Danelectro French Toast: 4.5V or 9V?

[umbrella]

It seems like some folks lift the effect board from the French Toast and wire it up in a 9V TB box, while posts like this one suggest a power bias to 4.5V is required: http://www.diystompboxes.com/smfforum/index.php?topic=47806.0

Which is it? Also, if I need 4.5V, why does the above thread seem to describe something more complicated than this? http://www.diystompboxes.com/smfforum/index.php?topic=63880.msg504172#msg504172

Thanks for reading

[danielzink]

Get out your multimeter.

Plug the wall wart into the pedal.

Find the white molex connector that connects the two boards together.

Probe and look for either 9V or 4.5V



Dan

[induction]

Rehousing the circuit while keeping the wiring intact is one thing, but if you plan to convert buffered bypass to true bypass, you need to know what you're doing. A schematic is always your best bet, but as danielzink says, probing with a multimeter is very useful, if you understand how effects and bypass circuits work. I don't want to insult you, but from your post, I get the impression that you don't. Many circuits require both a 9V supply voltage and a 4.5V reference voltage for biasing. It's not one or the other. I would avoid changing anything until you either figure out how the circuit works electronically, or you get a verified, paint-by-numbers recipe specifically for the French Toast. Otherwise, you'll end up with a paperweight.

At the very least, read ExpAnonColin's post in your first link again until you understand everything he says and know why he says it.

Your second link refers to reducing the supply voltage to alter the operation of the circuit and create a sonic effect. The result depends heavily on the circuit, and you may or may not like the result. It is not similar to simply changing from buffered to true bypass. However, the 4.5V bias voltage needed for many circuits is usually created with some variation on the voltage divider approach described in the link.

I apologize if I offended you or misinterpreted your question.

[umbrella]

Thanks for the replies. I read that rehousing a Danelectro is about 2/3 of building a PCB from scratch, so I decided that it would be a good second project.

Dan: Great idea. I actually thought about this while lying in bed last night contemplating what I would do next if I didn't get any responses to this thread.

induction: You're spot on--I'm certainly in over my head, but the same could have been said the day I spent a few hundred dollars on my first guitar. I've collected and read every web page about Danelectro pedal mods, and I created this thread because it seems that one of the following is true: a) Not all Danelectro pedals have this 4.5V bias, or b) They do but some people run them at 9V. I'm not worried about the risk of losing the pedal, it was 24$ shipped and that's a great deal on the knowledge I've gained so far. You haven't insulted me. I don't understand the difference between buffered bypass and true bypass yet. There is no paint by numbers recipe for the French Toast, and I hope to make one after I've paved the road.

edit: here is one of the posts that make me think people are just dropping the effect board into a TB box: http://www.diystompboxes.com/smfforum/index.php?PHPSESSID=1c9230292a2b6c978a969a44ee362d53&topic=25221.msg164930#msg164930

edit 2: here's another site that has expanoncolin's same reply but with some follow-up questions answered which i have yet to digest completely http://experimentalistsanonymous.com/board/index.php?topic=635.0

[induction]

Ok, good.

A couple of things that may help. The 4.5V bias is usually for adding a DC offset to a signal in order to center it between the +9V and 0V power rails. The signal from a guitar or another effects box will be centered at 0V and will swing up and down into positive and negative voltage territory, but an op-amps and transistors can't reproduce voltages that are outside their supplied rails (many op-amps can't even get within 1V of the rails), so a DC offset has to be added to the signal before it reaches the gain or buffer stage or else the negative voltage swings will be cut off (this DC offset has to be removed before the signal reaches the pedal output). That's where the 4.5V comes in, it's attached to the input of the gain stage so that the signal will ride halfway between the rails, allowing for both upward and downward swings. You can't replace this with 9V because that would boost the signal voltage to the positive rail and you'll have the same problem as before but reversed - the upward signal swings will be cut off (in practice you'll be so close to the positive rail that you probably won't get any signal at all).

This is all generalized, though. Sometimes you can forego the 4.5V bias in favor of a ground-referenced signal, sometimes not. Depends on the circuit and sometimes on the strength of the pickups. As far as I know, the French Toast is the same circuit as the Foxx Tone Machine. I don't think that circuit requires a 4.5V reference voltage anywhere, but I don't know whether Dano modded the circuit or just cloned it exactly.

As far as converting the pedal to true bypass goes, the question isn't just 'does the pedal use a 4.5V reference voltage?' (not every circuit needs one), it's 'is there a 4.5V reference voltage carried on one of the wires in the harness?'. If so, which one, what's it for, what should you do with it, etc.

The buffered bypass relay circuit is often as complicated as the actual effect circuit, if not more so. Figuring out how to convert your pedal to true bypass requires you to understand how the specific bypass in the French Toast works, as there are many different approaches. Doing this without a schematic requires you to reverse engineer your pedal's switching method, since apparently not all Dano's are exactly the same in this regard (though I would imagine they are similar enough that studying some of the other Dano pedals would be extremely helpful). This reverse engineering will be difficult or impossible without some electronic understanding of what buffered bypass is, and some hands-on experience with how it's commonly accomplished. I'd say it's a job for an experienced circuit designer, but if you want to have a crack at it, I'd suggest doing a lot of reading about true bypass vs. buffered bypass with and without relays. General electronics knowledge (op-amps, transistors, passive components, etc.) will probably be necessary as well. Luckily, the internet is full of resources for this if you know what to search for. Wikipedia has some good articles to get you started. The other forum has some threads about this very subject, in case you haven't found them yet. (Not allowed to link to there or even say the name of the forum, but it's all about stompboxes that are free).

All that said, it would certainly be much simpler to build a Foxx Tone Machine from scratch. I recognize that you may intend this as a learning experience, but even so, that may be a useful first step. Just an idea.

If I were doing this, finding a schematic of the French Toast including the bypass circuit would be my number one priority.

Best of luck.

[umbrella]

OK, multimeter job complete. The switch board sends these values to the effect board via my passive Jazz bass:

~3.86V send (blue)
~4.5V power (green)
0V ground (yellow)
0V no-bypass send (orange)
~4.5V return (red)
~4.5V LED power (brown)