After studying an old Dunlop shell compared with an original Boomerang it struck me that the pot rotation could be reversed by bolting in the bracket from a Stagg wah pot. These are sometimes sold quite inexpensively, complete with the pot and gear. The casing needs to be cut away and the bypass switch moved. A hairpin spring also needs to be bent up from spring wire (called piano wire here in England). The whole action is a lot smoother than the original Dunlop and the rotation increases by a few degrees. It more closely resembles the Boomerang mechanism.
The pot is the pedal's original - pre-HotPotz. Don't know the taper but the value is 100k. I found that adding resistors in an attempt to trim it to 25k didn't work as well as the pot on its own. I'd like to get a 25k pot to see what difference it makes. The common practice of adding supplementary resistors is flawed, as it doesn't really address what the wiper 'sees' in either direction. I tried a 33k resistor off each leg to wiper, making roughly 25k total at either end of travel, and 19k from the wiper to each end at the centre of travel. I wasn't convinced it sounded any better, just different.
Perhaps a standard 25k audio-taper pot may make a (short-lived) substitute, though many Colorsound wahs appear to use a standard pot and these last a while.
A few pics - quite large to show the detail...
http://www.avwz35.dsl.pipex.com/Wah_pot_1.JPG
http://www.avwz35.dsl.pipex.com/Wah_pot_2.JPG
http://www.avwz35.dsl.pipex.com/Wah_pot_3.JPG
OK, cool.... but what is the purpose of doing all that? Switching the two outside wires on the pot accomplishes the same thing, doesn't it?
It would, but then the pedal would work in reverse - heel down would be the treble position.
The feel, tonal sweep and pedal travel are much improved over a standard setup. Also, the plastic P clip on a Dunlop used to keep the rack in contact with the pinion limits the heel down travel. With this setup the rear rubber stop can be pared down to get more pot rotation - the rack will keep engaged down to the very last tooth.
There must be some reason why the original Boomerang uses this setup, while pretty much every other manufacturer installs the pot as per Dunlop. Perhaps the reversal optimizes the pot's curve in relation to the frequency response of the pedal circuit.
mick, are you the guy that modded that mrbillyhill's pedal? if so, nice job, that thing sounds excellent- very close to the freq response and richness of the nice originals.
either way, here we go:
modding a 100k pot down to 25k via limiting resistors does not do the correct job in a boomer circ. i found this on my own thru hundreds of experiments/measurements, but also had this independently verified by the man who designed the BG2, richard mintz ( he commented on this without any prompting from me as i was asking about other aspects of the boomer).
his exact words about the taper of the original BG2 centralab pots were " they were reverse audio taper, but slightly modified". keep in mind, in the late 60s or early 70s, if gibson, inc asked for a spec; ial pot taper, you as a mfgr would provide said taper. he later told me that the volume pedal or wah function would be compromised if a correct taper pot was not used in that circ, as the biasing and the whole circ was tuned exactly for that pot spec. he also said that the original centralabs would vary from 22k up to 28k. every vintage unit i have tested hits very near 30k with original pot.
i think the stagg might be similar to the washsburn/lyons wah unit i have here. however, it had a similar gear mech to a crybaby, so there may have been different versions. the pot in that thing looked like cheap chinese crap, i would not have trusted it for a gig, even if the the gig was only one song long. (every chinese 25mm pot i have seen made for wah is short life, including propot, the recent dunlop chinese made wahs, etc etc.)
to your Q about a standard 25k audio doing the job, if you do this, go back to the crybaby rotation, this will be more correct to the original sweep direction.
just saw the pics of your re-work. very nice. unfortunately, that pot looks like one of he ones that will last about 4 to 7 songs before going scratchy. hop i am wrong tho.
paul, no, just switching the direction of the pot by changing wiring does not do it. mick was correct in actually physically making this pot go the other way. in my experiments, the hump is totally in the wrong place if simply reversing the wiring, hence the dozens of hours making 'cam gears' to make hotpotz sound correct in these ( 33k limiting Rs included). we got close, but when zac came over and watched my foot movement and listened to the frequencies, " close" was still not as good as a real 72 boomerang we were AB'ing to. i have a vid showing this. will post it.
