Great guitar modification!!! and a question...

Pickups, wiring schemes, switch techniques and onboard active electronics for guitars and basses
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JakeAC5253
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Post by JakeAC5253 »

A few months ago I heard of a suggested modification for an unused tone knob in an electric guitar, but haven't tried it until now, and I think I was able to come up with an awesome sound, so I will share it with you.

The suggested mod was to put a single 1N34A Germanium diode in place of the tone cap on a tone knob to clip the signal as the knob was turned down... I thought it was a good idea, so I ran with it. Instead of using Germanium diodes I put a clipper pair of 1N4148's on the opposite lug from where the tone cap usually goes, which turns it from a "headroom" knob, into a "gain" knob because the sweep is backwards... or rather it's forwards... turn the knob up and you get more gain and clipping. I also decided to use a 1M pot because larger pot values means the potential for less clipping when the pot is turned all the way down, so you can get closer to your original unaffected tone. After testing, I added a 100pF ceramic cap across the diodes to smooth it out a bit so the clipping sound wouldn't be harsh. It is pretty subtle, but very very cool, a nice warm overdrive. I bet it would sound great, I mean really great, into an old vintaged plexi style amp sound. Lots of people use Tubescreamers and are looking for a subtle compression just before it... and I think this could be goddamn close to what they and I are looking for :D

Now... the question. I have noticed that there are really only two positions that I would ever use... full up and full down. So I would like to make this modification switchable rather than have to roll up/down the knob all the time. I need a DPDT switch, I know that much, and I would wire the outboard connections to the center lugs and leave the bottom lugs empty and the top lugs would be bridged by the mod components. About the mod components. Could I just simply use the two diodes and cap, or should I put the 1M resistor (equal to the value of the pot) in parallel with those as well? Or in some other orientation? Just wondering if I would have to account for the pot value in some way to get the exact same tone... because it's amazing!! And I don't want to detract from it at all by applying it to a switch instead of a pot.

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Post by RnFR »

when it's all the way "up", it's like the pot is out of the circuit. remember you also have to connect the diodes to ground on one side as well.
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Post by JiM »

JakeAC5253 wrote:The suggested mod was to put a single 1N34A Germanium diode in place of the tone cap on a tone knob to clip the signal as the knob was turned down... I thought it was a good idea, so I ran with it. Instead of using Germanium diodes I put a clipper pair of 1N4148's on the opposite lug from where the tone cap usually goes, which turns it from a "headroom" knob, into a "gain" knob because the sweep is backwards... or rather it's forwards... turn the knob up and you get more gain and clipping. I also decided to use a 1M pot because larger pot values means the potential for less clipping when the pot is turned all the way down, so you can get closer to your original unaffected tone. After testing, I added a 100pF ceramic cap across the diodes to smooth it out a bit so the clipping sound wouldn't be harsh.
:hug: This reminds me of my first FSB thread : https://www.freestompboxes.org/viewtopic.php?f=3&t=2100
I've found that two Si diodes don't clip much unless you have very hot pickups, wheras two Schottky or Ge diodes eat up too much volume. It's all about threshold voltage. Therefore i had one of each, for the extra mojo of asymmetric clipping. And using the "opposite lug" allows the tone pot to keep its cap and to remain a tone pot. Mine acts as an overdrive from 7 to 10, and as a standard tone pot from 7 downto 0.
JakeAC5253 wrote:So I would like to make this modification switchable rather than have to roll up/down the knob all the time. I need a DPDT switch, I know that much, and I would wire the outboard connections to the center lugs and leave the bottom lugs empty and the top lugs would be bridged by the mod components. About the mod components. Could I just simply use the two diodes and cap, or should I put the 1M resistor (equal to the value of the pot) in parallel with those as well?
You only need a SPST switch : one lug to the signal output, one lug to both diodes. The other end of both diodes goes to ground. No need for resistor. Add cap in parallel or series to taste.
I only give negative feedback.

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Post by HydrozeenElectronics »

JakeAC5253 wrote:A few months ago I heard of a suggested modification for an unused tone knob in an electric guitar, but haven't tried it until now, and I think I was able to come up with an awesome sound, so I will share it with you.

