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.
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?
Quote from: midwayfair on March 04, 2015, 01:15:56 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?
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.
does it act like volume pedal??, if so its you inductor measure the resistance in parallel with the inductor and see what you get
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.
Is the inductor in properly?
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Quote from: jimilee on March 04, 2015, 03:55:51 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. :)
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.
Fantastic news
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Quote from: Jebus on March 05, 2015, 08:08:38 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?
Quote from: Jebus on March 07, 2015, 06:34:28 AM
Quote from: Jebus on March 05, 2015, 08:08:38 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?
make it true bypass or buffer
Quote from: copachino on March 07, 2015, 10:48:15 AM
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. :-\
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.
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
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
Quote from: Jebus on March 09, 2015, 08:42:00 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.
Check. For a bridge, you said it was an etched board right? You may need to use a magnifier of some sort.
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Quote from: luks999 on March 09, 2015, 08:46:13 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
There's couple of pictures on the first post, but I'll take some more.
I don't believe that any component broke during soldering, I just quickly went through all the solders. But maybe the leads on the board itself? Need to measure.
I measured connections from the board and they are good.
Quote from: jimilee on March 09, 2015, 08:52:57 AM
Check. For a bridge, you said it was an etched board right? You may need to use a magnifier of some sort.
Yes, its an etched board. I'll try to check for any bridges! Don't think I have any kind of magnifier, but I'll do my best. :)
Alright, now I got sound again. One leg of Q2 was loose from the socket. Still sucks all the low end from the sound thou. :(
I measured all the connections both outside the board and inside it but didn't find anything wrong.. So next I think I'll quadruple check all values and components connections to board.
Quote from: Jebus on March 09, 2015, 10:09:22 AM
So next I think I'll quadruple check all values and components connections to board.
Oh gawd. The ceramic capacitors say "102". That's 1.0 nF (=0.001uF), right? Because they should be 0.01 uF. :D
Nope, that's 1n
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Switched the right size capacitors in and now it works perfectly. :D Thanks all for the help!
Quote from: Jebus on March 09, 2015, 09:04:45 AM
Quote from: luks999 on March 09, 2015, 08:46:13 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
ah sorry overlooked the pics there ;)
glad u got it working.
btw, do you have any noise with the wah? i have some with my weener wah and still couldnt find out why
There's couple of pictures on the first post, but I'll take some more.
I don't believe that any component broke during soldering, I just quickly went through all the solders. But maybe the leads on the board itself? Need to measure.
I measured connections from the board and they are good.
Quote from: jimilee on March 09, 2015, 08:52:57 AM
Check. For a bridge, you said it was an etched board right? You may need to use a magnifier of some sort.
Yes, its an etched board. I'll try to check for any bridges! Don't think I have any kind of magnifier, but I'll do my best. :)
Quote from: luks999 on March 10, 2015, 04:39:49 AM
ah sorry overlooked the pics there ;)
glad u got it working.
btw, do you have any noise with the wah? i have some with my weener wah and still couldnt find out why
Yeah, I'm very glad too. This project took almost ten years.. :D
I haven't tested it with band volume yet, but at least there's no noticeable noise at bedroom volume. What kind of noise does your wah make?
Quote from: Jebus on March 10, 2015, 05:24:54 AM
Quote from: luks999 on March 10, 2015, 04:39:49 AM
ah sorry overlooked the pics there ;)
glad u got it working.
btw, do you have any noise with the wah? i have some with my weener wah and still couldnt find out why
it sounds kinda pickup hum of single coils, but this noise is only with the wah and its clearer when increasing the sweep
sounds like a grounding issue to me, but i couldnt find a grounding problem...
can it be the enclosure?
Yeah, I'm very glad too. This project took almost ten years.. :D
I haven't tested it with band volume yet, but at least there's no noticeable noise at bedroom volume. What kind of noise does your wah make?
Quote from: luks999 on March 10, 2015, 06:17:42 AM
it sounds kinda pickup hum of single coils, but this noise is only with the wah and its clearer when increasing the sweep
sounds like a grounding issue to me, but i couldnt find a grounding problem...
can it be the enclosure?
Id say check all the ground connections with a DMM. You could also use an audio probe and check at which point does the hum come?
Edit. Also if the sweep of wah affects the hum then the hum comes before the potentiometer in the circuit.