Tone Bender building for dummies?

[Wonks]

Well there were certainly 5 full revisions of the Tone Bender design, Mks 1, 1.5, 2, 3 and 4 (Mk 1.5 is an unofficial name but it is a definite design variant). The Mk 4 is basically a Mk 3 in a different case but there were some later resistor and cap value changes.

And some of those deigns will have been modified to work with the specified circuit diagram transistors rather than the originals used. But yes, there are always likely to have been some 'close enough' substitutions made if parts ran out.

And some of the 'rebranded' Tone Benders such as the Marshall Supa Fuzz had 'near identical' circuits to existing Tone Benders, so probably the same layout with a few small component changes for a very slightly different variation in sound.

It was in the 70s that you started to get variations of the circuit design using different transistors, presumably as more reliable transistors came out and the original types became scarce. the support circuitry presumably had to change slightly as well.

And the Supa Tone Bender I had (introduced in 1973) was in fact a Rams Head Big Muff copy less a few decoupling components (I never knew that until now).

And the Sola Sound Fuzz was V3 Big Muff circuit!

So you can't blame the Chinese for starting the pedal cloning business!

[SecretSam]

Yes, if they'd made a generic Tone Bender Mk 2 design, with each one sounding a bit different, then $350 would have been far too much money, but it 's not a generic design, it's a very specific design, and one that did involve a lot of R&D.

Hm. Willing buyers, willing seller. Fair enough.

[SecretSam]

Right. Next stupid question:

Would it be a good idea to put a bias control on each transistor, not just one? So two bias knobs.

(Current thinking on labelling:

Volume= attention-seeking
Fuzz= fibrillation
Bias 1 = judgement
Bias 2 = prejudice

Now I have the wording sorted out, that just leaves the soldering. And the layout. And the component values.)

[Folderol]

Right. Next stupid question:

Would it be a good idea to put a bias control on each transistor, not just one? So two bias knobs.

(Current thinking on labelling:

Volume= attention-seeking
Fuzz= fibrillation
Bias 1 = judgement
Bias 2 = prejudice

Now I have the wording sorted out, that just leaves the soldering. And the layout. And the component values.)

Doubtful, most of the others are just emitter follower buffer stages - but which design are you going for? They are all somewhat different

[SecretSam]

I thought the Fritzing one. Because it has the optional mods of the one before it, plus a bias knob.

I have no idea really how else to choose.

Oh, and the printing is nice and clear.

It seems to use TRS sockets, which I don't really understand ....

[Wonks]

Bias pots are almost always set and forget items. You wouldn't want to have them easily accessible for twiddling. E.g. you don't have a big bias adjustment knob on the front of a valve amp, if there is one, it's hidden away.

You'd adjust the bias to achieve a certain output for a certain input for each transistor and there's a very small range of resistance either side of that setting that would be workable. You'd need to build the circuit, find out what the resistance value was and then replace yoiu variable resistor with a fixed resistor at a value at the lower end of that range, and have it in series with a pot that had a value that spanned the extra adjustable range e.g. if the useful bias resistance range was 4.75k to 4.85k, then a 4.7k resistor and a 100 ohm pot in series would work. I have no idea what values you'd need, that's just to try and show the principle.

It could be done. but you'd have to fully understand the circuit by building it first to find out what non-optimal bias settings did to the sound.

[Martin Walker]

Bias pots are almost always set and forget items. You wouldn't want to have them easily accessible for twiddling.

Agreed - a multimeter is recommended for setting up the optimum bias in many stompbox circuits where transistor gains vary from unit to unit. It's possible to adjust bias to what your ears prefer, but without a multimeter to check several voltages the chances are that the circuit won't be sounding as originally intended.

Martin

[Martin Walker]

I have in mind to look for an oversized casing in a junk shop, and add spurious controls labelled with words that might just be technical, such as 'mingle', 'fibulate' and 'squirt'.

That approach really appeals to the steampunker in me, but don't underestimate current price points! I'm often amazed at how much the average 'junk shop' (aka antique/curio emporium) is asking for battered old casings.