as a reference, hotpotz1 and hotpotz2 have a taper that looks very much like audio, but with a more pronounced dead spot on the high end ( i believe this was spec'd by thomas long ago to make the switching better, easier to adjust on multiple units with fewer warranty claims), dunlop has never changed the 70s hotpotz spec as far as my measurements of many units can find. the hotpotz2 is around 10k lower on average, but the ramp is near identical to any 72 -78 unit from thomas.
so in answer to this thread, yes, a boomerang, with opposite rotation would naturally be rev audio or rev log. mick did a good thing here.
here is the zac zagar boomerang clone. the pot is going in standard CB rotation. pot is a hotpotz1, but with a special offset gear to mimic sweep of original+ it has limiting resistors, i believe 33k.
the frequency of a boomerang is there, but the feel of the pedal is not the same. plus i believe that there is an actual parametric shelving action happening on either side of the two halves of the pot that is different from a real 25k pot. my theory has to do with the time quotient, ie; charge/discharge rate of the cap to ground off the inductor relative to the resistance of both sides of the pot at any given point in time as the player moves the pedal.
the vid does not show the comparo to a real boomerang, unfortunately, the test i referred to wa not on video.
if you listen just to the frequency curve, you can see in this well made BG clone, the same basic sweep. i have had similar experiences when brian temblay sent me soundsamples of his noomerang ( ROG gauss markov tweaked BG typ wa).
Quote from: Mick Bailey on February 20, 2012, 01:24:49 PM
It would, but then the pedal would work in reverse - heel down would be the treble position.
Duh. I should have thought of that. :icon_redface:
Quote from: joegagan on February 20, 2012, 01:29:30 PM
paul, no, just switching the direction of the pot by changing wiring does not do it. mick was correct in actually physically making this pot go the other way. in my experiments, the hump is totally in the wrong place if simply reversing the wiring.
OK, now I get it. Getting my foot out of my mouth now... :icon_confused:
Hmm... maybe I need to get out my Boomerang clone and tweak it. :icon_idea:
Joe,
Yes - I modded MrBillyHill's pedal - he borrowed mine and liked it enough to buy a pretty decent Dunlop donor pedal for me to convert.
The pot in my own is stamped on the cover 'Pro Pot 0349'. It's a little scratchy now, but has done quite a few years of gigging/rehearsals prior to my ownership and eases of after a few minute's playing. I suppose some Deoxit may help. Or a new pot.
I've only ever bought the Stagg pots for the brackets, as the track runout on the pot is extremely noisy so the full travel can't be used in either direction. They seem to be broken from new. I got caught the last time I bought some, though - I just got the pots and no brackets, so need to engineer something myself.
MrBillyHill's donor pedal had a rather nice inductor, which I momentarily coveted as I unsoldered it. A two-piece affair which can be unscrewed and re-wound. Who ever has inductor envy? Is this how it gets you? Would love to try an El-Rad or similar to further improve the pedal. I tried the green Fasel from my old 70s Jen and couldn't really detect any significant improvement. Need to find a cheap source of ferrite cores and press my old coil winder back into service and do some experiments.
As it stands, both pedals have got that classic 70s funk 'chop' sound when the pedal is quickly rocked back from the toe-down position with each chord, something I've found lacking in Vox and Dunlop pedals. Proper 'Shaft' stuff.
Just to be clear to anyone looking in at these posts - I can't claim any real innovation here - I've just applied Joe's experiments, advice and research to my own situation and based the build on Paul Marossy's excellent pedal, which is inspirational. Interestingly, I've been playing around with wah circuits for a couple of years and now have a graveyard of failed experiments/vero/PCBs which didn't do the trick. These things can take quite a while to tweak.
