Installing a "Resonance" control in my Bugera 333xl. Assistance please?

[Danglin' Fury]

I have already modded my amp for more gain on the Lead channel. Man oh man, I thought it sounded good before. It sounds like a 333XL with a 5150 lead channel now. The only thing I would like to do now is install a Resonance knob. I have looked at a "similar amp" schematic and found things are pretty much the same with a few exceptions. Does anybody here know what line off of the OT is the Negative Feedback? I'm not sure that Bugera used the same color scheme on the transformer wires that the "other amp" manufacturer did. This isn't the first amp I've modded but it is the first resonance control I've tried to install. Any help will be GREATLY appreciated.

[loudthud]

Since there is no schematic available, this is just a wild guess. Find the feedback resistor connected from the output back to somewhere near the phase inverter. I doesn't matter what tap it's connected to. The pot to connect as a variable resistor in series with it should be about 10 times the value of the feedback resistor. The cap value across the pot will require some experimentation but start will a value C=1/(2*Pi*Rfb*500) where Rfb is the feedback resistor and 500 is the break frequency. Increasing the cap lowers the break frequency.

[Danglin' Fury]

Thanks loudthud. If you look at a JSX schematic, almost everything is identical. So the feedback resistor should be the same. On the JSX schemmie, the Resonance pot is a 1 meg and the cap across the pot is a 1.8 nF (.0022 should get me in the ballpark). I'll double check the values in the Bugera when I get home.If they are not the same, I'll use that nifty little equation you gave me. (I appreciate that, it'll save me some lookin' in my college books). Since there is already a Presence control, could I just insert the Resonance control where it is? Thanks for your help.

[tedmich]

you could put something similar to the 6505 resonance circuit in

since its a blatant PV copy anyway...

[Enzo]

Instead of cramming that 6505 circuit into it, just use the JSX circuit.

SInce the JSX and 333XL are similar, the only differnce between the 333 and the JSX in this circuit is that the JSX has a 1meg resonance control in parallel with the 1.8nf cap. The Bugera has a 51k plain old resistor there - as if the resonance control were set at 51k. That is R42 on the Bugera, and should be on the board with the presence control itself.

Remove R42, and wire in its place a 1 meg pot wired as a variable resistor.

Voila.

[Danglin' Fury]

Enzo, you should change your forum name to Amp Ninja. Thank you immensely. I was going to use the JSX circuit but I am just now getting around to cracking the Bugera open. I had no idea they had already put the 1.8 nF cap in there. That little, but potent, piece of information you gave me just saved me a lot of time and a huge headache. Once again, thank you, oh great manipulator of electrons!

[Danglin' Fury]

Oh, one more question. Does the 6262 also have the fixed "Resonance" like the 333XL?

[Enzo]

Well, there is no control, so it would be fixed.

[ejc6stringer]

BUMP

Hey, I'm curious how this turned out. I have a 333XL and am interested in trying this.

[Danglin' Fury]

Do it. It really lets you control the low end response. Super easy to do as well. I didnt try to stick it
somewhere in the front. I just drilled a hole in the back and ran twisted wire to where the fixed resistor (R42) was.

[ejc6stringer]

Thanks for the followup! I just wanted to make sure that I got this right, since the 1.8nf cap is already in the circuit, I don't have to cap the pot, right? Also, which pin am I soldering to? Usually I'm dependant on diagrams for all the mods I've done (I can't read schematics very well) and I don't want to screw anything up. Thanks

[Danglin' Fury]

Its all in the post man. Take out R42 and Put the 1 meg pot in its place. Its that easy.

[ejc6stringer]

Thanks for all the help. I just got around to doing this today, super easy, fast and it yielded some great results. Any other mods out there for the 333XL?

[b.arzaga]

what does a resonance control do?

Hello what does the resonance control do? i also have a 333XL (infinium), im more familiar with guitar electronics than amps, can you show me how to do this?

Thank you

[Jazz P Bass]

Read Post #12.
"Its all in the post man. Take out R42 and Put the 1 meg pot in its place. Its that easy. "