Fender fuzz wah.

[Electromancer Effects]

Hi, everyone I'm brand new here and I'm not super good at computers so I hope I'm doing this correctly. I have just picked up a version 1 fuzz wah, the big chrome one with the side to side volume control, and when the wah is engaged the volume drops to a fairly inaudible level. I haven't audio probed or replaced the electros yet but I'll probably do that tonight.  I did go through and reflow everything as well as replace a few wires.

I have gone back through this forum and I'm pretty sure I've read just about everything about this pedal and I've seen posts with similar complaints but not a whole lot in terms of solutions, so I'm throwing this up here to say hi and ask if anyone has any tips that I may have missed. Thanks.

[Kevin Mitchell]

Welcome to our haven 
You'll want to find a readable schematic that matches your pedal.
Assuming I'm looking at the right one, you'll want to inspect for the guitar signal on Q3, Q4 then Q5.

Know that this pedal is positive ground - so probe ground goes to the positive side of the power supply/battery.

Also, we love pictures.
This is the first I've heard of this pedal. I'd be interested in seeing what you're working with.

[Electromancer Effects]

[Electromancer Effects]

As far as a readable schematic goes, this is it. I pulled it from this site and I think it's the only one out there. Judging by the transistors you referenced you already found it any way😂.

[Kevin Mitchell]

What is this, a gallery for ants?
 

The lack of resolution doesn't help much. Converting the schematic you have from PDF to jpg makes it worse - it was barely readable to begin with unfortunately, but doable.

Probe away 

[Electromancer Effects]

Oh wow. That is hilarious. I think I said I'm not too great with computers. Instagram and Reddit are the only places I ever share pics. I'll try not to embarrass myself next time. I changed out the electros and I can hear the wah now so at least that's something. As you would expect they where way out of spec.

[Electromancer Effects]

I'm gonna try this again.

[GibsonGM]

Rotate it left 90 degrees, and you've got yourself a deal! 

[Rob Strand]

Assuming I'm looking at the right one, you'll want to inspect for the guitar signal on Q3, Q4 then Q5.

It seems those PNPs are germanium. 

If the transistors have marginal leakage the bias could be off.  It would be wise to measure the DC voltages on the transistors.  Especially the collector voltages.

You will need a multimeter to check. 
meter black (-) lead on ground (+9V)
meter red (+) lead to the collectors

Some ball-park values.  Could be off by 1.5V or so.  The point is
you don't want to see values around 0V or -9V.

Q3:  perhaps -3V
Q4:  perhaps around -3.5V
Q5:  perhaps around -4.5V

From what I can see it would be normal for the the audio signals around Q4 to be lower than the signals on Q3 and Q5.

What's the note on the inductor say?

400 or 500 turns ?
#38
tap @
100 ? or 300 ?

[Electromancer Effects]

Looks like 100 turn #38 tap at 100 to me. I don't know anything about inductors.

[Electromancer Effects]

https://www.freestompboxes.org/download/file.php?id=13391&sid=461a66c0db5759785a412f18ee955084

Here's a link to the original schematic. It might be a little better than what I posted before.

[Rob Strand]

Looks like 100 turn #38 tap at 100 to me. I don't know anything about inductors.

It looks like that to me too but I know it isn't correct.  If I look at the hundreds digit in the number of turns and compare it against other numbers in the schematic I kind of think it's a 500.   That makes some sense and a tap at 100 turns seems to work.

The tap and turns affects the expected output level.   With 500 turns tapped at 100 turns the wah gain and general behaviour look pretty good.  I'm guessing C12 is 390nF (0.39uF).  You might be able to identify that cap on your board.

Here's a link to the original schematic. It might be a little better than what I posted before

Thanks.  I managed to find that one.  Also found another unclear one on Reverb.
I was thinking you had a cleaner copy on paper  .

At this point there's nothing obviously wrong with the design.  So I'd be checking bias voltages, as mentioned before.

[Electromancer Effects]

Ok. First off we'll get this part out of the way. Pnp germs are as follows.

Q3 e,0.035 b,0.140 c,4.787
Q4 e,0.721 b,0.857 c,3.663
Q5 e,0.197 b,0.316 c,4.215

I started probing and I have strong signal coming out of q3 through c3 then on the other side of r14 it drops out. On the far side of r14 signal should go to the wah pot as well as the start of the inductor. I see that the tap goes directly to ground here so I wonder it the issue is within the inductor. I also get continuity from the start of the inductor to ground 

I read in an older post here where someone was troubleshooting this same issue and I recall that they posted voltage on the inductor so here's that.

Start to tap, 42.7 ohms
Tap to finish 26.72 ohms
Start to finish .26.7 ohms

As I recall there was no resolution even after the op had replaced all components excluding the inductor. I'll see if I can find it to read it a third time.

In another old post I saw that someone had pointed out that inside the ferrite housing of the inductor there is a half moon that locks into a corresponding shape in the lid and presumably turning this adjusts the inductance. The one I have here sits below the level of the cap so the two parts do not engage. I can carefully lift out the coil of the inductor but the ferrite housing seems stuck to the board even with the nut removed. There is also some burnt up looking blistery crap at the bottom of the housing that I think may be from over heating the solder around the base of the bolt.

