Dunlop - GCB-950 Cry Baby Octace Wah

GorillaHuman · Post by **GorillaHuman** » 22 Aug 2013, 14:37

kh602 wrote:Does anyone happen to have pictures of the crybaby octave wah from
The early 90s? Gcb-95O. Would be amazed if anyone has gut shots of this pedal. I have seen
This wah knocking around once in a blue moon. Seems rare to come by.

Recently acquired one of those crybaby octave wahs. Bought it as defective. Well, yeah, its defective alright. But even its shot-out guts are worth taking a picture off, since I cannot find ANY info on these babies on zeh internetz.
The side pots regulating ?? and ?? are broken, the pot for the sweep is broken, there is a red LED missing next to the green one, and the inductor was delivered as shown at the last two pictures. I dont know if it works or is the original one. It has been removed using a cutter instead of desoldering. Bottom plate and the plate at the front are missing.
I don't know what this poor pedal did to the previous owner, but imma try to fix it and check out its sound.
Any suggestions on the inductor? I'll just replace the pots, but how can I salvage the inductor?

: Unknown inductor

Dirk_Hendrik · Post by **Dirk_Hendrik** » 22 Aug 2013, 16:23

I may be mistaken but the middle of those component view photo's show signs of acid like corrosion. Suggets leaking electrolitic caps.

Ice-9 · Post by **Ice-9** » 22 Aug 2013, 18:13

Dirk_Hendrik wrote:I may be mistaken but the middle of those component view photo's show signs of acid like corrosion. Suggets leaking electrolitic caps.

Agreed, picture 7 has two electros pointing in towards each other , one is marked 22uf the other is probs the same , they both look to be the culprits.

GorillaHuman · Post by **GorillaHuman** » 24 Aug 2013, 10:48

Yes, on closer inspection these do look nasty

Placed on my to-do list!
Can I fire the wah up without the inductor in place? What will it sound like? Like a fixed-wah or ..?

Dirk_Hendrik · Post by **Dirk_Hendrik** » 24 Aug 2013, 11:37

yes you can. There will be no Wah whatsoever,
So, while you've got some work to do getting that board clean again, and you could do that in the time you're waiting on a replacement inductor. By the time the soldering is good again, and possible defective electrolits are replaced without even wondring wether they still might be good (they're too cheap to leave in plave), your freshly ordered inductor will have arrived on your doormat.

christoba · Post by **christoba** » 22 Nov 2014, 16:24

Hello Folks,

I've got an old pedal that I've been trying to revive. Its a GCB-950 Octave Wah. Both the wah and octave distortion weren't working. I replaced some clearly bad resistors and the pots which ended up getting the distortion going. However, I am having a problem with the wah. If I disassemble the board and parts and then fire the unit back up, the wah will will work perfectly. However, if I turn the distortion on the wah will work with the distortion until I turn off the wah. Then the wah will no longer function with both the distortion on or off. So, engaging the distortion effectively knocks out the wah once the distortion has been turned back off. I was thinking that maybe a cap is going bad but they all look pretty good. Any ideas?

Post by **modman** » 22 Nov 2014, 19:34

christoba wrote:Hello Folks,

I've got an old pedal that I've been trying to revive. Its a GCB-950 Octave Wah. Both the wah and octave distortion weren't working. I replaced some clearly bad resistors and the pots which ended up getting the distortion going. However, I am having a problem with the wah. If I disassemble the board and parts and then fire the unit back up, the wah will will work perfectly. However, if I turn the distortion on the wah will work with the distortion until I turn off the wah. Then the wah will no longer function with both the distortion on or off. So, engaging the distortion effectively knocks out the wah once the distortion has been turned back off. I was thinking that maybe a cap is going bad but they all look pretty good. Any ideas?

