Wah pedal Nirvana finally found!

[deke99]

Hi all,

Just wanted to share my wah pedal experiences with everyone.  I gutted a standard Dunlop wah pedal and used a reissue Fasel yellow inductor and the schematic provided on www.generalguitargadgets.com (standard drop in wah replacement).  I have struggled with wah pedals for quite some time and could never find one that had the smooth sweep that I was looking for.  I figured the schematic from ggg would do the trick.  I built it but I still had a very distinct move from bass to treble at one point in the pot sweep.  There seemed to be nothing I could do to remove it.  I read RG's page about swapping resistors to change the range of the wah and smoothing the sweep, but nothing worked.

I finally figured out a big secret that I haven't found any real documentation on. . . the transistors used in the circuit.  The GGG circuit calls for MPSA18 transistors.  These transistors just didn't give the sweep that I wanted.  I'm not going to claim that I know every last inch of any particular circuit, I'm just sharing my experience.  I don't know the exact job of the transistor, what I do know is that when I put in BC109 transistors (mouser # 526-NTE123A), it made all the difference in the world.

If you've been struggling with your wah pedal as I have, try the transistor swap.

Derek

[sean k]

It seems the only difference  in the transistors is the bandwidth which is 160Mhz on the MPSA18 and 300Mhz on the BC109 apart from the voltage and that isn't significant.

[deke99]

interesting information.  Again, I'm not an expert, but the change in transistors make a huge difference in the tone of my wah, and I changed nothing else.

I guess all I'm saying is that if you build the ggg wah and are not happy with the sweep, try this swap.

[ExpAnonColin]

It could be that your second set (BC109's) of trannies were just better matched, or rather, the second trannie had a more appropriate hfe for the purpose...

-Colin

[Jered]

Deke99, up until today I have never been satisfied with the sweep in my wah, and have also tried all the sweep mods. The fasal inductor I bought from Aron was a big help in getting a better tone and a more vocal sound, but I still hated the sweep.
 After reading your post I decided to change out my MPSA18's and replaced them with 2N4401's, and now the sweep is really good. A HELLUVA lot better. So thank you very much. I would have never thought the NPN's would effect the sweep so much.
Thanks again, Jered

[Paul Perry (Frostwave)]

This business of swapping transistors in a wah has come up in the Nurse Quacky as well. Any circuit that relies on transistor parameters in a complex way like this is going to give highly variable results.
That's why I have never built anything depending on a fet as a voltage controlled resistive element (and I hope I never do!).
Note I don't say you CAN'T build terrific stuff like this (many on this list have proved it!) but, it is the explanation for a lot of pointless arguments and flames.
Case in point: the EA Tremolo. Get lucky with the fet, & all is well.
And the early EH stuff...

[ExpAnonColin]

That's why I have never built anything depending on a fet as a voltage controlled resistive element (and I hope I never do!).

Watch what you say... try an H11F3. I will never turn back to optocoupled resistors.

-Colin

[Ed G.]

Deke99,
There are different BC109 suffixes (B,C, etc.)
Which one do you have? I've got the BC109C (higher gain) in my wah, but I'm not convinced it's the best thing out there.
Someone earlier mentioned BC108...

[Paul Perry (Frostwave)]

[quote="ExpAnonColinWatch what you say... try an H11F3. I will never turn back to optocoupled resistors.-Colin[/quote]

Good one, Colin. You're quite right. I admit it.
If the H11F3 ever falls to 50c, then I'll be into them! The only downside is, when an LED/LDR circuit depends on the rise & fall time sof the LDR to do smoothing or act as an envelope generator.. the H11F3 has MHz of bandwidth!!!

[deke99]

Jered, glad I could help in your quest for the good wah tone.  It's nice to hear confirmation that I'm not the only one who hears a difference.

Ed G. - I did a search on Mouser.com for bc-109c and the cross referenced match came up as mouser part number 526-nte123a.  Here is a link to the data sheet:

http://www.nteinc.com/specs/100to199/pdf/nte123a.pdf

Deke99

[ExpAnonColin]

Good one, Colin. You're quite right. I admit it.
If the H11F3 ever falls to 50c, then I'll be into them! The only downside is, when an LED/LDR circuit depends on the rise & fall time sof the LDR to do smoothing or act as an envelope generator.. the H11F3 has MHz of bandwidth!!!

An LDR, though, is upwards of 10 bucks! and if you roll them yourself, it's a pain in the ass (to me) and good quality photocells aren't much cheaper than the 1.05 price on this page:
http://www.gerberelec.com/html/body_lookup_parts.php?search_manu=QTC&search_thresh=10

-Colin

[steve b.]

deke,thanks alot---it worked for me too.Great reason for using sockets---besides not killing them with too much heat u can also do an easy swap to see if u can find the certain tone your looking for.Also if some people used sockets or a breadboard they would also find out if certain caps or voodoomojo resistors make any difference in sound.See sometimes it's the little suggestions that end up giving someone what they were looking for.Love this sharing concept.

[Transmogrifox]

Well, I looked up the datasheet on the H11F3:

http://www.fairchildsemi.com/ds/H1/H11F3.pdf

And it's back to the same classic FET resistor problem that bothers me the most:  linear signal amplitude.  This thing could make a real cool distortion element, based on the transfer V/I transfer curves.  You only have a hi-fi linear transfer at 40 mV, which is not very useful for a filter with high Q, since some signal amplitudes can reach several volts.  Therefore, it requires the classic attenuation, which generally causes the signal/noise ratio to suffer.

I'm slowly becoming a fan of the OTA.  I think it's the only variable gain element that truly lends itself to musical effects in a friendly way.  I still haven't given up on PWM, though--It's just that this requires very fast IC's and a well-designed circuit board to accommodate them.

[ExpAnonColin]

It depends on where in the circuit you're using it, transmogrifox...  I am using one for a VCO, whose range is now something like 10000:1.

-Colin

[puretube]

Transmo...: I`m a  b i g OTA-fan, but: "inside" they also are restricted to the <50mV "hangup"   :roll:

[Paul Perry (Frostwave)]

The H11F3 did a terrific job in the Neutron, of course...
www.geofex.com/PCB_layouts/Layouts/neutronpub.pdf
I don't know why we don't hear much of this lately. Waiting for perf perhaps?

[ninoman123]

I put some low hfe transistors (2n3904) in my wah and it sounds....the same....I have the vox v847 I think it is. I think the sweep cap mod did the most for adding to my sound. Q control is worthless since It sounds the same from 33k - 133k.

[Ed G.]

Deke99, up until today I have never been satisfied with the sweep in my wah, and have also tried all the sweep mods. The fasal inductor I bought from Aron was a big help in getting a better tone and a more vocal sound, but I still hated the sweep.
 After reading your post I decided to change out my MPSA18's and replaced them with 2N4401's, and now the sweep is really good. A HELLUVA lot better. So thank you very much. I would have never thought the NPN's would effect the sweep so much.
Thanks again, Jered

I also tried the 2N4401 and I'm really happy. I built the GGG mod-wah some time back and could not get it to get the high end and the clearer low end of the Thomas Organ crybaby I had. I even transplanted the TDK inductor. Still no magic. The 2N4401 puts that tone back in. Better than the BC109C's I had before.

[deke99]

Jared and Ed G.,

Thanks for the input about the 2N4401.  I'll have to give those a try and see if I can improve upon the BC109C.

D

[Ed G.]

Funny how out of all the mods to a wah, the transistor types get the least mention. And so far, they make the most difference that I've heard.