Modifying volume and tone pots

[tonequester]

tonequester here.


Hey Chuck !

A very intersting circuit you have provided. I printed it off for "the journal". I've tested some pots that I had laying around, and got from 3-5 ohms where one would expect zero Ohms. This was true for each side of the pot. The "full value" was even further off. One 500K pot read 573 Ohms. One thing that I have been concerned with on my mod,
which is directed towards a "brown" sound, is that I still want to be able to get a decent clean tone as well. Your circuit looks good and i like the idea of a bright switch. I like the idea that the signal could be "brightened" BEFORE amplification. I'm leaning toward simplicity in controlling or adjusting the amp's tone, and this type of bright switch would change nothing at the
amp. Just switch to bright at the guitar, and leave the amp set for whatever tone that you have "dialed in'. The standard Strat wiring works for me. I had planned to go that route, as close as possible. I've always liked to be able to access varying tonal effects from the guitar, and most of my mods have reflected this. I've almost always had at least one added switch on my guitars, whether it was for an on-board pre-amp, or my take on a Varitone. Thanks for sharing your circuit, it may be just what I will need to clean up a little bit. I don't expect to have to go to far with this, this circuit may be all I need. The double-ganged pot even eliminates the need for a separate switch. Can't wait to hear it man ! Have a great day ! tonequester.

[Chuck H]

Thanks TQ (can I call you TQ?). The "bright cap or circuit" I mentioned would be a cap or a combination of cap and a resistor or two that compensate for the treble loss as the volume pot is turned down. It's not a bright switch. And it does nothing to the tone of the guitar with the volume up full. But... Since you did mention that you like to have a lot of tonal control with a minimum of peripherals, I would recommend a circuit like this. With many tube amp models a "bright circuit" on the guitars volume control can allow you to set up the amp for distortion and then turn down the guitars volume control for a clean tone with plenty of highs and very little loss in volume! The exact values for the circuit depend on the pickups your using, the value of your volume pot and, most important, your personal tastes.

[tonequester]

Greetings Chuck ! tonequester here.

TQ's fine. You can sall me s--- for brains if you want, for all the "good stuff" you've sent my way since I joined the forum. I picked up(no pun intended)
on the bright "switch" pretty quick. I had actually done this before. I got it from a book by Adrian Legg in"81, called Customizing Your Electric Guitar. He recommended a .001uf cap across
the volume pots tab that comes from the pick-up(s), and the output tab. He showed it switchable with an SPDT. I had a cheap a-- Fender Squire and I ended up with 4 SPDT's on it. I had one for a coil tap, one for a phase reverse(2 conductor pick-up, one for an on-board pre-amp(by Craig Anderton), and of course the .001 treble by-pass. Never could remember which switch was which ! The results were great, tone wise. I did get a lot of laughs though. Your ganged pot is a great improvement. I have only one toggle to use this time. i intend to use it for a switchable Q-filter(Bill Lawrence). I heard it demo'd on you tube and the variety of sounds it "produced' were impressive. This time I won't use a sub-mini though. They're too hard to grab in the middle of a solo. I gotta say that your "thumb-nail" circuits have been a great help. I've looked at a lot of circuits on this forum, and I gotta say some of them have looked like they might be left over from the space shuttle. You get to the point right off and you somehow seem to know just how much tech I can tolerate up front. You'd make a fine teacher. I always print off your instructional posts for my notebook. I swear, all too often a post of mine becomes a "battle of opinions". I end up having to try to Goggle them anyway. I don't believe that I've had
to do so with anything you have commented on. Some posts that I make I actually expect to end up with nothing but opinions. In those cases I'm prppared to take it all down, and then go looking for the simplest, and often the cheapest way out. Like I said, TQ is no problem for me. Hopefully I will get some I.Q. in time by sticking to this forum, in addition to what studying I
am doing. I hope that you realize that when I'm done with guitar and amp, I'll have to make room on the "name plates" for Chuck H. Have a fine time at whatever you are up to.(I'm scared to ask a "Yanker" like you just what you ARE up to). TQ.....out.

[Mark Hammer]

The volume pot compensating cap is EXACTLY the same as what the "bright switch" on an amp, or the bright channel on amps with two volume pots (e.g., 5F6-A Bassman) does. The effect of the bypass cap works exactly the same way. As the volume pot is turned down, a low-impedance path is provided for higher frequency content, such that more attenuation is applied to the bottom end than to the top when the volume is below full.

Where they differ is in the manner that the volume control is used. On amps, we rarely set the volume to full, more often having the volume pot below halfway, where on guitar we tend not to turn down below full all that often.

The net result is that, even though the bypass cap works exactly the same way, we have many opportunities to hear what it does with amplifiers, and few opportunities to hear what it does with guitars. Of course, if one DOES intend to turn down below 10 on the guitar, compensating caps can be very useful.

Context is everything.

[tonequester]

tonequester here.


