Tone Bender- diy?

[John_H]

I've got 6 pcb's for tonebenders on my bench right now. Word to the wise, fuzzcentral has a lot of mistakes on the website, don't trust any of the schematics. Also, few others things. Are you testing the transistors for gain and leakage? You need a certain amount of leakage for these to work properly. You also don't need the perfect gains and especially in the order of 70,70, 100 that everybody says you need. Most Russian transistors of the pnp variety, will have about 0 leakage, they often will not work at all, older date coded ones will have leakage. I have close to 2000 russians here and are not from eBay.

Thanks for your reply. I really appreciate the input. I built a rig to measure leakage like the one that R.G. detailed in his article about selecting transistors for FF clones at geofex.com

I bought 2 'sets' of AC125's from an online dealer. They were all marked with the gain, and leakage. I'll socket mount every transistor. There are plenty of PCBs available, but I thought it would be fun to DIY like the thread title says.

For all advice, search on diystompboxes and look for posts by LucifersTrip, aron, Electric Warrior and about 10 others, they have built and troubleshooted a lot of these. Electric Warrior has posted the voltages from a original good sounding unit, so you want to be near that ballpark. Also, don't do the bias pot thing on the 8.2k resistor on Q3, leave that alone and if you have to tweak the bias, use the collector of Q2, which may be 47k or 100k depending on which trannys you use. Also the base resistor on Q1 sometimes is 100k , other times 10k.

Thanks! This is the kind of information that I need. I'll check it out over there. I wasn't very familiar with tonebenders a few weeks ago, but I've picked up some. This is all fun for me. There's no better way to learn than to build a couple of them. I know that they are idiosyncratic, so this will help I'm sure.

My first board right now is going into a open enclosure, transistor sockets, 100 ohm resistor on the 1k fuzz pot(to stop the wide open oscillation these are known to do), switch for 100k/10k on Q1base, switch for 100k/47k Q2collector, and test points so i can meter Q2c and Q3c voltages. I have it working beautiful with totally stock resistor values, just by swapping out transistors of the proper leakage and secondly, gain.

Nice! I'm just a rookie at this, but I'm learning, and having fun along the way. I'll be able to change transistors easily. I had no doubt that would be important. Your switching should allow for a few variations in tone. Very cool.

[mozz]

These are really nice to have.
https://www.newark.com/peak/dca55/co...tor/dp/95K9102.

How much leakage do these "sets" have? You need about 150-200ua for this to work correctly. One source for pnp germaniums is old portable transistor radios or walkie talkies, the ones which said "6 transistor", "13 transistor" often cheap parts which work great.

[John_H]

These are really nice to have.
https://www.newark.com/peak/dca55/co...tor/dp/95K9102.

How much leakage do these "sets" have? You need about 150-200ua for this to work correctly. One source for pnp germaniums is old portable transistor radios or walkie talkies, the ones which said "6 transistor", "13 transistor" often cheap parts which work great.

Thanks for the reply. I ordered this transistor testing gizmo. https://www.gearbest.com/other-instr...ml?wid=1433363. Things take a while to arrive from this distributor, but it could be pretty handy.

The AC125's that I have all read between 170 - 230ua leakage.

I've been keeping my eye out for old pocket radios. I'll be at a flea market tomorrow morning. Maybe I'll find something.

[mozz]

Watch the rabbit hole. Last time i was building something i sunk $600 into a tele, but at least it's made of good parts.

Just picked up 3 "solid state" intercoms today at the flea market, sft323, sft325, 2n404, 2sb33 and some other germanium transistors, all useable. One even had tropical fish caps(used in classic wahs and other stuff). Sometimes you find the old small output transformers, they are often good for building a octavia pedal. Finding certain old transistors can sometimes be harder than finding some certain tubes.

