Jimi Hendrix' Gear and Mods at West Coast Organ and Amp

[daveweyer]

The labels may be slightly different than what I used, but it seems like you have most everything right. The input control is just a resistor at the input, between your guitar and the base of the first transistor. It has a lot of different and subtle effects, and works by changing the input impedance of the device as seen from the guitar. I believe the old Fulltone had a resistor there, and the modded Dunlop too. It started as a means to keep the wah from shorting out the feedback of the first transistor and causing a lot of squealing, but became a part of the tone shaping as we found out how it interacted with everything.

The second gain control adjusts the AC gain of the second transistor, a gain control within the feedback loop; as such it doesn't really control the overall gain of the circuit like the fuzz control does, but it adds internal gain and ends up controlling the quality of the distortion. In the old fuzzface, this was the fuzz control, adjusting the capacitor across the emitter of the second transistor.

There was also a DC bias control, but I don't know if Tek added that to your unit. It controls the operating point of the first transistor, and subsequently the operating points of the others as well. There is substantial harmonic difference between the two cutoff points of Q1; at one extreme there is a lot of second harmonic activity, at the other, mostly odd harmonics.

All the controls can be used to get sounds, and that is exactly why they were added; it should be a tweaker's paradise. I did make a recording of myself twisting the controls with a sustaining Strat, just to demonstrate the differences, but I imagine you have found many of the usable sounds already.

I found that a fuzz setting of 1 or 2 was plenty, and that practically anything could be gotten by adjusting the output gain into the amp, and the input control. I even recorded a bit of SSB with the settings like that, just to see if I could get sufficient sustain--more than plenty by overdriving the Marshall.

If you are going to change the 30K feedback resistor, keep in mind that lowering it may cause the unit to oscillate, I think that value was the minimum it would safely tolerate. Should be no problem going the other way.

[Tek465b]

There was also a DC bias control, but I don't know if Tek added that to your unit. It controls the operating point of the first transistor, and subsequently the operating points of the others as well. There is substantial harmonic difference between the two cutoff points of Q1; at one extreme there is a lot of second harmonic activity, at the other, mostly odd harmonics.

Yes its the 100k trimmer on the PCB .

[shakti]

Cool, thanks for your replies! I'll play with the PCB trimmer as well.

I think this fuzz has considerable commercial potential, to tell the truth. As I said, it sounds like a fuzzface, only an extremely good and hot-rodded one. It has the gain (even more so!) than a silicon fuzzface, with the warmth of a germanium, and none of the typical shortcomings. With a little bit of tweaking, I think this could be a fuzzface killer, and with a Hendrix connection to boot.

Have you patented the circuit, Dave?

[daveweyer]

No patent, just obscurity. Probably any of the fuzz guys could have come up with something like this, but didn't probably because it was such an unlikely circuit. As a general linear circuit, it's pretty bad, poor temperature stability and so on. I think I mentioned I got the idea from an old Navy AC voltmeter made by the Daven company; it was a tube circuit, but the arrangement worked just as well for transistors. I just used the same concept, i.e. two gain stages and a phase splitter for the third stage, except I took the feedback from the inverting side of Q3 (the terminal with gain, the collector) and the output from the non-inverting side (the emitter), just the opposite of the way the AC voltmeter was wired. This allowed Q2 to have variable gain within the feedback loop, and a lot of AC feedback signal for Q1's base, plus it allowed for the operating point of Q1 to be adjustable for getting lots of tone colors, among other things. You can see why Jimi liked this box.
Maybe Joe Gagan will copy the circuit and produce it like he did my Jimi wah design. He calls it the "Controversial Woodstock Wah".
Or, maybe Tek would like to produce the pedal on a larger scale. I do know it has a lot of ways to tweak the sound, something I should think guitar players would love.

[Tek465b]

It do what it does very well(sounding incredibly good), i think that was the goal
I love all the tweakability it has.

Yes i can produce the pedal on a larger scale if needed.
All the 8-9 pcbs are sold out, but nobody else asked for boards so i did not order more.

I can increase my stock(get more boards/component) make a revised PCB and keep a few assembled unit. if the demand arise i can have them commercially made(or home made on a larger scale, whichever people want).(if Dave is ok with that of course.)

Am curious too about the legal side.
Do you know that people cannot use/copy/modify/distribute your publied work even if there is no liscence(you need to grant them/us the permission).

Here's an interesting/short read:
https://choosealicense.com/no-permission/

[antosimoni]

please post clips!!

[Xplorer]

Damn !! So much reading i missed once again !
Wow, judging from what Shakti said, it's a very exciting fuzz ! And i'm jealous of you guys, although i too have received the pcb and some components to make mine, but time is it short supply on my side. i'll try to build it earlier though.
If Shakti says this ... mama !! lol, i must build this very soon !!!