I mostly build fuzzz and drives and I have zero experience with inductors.

Thanks y'all. Please let me know what you think.

[ElectricDruid]

Welcome Electromancer!

Just wanted to say what a cool-looking thing that is. I love the switches on either side. Good luck getting it going. If it sounds half as sixties as it looks, it'll be rockin'!

[Rob Strand]

Ok. First off we'll get this part out of the way. Pnp germs are as follows.

Q3 e,0.035 b,0.140 c,4.787
Q4 e,0.721 b,0.857 c,3.663
Q5 e,0.197 b,0.316 c,4.215

All those look pretty good.
(For the record hFE=75 and leakage ICEO=60uA for the transistors is about ball-park).

I started probing and I have strong signal coming out of q3 through c3 then on the other side of r14 it drops out. On the far side of r14 signal should go to the wah pot as well as the start of the inductor. I see that the tap goes directly to ground here so I wonder it the issue is within the inductor. I also get continuity from the start of the inductor to ground 

It's quite normal for the level to be low between R14 all the way through to the base of Q5.  You can get an idea how strong the signal is at Q3's collector compared to the other points in the circuit.  It only rises again at the last stage, Q5.    In the plots below the output at Q5 is fairly representative of normal wah levels.

[assumes 500 turns tapped at 100 turns]


[FYI:  what our eyes see as the part designations is likely to be incorrect.  If you label the part designations you will find repeats and that's because the text is actually unreadable.   The good thing is I see what you see so I can translate.]

I read in an older post here where someone was troubleshooting this same issue and I recall that they posted voltage on the inductor so here's that.

Start to tap, 42.7 ohms
Tap to finish 26.72 ohms
Start to finish .26.7 ohms

Those resistances are in the ball-park.  However, I suspect there's a measurement error somewhere as
"Start to tap" + "Tap to finish"  should equal "Start to finish".

As I recall there was no resolution even after the op had replaced all components excluding the inductor. I'll see if I can find it to read it a third time.

If the inductor is damaged it will cause problems.

The first thing to check is the DC resistances of the windings.  It would help greatly if the measurements were at least  consistent with the sums I just posted.  Otherwise things are starting out on the wrong foot.

In another old post I saw that someone had pointed out that inside the ferrite housing of the inductor there is a half moon that locks into a corresponding shape in the lid and presumably turning this adjusts the inductance. The one I have here sits below the level of the cap so the two parts do not engage. I can carefully lift out the coil of the inductor but the ferrite housing seems stuck to the board even with the nut removed. There is also some burnt up looking blistery crap at the bottom of the housing that I think may be from over heating the solder around the base of the bolt.

The lid should sit flat around the outer edge of the bottom part of the core.  If not there's a good chance the coil/former isn't sitting flat in the base of the the bottom part of the core.  If it's full of gunk that might explain it.  If this is happening the inductance will not be correct and you could lose some signal at the output due to poor coupling.

As I recall the machined half-moons don't lock.  The top outer edge should sit flat with any rotational orientation.  For the half-moons: when the lowest point of the lid and the highest point of the base are aligned the inductance should be maximum.  That's when the two halves touch.  When the half-moons don't overlap and touch there is an air-gap on *both* sides of the half-moon.  That gives the minimum inductance. 

For a wah I expect the two half-moons should be touching with full overlap, or at least close to it.    That gives maximum inductance and maximum coupling between the primary and secondary.

[Rob Strand]

Here's the old thread with the inductor details,
https://www.diystompboxes.com/smfforum/index.php?topic=119212.msg1126462#msg1126462

Start to Finish = 48.6 Ohms / 470mH
Start to CT      = 41.5 Ohms / 375mH
CT to Finish     = 7.2 Ohms / 8mH

We can now check:

Resistance: 41.5+7.2 = 48.7 ohm  which agrees with the direct measurement of 48.6 ohm.

The inductance roughly adds up:   (s=start, t=tap, f=finish)
Check: L_sf = (sqrt(375)+sqrt( 8 ))^2 = 493mH  ; expect 470mH
Based on inductance we might expect:    L_tf = (sqrt(470)-sqrt(375))^2 = 5.4mH
Based on resistance we might expect:    L_tf = 470 * (7.2/48.6)^2 = 10mH  ; assuming same wire
So hovering around the measured 8mH.

If the tap is at 100 turns then we can estimate the total turns
Based on inductance: sqrt(470/8)*100 = 766.
Based on resistance: (48.6/7.2)*100 = 675.
So around 700 turns total.

I'm having trouble interpreting what the turns is from the schematic, could the
100 really be 700?
The core diameter looks quite a bit bigger than most wah's so maybe 700 turns does fit.

If the core is a P26 pot core we can fit 700 turns and to get the resistance we need 36 AWG wire.
To get the resistance with 38 AWG wire we can only have about 530 turns.

Either 530 turns to 700 turns seems possible to get 470mH inductance with a P26 core, depending on the gap.
I have no idea the range of inductance adjustment on that core but it seems like we
are in the ball-park.
As a side comment, this thread
https://www.diystompboxes.com/smfforum/index.php?topic=103519.0
is about the fuzz level being low.

