PAB Mod

[Structo]

I stumbled upon this while looking over some ODS layouts.

Notice how the PAB is wired to the relay.

I have a real hard time visualizing how some switches and relays are going to work when when switched on.

It looks to me that the mid pot ground is connected to the normally closed contacts, allowing normal operation of the mid pot when PAB is not switched on.

The 22M resistor does not appear to be in the circuit at all in this layout.

A guy that built a Ceriatone clone changed his PAB wiring to this.
I'm wondering if this would allow the bass and treble pots to still operate in PAB mode.
Can one of you clever guys take a look at this to see if maybe this is a better alternative to the typical PAB switching?

[IMG:798:483]http://i23.photobucket.com/albums/b392/ ... PABMOD.jpg[/img]

Also, most clone layouts have the middle and right side (when viewing from behind) lugs of the mid pot jumpered as this layout also shows.
But the #124 layout shows the wire from the mid cap going to the middle lug only, with nothing on the right lug.

Which is correct and what affect does jumpering those two lugs together have?

Thanks, Tom

[Sonny ReVerb]

Jumpering the lugs is a type of 'fail-safe'. If part of the resistive carbon track wears away, instead of having an open connection it would revert to a connection across the whole pot and you'd still have signal. I'm not sure of HAD's intention, but either way works if the pot is functioning normally.

[LPSGME]

I stumbled upon this while looking over some ODS layouts.

Notice how the PAB is wired to the relay.

I have a real hard time visualizing how some switches and relays are going to work when when switched on.

It looks to me that the mid pot ground is connected to the normally closed contacts, allowing normal operation of the mid pot when PAB is not switched on.

The 22M resistor does not appear to be in the circuit at all in this layout.

A guy that built a Ceriatone clone changed his PAB wiring to this.
I'm wondering if this would allow the bass and treble pots to still operate in PAB mode.
Can one of you clever guys take a look at this to see if maybe this is a better alternative to the typical PAB switching?

[IMG:798:483]http://i23.photobucket.com/albums/b392/ ... PABMOD.jpg[/img]

Also, most clone layouts have the middle and right side (when viewing from behind) lugs of the mid pot jumpered as this layout also shows.
But the #124 layout shows the wire from the mid cap going to the middle lug only, with nothing on the right lug.

Which is correct and what affect does jumpering those two lugs together have?

Thanks, Tom

Being everything is relative, I keep thinking that the best way to simulate a boost is to simply have 2 general paths of signal; one being from the tone stack and the other straight out from V1a (as they sound different) with a pot to vary between them; and then use a PAB switch to simply produce a lower volume on the varied signal, so as to simulate a relative volume boost between PAB switch states.

Of course the Deep (cut) and Rock/Jazz switches would need to be revised accordingly.

Initially I wondered if my amp was mis-wired because, besides the large volume difference that everyone complains about between Normal and PAB mode, I also hear a tonal difference in PAB mode [less boom to the bass and a generally sharper tone].

However, after looking, I assume that it is normal. But to be sure, does anyone else experience that????

I believe the reason for it is that the PAB does not simply change the volume but changes how the tone stack connects.

For what it's worth (I could be wrong) here's what I see:

[IMG:505:314]http://i275.photobucket.com/albums/jj30 ... SG/pab.jpg[/img]

The tone stack separates the signal from V1a into separate the Treble, Mid and Bass paths similar to, but a bit differently than, a typical vintage Fender stack.

Path #1 (to the Treble control) passes on the highs (and additional mids if boosted) through the Treble control to the line leading to the 'input' Volume control connected to V1b. The the mids are normally blocked by a 300Pf cap, leaving only treble, unless the mid boost switch is closed.

Path #2 (to the Mid and Bass control) has the Mid control wired to roll off the mids and highs, where upon the remainder of the signal goes to the top end of the Bass control, where I believe the highs are further rolled off via a .001 cap going to the other end of the Bass pot [which has 10K to ground].

In Normal mode (no PAB) the wiper of the Bass control attaches to the bottom end of the treble control (just like in a Fender stack) - so that the Treble control functionally sweeps between Path #1 (Treble/mid boost) and Path #2 (Bass and Mids) just like a Fender. But unlike a Fender stack the Bass pot wiper is also attached the to the Treble wiper (and line leading to the 'input' Volume control before V1b) via a 100K resistor.

When in PAB mode, the wiper of the Bass pot disconnects from the bottom end of the Treble pot and instead connects through two 22 meg resistors in series, essentially leaving the Treble control signal (going to the Volume control) altered so as to contain less bass and just the Treble (and mids passed by the mid boost switch) and very little of the bass/lows it formerly had. Meanwhile the bass from the Bass control's wiper continues to stay connected to the 'input' Volume control of V1b via that 100K resistor, so some of the Bass (and the Mids from Path 2) continue to pass.

Thereby it seems like activating the PAB removes the ground path and load on the Treble pot allowing more highs (and additional Mids if boosted) to pass, but less lows [which is why I believe I hear a sharper tone with less boom to the bass with the PAB on].

[Structo]

I believe the 22M resistors are simply to keep the relay from popping when switched.

How PAB works is very simple, since this type of plate loaded tone stack is quite lossy, when the PAB is engaged it bypasses the tone stack resulting in a stronger signal to CL2.

