What values for a Resonance Control?

[Colossal]

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

Good catch. I updated the drawing to show the correct tap. I have since updated to version 3 anyway.

[martin manning]

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.

Standard Liverpool has 100k FB resistor and 4k7 tail, so this circuit would work fine; just delete the 25k pot and 0.1u presence cap. If you are using 100k FB, 1k2 tail and 0.1u cap and you like it (less FB than standard), then I'd say do as above, leaving the 1k2 tail, and delete the existing pot and cap.

Just keep the FB wire away from the power tube and PI grid wires.

[surfsup]

I don't have NFB now, but will add it to check it out. I do have a 47k, not a 4k7...not a typo

[martin manning]

I don't have NFB now, but will add it to check it out. I do have a 47k, not a 4k7...not a typo

Why don't you make it look like the standard Liverpool then?

Edit: OK, 1k2 is your bias resistor? If so keep that and make the tail 42k and 5k to replace your 47k.

[Colossal]

Upgraded to v3. Works really well!

Summary: Nice full, extended low end with the pot at <12 o'clock, switching over to the brighter "sheen" of presence at >12 o'clock on the pot's rotation. I tend to favor about 10-11 o'clock with my setup. 10-11 o'clock adds in a throaty low end with a bit of perceived sub-sonic punch while retaining some of the shimmer. With my 2x12 test cab, the resonance side produces an audible "whump" at heavy settings with palm muted chords, but still retains the amp's tightness. You can visibly see/feel/hear the cabinet working harder, rumbling away at the resonant frequency at the max setting. It does not get flabby at any setting. At max resonance it does seem to trim off the shimmer completely. I bet this would be killer with a 4x12.

Test amp: Modded Liverpool
Test cab: Closed back 2x12 with reissue Greenback Celestions
Conclusion: Really cool, very useful mod!

Great job Martin

[Structo]

Cool!

I'll have to give that a try on one of my amps.

Probably the 6V6 Rocket.

[martin manning]

Upgraded to v3. Works really well!

Thanks Dave, and thanks for doing the prototyping and the detailed report! Presonance Control discussion continued here: https://tubeamparchive.com/viewtopic.ph ... highlight=

[leadfootdriver]

I combed through a few schematics to check values on their Resonance controls. Cap values are all over. All pots seem to be audio taper. I'll have to experiment with different cap values on the Express.

Peavey Classic 120/120 1M/.015uf
Peavey JSX 1M/.0018uf
Peavey Windsor 1M/.01uf
Engl Powerball 1M/.01uf
Peavey Classic 50/50 1M/.0047uf
Egnater TOL 50 500k/.0047uf
Peavey 6505 1M/.0068uf
Peavey Valveking 100 212 1M/.01uf
Fryette D60 1M/.01uf?

[Colossal]

I combed through a few schematics to check values on their Resonance controls. Cap values are all over. All pots seem to be audio taper. I'll have to experiment with different cap values on the Express.

When making sense of those resonance cap values, check the negative feedback value as well as how the power amp is set up.

[Reeltarded]

It's so dependant on volume too. VHT Pitbull res sounds like mush unless the amp is about to deconstruct a pair of cabs, and the res is on about 1 and a half.

[leadfootdriver]

I found this calculator. It gives a rough idea of which cap values affect which frequencies. Cool.

*edit*
The more I think about it, the higher the value, the lower the crossover point. So a .01uf is only passing low bass frequencies, which would come off as perceived thump from the cab. While a .0022uf is passing more mid bass along with the low bass, which might come off as mud.


http://www.ampbooks.com/home/amplifier- ... capacitor/

[passfan]

Just installed it on a 4-4-0 and the results are promising. I have a massive range of sweep due to a linear pot instead of analog. Seems to increase in gain when going from bass to treble sweep. I was using a 10k feedback resistor and switched to a 100k. Should I change it back ?

[Reeltarded]

Yes. You should try it. I changed my preferences a little after installing Thee Martinizer in three amps.

What a brilliant design, one of my most favorite things.

*edit*
The more I think about it, the higher the value, the lower the crossover point. So a .01uf is only passing low bass frequencies, which would come off as perceived thump from the cab. While a .0022uf is passing more mid bass along with the low bass, which might come off as mud.

I split the usual stock Marshall .1u pres to .047 and it is perfection in my amps. you need to take what you have and split it closely into the two sides. There is some neat stuff to be found by using a .047 to ground, and a .068 in the control as well, or the other way round. That split makes a difference. [/quote]

[hans-jörg]

Hello,
I tried it too and its rearly a big jump.
The only question: the orig. Liverpool has a PI kathode with 1k / 39k. So mine.
Would it be better (for this circuit) to swap it with (the Express) 10k. Than the tail with 5k (4k7)// 0,047µF to ground.
Thanks in advance

Hans-Jörg

edit: "The Martinzer-Mod" is the best name for it. Sounds suspicious