Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: baerster on September 17, 2021, 07:39:39 pm
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Hi everyone,
I tend to like how many Fender tube amps have a dip around 800hz no matter where the tone controls are set. I like this dip for a clean and slightly overdriven sound but not for a heavily distorted sound.
I have an old blackheart Little Giant 5 that seems easy to modify because it has through-hole components and it's a simple design. I tend to use a 6 band EQ with it, to have the notch with a clean sound and to turn off the notch when using a distortion pedal. I use it with a Celestion 70/80 in a 1x12 Seismic cab, and the result is a huge, bright sound with so much bass that I usually turn the bass down when the amp is cranked.
A sane person would probably leave well enough alone and be happy that my EQ pedal gives me the sound I want. But I am wondering:
- Can it work to add a fixed EQ circuit like a twin-T before or after the existing EQ circuitry, instead of re-designing the tone stack so that there is more of an 800 hz notch? Or does that tend to cause more problems than it solves?
- If it is practical to add some fixed EQ before or after the existing EQ, where in the circuit should I add it? For instance should I add it to the grid and cathode for the first valve stage, such that any grounding happens on the leg that is attached to the cathode?
- Any suggestions for 12-inch guitar speakers that have a pronounced 800hz notch?
Thanks,
-Tom
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Can you post a schematic?
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Im busy but it's in the library under misc.
BH5.pdf, I think.
At least, that's the ballpark.
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Thanks SG. :icon_biggrin:
https://el34world.com/charts/Schematics/files/_miscellaneous/Bh5.pdf
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Look at this AB763 Super Reverb schematic.
Compare The verb channels tone stack parts values to your amps values.
You could change the parts in your stack to the AB763 values. The mid pot value of 25K compared to the 10K in the AB763 makes a big difference. Guys put a 25K in for the mid pot in Fenders to get rid of the scoop.
Your amps has ~double the value for the treble cap and 1M instead of 250K for the bass pot.
All these things up the mids.
What happens when you turn the mid pot to 2 or less, down to 0?
https://el34world.com/charts/Schematics/files/Fender/Fender_super_reverb_ab763_schem.pdf
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Here play with this tone stack calculator;
https://tone-stack-calculator.software.informer.com/
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> I like this dip for a clean and slightly overdriven sound but not for a heavily distorted sound.
If you disconnect the ground on a Fender tonestack, you get flat response. Use a switch.
A variant is to build with a Mid control but instead of 15k linear go 50k or 100k Audio taper. Full down is very dipped, full up is nearly flat.
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Here play with this tone stack calculator;
https://tone-stack-calculator.software.informer.com/ (https://tone-stack-calculator.software.informer.com/)
OR same thing in your web browser? https://www.guitarscience.net/tsc/info.htm (https://www.guitarscience.net/tsc/info.htm)