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Hey guys, not sure if I'm putting this in the right place, its my first thread so please bear with me.

So I have this crazy idea of trying to build a one knob hybrid booster/overdrive, with two transistors (one JFET, one germanium), for bass. I got the idea while looking at the vero for the AMZ Mini-Booster, cause I know it's fairly clean sounding normally, but I figure I can get a little bit of grit, warmth, and color from the incorporation of a germanium. The reason I'm thinking to have a 2 stage booster is that the first stage (JFET) would drive the second (germanium), so the JFET would be a nice and relatively clean, while the germanium would add the color and warmth that I'm looking for. I was thinking that the single knob would be sort of a master volume, that can organically drive the germanium stage. But, to control the overall gain I want to add a trimmer so that I can just set it and forget it.

I have a few questions:
One, what would be a good circuit to use as a jumping off point? Second, is how can I replace a JFET with a germanium transistor. Third, would it be better to use germanium clipping diodes? If so, how? Lastly, in general what is the best way to add color to a circuit?

I've been messing around with a lot of the pedals pre-made and making my own variations for guitars with good results, but I'm trying to do more to make some that are more of my own, so I'm trying to learn as much as I can. Thanks for any help in advance guys.

Welcome! (well, congrats on your first post at least)

rocket8810 wrote:So I have this crazy idea of trying to build a one knob hybrid booster/overdrive, with two transistors (one JFET, one germanium), for bass. I got the idea while looking at the vero for the AMZ Mini-Booster, cause I know it's fairly clean sounding normally, but I figure I can get a little bit of grit, warmth, and color from the incorporation of a germanium. The reason I'm thinking to have a 2 stage booster is that the first stage (JFET) would drive the second (germanium), so the JFET would be a nice and relatively clean, while the germanium would add the color and warmth that I'm looking for.

Doesn't sound crazy at all, I'm sure others have done it before - Here is the Crimson Drive by Earthquaker -

https://www.freestompboxes.org/viewtopic.php?f=7&t=12875

Schematic:
https://www.freestompboxes.org/download/ ... p?id=12540

Here, the first JFET stage is set up as a buffer, rather than a boost, but it could easily be adapted to do that by putting in a resistor between +9v and drain. This type of jfet circuit often benefits from having a trimmer (maybe 50k) in that position to adjust the bias to get the best sound (many people suggest 4.5 v on the drain, but i'd use your ears: It's pretty obvious when it sounds best). Alternatively, you could pick any JFET boost scheme you like, AMZ, Alembic Stratoblaster, Tilman preamp, Fetzer valve, Sparkle boost etc (google these terms to see the schems) and try it out on the breadboard (if you haven't got one, it's a fiver well spent).

The second stage looks like a Dallas rangemaster with asymmetric clipping diodes on the output, or you could view it as a bit like an Electra distortion.

With germanium, like JFETs, a trimmer on the collector ("same" as drain, different name) helps tune the circuit to work best with the particular component you have in your hand, due to inconsistencies in the manufacture of these devices. You need to check whether the germanium tranny you get hold of is npn (like in the Crimson drive) or npn, which will determine "which way up" the circuit needs to be connected.

rocket8810 wrote: what would be a good circuit to use as a jumping off point? Second, is how can I replace a JFET with a germanium transistor?

As you can see, you'll probably need a separate biasing arrangement, and therefore two different "circuit blocks" depending on whether the device is JFET, or BJT - And then whether it is a pnp or npn BJT (acronymyous!)

rocket8810 wrote:Third, would it be better to use germanium clipping diodes? If so, how?

Quite possibly - Here, the Crimson Drive uses two Ge diodes to ground in one direction, and one Si diode to ground in the other direction on the end of the circuit, therefore asymetrically clipping the Ge Rangemaster-boosted signal (the JFET buffer has no boosting effect).

A single Ge boost stage will clip on it's own (i.e. without diodes) if it is slammed with a big enough signal or run at very high gain. If you have it boosted with the JFET, it can definitely clip. It might not be a very pleasant sound, but if it's for bass, and just a small amount of dirt is needed, it might be fine. You could adjust the dirt level by controlling the output of the JFET boost, or the gain of the Ge stage (e.g. with a fuzzface gain control) or control both and mix and match the two effects with trimmers. You could then have a master volume on the very end of the circuit.

Again, I'd get out the breadboard, buy a few Ge transistors and diodes and play about until it sounds good.

One note about Ge diodes - I have had a very poor experience with them in the past, not because of the sound, but because I somehow always manage to shatter the glass body when bending the leads: Maybe it's the cheap(-ish: We're still talking x10 price of Si diodes) ones i tend tio buy or my inherent clumsiness, but caution is definitely advised.

rocket8810 wrote:Lastly, in general what is the best way to add color to a circuit?