I've only got twenty good summers left, so need to work a little faster from now on......
makes me happy to know that some of my posting resulted in another gearhead giving the boomerang a go.
i stumbled across the vid of mrbilly's wah yesterday, posted a note , he kindly got back to me and mentioned you had looked at some of my stuff.
questions.
is the one you made him running a standard rotation pot? what value? have you compared the two?
i looked up the stagg, it is not the same as a washburn/lyons, although it may have had a bent steel rack holding the pot like the stag, when i can dig mine out i will repost here.
It is a standard rotation pot, though I didn't measure the value or notice what type it was when I built it - will measure it next time I see him. There are no compensating resistors fitted and it works very well as it is. It was intended as a temporary arrangement until I could get some of the Stagg brackets. Surprisingly, when I did an A-B test with my own pedal the sweep was so close it didn't warrant the extra work.
On the face of it, the Stagg pots are pretty well made; they have a moulded thermosetting plastic body with a moulded-in threaded bush. The contacts are epoxied over the rivets and the shaft is accurately machined, with a well-fitting pinion. The cover fits tightly to prevent ingress of dust. However, when you rotate them they sound like an old wire wound rheostat, or like it was filled with sand. I haven't taken one apart to inspect the wiper arrangement or track. I had a Shin-Ei phaser that had an identical looking pot fitted from new and it looks like the Stagg is a copy of that component.
Shame, really - these could have been a really good, cheap replacement.
I've just pulled the cover off a Stagg pot. The first thing I noticed was the impressive track width. The second was that the wiper only contacts about 1/4 of this width.
The mechanical rotation is far greater than the electrical rotation - the wiper leaves the track by quite some distance at either end of travel. Now I know why these won't operate to the full extent of mechanical rotation.
The gritty noise/feeling is the wiper scratching the track. The design may have been inspired by a cat using a litter tray. Looks like it needs some Deoxit right from new - D100?
Bit of a grainy pic attached showing the wiper having left the track and how the wiper fingers don't make the best use of the track width;
http://www.avwz35.dsl.pipex.com/Stagg.JPG
Quote from: joegagan on February 20, 2012, 09:24:48 PM
makes me happy to know that some of my posting resulted in another gearhead giving the boomerang a go.
I built three or four of them and they never knocked me out. What schematic were you using?
Quote from: candidate on February 21, 2012, 08:43:35 AM
Quote from: joegagan on February 20, 2012, 09:24:48 PM
makes me happy to know that some of my posting resulted in another gearhead giving the boomerang a go.
I built three or four of them and they never knocked me out. What schematic were you using?
You should try reversing the pot like Mick did.
You know, it just occurred to me that I could use one of several 100K reverse log pots that someone sent me about five years ago in my Boomerang clone. That way I wouldn't have to modify the Crybaby shell at all and it might have a similar feel and sound to the real Boomerang. Maybe I'll do that tonight, or Wed night. I'll let y'all know what I find...
paul, i have had much better results using an unchoked 100k in the dearmond 1800 instead of the bg. there are minor differences but they seem to make the circ more forgiving of pot value. the differences are:
2.2 uf caps off pot instead of 1 uf
820k to ground from base on Q2 for biasing ( not on BG)
270k from Q1 collecor instead of 1.5M
33k to ground at Q2 emitter instead of 8.2k.
schematic:
(http://img.photobucket.com/albums/v311/joegagan/wah/dearmondwa-wa74.jpg)
i built a modded version of this, but will have to look up my notes. gus smalley and i were brainstorming the day i did the mods. you can hear the mod version here. it is smooth and not trebly. the subbing of a 100k pot makes the top end less intense. the rich mid emphasis reminds me of a boomerang, but with less treble at toe down.
mick, thanks for that report. there are some guys in Uk selling a wah pot made in china that looks very much like that. i have also bought some chinese 500k for volume pedals that look much like that, but i have never opened them up.
Quote from: joegagan on February 21, 2012, 11:50:54 AM
paul, i have had much better results using an unchoked 100k in the dearmond 1800 instead of the bg. there are minor differences but they seem to make the circ more forgiving of pot value.
