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Guitar Research Wah

Started by Govmnt_Lacky, July 19, 2011, 04:36:47 AM

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Govmnt_Lacky

July 19, 2011, 04:36:47 AM
Trying to debug a Guitar Research wah. Cannot find any schemos or good pictures of the wiring to go off of.

Can some kind soul post a good picture of the guts from one of these? The board number is SKA9003DL stamped on 2003-03-21

Thanks  ;D
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for an amount of 'up to and including my life.'

Govmnt_Lacky

#1
July 19, 2011, 05:36:10 AM
Did a one-for-one with your basic Cry Baby schemo and it looks about the same  ::)

I guess I really don't need the schematic.

Although it does seem odd that looking at this schemo:

http://media.photobucket.com/image/guitar%20research%20wah%20schematic/francm09/Wah%20Mods/dunlop_wah_wah_pedal.gif

It appears that on the Guitar Research wah, they "cascaded" dual 2SC1815 trannys where Q3 is on the schematic.

Any idea why they used the dual-transistor config  ???
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Electron Tornado

#2
July 19, 2011, 09:26:42 AM
Is it possible they're connected as a Darlington pair?

http://www.technologystudent.com/elec1/transis2.htm
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Govmnt_Lacky

#3
July 19, 2011, 10:04:45 AM
Quote from: Electron Tornado on July 19, 2011, 09:26:42 AM
Is it possible they're connected as a Darlington pair?

I do believe you are correct!  ;)

I will need to look at the board again however, it appears that your standard Cry Baby uses an MPS-A13 Darlington tranny in this position. They probably cascaded (2) 1815s as Darlingtons

Once again.... this is subject to another look  ::)
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Paul Marossy

#4
July 19, 2011, 10:07:32 AM
Yay, so it's not an EXACT copy of a CryBaby GCB-95. But it's close enough.  :icon_rolleyes:

Govmnt_Lacky

#5
July 19, 2011, 11:57:57 AM
I am thinking about just scrapping the board in this shell and builing a Hendrix wah. Got a few questions first:

1) What inductor is being used in the JH wahs nowadays?
2) Are the JH models coming with 100K or 470K potz?

Thanks  ;D
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

joegagan

#6
July 19, 2011, 01:17:02 PM
inductors in all the jh wahs i have seen are the whatever they are putting in everything else at the time. 90s, small inductor with brass nut at top, later the black cylinder, sometimes with a green dot of paint sometimes not. in this series, the tall ones seem to sound good at times.

the original issue JH1 had a 470k pot, i suspect this was to mellow the tone to make it sound more 60s -ish. very few other changes to the gcb95 formula otherwise. a small cap to ground off the pot ( would also possibly tend to reduce harsh highs), a small cap paralleling the inductor if i recall. but this also depends on when it was made and also if you believe the factory schem , which exists on the net somewhere. ( when you see it, don't freak out --there is also a spec listed  for a 'clavinet wah' which as far as i can tell never got released!)


at some point , dunlop just switched to 100k for the JH1. not sure if they made any other circ adjustments at this time to compensate. now, if you go to the duinlop parts website for wah parts, they tell you to replace your 470k pot with a 100k  since the 470k is 'not available".
my life is a tribute to the the great men and women who held this country together when the world was in trouble. my debt cannot be repaid, but i will do my best.

Govmnt_Lacky

#7
July 19, 2011, 01:20:49 PM
Thanks joe!

So... to grasp and summarize:

1) They now use 100K for the pot(z)

2) There is really no special inductor in the newer JH1s (like a Fasel, Whipple, etc.) Just the black cylinder?

Thanks for the info  ;D
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

joegagan

#8
July 19, 2011, 01:27:51 PM
correct on all, except i have not opened up one that is less than about 10 years old, so... dunno.

BTW, the stock ones from the 90s sound really nice to me. cool growl in the low mids like a (dare i say?) vintage wah!
my life is a tribute to the the great men and women who held this country together when the world was in trouble. my debt cannot be repaid, but i will do my best.

Paul Marossy

#9
July 19, 2011, 04:11:48 PM

Darrenj

#10
October 13, 2020, 07:04:01 AM
Sorry to hijack this thread but I have just purchased one of these and I am looking to do a true bypass.

Can anyone help?
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