just ONE footswitch to change btw 3 guitars.
Price: abt. 220 Euro

Item 1 and 2 boxes comes in a dark red color with clear white text print (I'm investigating best ways to get the print done right now).

Item 3. GKMX-42 KIT: A fully tested PCB with flatcable connectors + instructions on how to add auxiliary switches (not included) to make a GKMX-42, GKMX-31 or any hybrid in between, as a DIY project.
Price abt. 130 euro

Furthermore I'm investigating how to get short (1m) good quality GK-cables.

What do you guys think of above, mission impossible?
But I got more gear than I need...and I like it!

billbax

Hi CodeSmart,

How about a youtube demo, as you have a working model? It doesn't have to be a BBC HD Adobe 'After Effects' job with a 'rich' voice-over - just something tangible.

Price-wise with your top of the range unit, I would stick to £200.00GB tops. I don't know, but there is something morally wrong with a v-guitar/GK accessory costing more than £200.00GB.

Please don't feel anything by my comments, as I know the forum wants you to progress in your innovation. We are with you!

Bill


CodeSmart

Hi Billbax, you might be right. I probably also would like to have that price level I bought from someone else...we'll see if its possible. YouTube is a great idea but I would like to put some paint on it first.

Unfortunately I'm back from holiday doing the 9-5 now so hours are limited to work with this fun stuff  :(
But I got more gear than I need...and I like it!

gumbo

CS:

"I'm just doing this because its fun. But my hope is that I can get back the money spent and some for the design time."

...I hear you, and would agree that it's a great aim, but (for example) but when I think of about two years of extensive R&D, sourcing and purchasing acceptable componentry, designing and building specialised tooling, and spending upwards of $3K to just produce and bring to market a lowly 13-pin jack and its derivatives, I'm damn sure I'm in it for the fun and NOT the money...   ::)

....absolutely NO offense meant, BTW...   and yes, I'm still very interested in your product..   ;)
Read slower!!!   ....I'm typing as fast as I can...

Elantric

I know its the expectation to be rewarded with money for your efforts in creating tools other musicians can use.
(Others seem to do this task better than I do ;)
But from my perspective there are far more rewards to experience in life than always focusing on making money for every task. It helps if you love inventing something from nothing, or making a better mousetrap or improved Roland US-20 ;)

But the 13 pin world remains a small misunderstood  corner slice of the "Music Industry", and like most artistic endeavors most of the successful players / R&D Engineers do have big or bigger or way huge egos.  Ego and cash always trumps Talent (sadly)  But if you possess all three  - look out world!

But my point is the project you are working on today - even if it fails financially  - WILL be an important learning experience and allow you to progress to be more effective and efficient and productive on other projects where you will know in advance the potential pitfalls, because you had that prior lesson.

FWIW - I have offered a low cost mod for US-20's to provide a Guitar FX Loop suitable for GR-55 or VG-99 expansion - after 2 years Ive done 6 total.
https://www.vguitarforums.com/smf/index.php?topic=7245.0


CodeSmart

Wise words from a wise and talented man. Thank you for sharing Elantric :-) I'm starting to get the picture and expectations sorted out. I will aim at producing 10 great looking units later this fall and sell them at an affordable price. If the stock lasts 3-4 years, the great news is that I get more time doing other new projects (or play more guitar) :D
But I got more gear than I need...and I like it!

gumbo

Read slower!!!   ....I'm typing as fast as I can...

Gassghost

Hi CodeSmart!
I'm in for one if you plan on building additional boxes! This is exactly what I'm looking for. 4 in and 2 out. I'd be happy with one out but two takes the cake!!! ;D  PM me if you plan on making more. I'm in... (I'd even consider paying you for a one off custom....)

Thanks,
Gass
GR-303 updated electronics, Stetsbar, Sustainiac
GR-808 (original) + Stetsbar (FOR SALE)
79 Strat w/ GK-2A
Eastman El Ray 1 and El Ray 3
94 Fender Tele w/GK-2A, Stetsbar
2 Fender GTX 100's
VG-99, GR-55, FC-300
And studio full of stuff

CodeSmart

Hi Gassghost,
I've been working some nights now with the new PCB design that includes a 12V to +/- 7V converter to be able to power the unit with an optional external 12V DC adapter. Hopefully I can order the new PCB and new additional components within a couple of days. Production time for PCB is 10 days + shipping. Then I need some time for testing. Due to a long travel mid Sep to mid Oct a reasonable schedule is to have everything produced (at least 10-15 units) by November-December. I will also get a homepage ready.

Please hang in there  ;)

P.S. There are recent posts in this forum about noise at the GR-55 Guitar Out jack. I just realized this box also gives a elegant solution to connect the normal pups directly to the guitar amp using the Send jack at the rear of my box. I will do that at my next gig  ;D
But I got more gear than I need...and I like it!

whippinpost91850


Gassghost

#24
Hey CodeSmart...
I'm waiting with baited breath! :P  I've been hounding another VG Forum member with mad engineering skills now for awhile for something similar to your unit but not as much of a multi-tasker. When I saw your post a new glimmer of hope arose. This would be awesome for my rig. The "Missing Link" if you will.  It will actually tie together a bunch of loose ends. PLEASE do keep me posted! I want one ABSOLUTELY! The slush fund is locked and loaded! ;D

One question... (Pretty basic) Will the active input be able to send a signal to both/A/B outputs at the same time? I trigger my VG and 55 at the same time now and use the US-20 to run both mostly or just A or B from time to time. (I'm assuming yours will do the same I need to reread the thread)

Thanks,
Gass
GR-303 updated electronics, Stetsbar, Sustainiac
GR-808 (original) + Stetsbar (FOR SALE)
79 Strat w/ GK-2A
Eastman El Ray 1 and El Ray 3
94 Fender Tele w/GK-2A, Stetsbar
2 Fender GTX 100's
VG-99, GR-55, FC-300
And studio full of stuff