Boomerang Clone Update

[Paul Marossy]

Just a couple of notes to any potential builder of the Maestro Boomerang circuit:

1. For the two 1uF caps at the output, tantalum caps seem to give it a better tone than electro types.

2. I like the yellow reissue Fasel inductor best in this circuit.

3. I originally used 2N5089s for the transistors, but I recently tried some MPSA18s in it, and they sound better, especially for clean wah sounds. The 2N5089s have just a little too much gain. It actually sounds a little more vocal with the MPSA18s in it.

4. The original circuit appears to have been true bypass, I have had no issues with uneven output levels between modes except that with the wah engaged, the signal is somewhat boosted, but I think it's acceptable.

Here's the schematic that I derived my own clone from: http://www.montagar.com/~patj/mboomer.gif

I like this wah more than any of my three CryBabys (80's US made wah, almost stock GCB-95 or my GCB-95 with the "FatWah" mod) or my Italian Vox wah with Fasel inductor. The GCB-95 FatWah sounds pretty good to me as well. I like my Italian wah, too, but it's just not as fat as the Boomerand or FatWah. All of my wahs sound pretty vocal, i'm just comparing how fat, warm and smooth they sound to my ears. YMMV.

Which brings up a question: Why would tantalum caps on the output sound better than electros? Lower ESR?

[B Tremblay]

Thanks for sharing your findings, Paul.  What did you use for the pot?

[Paul Marossy]

Right now I'm using a standard 1/2 watt Alpha pot. I want to find something heavy duty like the original ICAR, AB, etc. type pots, but all that seems to be available is 100K pots. Maybe I need to get one of those vintage 100K pots and put a 33K resistor in parallel with it to get a 25K pot out of it? BTW, I also like the taper of the Alpha pot I'm using now.  

[B Tremblay]

BTW, I also like the taper of the Alpha pot I'm using now.  

And what taper would that be?

[Paul Marossy]

Oh sorry, it's linear. Once you find the range of the pot has to be in, it works well.

[petemoore]

Harrumph !!
 I put parts on a board to try to get one of these working with my 'ol Vox Inductor.
 I've been up and down following through on trying to debug...
 I'm getting a bit of a 'Q-ish', clear tone like it 'wants to wah, but not really a wah, sounds like it's saying 'eh' to the inductor or something...
 I tried different transistors and even a different pot, measured resistances, checked grounds, color codes numerous times, nodes...
 Voltages look ok, I don't know if there are voltage readings available for this I suppose I should have written them down to compare by, I don't think that's it though.

[Paul Marossy]

I tried using some lower gain transistors in it, but it didn't work out very well. It needs somes high gain transistors to work well - the MPSA18s seem to be perfect.  

[petemoore]

It's being a tuff nut...
 Looks wired nicely except
 2x 330k seriesed for the 620k, I don't see this as much
 Pot is a 100k or with 33k on lugs 1 and 3.
 I built a Darlington from a couple 3904's, here's with it in the Q1 position.
 Battery 10.51
 Q2
C  10.44
B  8.85
E  8.39
  Q1
C 1.81
B 1.79
C  .1
 Q2 expessially looks misbiased, I don't know what Q1 'is' but there's not much room for the collector to move.

[Paul Marossy]

I'm confused... so you have a total of four transistors in the circuit? Two for your makeshift darlington transistor and two for the Boomerang circuit? Which one is giving you the trouble?

[petemoore]

I couldn't find another high gainer, so i built a 3904 darlington for Q1 or Q2.
 I took the voltages using the darlington in Q1 and NTE47 in Q2 position.
 I don't know what to look for in Q1 except the collector voltage looks to be limiting the voltage swing and gain of it's output, Q2 looks misbiased so that it can't work.
 Because I'm hearing a 'circuitized' sounding output, Q2 must be a transistor implemented to illicit the sweep sound, so as saturated would just hold the sweep at one end...I guess.
 Anyway I RE re-relooked over the board for anything like misconnects, misvalues, even measured values and just can't seem to figure out the transistor voltages.

[petemoore]

I couldn't find another high gainer, so i built a 3904 darlington for Q1 or Q2.
 I took the voltages using the darlington in Q1 and NTE47 in Q2 position.
 I don't know what to look for in Q1 except the collector voltage looks to be limiting the voltage swing and gain of it's output, Q2 looks misbiased so that it can't work.
 Because I'm hearing a 'circuitized' sounding output, Q2 must be a transistor implemented to illicit the sweep sound, so as saturated would just hold the sweep at one end...I guess.
 Anyway I RE re-relooked over the board for anything like misconnects, misvalues, even measured values and just can't seem to figure out the transistor voltages.

[petemoore]

I couldn't find another high gainer, so i built a 3904 darlington for Q1 or Q2.
 I took the voltages using the darlington in Q1 and NTE47 in Q2 position.
 I don't know what to look for in Q1 except the collector voltage looks to be limiting the voltage swing and gain of it's output, Q2 looks misbiased so that it can't work.
 Because I'm hearing a 'circuitized' sounding output, Q2 must be a transistor implemented to illicit the sweep sound, so as saturated would just hold the sweep at one end...I guess.
 Anyway I RE re-relooked over the board for anything like misconnects, misvalues, even measured values and just can't seem to figure out the transistor voltages.

[RDV]

What happens if you try a 100k wah pot?

RDV

[petemoore]

oh that's another thing I forgot about, I'm using a 100k linear [and trying sometimes a 27k trim resistor between lugs 1 and 3] for the wah sweep.
 I just can't seem to figure what's wrong with the transistor biasing...

[Paul Marossy]

What happens if you try a 100k wah pot?

Yay! Apparently we're back online again. Cool!  
Anyhow, I don't know I haven't tried it. I'm afraid that it will loose the sound it has now. I guess I could always give it a try real quick.

[Paul Marossy]

I think I finally have it sounding exactly like I want it now. It's a very vocal sounding pedal, and it really is the best wah that I personally have heard. Anyhow, I went with the 100K Hot Potz II with a 33K resistor connected to the hot/ground terminals which gives me a 25K pot. The sweep is a little different than what I had been accustomed to, but now that I'm used to it, it seems to work very well.

The other changes that I made had to do with the transistors. I went from 2N5089s, to MPSA18s, but they still had a little too much gain. So I popped some 2N3569s in there and they sound pretty good. Q1 has an Hfe of about 230 and Q2 is about 205. I used a 22K resistor on the emitter of Q2 to bias it properly, so now there is no distortion at all now when I strum the strings hard. I am not sure what my yellow Fasel measures in terms of inductance, but this is a darn good sounding wah!

Just an update in case anyone is interested. 

[Paul Marossy]

Just for the record -  I think I have finally settled on which transistors to use. BC109s seem to sound the best in my clone circuit rather then the lower gain 2N3569s, which are supposed to be closer to what was originally used, but maybe the Fasel inductor changes things a little bit. Anyhow, I think there is a little better bass response now and the noise floor is lower than the other transistors that I have tried. The BC109s that I used have an Hfe of around 400. I guess the selection of transistors in a wah circuit is not as straightforward as it appears...