That one is easy, it's due to the divider form by R8 (470k) and R9 (100k) at the output of the fuzz section.  When you engage fuzz and wah you will get even more volume loss due to the low input impedance of the wah further loading the divider.

The fuzz level isn't too bad but you can hear some drop with fuzz + wah.

https://www.youtube.com/watch?v=Zuuj8QUyiAA
https://www.youtube.com/watch?v=6jDOqSZSzKE

[Electromancer Effects]

Wow. Thanks a ton. This is laying the groundwork for me to learn some new stuff. I didn't have time to get back into this thing last night but I'll definitely be spending more time on it this weekend. For now I'll re read what you have here and start trying to digest these new concepts.

I did re check the resistances on the inductor just now and it seems that I misidentified one of the pads. D'oh!
New readings are a bit different
S-t. 42.5r
T-f. 8.1r
S-f. 50.4r

This seems to fit with what you laid out earlier.

[Rob Strand]

Wow. Thanks a ton. This is laying the groundwork for me to learn some new stuff. I didn't have time to get back into this thing last night but I'll definitely be spending more time on it this weekend. For now I'll re read what you have here and start trying to digest these new concepts.

I did re check the resistances on the inductor just now and it seems that I misidentified one of the pads. D'oh!
New readings are a bit different
S-t. 42.5r
T-f. 8.1r
S-f. 50.4r

This seems to fit with what you laid out earlier.

Looks consistent with the other unit, which is a good sign.

The whole idea of pinning down the inductor a bit is to get a better estimate of the output level.  With the info so far it's certainly in the ball-park of normal wah pedal levels.

Given the bias voltages check out there's not a lot left to blame.   The assembly of the inductor is the only thing that needs to be checked.   If there's no gap on the outside where the lid and body meet it should be pretty good there too.   You can rotate the lid to tune the sound of the wah.

If you get that far the next step would be to inject a *low level* 1kHz sine wave (perhaps using a PC), tweak wah pedal position for maximum loudness.   You might then be able to measure the AC voltage with a multimeter.  It's not going to be accurate as noise affects the measurements.   You can compare the measured levels with those on the response plot I gave before.    The only thing you need to do extra is convert all the measured levels to dB relative to the input signal level.

[Electromancer Effects]

I'm starting to wonder if I've been pulling on the wrong thread. I got the cap of the inductor lined up properly and probed around some more. Getting that cap in the right place definitely helped but I'm still getting a much weaker signal at c of q5 than at c of q3. It seems like there is a slight volume drop from unity to wah engaged which seems like it might be normal however when fuzz and wah are engaged I have another volume drop. Fuzz on its own has more volume than unity. Sounds like I may need to take a look at the r8/r9 divider. Any suggestions?

Oh, thanks by the way for all your help. I'm really glad I jumped on this site after lurking for so long. I need to finish up with this thing so I can get back to the point to point op amp muff I started before I got this guy.

[Rob Strand]

I'm starting to wonder if I've been pulling on the wrong thread. I got the cap of the inductor lined up properly and probed around some more. Getting that cap in the right place definitely helped but I'm still getting a much weaker signal at c of q5 than at c of q3. It seems like there is a slight volume drop from unity to wah engaged which seems like it might be normal however when fuzz and wah are engaged I have another volume drop. Fuzz on its own has more volume than unity. Sounds like I may need to take a look at the r8/r9 divider. Any suggestions?

Oh, thanks by the way for all your help. I'm really glad I jumped on this site after lurking for so long. I need to finish up with this thing so I can get back to the point to point op amp muff I started before I got this guy.

Sounds like the wah level is getting close to unity gain now.

There's actually three gains to tweak:
- fuzz alone
- wah alone
- fuzz + wah

fuzz alone is set by R8 or R9.  Try increasing R8 to decrease the fuzz level.  Normally R8 is preferred but I suspect the fuzz + wah level will might ultimately be low so it might end up adjusting R9 is better (see fuzz + wah level below).

The wah alone level can be changed by tweaking R22 R23.

R22      R23R24
680k      15k        (normal values)
820k      18k        +1.4dB
1M        22k      +2.7dB
(R23R24 sets the gain and R22 sets the bias voltage on Q5's to be what is was initially.)

The wah+fuzz level should only set after previous two have been set.
To increase the level decrease R8 and R9 by the same factor.
What this does is sets the output impedance of the fuzz so the it looks like a guitar (roughly).
Since the output impedance is largely set by R9 (100k), which is higher than the guitar impedance,
there's a good chance the wah+fuzz level with 470k/100k will drop.  So it might turn out we need to
scale these values down by factor of 2 or so to raise the wah+fuzz level, without affecting the
fuzz only level.

All easy to do but it takes time to tweak.

Here's my best guess for the wah signal level.  Standard part values and 700/100 turn inductor.  The peak levels in the response are very much like a standard wah, maybe a tad low.  In reality the input impedance of the wah will load the guitar pickup and bring those levels down a bit.  So we might expect the wah gain needs to increase a bit.