What colour are you after? I quite like purple.

Hey man, thanks a lot for the help so far. I got a lot more to look at and work with now thanks to your help. What I meant by color is that the sound of the signal is changed some how, tonal color, it's not "transparent." You mention something that I have been confused on for awhile, what makes a booster circuit different from a buffer? But, strangely enough I am planning on putting this into a purple enclosure that has been sitting in my workbench for awhile.

I found something similar to what I was thinking, but cant find any schematic to help me with my design. Wren and Cuff makes the phat phuk b for bass. I found this which he explains how the circuit works, which is similar to how I was thinking I wanted this pedal to work, and what I want it to do it.

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And I found a gut shot of the phat phuk b too.

Nocentelli wrote: somehow always manage to shatter the glass body when bending the leads

If you hold one of the diode leads with a fine pair of pliers, right up next to the body, then you can bend the lead, at the other side of your pliers, with your fingers (or another pair of pliers). The other lead can then be bent in the same manner.

By holding the lead in the pliers, you take the bending strain away from the glass body, so you should have no more damaged diodes.

Thanks for the help so far guys, but I have a few questions still since I've started on this project. I've been messing around with a few circuits and think I've gotten the second Ge stage ready, but I'm not sure where to begin for the first stage. I've been looking at some JFET boosters that are know for being "clean," like the SHO, Lovepedal Delux Sixty, or possibly modifying the Escobedo Duende JFET, but I'm not yet sure how to remove the volume pot and add an input cap. I really want to go JFET as from what I've read they were made to emulate some of the characteristics of tubes. If I understand correctly J201's are similar in sounds to triodes, and bs170's are similar in sound to pentodes, but not sure which way to go. The problem is I want the first stage to add clarity to notes and a tube-like warmth, so it can open up the sound like a "tone enhancer" to thicken and sweeten the sound. Kinda hard to explain what I'm hearing in my head, lol. Any suggestions?

rocket8810 wrote:I really want to go JFET as from what I've read they were made to emulate some of the characteristics of tubes.

OK, let's get a few things straight Transistors were not invented so guitarists can argue about the way they sound. FETs and valves are somewhat similar in the sense that they are (usually) depletion-mode devices.

If I understand correctly J201's are similar in sounds to triodes, and bs170's are similar in sound to pentodes

No. It would help you in the long run to rid yourself of ideas like "X sounds like this and that". The particular way the active devices are used can be at least as important as their intrinsic properties. E.g. under some specific circumstances, a JFET could be coaxed into behaving (i.e. having a similar transfer function) like a triode. If that entails that it will "sound" like a triode amplifier of sorts or if such circumstances are necessary to make it "sound" in such ways is a different discussion altogether.

Kinda hard to explain what I'm hearing in my head

That's the chief obstacle and not easy to overcome. Some may appoach it by building a lot of effects and endlessly tinkering with them, so as to draw some conclusions about what does what. Such conclusions can be fallacious and benefit from as much experience as possible. Some may approach it by a thorough investigation of the underlying principles, followed by fairly involved math and simulation before actually building anything. Most do a bit of both, which is probably the best way to go. But any way you take it, it's gonna take time to become any good at it.

Now for your particular project: the easy way would probably be to look for a commercial pedal or DIY project that already does what you want (as you did) and build one of those. Tweak to taste.
If you've become convinced by the Wren and Cuff effect you found and it has't been already traced, try to get a hold of one or get someone else who owns one to take some clear pictures of both sides of the board and read/measure the pots' values. Then employ the power of this community, as you'll most likely find that you are not the only one interested in this effect.

Thanks FiveseveN. It's hard to get out of that mindset of "x sounds like....." when there is so many discussions, arguments, and ultimately how people try to describe the sound. I'm going at this one step at a time, carefully learning as much as I can, tinkering, and tweeking to get what I'm after. It's funny that no musicians don't understand how hard it is to explain what we may hear, or the sound we may be after, like we're all crazy. That Wren and Cuff pedal is so close to the sound I'm after, but there is no trace of it, so I figure with a couple builds under my belt I'm diving head first to try and create it.

How is this project coming along?

It's been coming a long. I have a layout that is basically a JFET booster into a rangemaster. I had to build it and box it cause it was so noisey when I was breadboarding it. It works, but I'm still tweaking it and playing around with it all. I like it so far, but it's not where I want it to be. It's had to be on the back burner for a bit, once summer starts I'm going to get back on it and hopefully get it where I want it to be.