Bass Tube Preamp Schematics?

[PrecisionB]

Hello all out there. I was wondering if anyone knew of any tube preamp designs that sound best for bass. I use an Alembic clone that I made which sounds nice (just a copy of a vintage fender preamp) But I was just curious to know what else is out there. Simple is always nice too...

[Bear]

Best is probably one of those subjective things. Probably old Ampeg designs would have to be considered, although there's supposed to be a oddly large bass roll-off somewhere in the SVT circuit.

Truth be told, most of the classic guitar amps were "all purpose," relatively close to the bass versions, or, of course, bass amps themselves. The bass roll-offs are going to be the limiting factor for a lot of guitar preamps once you get a capable power section and speaker setup attached. It might not be a very modern sound, though, or cover deep and tight from the low B on a five string bass.

[andrew_k]

Couple of gain stages, minimum 50uF cathode bypass caps, baxandall tone stack, done.

[PrecisionB]

I suppose I wont know what I want until I hear it. I like vintage tone, I have an old b-15-n portaflex which I adore. That type of sound has always been very sonically pleasant to my ears. But every once in a while i'll hear a recording with a slightly more "active growl" which really pulls me in. (i guess that's more pickups and onboard pre. than anything else) To get a tone of a cross between the two with my old fenders would just be heaven.
Andrew_k,
Have you built a preamp with a baxandall tone stack? If you have, what differences, if any, are there between that and the fender-style?

Thanks!
-Patrick

[PrecisionB]

*sonic differences that is.

[Firestorm]

I suppose I wont know what I want until I hear it. I like vintage tone, I have an old b-15-n portaflex which I adore. That type of sound has always been very sonically pleasant to my ears. But every once in a while i'll hear a recording with a slightly more "active growl" which really pulls me in. (i guess that's more pickups and onboard pre. than anything else) To get a tone of a cross between the two with my old fenders would just be heaven.
Andrew_k,
Have you built a preamp with a baxandall tone stack? If you have, what differences, if any, are there between that and the fender-style?

Thanks!
-Patrick

On the bass amps I build, one channel has a James/Baxandall type tone control tweaked to be a bit mid-rangey which does the Ampeg tone pretty well. The other channel is 5F6-A (same as in a Marshall bass amp) which makes the floor shake (with the right output tubes). If you keep the channels in phase, you can bridge the inputs and mix them.

[PrecisionB]

Has anyone ever thought to cascade a fender with a Baxandall? Would a single 12ax7 have enough gain for such an application?

[Andy Le Blanc]

Id try a SRPP, you have an impedance choice with the configurations output
and plenty of bandwidth and drive but you'll need two tubes to try it around a tone stake.

[KellyBass]

[/quote]On the bass amps I build, one channel has a James/Baxandall type tone control tweaked to be a bit mid-rangey which does the Ampeg tone pretty well. The other channel is 5F6-A (same as in a Marshall bass amp) which makes the floor shake (with the right output tubes). If you keep the channels in phase, you can bridge the inputs and mix them.[/quote]

I'll bet that sounds great! I love the bax tone stack for bass...aspecially the hiwatts. You don't happen to have a schem/layout for this do you?

[Firestorm]

I'll bet that sounds great! I love the bax tone stack for bass...aspecially the hiwatts. You don't happen to have a schem/layout for this do you?

Unfortunately no. I should. The 5F6A channel is stock: gain stage - volume - gain stage - CF - tone stack. The James channel is like a stock blackface channel with the James stack and volume control inserted in between the two stages. You just adjust the values in the James stack to taste. You can simulate it with the Duncan tool.

The real key to a good tube bass amp is the output tubes: 6550s or KT88s. Plus big capacitance at the main filters: 100uF or more. Needs a good PT and OT. For bass, ultralinear OTs work very well.

[jaysg]

Has anyone ever thought to cascade a fender with a Baxandall? Would a single 12ax7 have enough gain for such an application?

You can delete the MosFet if you only send the output. I have an extra out before the Baxandall.

[PrecisionB]

thanks for all the input everyone.

P.S.
I am using a PA amp for my power-amp. Tube power-amps are too big and heavy for bass. (although I think peavey came out with a all tube bass head that incorporates a super light switch-mode power supply, very cool!)