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Post subject: The Tone Stack.
Posted: Mon Mar 28, 2011 6:13 pm
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Hey everyone, I'm considering building my own DIY amp. I plan to start on this Years from now when I have this stuff figured out and have a solid plan. I was thinking starting with Something like a Fender Champ, Then, add circuits to it like a Master Volume Control then a Tone Stack, I'm a little familiar with the system of high and low pass filters. I'd like to better understand how the values of the Capacitors and Resistors affect the sound. Does any one have a good explanation for a dummy like me? It would be much appreciated.


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Post subject: Re: The Tone Stack.
Posted: Wed Mar 30, 2011 7:39 am
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Hi ToneJunkie,

Here are a couple of good places to start. :)

http://www.allaboutcircuits.com/vol_2/chpt_8/3.html

http://www.duncanamps.com/tsc/

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Post subject: Re: The Tone Stack.
Posted: Wed Mar 30, 2011 3:49 pm
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Thanks for the help.


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Post subject: Re: The Tone Stack.
Posted: Wed Mar 30, 2011 4:29 pm
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I've found the tone stack on BF and SF Champs kinda wipes out some of the lush midrange. I actually bypass them and go back to narrow panel 5F1 gain stage, minus any tone controls. To me it actually sounds richer. And your guitar's knobs work just fine with this setup.

This can be done to BF and SF Champs and VC's by replacing the 250 picofarad cap between 12AX7 halves in input stage with a 0.02 mfd/600VDC coupler. And removing the 100k-ohm resistor connecting the 250pfd cap with the 0.1mfd cap of the stack. Keep the 100k-ohm resistor that goes to the PS intact.

It's really an old-time "fix" I got some time ago, from another tech.


http://www.ampwares.com/schematics/champ_aa764.pdf

http://www.ampwares.com/schematics/champ_5f1.pdf

Edit: If you look at the two schematics, a couple of other "things" pop up. Like the amount of feedback off the OPT. And the plate voltage applied to the input stage. These are also fairly quick fixes. Note: The position that 22K-ohm resistor of the NFB goes to on the tweed 5F1 versus the AA764 circuit. If you do these mods and add a good speaker... you have in essence, a "tweed" 5F1 Champ.


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