Also, a grounded metal enclosure makes more sense, as fuzz boxes tend to involve high gain amplification, and are therefor more prone to picking up stray hums.

Martin

[SecretSam]

Bias pots are almost always set and forget items. You wouldn't want to have them easily accessible for twiddling. E.g. you don't have a big bias adjustment knob on the front of a valve amp, if there is one, it's hidden away.

You'd adjust the bias to achieve a certain output for a certain input for each transistor and there's a very small range of resistance either side of that setting that would be workable. You'd need to build the circuit, find out what the resistance value was and then replace yoiu variable resistor with a fixed resistor at a value at the lower end of that range, and have it in series with a pot that had a value that spanned the extra adjustable range e.g. if the useful bias resistance range was 4.75k to 4.85k, then a 4.7k resistor and a 100 ohm pot in series would work. I have no idea what values you'd need, that's just to try and show the principle.

It could be done. but you'd have to fully understand the circuit by building it first to find out what non-optimal bias settings did to the sound.

That sounds like a depressing amount of work. What about just including one of those tiny knobs that you adjust with a screwdriver and leave hidden inside the case? Just fiddle until it sounds right, then leave it alone.

You do see fuzzes with bias controls. But they are built by proper electronic geezers I expect.

[SecretSam]

I have in mind to look for an oversized casing in a junk shop, and add spurious controls labelled with words that might just be technical, such as 'mingle', 'fibulate' and 'squirt'.

That approach really appeals to the steampunker in me, but don't underestimate current price points! I'm often amazed at how much the average 'junk shop' (aka antique/curio emporium) is asking for battered old casings.

Also, a grounded metal enclosure makes more sense, as fuzz boxes tend to involve high gain amplification, and are therefor more prone to picking up stray hums.

Martin

I fondly imagined that a metal box works like a Faraday cage. What is this grounding of which you speak?

There are still a few charity shops around here where people drop off junk like old clocks and radios and pans and stuff. If all else fails, maybe a small metal cashbox - which would handily hinge open for changing the battery.

[Wonks]

Yes, certainly include a trim pot for that purpose.

You’ll probably find that those fuzzes with bias pots have been through a similar process to that I described. It’s not that hard to do. Just set the circuit up on breadboard so it’s easy to change components, work out what the useful adjustable range is and pick a resistor and pot as appropriate. It obviously helps to have a good range of basic components like resistors and caps to hand. Other bits you can order as required.

On the box thing, you were talking about cases, and without being more specific, a lot of those in junk shops will be wooden. If you only meant metal cases , then that’s fine.

[Folderol]

I made an interesting discovery today. Farnell still sell 1N270 germanium diodes, and seem to have a large stock of them. With all this talk about fuzz, I was reminded of my (ancient) idea for an asymmetric fuzz effect
However...
Farnell's minimum order value for free delivery has shot up to £40, otherwise delivery charge is £10 (used to be about £3)

[Wonks]

Have they switched to courier-only after the Royal Mail was so unreliable during the winter months?

[SecretSam]

Put another way, forty quid's worth of diodes could set you up with a profitable side-hustle building boot-eek pedals.

[Folderol]

Put another way, forty quid's worth of diodes could set you up with a profitable side-hustle building boot-eek pedals.

That's only 20 diodes actually Besides, In view of how few Yoshimi Pi's are out there (YP003 still not sold) I'm not keen to risk limited resources.

[Folderol]

Have they switched to courier-only after the Royal Mail was so unreliable during the winter months?

I think you'll find it's RS that use Royal Mail. With Farnell, round here it's always been the shittiest of the lot - Hermes.
Last December a next-day order I made, arrived 2 days late, and was delivered to a shop nearly a mile away - the driver claiming that nobody was in. This was a lie of course, and even so, within sight of my front door is a shop that is well known for accepting deliveries from all agencies. The one the driver used coincidentally happened to be on an easy route in and out of Medway.

