What values for a Resonance Control?

[martin manning]

Dave, is this this the way you implemented the original, but without C2 and R4?

I did it this way:

Yes, that was the original intent exactly.

[sliberty]

What did you by "a little unstable"? Is it oscillating, or motor boating?

[ChrisM]

Is the NFB ratio the 100K to 5K?

[martin manning]

Is the NFB ratio the 100K to 5K?

At low frequencies, yes. Otherwise, it's frequency dependent. Update: the v.2 response looks interesting without R4, but match C1 and C2 at 0.05u. Call that v.3. Room to tweak here...

[Colossal]

What did you by "a little unstable"? Is it oscillating, or motor boating?

Yeah, it started oscillating/whistling at max Presence on the Presonance control. It's not the mod's fault. My build is largely point-to-point and for proof of concept; to dial in the tone I'm looking for. I've bent every Trainwreck rule there is. The amp has been cooperative up to this point. I'll re-route the NFB wire (maybe even shield it) as it is flying now, even though it rests against the shield plate. I'm not concerned about the oscillation as this amp is just to get what I want out and then I'll transfer the values to a newly made "permanent " amp that uses a traditional turret board layout with proper lead dress. I'm running the tone stack dimed and the Volume at 8 (with a PPIMV up when no one's around) so the amp's pushed in terms of stability. It can produce a killer prog metal grind. Fantastic tone. I gotta say though the PTP tone is great. The Presonance control is pretty cool; one less pot...a two-for-one special.

[martin manning]

Here's v.3. On paper I like this one best because it replicates what the original presence does, and adds the resonance. In the frequency response plot the green is the original and the blue is the v.3 presonance. But the proof is in the listening...

[Colossal]

Dave, is this this the way you implemented the original, but without C2 and R4?

I did it this way:

Yes, that was the original intent exactly.

Cool, glad I got it right. I'm going to try v3 tomorrow. All I have on hand are 0.047uF so they'll have to do for a test. Nice work Martin. Thanks for the SPICE model.

[leadfootdriver]

What would the difference be if I used a 250K pot instead of a 1Meg pot with the .0047 uf cap for Resonance?

[ChrisM]

What would the difference be if I used a 250K pot instead of a 1Meg pot with the .0047 uf cap for Resonance?

Lower feedback ratio at max setting.

[Reeltarded]

Welp, that is another brilliant idea.

Thanks for designing it with spare parts I have laying around in abundance!

[martin manning]

Thanks, Reeltarded. Are you going to try this on a TW, or some other amp? It'd be nice to see if it can be scaled, and what the effect of it is on another platform.

[Reeltarded]

Metal panel Marshalls, and The World's scariest 100+ watt Express that takes 3 years to build*. ( *tm 2009, 2010, 2011 All rights reserved)

Have you tried it with a variable NFB control? One of my amps is constantly variable from around 20k to 100. What if I stuck this @ R1?

I need some red tape. I am labeling this control Martinization.

All mine are going to be with C1 and C3 .047 because that's what I have handy. I imagine it works close enough. My .047s are huge though. We'll see when we get there!

Having trouble with the last version. I am not sure why. The first one with the .1 cap was in and working before I could finish reading. I think I need more coffee.

[martin manning]

Have you tried it with a variable NFB control? One of my amps is constantly variable from around 20k to 100. What if I stuck this @ R1?

That would mess with the frequency break points. You could put a variable resistance between this network and the OT tap, that would reduce NFB. Going the other way (increasing) would require reconfiguring the presonance network for more NFB and then adding another pot upstream to turn it down.

All mine are going to be with C1 and C3 .047 because that's what I have handy. I imagine it works close enough. My .047s are huge though. We'll see when we get there!

Yes, close enough.

[Reeltarded]

Ahh I see. Figured as much. So, not that I tried the simple 1st one, and attempted the last I realize it's not just coffee. I'm a newb with enough knowledge (I believe) not to hurt anyone.

I can't get version 1 to work now. I shall undo the done and begin the redos.

Thanks again. You guys make my records sound good. Credits will be where credits are due, yessir.

[surfsup]

I did it this way (so yes, without C2 and R4).

Colossal, shouldn't the tap come from the 8R not the 16R? Your drawing shows the 16R...

Martin, two noob questions:

If I were to put this on a LiverPool, with a 1k2/47k PI tail resistor combo, does this affect anything? (the Express has a 5k pot, the LP has a 25k pot). My amp only has an 8R tap so wondering if that will work for me.

As having never dealt with lead dress for NFB/Presence, any tips on how to implement? I read shielded vs no shield. I'll try this on my amp with is a LP-clone (Xits X10). I should have all/most of the stuff.