"Presonance" Control Mod

[HobbswheresCalvin]

Is there a huge difference going from say a 5kA to a 10kA on this mod, or can i try it with the presence pot that is already in my express

[martin manning]

I'd keep it up at 10k. The pot is accross the output of the OT, and if you make it smaller it will have to dissipate more power, maybe too much. Be careful and watch out for oscillation, too. Seems like there might be something going on with this mod that can cause an instability.

[surfsup]

Martin, just to be 100% on this, since the wiper would short R3 at full rotation, I assume there is no connection between the left side of the FB resistor (R1) and the wiper/cap (RV1/C1). The circuit should be wired like this:

[martin manning]

Yes. If "dots" are used to indicate electrically connected lines, then lines that cross with no dot are not connected. Lines that meet in a T must be connected and so don't need a dot.

[cbass]

I tried martins presonance control on a concorde type build in my mule chassis.

Its freakin huge!I had some problems with motorboating but was able to solve it with some chopstickin.

I have 4 and 8 ohm taps on my OT I'm gonna try a switch to select nfb coming from each.

[martin manning]

cbass, what are the details- original presence circuit, and values for the caps and pot used in the presonance circuit? Thanks for reporting back!

[pablogt]

As far as I know, the original presence circuit is 5k pot / .1uf cap / 47k NFB

Pablo

[cbass]

Pablogt is right.

My concorde is a little different I added a PPIMV.I only have 80uf at the first B+ node.Running aroud 505vdc on the plates.I belive my OT is 4.2k primary.

I built it in a mule chassis.That I've built about 10 different amps in its a real mess but its the best sounding amp I've built
.I plan to put it in a real chassis ,get the right OT and boards , build it closer to spec and build a nice cab.


All I had was a 10k linear pot.So the taper is off.But i still get the effect tll i cna order some parts.

I used the values Martin originaly posted.Haven't tried any other values yet.

I will definately be using the resonance circuit when i build it into a real chassis.

Thanks for this cool little circuit.

[Structo]

Anybody try this on a Dumble instead of the traditional presence control?

That is one thing that always kind of bugged me about my amp is the presence doesn't do much until about 3:00 then it is subtle.

I've tried the #102 Ford presence but didn't care for that either.

[John_P_WI]

Also curious if anyone has tried applying this to the cathode of a gain stage before a concertina splitter?

[bcmatt]

I've been reading around these "presonance" threads for about the last hour (been meaning to check out all this fuss for the last couple months), and I got to admit I am intrigued and want to try it on my Liverpool (with VVR). I find myself running my typical presence control all the way down.

I am still a bit confused about the final version people are happy with and whether stock Liverpool PI values are changed or not. Can someone help me with this please?
Do I want to go with a 10K pot?
Thanks guys; I got a little lost and mixed up trying to keep track of which amp each person was applying this to.

[Colossal]

bcmatt,

I used the stock values in the Liverpool PI (1k/39k). I also went with Martin's revised version (v3), the one currently posted. I used a 10kA pot.

[bcmatt]

Thanks Colossal,
I was hoping you would respond, short of PMing you.

Ok, so I'll follow this one:
http://ampgarage.com/forum/download/file.php?id=20912

So, it looks like I just need to make sure I have a 10KA pot and two .05uF caps, and I'll be yanking a .1uF and the 25K pot. Seems easy enough.
Thanks for the clarification.

[martin manning]

It'll be interesting to see how it works with VVR... I don't think anyone has done that yet. With PPIMV the effect is much reduced when the master is turned down, and with the Express it's hard to find the opportunity to use the amp with it turned up.

[Colossal]

Thanks Colossal,
I was hoping you would respond, short of PMing you.

Ok, so I'll follow this one:
http://ampgarage.com/forum/download/file.php?id=20912

So, it looks like I just need to make sure I have a 10KA pot and two .05uF caps, and I'll be yanking a .1uF and the 25K pot. Seems easy enough.
Thanks for the clarification.

Yep, that's the one! You could use 0.047uF but since you have 0.05, you're good to go.