Oh yeah, the Boomerang uses a 25K pot. Geez, too much on my mind lately with all this stuff I have to do since my father passed away. :icon_confused:
Anyway, just for kicks I'll put a 100K reverse log pot in my Boomerang clone in a Crybaby shell to see what it might sound like. I'm not looking to make an exact clone of the real Boomerang, but if it gets me closer in sound and feel then I'll be happier with it. I like my BG-2s, but they are so freakin' huge that I just can't put them on my pedalboard. A Crybaby sized pedal just works much better for me.
Quote from: candidate on February 21, 2012, 08:43:35 AM
I built three or four of them and they never knocked me out. What schematic were you using?
Paul Marossy's BG2 schematic and layout, with the components removed to mod it to BG1. Transistor selection is important - doesn't seem to work very well with anything other than low-gain types. I also increased the 6uf cap as per Joe Gagan's findings - mine comes out at 7.9uf (1 + 2.2 + 4.7). Hence my little sub-board where a single cap should live.
Yeah, the lower gain transistors are better. Higher gain ones introduce noticeable distortion.
agree. Q1 sounds good at 120-150 hfe, q2 can be a little higher, but still under 200, for juiciest tone.
here is the other one mick built (mick, which one was first?)
Q2 in the boomerang is just a simple base to + resistor bias that is why that matters
Q2 in the Dearmond is biased more predictably however if the hfe is low it might have a loading tapering effect on the wha potentiometer.
Lets do some math 810K||810K= 405K
Then you have the( hfe x (the combination of 33K in || (with the 5.6K and .1uf cap in wha mode))) in || with 405K
You could work this out for the transistors you like then rework the input bias resistors or just try a high hfe for Q2 and a 680K B to +9VDC and maybe a 810K B to ground
Quote from: Gus on February 23, 2012, 07:40:57 AM
Q2 in the boomerang is just a simple base to + resistor bias that is why that matters
I remember someone once suggested to me that is part of what makes the Boomerang sound like it does, and it's because of some small amount of distortion created at Q2. Apparently that distortion grows to much larger levels with higher gain transistors. I can certainly hear it.
Anyway, the Boomerang to me has a more interesting sound than the Crybaby does. The Crybaby just seems bland and over focused to my ears. Crybabys work great in certain settings, but it sure ain't my go to wah pedal.
gus- i see where you are going with that. thanks for reminding us that we need to do the math :icon_wink:
your suggestions helped when i built an 1800 dearmond clone ( this was after modding the first one you and i worked on last summer), i found the 1800 was more tunable than a boomerang due to Q2's biasing, like you said. i had trimmers all over the place. the 33k of the 1800, as compared to the 8.2 k to ground on q2 emitter- sounded best at the stock 33K. this was with a 100K hotpotz1 with no limiting resistors. the 47k R parallel to inductor sounded best at under 25k in this config.
inductor had a an overall Mh of 700 ( put a second 100 mh inductor in series, i believe two inductors gives a richer tone, might just be superstition, ha). this required lowering the sweep cap to .0089 from .01 to compensate since the customer didn't like the low voicing of my original build. when you increase the Mh, you lower the center frequency of the sweep. this is easily remedied by lowering the sweep cap.
built in a vox shell in standard CB rotation. the weird thing was, the wah was WAY louder than bypassed signal, when i tried to lower the volume at the emitter/GD R at Q1, th tone of the wah suffered, so my final solution was to add an external input vol control in place of the input resistor (100k pot with 10k in series to ground so it wouldn't turn off when turned all the way down)
unfortunately, i did not take hfe readings of Q1 or Q2, i think i used 2n2222s or 2n3904s.
the wah quickly went to the customer in LA who has been using it on sessions and is very happy with it.
you can hear the final result here: ( first wah {left of 3} in line the one in the stock vox shell ). a good comparo to a standard stack of dimes crybaby ( far right of 3 ) in this vid.
paul, i agree. the boomer is more interesting in the mids than a vox/cb. there are two comparos that corroborate this claim. brian temblay made a comparison of his 'std' wah to a noomerang (boomerang clone from runofgroove), and the recent vid from mrbillyhill referenced above , all comparisons all show the same difference. the boomerang type has more interesting, pronounced mids.
