Joe Hart's Wacky Wah Adventure

[Joe Hart]

I'm messing around with a Dunlop GCB95 Cry Baby Wah (Rev. H) and figured I would do a "rebuild" report on it. I know the mods have been done to death, but another opinion never hurts. I figure most people would rather have too much information than not enough. And maybe I have a new tidbit of info to add to the wah mod cannon.

Anyway, the first thing I did was play with the transistors. I ended up with some transistors from a late 1960's organ (not a Thomas!). They are Si and I settled on Q1 with a gain of 292 and Q2 with a gain of 250. I had read that changing the transistors can make a big difference, but I did not find that to be the case. I had read that you should have gains of 300-400, that you should have the higher gain transistor in Q1, and that if the gains are closer together the wah sounds a bit "cleaner" and "smoother" -- whatever that means! I tried transistors all the way up to 400hfe and didn't really hear much difference, although I *think* the transistors that I ended up with sounded a little better (less harsh and a the transition from bass to treble was a little smoother). But I may have been swayed by the fact that the transistors were "old" and were in little "top hat" type shapes rather than the usual "half moon" type package. I'm just trying to be honest here!

The lack of difference may have been that I didn't change anything else on the pedal. It seems that a few changes can add up to a much better pedal, so the transistor changes may mean more after some other changes, but I had to start somewhere and doing four different changes would kind of ruin the "trying to see what each change actually does" thing!

That is all so far! Stay tuned!!
-Joe Hart

[joegagan]

cool, thanks for sharing, looking forward to the wacka wacka

[Joe Hart]

I replaced the 4.7uf capacitor with an old Callins 4uf (like the originals) capacitor and didn't notice any difference. So I'll leave it in. It's the original value (although I have read that the old Callins caps can be notoriously off spec) and it has extra "mojo"!

Also, with the transistor changes, I now pick up radio signals. But I'll wait until I'm all finished to address this issue. I believe you can put a couple of small caps across some part of the transistors to suppress this. But it may not be too bad once it's all back in the metal wah shell.

And another thing I noticed that I haven't heard anyone else talk about is that as the battery gets weaker, the wah starts to wah less. So when you're testing any wah mods, make sure you use a good battery!
-Joe Hart

[Johan]

my GCB95 (dont know wich rev. but ca-95) is stock exept the transistors. I played around with the transistors quite a lot for a while, mostly trying to get the noice down. the only ones that stuck out as clearly different was BC109c, wich I found thin and weak and BC550c wich is the ones I've had in there for a few year now. they didnt help with the noise, but the tone was stronger somehow..perhaps ballsier or more potent would be a description...
...and I usually dont like it when partnumbers make a differance. ...do repairs for a few years and you'll see my point of view...however, in this case it did make a differance, and if you're trying to get your wha to stick out a little more, I'de recomend you try them.
J

[Joe Hart]

I also noticed a lack of huge differences with the transistors (and not a big difference with the noise either). But, for now, I am happy with the transistors that are in it. But we'll see after I do more mods!

I changed the 1.5K resistor (R1 on my board) to a 2.2K. The original actually measured 1.47K and the replacement measured 2.46K. This is the "midrange" mod and it did thicken up the tone a little. It wasn't very earth shattering at all. Kind of a let down for such a famous mod! But I will soldier on -- I know these mods are cumulative.
-Joe Hart

[davent]

Watching closely... waiting for the enclosure mods!

dave

[Joe Hart]

waiting for the enclosure mods!

Such as?
-Joe Hart

[davent]

Earlier in the year i had a thread on my far ,far from successful wah shell mods. Before i go destroying another shell with a second attempt i need to see it done properly. As for the mod, it was just a hole in the side for a cap switch.

Old thread.  http://www.diystompboxes.com/smfforum/index.php?topic=83177.0

Take care
dave

[Joe Hart]

Ah yes. I remember that! I'm not adding any extraneous controls. I just want a straight up wah pedal that sounds as good as I can get it.
-Joe Hart

[Joe Hart]

I've been playing the wah a bit and have noticed something odd. The wah sounds pretty decent on the higher strings, but barely wahs on the lower ones. Like an open E5 barely wahs, while an open DM sounds good, and the wah sounds even better playing higher up on the top 3 strings (G, B, and High E). Any ideas what might cause this?
-Joe Hart

[John Lyons]

You can also grind the bottom of the heel down on the treadle to get more sweep.

[Gus]

Simple wha 101

The "standard" inductor based wha

Input gain stage
wha voltage divider(volume control) wha pot
Emitter follower(EF) buffer
sweep cap
Changing  one affects the overall response

Simple gain stages like the vox input gain stage
Available power supply voltage can effect the gain
series input resistor affects gain
emitter resistor(if used) works with the collector resistor and bias string to set the fixed gain

wha pot is a voltage divider that is buffered by the EF(IMO the EF section should have a low noise high Hfe transistor because this stage does not matter as much it is a EF buffer)
With the vox like circuit there is a mixing from the EF bias used

If you up the first stage gain lower the sweep cap value for closer to the same sweep
If you lower the gain increase the sweep cap value
Changing the gain say you increase the gain the wha pot wiper will have a bigger signal at the same setting changing how the sweep cap works

If you change the pot the taper changes how the sweep cap goes through its range and can cause "bunching" at different ends

People get hung up on this part and that part, with the "standard" inductor wha you need to think about all the stages and how changing one affects the overall response.

this stuff and MORE is in the wha patent and R.G.s writeup you can find on the web.

