Mods for improving 5E5-A tone stack?

[funkgang49]

Built myself a SE amp awhile back with a 5E5-A inspired tone stack. The amp sounds great but the Treble & Bass add volume as well as breakup when turned up, which I can live with, but when each control is turned down the respective Treble & Bass frequencies become muffled.
I tried a 5F6-A Bassman style tone stack TMB which solved the muffled frequencies as well as the volume boost thing but the overall amp magique has been lost.
I am contemplating returning to the original 5E5-A style tone stack but before I do I was wondering if anyone might have some suggestions on improving or mitigating the tone stack quirks?

[billyz]

Might try lifting the 5 meg feedback resistor around V2.

I like to disconnect the 220k To ground as well, but then youll have alot more gain !

[bluesfendermanblues]

Here is a mod for improving the tone stack - but not mitigating the quirks.

I have build a 5F4 super and didnt like the scooped mid in the design, which sounds more like blackface than (Champ or Deluxe) tweed

So I have put a switch, between V2 and V3, on the bottom of the chassis, with a 680pf cap. This allows me to up the standard 250pf on the treble pot, from 250pf to 930pf.

This warms up the middle tremendously.

[funkgang49]

Might try lifting the 5 meg feedback resistor around V2.

I like to disconnect the 220k To ground as well, but then youll have alot more gain !

Hey Billyz,
Will eliminating the 5meg & 220k series resistors to ground change the response of the Treble & Bass controls, improving the clarity in the counterclockwise rotation?

With those resistors in place the amp has plenty of gain.
I was running it without any negative feedback - sounded best!
I am also utilizing one output from an LTPPI, as in the Gulsekt-88 and with help & guidance from MattH, which has given this amp a BIG amp sound.

It has slightly greater output (volume) than my '65 Reverberocket (2-7591A's in PP), as big a frequency response, but much better harmonic content, overdrive characteristics, and touch sensitivity.

Very impressive as far as I am concerned.

My only niggling issue is the response of the tone controls.
When playing I just set the controls to 12 noon and make all my adjustments from my guitar. Great!
However, like many DIY'ers, I can't leave well enough alone - must keep tweakin' & improvin' whenever possible.

So I have put a switch, between V2 and V3, on the bottom of the chassis, with a 680pf cap. This allows me to up the standard 250pf on the treble pot, from 250pf to 930pf.

This warms up the middle tremendously.

Thanks BFMB - I will definitely play with that!

[matt h]

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[funkgang49]

Hey Matt!
When originally voicing this amp I was concerned with getting the most clean headroom/highest volume level before breakup out of it.
The idea was that I could get earlier breakup with the use of a 6V6 then increasing headroom incrementally up with 5881, 6L6, EL34, KT-77, etc.
Ya' know - a good range of output and flavors to shift to while on the fly(cathode biased).

However...

After playing with all those different output tubes I whittled it down to 6L6, EL34, & KT-77.
I found that the JJ KT-77 had the best of all worlds - great cleans and outstanding overdriven tones.
I was using a 500ohm 10watt Cathode resistor/1K 5watt Screen Grid resistor with about somewhere between 360-370V on the Anode (have to check my notes) with a 5U4GB rectifier (sounded best).
I will be installing a VVR controlling voltage only to the output tube to simulate 5Y3. Further voltage drop will be in lieu of a Master Volume control.

I had tried a Presence control off the LTPPI but found that at best it had little effect so I dropped it.

I played with multiple different values of NFB: 100k, 82K, 56K, 33K, etc. while trying to achieve max headroom, but found that despite losing a little in the headroom department the overall response of the amp sounded outstanding with no NFB.

I came to the realization then that I was probably asking TOO much of the design and that tone and response was way more important than clean headroom.
I could achieve that in copying this format into a Push-Pull amp.

So...
Back to your suggestion:

Rather than yanking the NFB loop, you may actually want to try out increasing the NFB. I know it sounds counterintuitive, but give it a whirl. If you've got a second 5M resistor kicking around, just clip it in parallel to the one already in there as a quick test.

I've got both a 4.7M as well as a 5.1M available.

What would the parallel 5M achieve? And with what value NFB resistor?

[billyz]

I run those changes with the stock nfb circuit. Removing the nfb will certainly increase the gain as well. I probably would do both. Since the tone circuit is passive, your throwing away gain at those frequencies the more you roll them down.
I find the 5meg local feedback tends to squash and flatten the sound. I would think reducing the 5meg would further this affect. Everyone I have done this mod for absolutely loves it.
All I can say is try it all the ways mentioned here. There is no one right way, it all depends on what you prefer for your sound and feel. I like my amps pretty lively. Some like em smooth and refined.

[matt h]

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[billyz]

I meant to say I would not remove both feedback loops. Cant type anymore and never could.

[funkgang49]

I got what both y'all are sayin'!

I already have a 52K Global NFB resistor hooked up from the end of the PI tail resistor to speaker jack from the 5F6-A tone stack scheme that I just removed. I'll keep that in place for now so I can see how the amp sounds with and without it after I finish rewiring for the original 5E5-A tone stack.

I wired in a 4.7M from the 2-270K resistors coming off the 2 Volume controls and connected to the end of the .1uf cap. Instead of connecting a 220K resistor from the end of the .1uf cap to ground I'll leave it out and use a jumper wire to make the ground connection.

See how that sounds, then try paralleling another 4.7M, etc.

I've almost finished rewiring but I have to stop soldering now.

I have off tomorrow and will finish up then test!

[matt h]

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[funkgang49]

Instead of connecting a 220K resistor from the end of the .1uf cap to ground I'll leave it out and use a jumper wire to make the ground connection.

On top of that! Just eliminating the resistance not the connection to ground.

[funkgang49]

OK fellas, just for clarifications sake('cause now I'm not so sure) -

I remove the 220K resistor and replace it with a jumper wire
OR
do I remove the 220K and disconnect the connection to ground at that point altogether?

[funkgang49]

As Emily Latella would say "nevermind"!

[funkgang49]

Gentlemen, thanks a' plenty for all your input!

The amp she's a' singing!

After trying different combinations of the suggestions made by Billyz & MattH,

I have settled on removing the 220K resistor (improvement of the clarity in both Treble & Bass controls) as well as removing the 4.7M resistor (further improvement in clarity & an increase in gain).

Great mod Billyz!

I removed the 56K Global NFB resistor, however, I am leaning towards reinstating the GNFB with a lower amount of feedback - 82K or 100K just to rein in the wildness a tad.

BFMB - I like where the overall tone of the amp sits right now so I'll play with it for a bit before I try upping the 250pf cap on the Treble pot to say 390pf, 500pf, etc. probably over the weekend.

Thanks for that suggestion!

The amp is really great sounding now - very touch sensitive, great overdriven tones with both 6L6 & KT-77 with very musical and open cleans. The amp is always articulate clean or overdriven but because of the harmonic content it is never harsh or sterile sounding!

Me likey!

A key component to this amp sounding SO big and beyond what a SE is normally capable of is due, IMHO, to the inclusion of the LTPPI as suggested by MattH.

Kudos to you Matt!

Thanks to everyone for their input - it's what makes this forum priceless!