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Re: Resonance control, anyone?

:

7/1/1999 9:30 AM

Re: Resonance control, anyone?

The effect is the lowering of the damping factor. With the resonnance control on max, the speakers can "move freely" when they reproduce bass freq (they "resonnate"). You then get that typical thump. With the resonnance control on minimum, the feedback loop impedes that resonnance so the bass freq sound tighter.

The resonnance control and the C and R values have to be tweaked depending on the cab (and its resonnance freq) you are using for maximum effect.

7/1/1999 2:33 PM
John K>	So is this a circuit that uses a pot to control how much negative feedback is being used?

7/1/1999 3:11 PM
jason	Essentially yes, but the pot is paralleled by a cap. jason

7/1/1999 5:08 PM

it is altering the amount of -fb yes, but it is not altering the amount evenly across the freq spectrum.

Since -fb is trying to correct gain anomalies in the loop, when you cut LF info from the -fb you boost LF gain (because there is less LF info in the -fb now). Presence controls work by doing the opposite - allowing HF info to bleed to ground so that the power amp goes back towards open loop gain at HF. (-fb cuts gain, lowering the amount of -fb will give back some of that gain.)

7/2/1999 9:00 AM

There's yet another variation that i remember seeing a while ago. It was used in a hi-fi amp, heathkit maybe. I think it involved taking feedback from the ground side of the OPT and sending it back to the grid of the driver pentode in front of the phase splitter. I can't remember all the details but it seemed to give you LF positive feedback. Can somebody refresh my memory here? I'll see if i can scrounge up a schematic and post some more details later.

Regards;

Carl

Summit Amps

http://www.geocities.com/CapeCanaveral/Station/1655/

7/4/1999 12:12 PM

Carl:

I'm not sure what particular resonance circuit this thread is referring to, but here is a post I saved from 1997 or 1998:

Resonance control mod:

"This mod was first posted by Mark Cameron. I have used it on Fenders and Marshalls with great results. Basically, it is the opposite of a presence control, allowing you to tighten up the bottom. I will try to talk you thru the wiring.

"Looking at the back of the 1meg audio pot, left to right, numbering pins one two and three. Disconnect your feedback wire from the output jack and solder to pin three.

Solder a new wire from the output to pins one and two.

Solder a .0047 cap from pin three to pins one and two.

That's it! I use the master volume control on Silver-face amps, which is a 1meg audio taper.

"Good luck!

"James"

Steve Ahola

P.S. The last time I posted this here at AMPAGE I think Trace tried it out and had some problems with it so he took it back out. If revisions are necessary maybe someone can post them here...

7/5/1999 9:12 AM

Ok....I found the schematic for the circuit I was refering to and it's really different! The amp is a Heathkit W6 and it's available at the Triode website. It's really too complicated to describe so I would suggest going and checking out the schematic there. It should be a really easy circuit to implement on a Princeton Reverb with some changes in component values.

Regards;

Carl

Summit Amps

http://www.geocities.com/CapeCanaveral/Station/1655/

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