3rd example, the comparo made in summer of 2010 filmed by zac zagar , a modded vox vs a stock 67 boomerang BG1
Quote from: joegagan on February 23, 2012, 11:48:56 AM
paul, i agree. the boomer is more interesting in the mids than a vox/cb.
Agreed! :icon_cool:
OK so tonight I put a 100K reverse log pot in my Boomerang wah clone in a Crybaby shell and changed the transistors to some metal can 2N2222s and the results are actually pretty nice. It has a very similar feel to the real Boomerang and it sweeps in a very similar way except that to my ears it sounds a little more lively than the real Boomerang does. Hmm....this pedal may go on my pedalboard now!
So I guess the OP is onto something. I never really noticed that the Crybaby and Boomerang pot mountings were opposite of eachother. There is something to that. (I know, duh!)
Quote from: joegagan on February 22, 2012, 09:27:52 PM
here is the other one mick built (mick, which one was first?)
The reversed pot one was the first. I was playing around with it before the reversal mod and decided to try it reverse operation (heel-down-treble) by reversing the pot leads. This made a big difference in sweep, but I didn't like the backwards operation of the wah. I then came across your clip showing the modified Dunlop pot action and rebuilt the pedal as per the original Boomerang.
I like the idea of a crank arrangement, though. The shape of the slot could be changed to give different sweep patterns. I'm looking for a milling machine at the moment - this would be ideal for such work.
The Colorsound wah has an interesting cam & slot arrangement which I have heard makes a linear pot act like a log pot. In any case it's kinda cool engineering.
wow, paul, that is great news. glad you found a combo you liked. did you happen to measure the hfe of those 2n2222s?
mick, thanks for the clarification. you can imagine how it felt to stumble across mrbilly's video and then later that day find out i had something to do with the wah being built. very cool feeling indeed.
because i had a large stock of hotpotz1s, i was trying very hard to come up with a way to make them work in boomers. i tried all sorts of slotted lever arrangements , based on the colorsound rack and rod idea. never could get a sweep i liked that would not have involved an extra spring to pull the lever past the midpoint due to the curve i had to put in the slotted lever. this was mostly due to the quick ramp taper of the hotpotz1, it is very hard to mechanically overcome.
the main problem i see with the colorsound arrangement is its limited travel across the pot. even 150 degrees of the pot's rotation is hard to achieve, whereas the gear of crybaby type can get more than 165 if i recall correctly.
Joe: the Hfe on those 2N2222s is about 175
cool, like that range.
Quote from: joegagan on February 24, 2012, 12:19:15 PM
cool, like that range.
Yeah in the Boomerang at least that seems to work pretty well. :icon_cool:
The following screen shot might help to understand why the transistors need to be selected for the Boomerang wha.
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=47101&g2_serialNumber=2)
Using LT spice I picked two different transistors one with lower hfe and one with higher hfe.
Note Q1 collector voltages and Q2 emitter voltages
The biasing of the first stage Q1 is a Resistor C to B, R5 1.5meg in series with (L1 || R10 47K basically the resistance of the inductor) in series with the R6 4.7K
This type of biasing is a little more stable than the output biasing of Q2 however it is sensitive to R5 and the transistor used
The biasing of Q2 is a resistor B to +9VC sensitive to R2 resistor value and transistor used
Another transistor number to try would be a 2n4401
R8/R9 is the wha potentiometer more to the bass end. This screenshot is to show more about the biasing of the transistors.