This is a circuit that I am surprised a newtweeker has not used yet
http://www.aronnelson.com/gallery/main.php/v/gus/wha1.gif.html?g2_imageViewsIndex=1
Make the sweep cap smaller than "standard" because of the gain of the first stage(grounded emitter on purpose)
EF section allows one to taper the pot with a resistor on the wiper because the EF section has an high input resistance being bootstrapped and not loading the wha pot.  When people post changing the EF section transistor changed the sound it could be just the change of the loading of the wha pot with the input resistance.  Also note the collector operating point is in a better place.
when people post changing the caps to and from the wha pot again changes the loading at the place the RC time constants are happening

There is more like changing the resistor to the base affecting the gain

Wha patent
http://www.google.com/patents/about?id=pd1UAAAAEBAJ

[deadastronaut]

hi joe,

ive breaded the old morley classic wah recently, nice and simple too, and changed caps etc...getting really low end on heel position...and super tinny at toe position...

ive been trying to get the most usable range that i like out of it...without the waste travel/sweep/...pulling out the juicy stuff!..

i find i dont like a lot of the low end side of it pretty unusable,, so im changing out bits to best suit...

its been great experimenting with it..... of course no inductor etc...but it sounds pretty cool...i find my sweetest spot and work from there...forwards/backwards cap changes..

[Joe Hart]

If you up the first stage gain lower the sweep cap value for closer to the same sweep
If you lower the gain increase the sweep cap value
Changing the gain say you increase the gain the wha pot wiper will have a bigger signal at the same setting changing how the sweep cap works

Very interesting. I've done a fair bit of research online about modding wahs and I've not come across this bit of info. And I like information presented this way -- "if you do this, then that will happen." Thank you. I will mess with the sweep cap next.
-Joe Hart

[Joe Hart]

People get hung up on this part and that part, with the "standard" inductor wha you need to think about all the stages and how changing one affects the overall response.

I agree. With the research I've done, it seems that a lot of people write things like "you have to do this mod, change this to this and it will sound great," instead of "and this sounded great to me with my guitar and amp, etc." Not only does the circuit (as do most) depend on all of the elements to create the final sound, but the gear used can also change things quite dramatically. I tried a couple different guitars with this wah pedal and the wah reacts differently with different guitars/pickups. And what you stated also is a pain because you can't always just say "do this to achieve this result." I guess, if it were that simple everyone would just do it!
-Joe Hart

[Joe Hart]

I've been playing the wah a bit and have noticed something odd. The wah sounds pretty decent on the higher strings, but barely wahs on the lower ones. Like an open E5 barely wahs, while an open DM sounds good, and the wah sounds even better playing higher up on the top 3 strings (G, B, and High E). Any ideas what might cause this?
-Joe Hart

All righty! I'm certainly not above admitting to silly mistakes (like spending three days trying to figure out why this wah isn't working at all and then realizing that, with the board hanging out the side of the pedal, I had mixed up the input and output jacks!!). Anyway, after replacing the transistors and the 4.7uf cap, the wah barely whas, picks up MAJOR radio signals, and (oddest of all) is VERY noise and gets even noisier as I rock the pedal BACK! Not "toe down" where all the treble frequencies are, but "heel down"! I eventually realized that constantly moving the board around had broken off one of the wires to the pot. I soldered it back on and, lo and behold, the pedal works much better!

So on with the actual planned mods!
-Joe Hart

[joegagan]

takes a big man to admit to those little overlooked things, but it is a good reminder to all of us to check the obvious first.

these are all things we've done, thanks for admitting it!

[Joe Hart]

I replaced one of the .22uf caps (C6) with an older .22uf cap that looks like a bunch of silver plastic sheeting all wrapped up into an oval. I'm not sure what kinds these are, but I have used them before and they sound good to me and I have even seen them in older wahs. This did make a difference. The wah sounds a little fuller, but it may have been an off-spec cap and that different value caused the change.

I also tried this trick from Mr. Teese: Locate the .22uF cap that feeds the wiper of the wah pot.  Replace the original .22uF with a .33uF.  That's it.  Use this with the standard Dunlop HotPotz to simulate the Icar taper.

I tried it and all I got was a strange. slow feedback thing happening at the heel down position, the whole circuit was microphonic, and the wah pedal acted like a reverse volume pedal where the heel down was loud and the toe down was almost off (and very tinny at the toe down). I tried a couple of other caps, and just ended up with the original cap back in there. I was changing C8. Is this the correct one?

The pot that's in there is a Hot Potz II. Is this already an ICAR taper? Any other thoughts on this? Thanks.
-Joe Hart

[Joe Hart]

Also, I am trying to get rid of the "quick" transition in the middle of the pedal's travel. It sounds fine in the heel down position, fine in the toe down position, but there's a quick "jump" just past the middle of the pedal's travel (going towards the toe down). I would LOVE to expand that "middle bit" because there are some great frequency boosts there. Any thoughts on the easiest way to accomplish this? Adding tapering resistors to the pot, and if so, any suggestions on that? Thanks!
-Joe Hart

[joegagan]

hotpotzII is , in a general sense, quite close to an icar taper in my experience. if you have a capacitance meter, play around with caps closer to the actual .22 value. slightly under ( .215+ ish), to .223 is likely to get the wah back into regular wahing territory. never tried the .3 trick.