Recipe for a moderate and FAT PAB circuit

[stelligan]

Anybody have one? Sorry to revisit this topic, but my quest continues to be an improvement or "alteration" to the PAB circuit in my amps. For me - I wish it would keep a bit more low end and not be as pronounced a boost. I have toyed with deviation away from the 22M resistors to lower values - and that helps with the level jump. I still long to retain low end in my HRM with PAB engaged. For reference - my treble, mid, and bass are at: 11(o'clock), 11, and 1 respectively. One idea was to come up with a switchable fixed resistor value at the volume pot. Another was to try to introduce more low end in stage 1 so that the bass pot's level lives nearer the others during use of the clean channel to start with. Any help with this is greatly appreciated.

[Normster]

Just a thought, but you might have better luck experimenting with the mid boost circuit. Less boost, a bit more drive, less loss of bottom end.

[dogears]

Mine retains the bottom. It took me a long long time to develop the fix. No way I am publically posting it though as a ceriatan individual will steal it and use it...... Maybe if I get a royalty....

[stelligan]

Thanks Normster,
I do have a mid boost on most of the amps and like it a lot - Especially with Fenders. Just looking for the PAB function to more closely mirror the clean tone. I can get whatever I want or need from these amps with some knob twisting, but I would like a gig setup that went from squeaky to freaky without having to twist my guitar and amp knobs. Perhaps too lofty a goal?

Dogears,
If you can steer me in the right direction, I would be forever indebted. I can tell from the most recent clips that the OD PAB thing you have going is much more like it. I would like to hear that amp being switched from one voice to the other to hear how the tonality shifts or does not.

[bcook]

I can tell you what works for me. Leave the bass pot wiper connected and change the other resistor to 470k.
-Bob

[ayan]

I can tell you what works for me. Leave the bass pot wiper connected and change the other resistor to 470k.
-Bob

I toyed with that a bit and agree that it sounds very musical. Then thing is that the tone controls remain active when in PAB mode, so that may or may not affect people psychologically (as in: hmmm, there is some additional gain to be had here).]

Lifting the whole stack, like Boogie did in their early Mark Is and IIs is another possibility. I tried it and thougt it sounded too bassy that way. You can not quite lift the entire stack, but float it on a resistor... once again 470K sounded pretty good, but it does leave the tone controls active.

Cheers,

Gil

[ElectronAvalanche]

Hi there,

IMHE (experience) in a non-HRM:

leaving out the LNFB (44M or 22M with 0.05uF on grid of second triode) makes for a much more useful PAB.

I have come to not like the LNFB that much anymore.

This probably does not help you unfortunately with a HRM-

Cheers,

Dominik

[TimS]

How does the non-HRM sound in clean and OD modes without the LNFB?

[d95err]

(semi thread-hijack)

...while on the subject of the PAB. In the D-Lite, the PAB switch is an SPST switch, while in the more complex models a DPDT swich is used.

Is this essentially the same boost design? (I.e. is the D-Lite PAB what remains when you get rid of the Rock/Jazz and Deep switches of a regular Dumble?)

(I've tried to figure this out, but I get lost in the complexity of all those switches. I'm lazy, I know... )

[stelligan]

Thanks for all the input everyone. I have lots of ideas to try.
I keep going back to using a Keeley Katana in front when I want to goose the amp and keep the bass happening. I really want to take that off my board if I can.

d95err - I built a D'Lite. If I recall the original layout did not use 22M resistors in the PAB circuit. Using them was an improvement, but still not where I wanted to be. I think I put them in series to pad it a bit more(22M x 4). The addition of a mid boost is very fun in that amp - and when switched in with the PAB does add some low end content to the OD PAB sound.

[mlp-mx6]

The addition of a mid boost is very fun in that amp - and when switched in with the PAB does add some low end content to the OD PAB sound.

Having the mid-boost footswitchable is extra nice, especially if you can step on both simultaneously. If you put the 3 switches in a triangle configuration on your footswitch box you can hit any 2, or all 3 at once.

[nickt]

(semi thread-hijack)

...while on the subject of the PAB. In the D-Lite, the PAB switch is an SPST switch, while in the more complex models a DPDT swich is used.

Is this essentially the same boost design? (I.e. is the D-Lite PAB what remains when you get rid of the Rock/Jazz and Deep switches of a regular Dumble?)

(I've tried to figure this out, but I get lost in the complexity of all those switches. I'm lazy, I know... )

(demi-semi thread-hijack)

I keep promising myself I'll sit down with all the schematics, a pot of coffee and a crochette needle and unpick all the combinations so the average blockhead (eg that nickt guy) can get a grip on the options available. Will stick in the files section when done.

One day, one day soon ... ish...

[stelligan]

I'm gettin' somewhere with the fatter PAB thing. Thanks to all for the help. My 50 watt HRM skyliner with a slightly modded PAB. Mid Boost on. Might be getting too fat - if there's such a thing. Here's a clip of mindless wanking:

http://www.jonesin.org/dave/fatPAB.mp3

Please comment/suggest

[odourboy]

Sounds VERY fat!! Can you post (or PM) the mod? I'd like to mess with it. I feel it'd like to add a bit of chesty-ness to my Skyliner HRM BM PI build in a way the the mid boost is not satisfying and you could be on to something.

[yeahyeah]

I like to use 4.7M resistors in place of the 22Ms
Fattens up the bottom nicely.

Another thing i thought of would be to add a small cap that switches in parallel to the treble cap. smaller than the usual mid boost cap to keep it from getting too extreme...of course that is getting you mostly more low mids too.

OR heres a thought...Maybe instead of adding bass, we could remove some highs and high mids? that would increase the apparent bass and also give a less hot boost.

just thinking out loud.