The suggested mod was to put a single 1N34A Germanium diode in place of the tone cap on a tone knob to clip the signal as the knob was turned down... I thought it was a good idea, so I ran with it. Instead of using Germanium diodes I put a clipper pair of 1N4148's on the opposite lug from where the tone cap usually goes, which turns it from a "headroom" knob, into a "gain" knob because the sweep is backwards... or rather it's forwards... turn the knob up and you get more gain and clipping. I also decided to use a 1M pot because larger pot values means the potential for less clipping when the pot is turned all the way down, so you can get closer to your original unaffected tone. After testing, I added a 100pF ceramic cap across the diodes to smooth it out a bit so the clipping sound wouldn't be harsh. It is pretty subtle, but very very cool, a nice warm overdrive. I bet it would sound great, I mean really great, into an old vintaged plexi style amp sound. Lots of people use Tubescreamers and are looking for a subtle compression just before it... and I think this could be goddamn close to what they and I are looking for :D

Now... the question. I have noticed that there are really only two positions that I would ever use... full up and full down. So I would like to make this modification switchable rather than have to roll up/down the knob all the time. I need a DPDT switch, I know that much, and I would wire the outboard connections to the center lugs and leave the bottom lugs empty and the top lugs would be bridged by the mod components. About the mod components. Could I just simply use the two diodes and cap, or should I put the 1M resistor (equal to the value of the pot) in parallel with those as well? Or in some other orientation? Just wondering if I would have to account for the pot value in some way to get the exact same tone... because it's amazing!! And I don't want to detract from it at all by applying it to a switch instead of a pot.

I read a while back that Jack Bruce had a similar mod done on his SG Bass when he played in Cream. I've always wanted to try it.

Thanks

:applause:

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Post by skylark44 »

Hey Jake, it's Norm (from GW forums)...I've got a useful update!
As you know...I had several posts on the GW forums about the similar "Underdrive" mod (from Guitarheads.net), and I've installed several of 'em in my guitars (and a few of my customer's guitars as well). So...I finally decided to "De-Goop" one of them...and they're just two "BAT46" Shottkey diodes, soldered-in parallel...then dipped in a protective coating (just to look more sophisticated than they really are)...that's all. So do like I'm doing...just buy yourself a bunch of 'em (I just ordered a shitload of 'em), from www.futurlec.com (they're only .28 cents each!). Have fun guys! :mrgreen:
Also, anybody have an idea if adding a third diode would make the clipping effect better, or worse?...just curious. :mrgreen:

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JakeAC5253
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Post by JakeAC5253 »

skylark44 wrote:Hey Jake, it's Norm (from GW forums)...I've got a useful update!
As you know...I had several posts on the GW forums about the similar "Underdrive" mod (from Guitarheads.net), and I've installed several of 'em in my guitars (and a few of my customer's guitars as well). So...I finally decided to "De-Goop" one of them...and they're just two "BAT46" Shottkey diodes, soldered-in parallel...then dipped in a protective coating (just to look more sophisticated than they really are)...that's all. So do like I'm doing...just buy yourself a bunch of 'em (I just ordered a shitload of 'em), from http://www.futurlec.com (they're only .28 cents each!). Have fun guys! :mrgreen:
Also, anybody have an idea if adding a third diode would make the clipping effect better, or worse?...just curious. :mrgreen:
Haha, as if I would forget who you were. Haven't talked in a while though... PM me your email address so we can keep in touch?

If you put the third diode in parallel then there should be no discernible effect, but put it in series with one of the existing diodes (and correct polarity) and the effect will be lessened. The only way to get more clipping would be to use diodes with a lower forward voltage (Vf). Like a 1N34A. I have a box of those lying around in the basement and I'm planning on trying them sometime as well. I may have to pick up some of the ones you mentioned as well.

I feel like I should comment on this now, before people have unreal expectations of this mod. The mod is very subtle, and only really noticeable with humbuckers, the hotter the better. In my opinion it almost sounds like it turns your pickups into active pickups because of the peak clipping. A bit tighter. This is why I want to apply this mod to a switch instead of a knob. If you want an actual "gain" sound, then I would try something with a lower Vf than 1N4148 silicon diodes.

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Post by skylark44 »

Cool Jake, it's good to hear from you again (I erally miss the GW forums :cry: ). I finally dug the diodes out of all that plastic "goop", so I could see what was inside...and I was kinda surprised how simple they actually are (and I bought a few of 'em, for $7.99 esch :slap: ). I just ordered a bunch of those diodes (BAT46's), so I'lllet you know how they work...I've also got a bunch of silicon INF41's, I wonder if they'd work they same way (any idea?:scratch:) . I'll PM you my email, so we can keep in touch (I still talk to Chie & Craig, from the ld forums too). :mrgreen:

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