Edit: If you go searching the web for tonebender tranny gains and leakages, 50% of the builders use the RG tester and the other half use the Peak DCA55, readings are similar but not the same due to test voltages and currents. I was gonna order one of those chinese testers for under $20(ebay) just to see how the readings compare. One thing i did notice was checking germanium diodes for voltage drop, 2 of my radio shack bench meters, fluke handheld, and the DCA55 all gave me different voltage drop readings.

[nickb]

Thanks for your reply. I really appreciate the input. I built a rig to measure leakage like the one that R.G. detailed in his article about selecting transistors for FF clones at geofex.com

I bought 2 'sets' of AC125's from an online dealer. They were all marked with the gain, and leakage. I'll socket mount every transistor. There are plenty of PCBs available, but I thought it would be fun to DIY like the thread title says.

Thanks! This is the kind of information that I need. I'll check it out over there. I wasn't very familiar with tonebenders a few weeks ago, but I've picked up some. This is all fun for me. There's no better way to learn than to build a couple of them. I know that they are idiosyncratic, so this will help I'm sure.
Nice! I'm just a rookie at this, but I'm learning, and having fun along the way. I'll be able to change transistors easily. I had no doubt that would be important. Your switching should allow for a few variations in tone. Very cool.

[ATTACH=CONFIG]52328[/ATTACH]

Sounds like you are having fun with this. Seems like after the Wah you might be getting into pedals?

Just, by the by, I happen to have a Vox Tonebender MkIII here right how. One of these (pic grabbed off Reverb com). They are asking amazing prices. The owner had no idea of the potential value.



Here's (poor) picture of the PCB All unmarked germanium and all original.



Schematic is here http://fuzzcentral.ssguitar.com/3knob.php

[John_H]

Watch the rabbit hole. Last time i was building something i sunk $600 into a tele, but at least it's made of good parts.

Just picked up 3 "solid state" intercoms today at the flea market, sft323, sft325, 2n404, 2sb33 and some other germanium transistors, all useable. One even had tropical fish caps(used in classic wahs and other stuff). Sometimes you find the old small output transformers, they are often good for building a octavia pedal. Finding certain old transistors can sometimes be harder than finding some certain tubes.

I know how easy it is to spend money once you get started. I bet that's a sweet tele. I always try to keep the projects inexpensive, but it doesn't always work out that way.
I'll keep my eye out for any electronics from the period tomorrow. You never know what you'll come across. Thanks for the subtle advice.

Sounds like you are having fun with this. Seems like after the Wah you might be getting into pedals?

Just, by the by, I happen to have a Vox Tonebender MkIII here right how. One of these (pic grabbed off Reverb com). They are asking amazing prices. The owner had no idea of the potential value...

This is fun. I've been buying kits, and PCBs for a couple of years now. The wah was a fun project. I like the whole idea of starting from scratch. So yes, after the wah I decided to change my aproach a little.
The history behind some of these pedals is really interesting. The prices are driven up by crazy collectors. Replica pedals demand high prices also. I know that this is an old road that many have been down, and I don't expect to get amazing, and immediate results, but I'm enjoying the process.

Thanks for the pictures, and schematic. I've been saving stuff like that.

[John_H]

There's some progress here. I made the little eyelet board, and mounted the passive components. I put the sockets for the transistors on pigtails.

[mozz]

Those header pins work for a transistor socket, but they are not really a socket. Try and find some cheaply priced transistors sockets, they don't exist. I have used those before but once i find the trannys i want in q1,q2,q3, and my voltages are correct, i solder the transistor to the header. Watch out, they melt fairly easy.

Did you use 2 pins for a bias pot on Q2?

[John_H]

Those header pins work for a transistor socket, but they are not really a socket. Try and find some cheaply priced transistors sockets, they don't exist. I have used those before but once i find the trannys i want in q1,q2,q3, and my voltages are correct, i solder the transistor to the header. Watch out, they melt fairly easy.

Did you use 2 pins for a bias pot on Q2?