[JD0x0]

personally i have never had the "volume jump" problem on my ceriatone OTS when the PAB is engaged. And the the tonestack doesnt seem to be as "lossy" It may just be because i run the amp with the mid boost always on which reduces the amount of gain that is lost from the tonestack

[LPSGME]

I believe the 22M resistors are simply to keep the relay from popping when switched.

How PAB works is very simple, since this type of plate loaded tone stack is quite lossy, when the PAB is engaged it bypasses the tone stack resulting in a stronger signal to CL2.

I guess that the 22M resistors could be, as you say, to eliminate a pop; as they are simply wired across the switch. But doesn't that still leave what I said about the PAB mode, i.e. that it disconnects the wiper of Bass pot from the bottom of the treble pot thereby removing the bass signal while leaving a 100K resistor path? I don't see that simply as a bypass.

Plus, even if the BAP truly bypassed the stack, that doesn't seem to be what I've read a lot of people say they'd like. I think they've said they just want a volume boost with the signal still affected by the tone controls.

[Structo]

The boost you get by the PAB relay or switch depends where you have your tone controls set.

If you have the bass and treble up above noon, then the boost won't be as dramatic.
If you have the tone controls at less than 11 O'clock then you will get a bigger boost.

A guy suggested to me on another forum that it may be better to wire the boost.

He suggested instead of lifting the entire tone stack, try switching in a 33k-47k resistor with a .001-.005 cap in parallel off the midrange tab to ground. It boosts gain and volume without deactivating the tone controls.

I haven't tried it yet.

[briane]

I believe the 22M resistors are simply to keep the relay from popping when switched.

Yes thats part of it, but more importantly the value sets the volume of the PAB. Bigger resistance == more volume. Its a balance to the normal.

I have some builds without the resistor, and no pop. Max volume from PAB, but a bit louder than normal.

[JD0x0]

FWIW i believe "Pickmaster" on ceriatone forum has a knob on his amp to set the volume of the PAB. I also believe he has a "sticky" with all his amp mods on the layout

[ChrisM]

http://ceriatoneforum.com/index.php?topic=740.0

Too many switches for me but neat ideas.

[Structo]

I had looked at that layout before.
That is some extreme modding.

I kind of like the boost idea but not enough to drill another hole.

[LPSGME]

The boost you get by the PAB relay or switch depends where you have your tone controls set.... [snip]

...A guy suggested to me on another forum that it may be better to wire the boost.

He suggested instead of lifting the entire tone stack, try switching in a 33k-47k resistor with a .001-.005 cap in parallel off the midrange tab to ground. It boosts gain and volume without deactivating the tone controls.

I haven't tried it yet.

EDITED:
I asked: Wouldn't adding more resistance between the Midrange and ground merely increase the midrange, no differently than if it was cranked?

But I overlooked the cap that would bleed off the Midrange... right?

I tried lifting the 10K to ground from the bass pot, and that added a slight bit of gain to the Normal setting without disabling the effect of the Bass pot.

But I still think the cleanest way to simulate a volume boost is by simply bridging the two 22M resistors and removing the 100K resistor - and then inserting the PAB relay and a switchable pad after the Treble pot wiper?

Then the Normal level would be with pad in, and the gain with pad out.

Then, a simple SPDT toggle could also provide the choice of using the stone stack or the bypassed sound straight out of V1a.

Otherwise I still don't see how the PAB completely bypasses the stack.

[Structo]

Something I noticed today when I was playing my amp.

For some reason, the boost in clean mode is huge.
When I step on the PAB in overdrive it hardly boosts it at all, more of a tonal shift.

I have the two resistors on the PAB relay but I can't remember the values.

I know I didn't go with the 22M ones because that hadn't been posted before.

Can anybody tell me why the PAB would be so huge on the clean channel but not on the OD channel?
That is where I would prefer the boost to be for soloing.

So mine is wired this way but the resistors on the PAB relay are smaller, maybe 10M.

I am also considering adding a tone control for the OD channel.
Not HRM but a single knob tone control just for the OD.[/code]

[Structo]

LPSGME,

If you look at the schematic, when the PAB is switched on it opens the relay switch that connects the bass and treble pots together.

So when it opens, the signal only goes through the treble cap and treble pot to the next stage.
The mid and bass pots are bled to ground.

[LPSGME]

LPSGME,

If you look at the schematic, when the PAB is switched on it opens the relay switch that connects the bass and treble pots together.

So when it opens, the signal only goes through the treble cap and treble pot to the next stage.
The mid and bass pots are bled to ground.

Yes, I see that. You are right.

But in the drawing that Nik kindly sent [below], the Bass wiper has a 100K resistor [not included in the schematic you showed] going [via the Rock/Jazz switch] to the wiper of the Treble Pot.

Doesn't that leave some of the Bass and Mid signal still mixing in?

In any case, the signal going through the Treble control alone seems even more bass limited by the 330pf cap; and not merely a bypass.

That's why I keep thinking, why not take the tone stack output and switch between 2 levels to simulate a boost.

PS: I think that .05 off the Rock/Jazz [in the schematic I'm showing] is a mistake. Shouldn't it be .005?

[IMG:505:314]http://i275.photobucket.com/albums/jj30 ... SG/pab.jpg[/img]