Greetings Mark, and thanks for the reply. In all actuality this is one Mod" that I've been using for years. it was the first such thing that I ever did to a guitar(1981 Squire).
I got it from Adrian Legg's book "Customizing your Electric Guitar"(1981).He called it "the switchable .001 treble by-pass. It was the first "mod" in the book, probably because it was the simplest. You basically just placed a .001uf cap across the volume pot's output tab, and the tab which takes input from the pick-up(s). Even with that piece of junk Japanese Strat, I could tell the difference that it made. No "big deal" mod for sure, but so easy that I've always used it for decent improvement in treble at lower volumes(guitar). You might not believe it, but the Squirer cost me $350.00 in '81 and it was horribly made. It did come with a now "vintage" 15W. s.s. Squirer practice amp. It had all of the tone of a $10.00 transistor radio set to AM.
That's how I got started doing guitar mods. That Japanese Strat ended up with 4 mini-toggles and a push-pull volume pot. It had the switchable "bright' mod, coil tap on the stock humbucker,out-of-phase on the single coils, and also series-parallel. When I got done with it, the darned thing had a lot of tonal variety, but it's playability was so bad I couldn't give it away.
I toyed with it for a couple of years, even putting one of the early on-board pre-amps in it, which involved routing a cavity for it and a 9 volt battery. My oft' used pawn shop wouldn't even touch it, but I sure learned a lot in my steady experimentation with it. The biggest lesson learned : No amount of money can make a bad foundation into a mansion. Now when I look for a "fixer upper"( and I only do for the enjoyment ), I spend a lot of time playing and checking it out UNPLUGGED ! I'd much have to come up with improvements to make to the circuitry,
than to have to try to improve the basic acoustic foundatation. Perhaps the worst thing about trying to do that, is the cost of all of the specialized tools one really needs for what amounts to
luthiery. Take for example doing a nut properly. Stewart-Mac prices(and I've been a loyal customer since '81) : one set of 6 guaged nut files-$77.70(my local music store does a replacement nut for $70.00), but first you need a set of rough-in nut saws, 6 for $39.90, how about a nut seating file ?, $19.23-$35.23 depending on width needed. If you want a file to rough-in the shape of the nut, that,s $26.75 for 2(different cutting surfaces). That works out to at the least : $163.58. Whoops ! I forgot the $13.95 for shipping. Maybe for most that's a good deal when you are looking at doing "nut jobs". Me. I try to avoid them. I just did it to the Kramer I'm modding. It turned out
damned good. I used a few pieces of used strings, and a Dremel tool. I know that dimensionally it's right because my brother(metalworker/welder) let me borrow his mic and feeler guages
to check it out. It also plays great in all positions, and stays in tune. I'm not quite as "dumb" as it might seem from my posts, but above all other things on this forum, I try to approach it like I'm the "low man" in everything. There's a lot of good people here who are helpful, and a lot of real experts. I've already been shown a dozen things that I didn't know and I've been corrected on another dozen where I thought I knew what I was doing but was dead wrong. I don't kiss a--, but I am truly amazed at how many try to help here WITHOUT attitude.
I can't but repeat over and over again. Thanks for your reply, I really appreciate it. I had a guy who "listened" in to one of my ongoing posts about the best way to go about getting more electronics theory under my belt. He sent me the 1957(my birth-year) ARRL Handbook. It was $3.50 then, it's $69.00 now. The kicker is that he paid $28.37 to ship it to me. I sent him
the shipping, but the book is priceless to me. The new ones don't even really get into tubes. The '57 edition barely gets into transistors ! Didn't mean to go on and on. I do truly appreciate
your reply. I hope to here from you anytime you have the interest. Best wishes to you and yours. tonequester.

[tonequester]

tonequester here.


I have used this mod several times in the past with good results. it's not a wonder worker, but I never said that it was. I tend to believe what Gerald Weber, founder of Kendrick Amplidiers has to say about the modification in his 1997 book(his second). "As you turn the control all the way up, the wiper that normally is always on the conductive carbon will reach the point that we've removed the carbon from and will be resting on an insulator. This opens the circuit just like a switch.The real gimmic here is that we've created a tone control off "switch" ! "And now a word to the guitar companies...I've been using and teaching this trick for over 30 years." "Don't go runnung off to the patent office, it won't stick."(page 257,
with diagram on page 256. He calls it the Trainwreck Drop Out Tone Pot, because The Trainwreck Pages(Trainwreck Amps, circa 1983) printed the mod first. The Weber book is titled,
Tube Amp Talk for the Guitarist and Tech. The position that it becomes an open circuit at depends on how much of the resistive track that you remove. The pot functions normally until you engage that position. A pot with a detant can be used to make it more precise. I have his first book as well. A Desktop Reference of Hip Vintage Amps. Both books are loaded with info,
that includes :amp design, troubleshooting, many modifications, how to build some special test apparatus like a current limiter, signal tracer,and tube tester/matcher, tune-ups, basic electronics, and a great Q&A section. He also re-prints the Trainwreck Pages. The first book dealt much more with specific brands and models, they're posible problems, solutions, and modding them as well. I actually learned the mod from Dan Torres, of Torres Engineering. He offered it in some of the kit mods that he was selling in 1981. As Steve Conner pointed out, Fender sells factory made examples of this modification. i doubt that they would do so if it was all "smoke". I will repeat, that this is not some wonder worker mod, however it makes a
detectable increase in treble, and I have moderate high frequency loss in both ears. Thanks for the interest, and for your reply. have a great day ! tonequester.

P.S. No schematic would be needed as it hooks up the same as a regular pot does. The simple diagram in the book merely shows about 5% of the resistive track missing at it's end. As for playing Devil's Advocate, I have no problem with it. I will add, that everybody who has a "better" mod can use it themselves.
Hey, maybe rjb is right. Just eliminale the guitar's volume control and make all changes in volume at the amp. I think I'll stick with what I know to work for me. It,s been working for at least 3 well known amp designers/manufactures for 30+ years. Now I find that Fender themselves offers a factory made version.
Whatever one chooses to use, or to do, I wish them well on whatever they are trying to accomplish ! tonequester.