You're right about the transistor sockets. I wish there were better options available. I've got some header pins that snap together well, so I was planning to mount connectors to the transistors also.

They do melt easy. I use 63/37, so that helps a little.

There's no bias pot on this one, and I'll use the 8K2 for now. I can always change it to a trim pot later if I feel the need. It'll be pretty easy to swap any component. Here's the schematic that I'm using.

[mozz]

As i said, beware of any schematic or info from fuzzcentral, there are many mistakes, some have tried to contact them to have them corrected but to no avail.

It has been said to use a 100k pot on q2 for bias adjust and leave the 8.2k stock. These don't seem to clean up with your guitar volume control as well as a fuzzface does, but that's how it is.

Been working on a FZ1 Maestro fuzz clone and trying to get that sorted out, my 5 tonebenders are mostly populated and waiting a few resistors from Mouser. I'm having better luck using older American germanium transistors than any japanese or russian trannys at the moment. You need a certain amount of leakage for certain Q positions. I measured trannys with the same gain and same leakage and they would sound different, so it's really a matter of swapping them around the sockets until you find what you like.

You may have to up the 470 ohm to maybe 1k if you need more than unity volume. Also just found out the 0.1uf caps i used (ceramic)are microphonic and were really loud when tapped with a pencil, i swapped them out for film caps and got much better.

[Helmholtz]

You need a certain amount of leakage for certain Q positions.

Just an idea:
If some leakage is necessary for optimal sound, I understand that for given DC gain the leakage changes the operating conditions (circuit voltages) to better clipping characteristics.
The same effect can be achieved by wiring a suitable resistor (or trimmer pot) of say 100k to 220k between collector and emitter of a low leakage transistor. This way the best operating condition/sound can be dialed in for a given transistor. Also sound will depend less on ambient temperature compared to a higher leakage transistor.
And you can use lower leakage transistors as well.

Of course the trimmer could also be added and adjusted when testing transistors for beta and leakage.

[mozz]

Was under the impression that collector to base leakage was needed. Some fuzz designs will not hardly pass signal with low or no leakage transistors. I have a 3meg pot to use for this test later today. The FZ1 (anyway) needs 150ua_200ua before it starts to work. The FZ1 actually has the 470k shown in the fz1a schematic. Many people build it without and have a hard time getting it to work.

[Helmholtz]

Was under the impression that collector to base leakage was needed. Some fuzz designs will not hardly pass signal with low or no leakage transistors. I have a 3meg pot to use for this test later today. The FZ1 (anyway) needs 150ua_200ua before it starts to work. The FZ1 actually has the 470k shown in the fz1a schematic. Many people build it without and have a hard time getting it to work.

You're right, looking at the FZ schematic the transistors would run at zero idle current without some base (leakage) current. Base current influences gain and clipping symmetry. I wasn't aware of the missing base bias. So it seems a better idea to emulate collector-base leakage by a trimmer in the M-Ohm range wired between collector and base and adjust for appropriate collector leakage current in the tester or circuit.

The principle is the same: Emulating leakage by external bypass resistance and thus reducing temperature dependancy.

[John_H]

Thank you both for the help on this. It wouldn't be hard to add a trim pot. I primarily want to get a decent baseline design to start out with. I knew that there could be problems, but figured that I could design a layout with what I had.
Mozz, do you have a schematic that you prefer?

[mozz]

Basically just using the one you posted above, except instead of (2ea)5uf, i am using (2ea) 10uf (like the marshall supa version). I had no 4.7uf or 5uf on hand. Also changed the 470 ohm to 1k ohm to get more volume. Removed the input 0.01uf as some models didn't have that. Q2 collector i have a pot 100k but will sub in the resistor once i figure what works best. Anything i changed i have not A-B tested yet so it's still all up in the air.

Finally put the FZ1 clone back on the shelf to try and finish up the tonebenders first. I bought the pcb's for these and they have the charge pump so still even tweaking the caps near that to lower noise.