I merged your topic with an existing one, because maybe the solution is in this thread.
I don't think we have a schematic - but worth checking for corrosion.

astrobass · Post by **astrobass** » 22 Nov 2014, 20:09

Does it use FET switching or mechanical bypass?

christoba · Post by **christoba** » 23 Nov 2014, 01:47

I'm thinking that the 2 SCL4016BE chips are responsible for the switching. The pictures of the pedal are exactly the same as my pedal. I'm wondering if I should go after the caps as I would guess they are not giving up the juice once I cut the power which would cause my issue. Does that make sense to anyone. Its okay if it doesn't, I'm a mechanical engineering kind of guy; electronics confuse the hell out of me for some reason.

Post by **digi2t** » 25 Nov 2014, 01:43

I traced this pedal a while back, UKToecutter drew up the schematic. It's in a large format, so right click the image, and save it to your computer. Then you'll be able to zoom to your heart's content. Here you go;

christoba · Post by **christoba** » 25 Nov 2014, 21:22

Holy awesome! Thank you for putting in the time on that. BTW, if anyone wants to pull out that fuzz circuit and copy it, its a pretty weird one. Anywho, Does anyone have an idea as to what may be causing my intermittent wah availability?

Thanks,
Chris

Dirk_Hendrik · Post by **Dirk_Hendrik** » 25 Nov 2014, 22:41

Holy quack indeed. Thanks for the time invested that provides this starting point.

When going for readability/signal flow a redraw is required. As for a first impression, a 100n (C31) from input to ground?? Hard to believe.

Post by **digi2t** » 28 Nov 2014, 02:13

Dirk_Hendrik wrote:Holy quack indeed. Thanks for the time invested that provides this starting point.
When going for readability/signal flow a redraw is required. As for a first impression, a 100n (C31) from input to ground?? Hard to believe.

Read it and weep. Here are all my tracing pics. PLEASE TAKE NOTE THAT THE FUZZ POT IS A B22K, AND NOT A B10K. I'VE UPDATED THE PICTURE, BUT I DON'T KNOW IF IT WILL SHOW. I still have this unit, and when I bought it, some doofus stuck a 10k in it, for I don't know why. Research, and confirmation from a Dunlop tech, has this pot as a B22K. The A470K pot is correct. My unit now sports the correct Omeg pots that it originally came with. As with the schematic, save them to your computer to see them full size.

Wah pot board;

Enhanced trace side;

Components and notes (fuzz pot is B22K, not B10K);

Component side traces (this is a double-sided board);

Redraw? Knock yourself out brother. I've stuck a fork in this sucker.

Dirk_Hendrik · Post by **Dirk_Hendrik** » 28 Nov 2014, 11:14

Read.
When did a 220pF cap (C31) become a 100n?

220p makes sense as a RF eliminating cap (and the first part to remove, get rid of tonesuck and fck the FCC).

I do not get where C10 (220n to gnd) came from either.

Post by **digi2t** » 28 Nov 2014, 17:23

I'll check it again tonight Dirk. They're small, and the eyesight's not what it used to be.

As for the intermittent wah, the small board is soldered directly to the pot, and there is no other support for it. I could see the solder cracking here.

Dirk_Hendrik · Post by **Dirk_Hendrik** » 30 Nov 2014, 09:22

Redraw of above schem to get the signal flow (a little more) clear. The 4016 based switching screws a lot. Unverified for component values. Just a work in progress. Questions raised: 1) The power supply transistor suggets being a PNP type and not the MPSA18 in the photo. 2) A connection expected between U1 pin 3 and U1 pin 8. U1 pin 3 was that 4016 gate that was connected to a 2M2 only. The connection in the below schem makes far more sense.

GCB95O.pdf: (27.8 KiB) Downloaded 83 times

Dirk_Hendrik · Post by **Dirk_Hendrik** » 30 Nov 2014, 10:43

Correction:

GCB95O.pdf: (27.89 KiB) Downloaded 183 times

Dunlop - GCB-950 Cry Baby Octace Wah [schematic]