Can you usually lift the ground on the tone stack?

[CitizenCain]

Does this work on most any tone stack design? I thought it would be a neat feature on the Heathkit I'm putting together. I've read about doing ot on Fender tone stacks, the Heath has a Baxendall stack. It's still gorunded like any other tone stack. If I lift the ground via a switch, will that basically bypass the tone stack to give me a boost?

Thanks

[Chuck H]

If it's a passive bax (aka "james") it should work fine. If it's a real bax I don't think so. A true Baxandall is an active circuit that uses NFB and IIRC there may, or may not be a ground reference. I read somewhere that the original bax did have a ground reference, but since it worked fine without it most designers didn't include it. So if thats the case, if your bax is the active type, lifting the ground should do little or nothing.

Chuck

[loudthud]

It won't hurt to try. Hopefully both tubes are right near the controls, long wires may be subject to noise pickup and/or oscillations. You could use the switch on the back of the treble pot or a separate switch.

[CitizenCain]

Yeah, it's a passive bax so I think I should be OK.

That's exactly what I was planning on, using the old on/off switch on the back of the treble pot. I'm running shielded wire from the treble pot to the next tube stage, should be OK, eh?

BTW, this is the one I'm rebuilding into a Princeton Reverb chassis for my friend, so the layout is not like the original.

Thanks guys!

[hasserl]

Well, there are two ground points in the bax stack. Are you going to lift both? One off the Bass/Mid circuit, one off the Treble circuit. You could lift the Bass/MId ground and be left with basically a Treble bleed off control like other amps with a single tone control. Or you could lift both to completely bypass the stack and send all of the signal on to the next stage.

I work with a lot of amps that use a modified version of the Bax stack. A popular mod is to add a bypass around the stack, taking the input after the coupling cap from the preceding stage (anode driven stack) and running it to a 1M pot wired as a variable resistor then on to the output of the stack. This allows the user to dial in however much bypass they want, from none at all to toally bypassed. It works rather well. I typically use the control set to bypass some of the signal, reducing the effectiveness of the Tone controls, but not completely bypassed, so they still have some effect.

[Chuck H]

Like a Kendrick "Texas Tea" control but for a Bax. Doesn't Dr. Z use Bax tone stacks.

So when this amp is done it could have a Dr. Z type tone stack with a Kendrick Texas Tea control.

Could be the ultimate "boutique" tone stack.

Chuck

[CitizenCain]

This must be a modified Bax, or a James stack or something. There's only the one ground connection. The Sundown head I have also has this same design, which was used in some early Ampeg amps, too.

Here's a schematic of the Heathkit.

http://www.visi.com/~sstolle/heath/aa-23-mod-005a.JPG

[Chuck H]

It's a passive "James" type. The two ground points mentioned are simply tied together. This isn't always shown schematically but in actual wiring I'm sure most James type tone stacks have the grounds tied together. Lift that ground point and see if you like it. You should try the variable bypass too. It might be worth the extra hole.

[CitizenCain]

Yep, the new schem I've got incorporates both features