[SecretSam]

First world problems...

The last shipment I got from musicstore.de took eight days to reach Johannesburg, then three months to make it to Cape Town while SA Customs decided whether to tax it, steal it, or ignore it altogether by claiming they can only process one parcel a day due to covid.

[ef37a]

Hi Sam, I would like to add some further ideas to those of Will et al.

When have soldered up your veroboard go over it with a lens and look for blobs and 'spikes' that could cause shorts. Happens to the best of us!

If all ok hook a testmeter on Ohms (not 'diode') to one supply rail and test each leg of each transistor, the while looking at the schematic. You are checking to see if the resistances you read make sense from the circuit.

If all seems to make sense, use a part buggered battery as Will suggests.

Dave.

[ManFromGlass]

Never heard of the Tone Bender so I went to Reverb.com
An original Vox model is over $3200 Cdn.
A Sola Mark III is only $900.
Both in the UK.
Whoa
Oh yes, the vendors will take offers!

[merlyn]

It seems to use TRS sockets, which I don't really understand ....

You're talking about this circuit :



The TRS at the input is acting as a switch -- when you plug a lead in it connects the battery. The TRS on the output is completely pointless. Worth noting that this circuit has a positive ground to accommodate the PNP transistors.

Talking of switches -- there isn't a stomp switch in this circuit. For simplicity you could put in a true bypass switch although that will annoy ef37a

Fritzing looks like a cool idea :

https://fritzing.org/

There is free, open source software available to download. I haven't tried it but I would imagine you can simulate circuits with it. You can see the signal going from completely mangled to utterly mangled.

It looks as though someone has used Fritzing to come up with their own spin of the Tonebender circuit. I can't imagine the bias control will do anything audible as the signal will be so eh ... mangled by that point.

[ef37a]

"true bypass switch although that will annoy ef37a "

Normally yes Merlyn but this is such cockeyed, iconic design 'mess that seems to work' that buffers would I am sure spoil whatever it is folks like about it!

Dave.

[Wonks]

Because of the +ve ground of that circuit, you'd need a fully isolated PSU output to supply it if you added a PSU connection, or replaced the battery completely with a PSU input. So a make that's known to have properly isolated outputs, not a cheap PSU that just claims to have isolated outputs.

The battery +ve is connected to the normal ground connection of the guitar connection. A battery voltage is fully floating until you reference it to something in the circuit, so whilst it still outputs 9v, the +ve side is at the system 0v/ground reference and the -ve side of the battery is at -9v with respect to the signal ground. So it's different from the normal +ve =+9v, -ve =0v that you normally get in a pedal.

A fully-isolated PSU's output voltage will also 'float' like a battery can, but if you try using the circuit with a non-isolated PSU, it will short out.

Just make sure the -ve side of the battery doesn't come into contact with the ground or enclosure casing, as it's normally the +ve side you worry about.

Current draw on a circuit like this is very low though, so you won't have to change a battery very often, so probably safest to keep it battery only. With a largish enclosure, you could even mount a battery draw on the top if you wanted to permanently install it on a pedalboard.

[Hugh Robjohns]

It seems to use TRS sockets, which I don't really understand ....

You're talking about this circuit :



The TRS at the input is acting as a switch -- when you plug a lead in it connects the battery. The TRS on the output is completely pointless.

Just to make it completely clear for Sam or anyone else, the 'switch' action' relies on plugging a TS instrument cable into the TRS input socket, whereupon the plug sleeve shorts the ring and sleeve terminals, thus connecting the battery +ve terminal to the unit's ground and firing up the circuitry.

Plugging in a TRS plug to the input will result in all manner of non-functional/damaging scenarios!

I imagine the use of a TRS socket at the output was just to simplify the component ordering -- two identical sockets instead of one TS and one TRS.

[Wonks]

And in 99.9% of all other cases, it's the battery negative connection that is wired to the R(ring) of the TRS socket, so that a TS jack completes the battery circuit via connection through its sleeve when plugged in.