If you adjust R5 and R2 for the transistors you are changing other things. If you adjust R2 are changing the loading of the potentiometer and the collector of Q1( more at max bass).
looks great gus. this really shows how much things change simply going to a higher gain trans. this explains a lot, ppl swap trans in and out and the whole dynamic would change. one note from past xperence- if the gains of Q1 and Q2 are not within 50 or so hfe of each other ( and no R bias adjustments made ) , the wah gets boring. seems these circs like a fairly nice balance of gains on both trans. makes sense when you consider the pot is a balance act between the two.
the 2n2222 is probably close to the stock hfe of boomer transistors-they usually hit between 170 to 250.
it is very interesting how sensitive the higher gain trans are, you made r2 and r5 4X larger to get the bias similar to lower gain trans. is it the interaction between the inductor/pot that makes this so wide a swing? the swing is more extreme in Q1, i assume this is because of the parallel inductor circ ?
i don't think i have ever seen anyone suggesting that gains and biasing of Q1/Q2 can affect the taper of the pot before you brought this up.
just a reminder, the widely seen schems online have an error R2 is actually 820k, although i can see after looking at the bias voltages, the 200k difference between would not change bias much. i recall paul marossy got a better result when he removed the 620K and swapped in the correct 820K in his early boomer build.
one other thing i failed to mention as a dif between dearmond 1800 and boomer is that on Q1 for dearmond, there is a 100k bias resistor B to ground, which the boomer does not have.
besides the 620K Q2 resistor error on many boomer schems ( should be 820k, some schems show this corrrection),
there is one other error on nearly every BG2 schem i have ever seen , including fuzz central's. it relates to the vol pedal function, so many people didn't even use this part, but the 56k right after the 'vol' switch is supposed to be 5.6K.
I wouldn't put 2N5089s in the Boomerang, it would sound distorted. I intuitively tried the 2N2222s and they work really great. I'm guessing they are close to what was used originally as far as Hfe range is concerned.
i think what gus was illustrating is that by manipulating the bias, you can use higher hfe transistors, and that the boomer circuit is more adaptable than cb vox due to the independence of q1/q2 in boomers.
Paul Marossy
Quote from: Paul Marossy on February 25, 2012, 11:17:01 PM
I wouldn't put 2N5089s in the Boomerang, it would sound distorted. I intuitively tried the 2N2222s and they work really great. I'm guessing they are close to what was used originally as far as Hfe range is concerned.
If that was a reply to the screenshot. I was not posting to use 5089s. I was trying to show how the operation points of the boomerang transistors are sensitive to Hfe. In the blue notes you will see different collector and emitter voltages for the different transistors and with changed R2 and R5 values.
With stock resistor values a 2n2222 at Q1 sims at about 4.2VDC at the collector and a 2n2222 at Q2 sims at about 6.09 at the emitter with the wrong 620K value however it will sim a little lower with a 820K so both transistors are in a good range for headroom.
MAYBE with an even lower Q2 transistor Hfe 620K would work better so maybe 620K might have been used in some of the builds this is just a guess.
Note with the higher Hfe transistor 2n5089 and the stock resistor values Q1 C sims at about 2.7VDC and Q2 E about 7.6VDC.
From the sim I would think you could change Q2 with maybe a small change in sound by adjusting R2 value. Q2 is a emitter follower (EF) so it's "sound" is often more if it is biased for good input output voltage/current swing.
I am still thinking about what is going on around Q1 if you change R5 value to bias Q1. R5, C5, L1, R10 node
A 2n4401 might be fun to try at Q1
Quote from: Gus on February 26, 2012, 10:20:48 AM
If that was a reply to the screenshot. I was not posting to use 5089s. I was trying to show how the operation points of the boomerang transistors are sensitive to Hfe.
I know, I was just sayin. :icon_wink:
That is an interesting point, though.
Quote from: Gus on February 26, 2012, 10:20:48 AM
2n5089 and the stock resistor values Q1 C sims at about 2.7VDC and Q2 E about 7.6VDC.
This is bias/base voltage?
when he says C that is collector to gd.
E= emitter to gd.