Boost switch explained

[Tdale]

The switch breaks the cold lug (1) of the treble pot and the wiper of the bass pot. The signal then travels mainly through the treble cap and lugs 3 and 2 of the treble pot. It also leaks a little through the slope resistor and bass pot (the maximum value of the pot).

Please point out errors in the drawing.

-Jake

Very nice schematic! I can see that the boost switch will break the contact between the bass-pot wiper and the treble pot in one position.

I can also see that when the boost switch is in the other position, there will be contact between the bass-pot wiper and the treble pot BUT, it seems that the rock/jazz switch has to be in a certain position for that to happen.

With the rock/jazz switch in a positon where the commons are in contact with the two upper lugs, there will be contact between the bass and treble pot.

But in the other position, the signal from the bass pot will go through the 100K resistor, directely to the volume pot

Also, when both switches are in the position shown, the upper bass-pot lug and the bass-pot wiper are connected through the switches....is that correct?

Tommy

[Tdale]

And here's the layout. I haven't use a Jazz/Rock switch so this is the one that went in my two amps. It is pretty effective. FWIW, I broke the two hot legs off the relay so I didn't have to install extra turrets. sh

Hmm. should the wiper of the bass pot and lug 1 be connected at all times, as shown in this schematic?

Tommy

[Tdale]

Until I some day completely understand this, will the hybrid-a switch arrangement work as it's shown on the schematic, also if I remove the deep switch and it's components?

Tommy

[Luthierwnc]

Tictac: would you use this for an HRM as well? Skip

[HiGain]

I'm going on my reading of previous schematics rather than experience with actual amps...

My understanding is that the boost switch always works. However, the Rock/Jazz switch will only work when the boost switch is not engaged.

Makes sense. It's not very logical to expect a boosted jazz setting.

Jake

[Luthierwnc]

Yup. The purpose of the boost is to bypass the majority of the tone stack. Years ago, one of the first popular mods on guitar amps was to do exactly that on the normal channel. sh

[Tdale]

But the rock/jazz switch also breaks the connection between the bass wiper and the treble side-lug... But I guess it's supposed to do just that..

Tommy

[tictac]

To Luthierwnc:

Actually the boost circuit I use is different than the PAB. Mine is a .002 cap with a 220K in series and a 1Meg trim pot wired as a rheostat to ground after that.

The cap goes to the plate of V1A (same as treble cap and slope resistor)
The output side of the pot goes to the N.C. side of a relay the treble control output goes to the N.O. side of the same relay. The common of the relay goes to the input of the clean volume control.

With the relay on = clean, relay off = boost.

This boost control is like having the mid control and the boost in the same circuit. Plus you can adjust the amount of boost you want. You can get some Boogiesque with this boost if you want. I like mine set at about 150k from ground myself. The PAB as shown has all of the signal passing thru a 500pf cap. That's a bit thin for my taste, maybe it sounds good to some, I've never tried it myself.

Well now my secret is out.

TT

[Luthierwnc]

I have experimented around with a couple versions and they all have their own merits. The amp I am (well, rewiring) now is going to get the version where the entire 500k of the bass pot is still in play off the slope resistor and the wiper is connected to bass lug 2 when disengaged. This amp is a little too bright in boost mode so this should add back some bottom. So far I have been lucky in that most of the variations I have tried have worked. It is mostly a matter of tuning the whole system.

Skip