I wanted to put a simple treble cut on my Champ clone, so put the Deluxe "stack" in it. Two caps and a pot, between preamp stages, before the vol pot. Rolls off the treble but not enough... My question is, why two caps, for just an adjustable RC filter? I could play with cap values and see what happens, but would like to know more about what is going on... Cap values are. 0005 and .005uF, pot is 1Meg. Its not on the Duncan calculator, and all my theory resources are for more complex tone circuits. I've had difficulty understanding the dynamics of this aspect of tube amps, but hope I can wrap my brain around this one. Thanks!
http://bmamps.com/Schematics/fender/deluxe_5c3_schem.pdf
There is the 5C3 schematic.
It isn't an EQ, it is a tone control. With the wiper at the 0.0005uf end (500pf) you have essentially the 500pf as a bright cap across the upper volume control. The 1 meg of the tone pot keeps the 0.005uf cap from having much effect. As you turn the wiper towards the lower end,, you get less and less bright boost on the upper volume, but now the lower cap becomes more and more effective as a rolloff from the grid to ground. So this is more than a simple treble cut pot.
You can separate it into two pots if you want. From the grid of the second tube to ground, you can have a 1 meg pot in series with a cap, just like in a guitar. 0.005 is a place to start, but you can experiment with other values to see what you like. And you can either make a bright switch for the 500pf in or out, or add another 1 meg pot in series with it for variable bright. Sounds like bright isn't on your agenda, so no need for that.
But remember, the whole circuit makes the tone of an amp, not just the tone control, and the first and most effective way to change the tone is to change the speaker. You can increase the negative feedback of highs with a cap across the feedback resistor. And so on.
There is the 5C3 schematic.
It isn't an EQ, it is a tone control. With the wiper at the 0.0005uf end (500pf) you have essentially the 500pf as a bright cap across the upper volume control. The 1 meg of the tone pot keeps the 0.005uf cap from having much effect. As you turn the wiper towards the lower end,, you get less and less bright boost on the upper volume, but now the lower cap becomes more and more effective as a rolloff from the grid to ground. So this is more than a simple treble cut pot.
You can separate it into two pots if you want. From the grid of the second tube to ground, you can have a 1 meg pot in series with a cap, just like in a guitar. 0.005 is a place to start, but you can experiment with other values to see what you like. And you can either make a bright switch for the 500pf in or out, or add another 1 meg pot in series with it for variable bright. Sounds like bright isn't on your agenda, so no need for that.
But remember, the whole circuit makes the tone of an amp, not just the tone control, and the first and most effective way to change the tone is to change the speaker. You can increase the negative feedback of highs with a cap across the feedback resistor. And so on.
Thanks ENZO for the great explanation - it is a simple RC hi-cut filter, just with a bright cap in it. The work "boost" confused me tho... passive filters only cut, so boosting something is really cutting something else?
Attached is the Deluxe 5C3/5E3 preamp schematic, and a drawing of it with different vol pot wirings. The lower right dwg shows the vol pot in my Champ (wiper to grid), and the upper left dwg shows how one vol pot of the Deluxe is wired. Am thinking the two are NOT the same, as the wiper of the tone pot see different resistance from the vol pot as it is changed on one dwg but NOT the other. I have read that Deluxe controls all affect each other, even the vol pot of the UNUSED channel... This is where it gets too complicated for me.... I have a decent Jensen spkr in the amp, and have played with the NFB, had a pot on it, now a switch (opens for dirty, or 47K for clean). Amp has plenty of treble, no hi rollof components in the circuit, so I just want one pot to do it when I need some. Thanks again!
Attached is the Deluxe 5C3/5E3 preamp schematic, and a drawing of it with different vol pot wirings. The lower right dwg shows the vol pot in my Champ (wiper to grid), and the upper left dwg shows how one vol pot of the Deluxe is wired. Am thinking the two are NOT the same, as the wiper of the tone pot see different resistance from the vol pot as it is changed on one dwg but NOT the other. I have read that Deluxe controls all affect each other, even the vol pot of the UNUSED channel... This is where it gets too complicated for me.... I have a decent Jensen spkr in the amp, and have played with the NFB, had a pot on it, now a switch (opens for dirty, or 47K for clean). Amp has plenty of treble, no hi rollof components in the circuit, so I just want one pot to do it when I need some. Thanks again!
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I changed the tweed TC (as well as everything else) on my peavey Royal 8 to the bitmo tone control mod. This removes the interaction with the volume. Very happy with the change. Google is your friend for schematics.
The bright cap's effect is also dependant on volume, as it is shorted out at full volume. Was this intentional?
If the volume is up half, you get half signal at the grid. If you then add the bright cap by turning up the tone control, you get more trebles than you had without. That is not signal amplification, but it is a relative boost. As you turn up that tone control, your highs increase. How much more does it need to do to be a boost? True, no matter what, you don't get greater signal out of the tone circuit than what went in, but boost or cut is relative to the user.
1950's Fender design - quick & cheap for the practice amp market of the time.
The bitmo mod adds one resistor and a wiring change to make the tone control independent of the vol pot setting.
Well, I decided to keep it simple, added just a pot and a cap (ala guitar), to keep insertion loss low. I did build a Big Muff style stack (got it from another thread), but will be using it on my 2nd build - never put tone controls in it either - a Princeton clone with tremelo. My Champ is done (for now), also now with a switch on the NFB for clean/dirty. Finally drew up the schematic - menial labor but still useful down the road. Thanks for all the help!
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