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Resonance control, anyone?

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6/17/1999 4:47 PM

Resonance control, anyone?

Hello to all. Could one of you folks maybe suggest a resonance control circuit for, say, a Marshall 50W or SLO100? I am designing an amp and I don't have any resonance controls in my files. I know that it works like a "bass presence" control by (probably) high pass filtering the negative feedback in the power amp. Basic circuitry and some starting values would be greatly appreciated! Thanks!

6/20/1999 1:35 PM

MBK;

Hey you! How have you been?? Busy I'm sure. Here's a mod I got frm Mark Cameron. I wasn't sure of the exact value as far as the pot is concerned so I ran with what sounded good and so far it's been fantastic!

50K lin pot (with shaft facing you --> in=pin#1, out=pin#2 (center), ground=pin#3

1.) Grab a .002uF cap (High gain amps seem to like a .002uF cap) and solder it to pin #'s 1 & 3

2.) Solder a jumper wire to pin #'s 2 & 3

3.) Remove the feedback wire from the speaker jack and solder it to pin#1

4.) Solder a lead wire to pin#3 and connect it to the speaker jack.

As Mark told me, you can use anything from .001 to .006 (this gets into the lower mids) Fenders seem to like the .001uF alot where Marshall's and other high gain amps seem to like the .002uF. It's really all just personal taste really so see what you think. You could also use a 25K, 50K, 100K or up to a 1meg pot if you wanted to. I found that a 50K was pretty much ideal but some people enjoy the 1Meg. Try it an see what you think.

Happy soldering;

Trace

6/21/1999 12:08 PM
MKB	Hello again, Trace! And, thanks again for your help! What you described is pretty much what I had imagined. I'll report back when I have tried it. Thanks again!

6/30/1999 1:16 PM
Trace	MKB; Let me know if you have any problems with it. I've been wiring alot of these and I still the darned things backwards! (ha, ha) Trace

6/30/1999 6:53 PM
John K.	I read about one of these mods about two weeks ago, didn't really understand it. I probably would now if you could take the time for a brief explanation. How does it interact/differ from the bass control? Thanks for all your help so far.

7/1/1999 0:56 AM

John;

Well, I'm one of those guys that was a player and then got into learning about tube amps so I'm not up on what alot of things do as far as the "math" part of it is concerned. I know Speedracer, Doc, Graywater, Bruce, Richie, etc, etc are WAYYY more knowledgeable than I am when it comes to this. I sort of just go for what sounds right

I know that sounds lame but I've horrible when it comes to taking the time to learn about the math end of it! (ha, ha) It certainly wouldn't hurt me to know but I believe it lowers the feedback resistor and I'm sure someone will hop in and explain this (pretty please!) Ha, ha.

Thank god the bbs is back!!

Trace

7/1/1999 1:18 AM

Probably easiest to see looking at it with the pot rotated full cw and full ccw.When the pot is turned to where it is shorted you get pretty much full spectrum negative feedback.

With the pot rotated the other direction you have your pots value in parallel with you cap. Most of you highs are going to go through the cap and leave the lower freq to get attenuated by the pot resulting in a negative feedback signal made up of predominetly highs.

I don't like math...I believe the formula you would use is 1/2Pi X R(pot value) X C

somebody help me here.

jason

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