Tone problem w/ Fender Pro Jr. (Attn: Ric)

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Tone problem w/ Fender Pro Jr. (Attn: Ric)

Postby grady » Sat Feb 10, 2007 4:47 am

Maybe Ric or some of you other guys can help me out with this.

My Pro Jr is way too "Chimey" even with the Tone knob turned all the way down.
I want to get rid of some of those "highs" and boost the Bottom-End some.

I tried a EQ pedal, it didn't help any.

I checked the Schematic and there's a .01 cap between the Vol & Tone knobs.
It looks like there's a .033 after the Tone knob in the circuit.

Anyone have any ideas about what I can do ??

Thanks,
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Postby slickcat » Sat Feb 10, 2007 1:15 pm

Hi Grady,
My 5e3 deluxe has a .0005 between the volume and tone controls and a .005 after the tone control. The pots are 1meg.
Its a pretty smooth amp.
I think Ricochet may have some suggestions...hes good with electronic stuff. :wink:
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Postby slickcat » Sat Feb 10, 2007 1:35 pm

I think the general rule is...the larger the capacitor the more high frequency's get sent to ground. So larger value caps will provide less treble.
Im thinking if you have a .01 and .033 you might consider a .02 and .047
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Postby bignick » Sat Feb 10, 2007 2:06 pm

Would a preamp tube change help at all? I'm still learning.
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Postby rustyslide » Sat Feb 10, 2007 5:58 pm

I think, looking at the schematic, that increasing the .0033µF cap (C4) would let you roll off more treble. The 0.01 µF (C3) looks like it lets the treble bypass the volume pot when the tone control is up.

...I think.
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Postby ricochet » Sat Feb 10, 2007 6:19 pm

First thing I'd try would be lifting one end of C2, taking it out of the circuit. That's a "bright cap" that lets treble frequencies bypass the fixed 470K resistor ahead of the volume pot, R5. The midrange and bass frequencies are attenuated by R5, but the high stuff skates right on through C2. If that darkens your tone too much, replace C2 with a smaller cap. And if you decide you want it back like it was, if you've just lifted one end it's easy to put it back.

Replacing C1 with a .1 uF cap will let lower bass frequencies pass through, but probably won't make a lot of difference with guitar.

Replacing C4 with a larger cap will let lower frequencies bleed off to ground through the tone control. So will increasing C3.

(Fixed a bit of my typing.)
Last edited by ricochet on Sat Feb 10, 2007 6:27 pm, edited 1 time in total.
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Postby mickeypainless » Sat Feb 10, 2007 6:24 pm

That all went right over my head Ric but it sure sounds cool! 8)
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Postby grady » Sat Feb 10, 2007 7:41 pm

Thanks guys !!!

I'll give it a try.
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Postby slickcat » Sat Feb 10, 2007 7:49 pm

Rico...you Da Man!!! :)
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Postby grady » Sat Feb 10, 2007 9:12 pm

One more question.

How do I "bleed" this amp so I don't get killed working on it ???

I know how to do the old Fender amps with the Filter cap canister but, I've never worked on a new Fender amp.
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Postby ricochet » Sat Feb 10, 2007 9:21 pm

With any amp: Unplug it. Use a resistor of around 1K ohms to jump the positive and negative terminals of the first filter cap. If you use a resistor of 1W or bigger and are real careful to hold it by the body, you can do that directly without frying yourself. It's safer to use a lead with a clip on one end to ground on the chassis and tape the resistor to a chopstick to touch the other end of the resistor to the "hot" (positive) terminal of the resistor. Leave it touching for a half minute or so to be sure the caps are bled down, then clip a jumper across the cap terminals so it stays that way. If you use a straight jumper wire or screwdriver without a resistor, it'll arc and burn holes in the metal.
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Postby grady » Sun Feb 11, 2007 4:03 am

Clipping C2 out of the circuit took care of it.

Thanks, I really appreciate it.
I owe ya one.
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Postby ricochet » Sun Feb 11, 2007 4:33 am

Good deal. Glad that worked for you.
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