Author Topic: Wah doesn't wah  (Read 3439 times)

Jebus

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Wah doesn't wah
« on: March 04, 2015, 03:02:58 PM »
Hey!

Little bit of backstory first: when I first got into pedal building in 2005 I ordered bunch of boards from a guy here in Finland. He etched these himself and they we're really cheap. Also the quality was a bit cheap. So, one of the boards I ordered was a Vox V847 -wah-wah replica from GeneralGuitarGadgets. I never got it to work (only bypass worked, no sound when it was on) and after some testing I just gave up.

A month back I found the board and decided to make it work. I re-wired everything and put it into a Crybaby enclosure. Hooked it up and it still doesn't work. Previously there was no sound, no there's sound but no effect. It basicly sounds like a wah that is left to "middle" position (=little bit of lows and highs are cut). The potentiometer doesn't seem to do anything.

Had to use Internet Archive to found these pictures, but here is the schematic and layout I used (thou I did the switch differently - so that the pcb input is grounded when its bypassed):
https://www.dropbox.com/s/q2q8gh4wuoxzc5y/wah_847_lo_tb.gif?dl=0
https://www.dropbox.com/s/70yf4nmjcqt12ur/wah_847_sc.gif?dl=0

And here's couple pictures of my build:
https://www.dropbox.com/s/9ucogx2jzqdsaxb/IMG_3997.JPG?dl=0
https://www.dropbox.com/s/nfdzu6k8mxqsd8c/IMG_3998_2.JPG?dl=0

And here's the voltages of the transistors:

Q1
C 4,14 V
B 0,69 V
E 0,12 V

Q2
C 9,03 V
B 3,72 V
E 3,29 V

I have triple checked all the capacitor and resistor values. They seem correct to me. I didn't have any MPSA18s so the transistors are BC550Cs.

Any ideas? This is currently driving me nuts.  :D

Edit. I just realized that those pictures are not that good (noisy). I'll take better ones tomorrow in daylight.
« Last Edit: March 04, 2015, 03:04:32 PM by Jebus »

midwayfair

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Re: Wah doesn't wah
« Reply #1 on: March 04, 2015, 03:15:56 PM »
measure the resistance across the pot and between both pins. Check that it's actually changing the resistance.

Do you get ANY change in sound, even a tiny one when you sweep the pot?
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Jebus

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Re: Wah doesn't wah
« Reply #2 on: March 04, 2015, 03:36:34 PM »
measure the resistance across the pot and between both pins. Check that it's actually changing the resistance.

Do you get ANY change in sound, even a tiny one when you sweep the pot?

Across the pot is 93 kOhm and between both pins the resistance is changing from about 0 Ohm to 80-90 kOhm. So the pot is working.

I don't hear any change in sound. I'm testing this with my computer and stereos because I have no guitar amps in house. But I think I'd still hear if there's anything going on.

copachino

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Re: Wah doesn't wah
« Reply #3 on: March 04, 2015, 03:46:58 PM »
does it act like volume pedal??, if so its you inductor measure the resistance in parallel with the inductor and see what you get
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Jebus

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Re: Wah doesn't wah
« Reply #4 on: March 04, 2015, 03:48:50 PM »
Nope, it really doesn't do anything when the potentiometer is sweeped. Just same sound. Little bit of highs and lows missing and volume a bit lower than on bypass.

jimilee

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Re: Wah doesn't wah
« Reply #5 on: March 04, 2015, 05:55:51 PM »
Is the inductor in properly?


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Jebus

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Re: Wah doesn't wah
« Reply #6 on: March 04, 2015, 06:15:17 PM »
Is the inductor in properly?


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At least it looks like it. I'll remove it tomorrow, measure it (just to be sure) and re-solder.  :)

Jebus

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Re: Wah doesn't wah
« Reply #7 on: March 05, 2015, 10:08:38 AM »
Hah, removed the inductor and re-soldered - it works!  ;D Cold solder, probably. Thanks a lot for all the suggestions!

The output volume is bit lower than the bypassed. I'll try it at band practice on saturday, but I'm guessing it needs some kind of booster / buffer after it. At least there's plenty of room for one. Any suggestions?  :)

Also still need to fiddle with the pot. Its kinda on the bright side currently.

jimilee

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Re: Wah doesn't wah
« Reply #8 on: March 05, 2015, 10:26:43 AM »
Fantastic news


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Jebus

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Re: Wah doesn't wah
« Reply #9 on: March 07, 2015, 08:34:28 AM »
The output volume is bit lower than the bypassed. I'll try it at band practice on saturday, but I'm guessing it needs some kind of booster / buffer after it.

Tested it today. Sadly, it doesn't work correctly. It eats all the low end from the signal - I didn't notice this at home because I used just my PC -speakers.. Any ideas?

copachino

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Re: Wah doesn't wah
« Reply #10 on: March 07, 2015, 12:48:15 PM »
The output volume is bit lower than the bypassed. I'll try it at band practice on saturday, but I'm guessing it needs some kind of booster / buffer after it.

Tested it today. Sadly, it doesn't work correctly. It eats all the low end from the signal - I didn't notice this at home because I used just my PC -speakers.. Any ideas?
make it true bypass or buffer
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Jebus

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Re: Wah doesn't wah
« Reply #11 on: March 07, 2015, 06:54:15 PM »
make it true bypass or buffer

Sorry, badly worded.. It eats the low end when its on. Its true bypass and the bypass signal is good, but when I engage the effect it eats all low end. In other words, it works as high pass filter.  :-\

Jebus

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Re: Wah doesn't wah
« Reply #12 on: March 09, 2015, 09:42:00 AM »
Oh god.. Started debugging this again today. I re-soldered everything on the board, because I thought there is another cold solder somewhere. Instead of getting it to work, I completely broke it. Now there's nothing on the output when the pedal is on.  :-[

Starting to think that the problem is the low quality circuit board. There's something really strange going on.

luks999

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Re: Wah doesn't wah
« Reply #13 on: March 09, 2015, 09:43:16 AM »
hmm i would check if all other parts are soldered correctly and if the wires are good
which wah are u ralkin about? which trannies do you use?

maybe the whack cap has a too low value? then the sound is also thinner, more highs

luks999

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Re: Wah doesn't wah
« Reply #14 on: March 09, 2015, 09:46:13 AM »
sry you were quicker  ;D
can you post some pics? did you measure the connection to / from the board?
maybe some part got dead during soldering?
just some ideas