Thanks again a ton Dave and Mathieu, in advance, and i'll reply as soon as i build mine, with some clips too.

i'd like to use it with the west coast amp, and i think i'll mod one of my wahs to jimi's specs. Also, modding one echoplex to Tom scholz's fantastic effect. with one pedal rotating horizontaly and verticaly he could control the tape echo delay time, and the feedback. that's how he got these really interesting effects while playing in his Boston albums. the guy was in mit and i love this simple principle for this mod. endless notes, space effects .. Imagine what it could do with jimi's effects and amp from Dave !

[bobtec]

I bought a I bought a 63 bandmaster from the Hollywood Bowl in 1971 when they were remodeling it West Coast worked on it it has three plate resistors on each preamp two 100 and a 220 it's a great sounding amp

[Xplorer]

I bought a I bought a 63 bandmaster from the Hollywood Bowl in 1971 when they were remodeling it West Coast worked on it it has three plate resistors on each preamp two 100 and a 220 it's a great sounding amp

Oh nice ! That would be great to see it if you're ok with it.

[Tek465b]

Ok, so order placed for 40 more boards :O.
New board rev changes are

• BLACK solder mask
• milled top corners
• PCB mounted pots and wild switch(you can use a on-on OR on-off-on switch to disconnect the FB, you can also omit the wild switch and place a wire jumper instead)
• moved test point to the top layer
• removed the pad for the always on bypass switch(can be hardwire into the pcb if needed)
• Added pad to parallel 1u/820n input cap for 1.8u
• everything else is the same

[shakti]

Just a few more observations;

- the "always on" feature can actually be very useful. However, there is one thing that prevents it from working well in its current setup; in off mode, only the In and Volume controls are working. I prefer to set the In (input impedance) control just raised a notch or two to allow wahs to work properly and to not have the Off mode sound very muffled. But the problem is that to get it even to unity level the volume has to be set very high, and this adds a lot of hiss.
HOWEVER, if I then switch it to ON mode, the gain control comes into play. With gain on 0, it is essentially the same as the OFF sound. But raising the gain control just a little bit adds more gain and beef to the sound, to where it starts to sound like that "mysterious boost" Dave talked about. So IMHO, for the "always on" feature to be really useful, the gain control would have to be part of it, at least at a low level.

Then enter the "wild" switch, where the gain control enters the next level, so to speak. If this fuzz could have two footswitches, it could be the ultimate killer fuzz;

- one footswitch for true bypass on/off
- one footswitch to switch between low level gain and "wild mode" gain.

This should be easy enough to achieve, shouldn't it?
Another option would be to have a toggle for true bypass or "always on", with the footswitch always going to wild mode.

[Tek465b]

I agree with you, this is exactly what i am thinking.

1. If you wire for true bypass you probably want to do it like the drawing below(or add a 1Meg to the input)
2. You can run the wires(and 1Meg resistor) from the wild mode toggle switch to the stomp switch.
last option. You can move the always-on switch wire to the now unused toggle switch.

That was easy(except the drawing part lol)

[shakti]

Will have to study my own unit to see if I get how to wire this.

I tend to prefer simple and non-crowded units, so I think a single footswitch is the best option for me, plus a toggle to select either true bypass or "always on".
I might even prefer the In control as an internal trimpot as I just tend to set and forget it. The fuzz control is rather subtle and could also even be set up as an internal control, leaving just Gain and Volume on the front like a classic fuzzface.

[daveweyer]

I hope I don't confuse the issue here, but the On mode is the same as the OFF mode except for the little resistance the 1 (or 2meg) meg pot has at the end of its travel, and the 100pf cap which bypasses that resistance; in other words there is not quite as much feedback to the base of Q1 when the unit is set to ON, so it has a little tiny bit of gain more than when in the OFF mode. Otherwise it is the same thing, only the OFF mode shorts out the fuzz pot completely--so it obviously has no effect at that point.
Maybe the OFF mode should have a small resistor in the feedback loop so the gain is not driven below unity. One thing I did not do on the circuit was provide a balance circuit so that when the unit is switched to ON, it attenuates the output signal so that there is no difference in level between the ON and OFF positions. In many ways, the OFF control is irrelevant, because you can do almost the same thing by turning down the fuzz control.
By the way, the Q2 gain control always works, even though the tone change is rather subtle when the unit is in OFF mode or minimum ON fuzz gain. Same goes for the Q1 operating range control, there are subtle tonal differences in the OFF or minimum fuzz gain ON modes.
That mysterious boost that Jimi obviously used on some recordings was probably provided by a unity gain, or unity gain plus a small percentage setting--it just fattened up the guitar signal enough to spank the Marshall a bit.
A commercial unit probably ought to have a network to balance the output signal with the various settings of fuzz gain and output level to keep them even under any circumstances of switching.

[Tek465b]

Maybe the OFF mode should have a small resistor in the feedback loop so the gain is not driven below unity. One thing I did not do on the circuit was provide a balance circuit...

I covered this but i think it went unnoticed.

To fine-tune the bypass/off mode.
Try adding a resistor in serie with any one of the wire that run to the bypass switch(something around 68k-100k or more if needed), or have a potentiometer/trimmer instead, so you can fine tune the bypass/off sound. Or you can also change the 30k on the board to a higher value.