Wah Component Comparison Chart

[Paul Marossy]

Paul, thanks for publicizing how cool this circuit is.

Well, I like it!  

When you guys mention the "DeArmond shell", are you referring to the shell that the Boomerang is in? I much prefer the good old CryBaby type shell. I built one of my Boomerang circuits in one. It's on my pedal board right now as a matter of fact. You can hear it in action on the tunes called "Wholed Me" and "I Let Go" at http://www.myspace.com/j201jams 

[matt239]

...
1. 820K (not 620K) feedback resistor on Q2
2. 1uF caps at hot and wiper of 100K pot
3. 1.5M resistor from collector of Q1 to inductor

I think these are then main factors in what makes the Boomerang sound different.
...

How much difference do you guys think the 1.5M resistor above the inductor, and the 25k (or simulated 25k..) pot make to the Boomerang vs. Vox/Crybaby?
What about the 820k resistor on Q2?

I'm building a Crybaby, but I think I'll sub some Boomerang values, at minimum the 1uF caps.

[matt239]

What difference does the 25k pot in Boomerangs actually make, vs 100k?
I know it's "more correct" for a Boomer, but what does it DO differently?
Does it mostly change the sweep? - Does it affect the overall tone? - Does it also affect the range?
Does it sweep through less total range, or sweep through the same range faster?


What about the 1.5Meg resistor from Q1 collector to the inductor, etc. It would affect the biasing, and also the Q, Does it also affect the frequency, or tone?

Boomerangs have, nominally, the same inductor, & the same sweep cap as a Crybaby, but a lot more low end gets through.
The MAJOR differences I see are the 25k pot, & the 1.5Meg resistor.. Can anybody offer more insight on the effect of the 1.5Meg resistor?
It LOOKS to me like it would cause less bass to be attenuated by the inductor, but I don't know if it really works like that?

[joegagan]

the boomerang is designed around the 25k pot except the stock centralab pots often were 29k average. with a 100k , the biasing is not correct, circuit sounds weak.
2. to make matters worse, the pot is on opposite side of wah , thus needing rev log instead of log, when people put a 100k wah pot, they get it wrong twice. the emphasis is completely off when a log taper is used.

the old trick of putting a 33k across the outer two lugs of a 100k wah pot does not work well, sounds awful compared to the correct pot. not to mention taper is wrong , see # 2.

the 1.5 meg is not critical, in fact, the dearmond 1800, which is an improved clone of the boomerang has a 270k there ( and 100k Rs to Gd at base of each trans.)

the BIG difference is the lack of the 470k mix resistors. the 1.5 meg takes the place of one of them, but there is nothing tying the bias of Q2 to the bias of Q1 the way a crybaby works. this allows better tuning of the first stage in my experience and is part of why the boomers were consistently able (unit to unit)  to get such a wide sweep in stock form despite parts tolerances of the parts of the time. 

if you have time, my article on boomerangs is here, it has mostly general info but you may enjoy it : ( pinned aritcle at top of my Fb page )
https://www.facebook.com/WahWahByJoeGagan

[matt239]

Thanks Joe. I enjoyed your article.
I was mostly thinking in terms of modding the crybaby circuit to be more boomerang-ish.

I can certainly see how trying to use a log pot would be unsatisfactory when mounted on the other side of the shell, that's all backwards..
- The pot shouldn't affect the bias, it has those DC blocking caps..
The crybaby circuit could use an update with a few more resistors. As it stands, it IS a little tricky to get bias & gain just right, everything is interdependent.

- I just built a wah on a Tonepad crybaby board. I used 2n5088s, didn't measure the hfe, but they are probably pretty high gain.. It turned out super quiet though, very low noise. I measured the voltages & played around with the bias & gain.

I ended up with something Noomerang-ish. - No 820k to the base of Q2 though. - I chose 680k in series with the inductor. (Where the 1.5M goes, or 470k in crybaby..) 
- 1uF caps around the wah pot. .047uF input cap, 320R "gain" resistor, (Q1 emitter resistor) kept the .01 sweep cap, & 33k "Q" resistor.
I ended up liking 3.3k for the feedback, or "midrange" resistor. & I liked 47k in parallel with the wah pot.

This was a HUGE improvement for me, over the standard, modern crybaby. Mellower yet clear, lots more bass. & the sweep seems pretty usable.
I haven't played that many wahs though, & never a real boomerang; maybe I don't know what I'm missing..