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seamusoc

Diodes in a Guitar?

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Will all diodes affect the tone of a guitar? Specifically if I have the signal from a pickup going through a diode, how will it change the sound? And if the signal from a pickup comes to a reverse bias diode, will that signal be blocked completely or will a small amount of that signal still bleed through?

Looking to make a custom circuit, and without going into too much detail I'm just wondering if diodes can be used to stop unwanted pickups bleeding through into the guitar's output signal?

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Signal diodes conduct when the forward voltage exceeds 0,7v for silicon. They would block the entire signal on negative-going excursions whilst chopping off the bottom 0,7v on positive excursions. To answer the first question, "yes". They're not useful in passive circuits really (except maybe black ice circuits?) and produce unmusical modifications to a signal.

You'll probably have to go into too much detail for specific advice. Not much to go off and mystery isn't helping here. :-)

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I'm going to rewire a HSS strat style guitar. 5 way switch, 1 Vol, 2 Tone, and a DPDT switch. The DPDT will 'override' the guitar circuit and send the bridge humbucker straight to the output (passing Lane mod). I also want an auto split (bucker will split when in the bridge/middle position). So one side of the 5 way switch will be a pickup selector and the other will control the auto split. One tone knob will control the neck pickup, and the other the bridge. I was wondering if there was any way of connecting the middle pickup to the bridge tone knob without having it bleed across. I know it could be done with a super switch but I don't have one handy and was wondering if it could be done with what I had lying around! Though diodes would affect the signal alright, but from my basic understanding of semiconductor doping I thought it could be possible to make one suitable for guitar circuits and was wondering if they were around. Might just leave the mid pickup without a tone control seeing as I never really use position 3 anyway

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Diodes won't have the "signal steering" effect you're after. Essentially they are a one-way valve, allowing current to pass in a single direction only. The signal output of a pickup is bi-directional, partly spending its time "pushing" in one direction and then turning around and "pulling" back the other way. If the pickup signal didn't alternate between push and pull we wouldn't hear anything. Diodes also have a threshold that must be overcome before they will allow the flow of current - roughly 0.7V for silicon (as Prostheta suggested above), 0.3V for germanium, 0.2V for schottky. In comparison most pickups will only have an output of around 0.1 - 0.5V depending on how hard you're playing.

Placing the diode on series with the pickup would probably result in no sound (or extremely weak, distorted sound). Diode in parallel (ie, between pickup hot and ground) might be interesting, probably introduces some mild overdrive depending on the type of diode you use, and is probably what's inside the Black Ice blob.

Guitar pickup signals are dumb and need to be told what to do by mechanical switches. Asking them to perform acrobatics with diodes will usually result in unexpected (but possibly happy) side effects.

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A couple of observations:

  • Volume pot is missing its ground connection on the right hand lug.
  • Assuming your diagram is showing the pots viewed from the back the tone pots are wired back-to-front - move the connection on the outside lug of each to the opposite (as yet unterminated) side.
  • Passing Lane switch has a cap across the top pair of lugs - should be a straight wire link.
  • Extra cap on the lower tone pot between the case and earth should be replaced with a straight wire link.
  • Neck pickup hot lead is tied directly to the volume pot via the common tab of the 5-way switch. It will always be active irrespective of the 5-way switch position. Should be moved to the next lug up if you're after proper selectivity of the neck pickup.

The only caveat as far as I can see (maybe this is already known to you) is that the bridge tone control will affect middle pickup when in bridge+middle position. Likewise, the neck tone control will affect middle pickup when in neck+middle. Only time middle pickup will be unaffected by tone controls is when it is selected by itself (position 3).

The super switch is definitely the easiest way to achieve your requirement of middle pickup -> bridge tone control without the signal leaking into the bridge pickup when in position 1. Perhaps you can get one from your local music store? They're fairly common replacements for Yamaha and Ibanez super strats.

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i only found one useful scenario in which i utilized diodes in a switching circuit inside a guitar. about a year later i found a way to modify the switch to my needs. general consensus is they make special switches and what they say here is accurate its not the way to go, however you are on the right track.

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