Bass Guitar Tube Amp

[Charles BL]

Colt 45
Sorry to be so long getting back, I opened this thread late and had to wait for lunch hour to reply. Power req'd is not huge, practice amp size, maybe 15 to 30 watts?

[Magnetmaz]

boo! if you're going to build the kid something, at least build him something substantial!

Maybe an 8x8" cabinet, with a 650 watt head?

You can use it to strip paint off the side of your house when he's not practicing....

[Charles BL]

Magnetmaz,
He's playing Jazz, Ska? grunge?... He goes to sleep listening to Miles Davis, does school performances in the Jazz combo, does club gigs (just starting) in ska? He plays a fender jazz bass soon to have a Warmoth fretless neck. He'll probably use my Washburn w/active Duncan when he does'nt want the fretless sound. He say's he wants the tube sound, but I'm not entirely sure he identifies it correctly. However, I'm all for it.
Thanks

[phase_accurate]

Hi Charles

IMO a good compromise (which isn't actually one at all !) would be to build a decent tube- or hybrid- preamp which he can use with a weak amp now and also with a "paint-stripper" later on (don't forget to add a headphone output !).

In a bass-preamp I built 10 years ago I used a triode as the first stage (the rest was all op-amps). I could set the bias of the tube from the front-panel to get more k2. This gave some warmth to the tone of my fretless but was annoying with my fretted bass.

Regards

Charles

[nobody special]

I would agree with that... it would be a good idea if you could seperate out the preamp and power amp. It makes your possibilites open up a lot.
You could build a solid state P-P amp, mosfet or IC, cheaper than a tube amp, and it would put out much more power. A tube preamp would be nice. Make it with a pre/post gain setup so you can get a very clean or a slightly dirty sound. One thing that would be beneficial with a solid state preamp is that you could easily implement active EQ without needing another power supply... passive tone controls don't do much, in my experience. By seperating out the amp from the preamp, you could also easily insert an outboard EQ, or later build an active cross over and use the wimpy amp for the highs, and build a bigger amp for a future bass cabinet. Just some ideas.
-NS

[Charles BL]

Phase _Accurate & Nobody_Special

Great ideas. I think I could easily slide by a hybrid as he probably would'nt know the difference yet. Do either of you have a specific pre design to suggest?
Thanks

Charles

[scottnixon]

http://www.taosnet.com/f10/fender_pre.htm

This is close to what the Alembic f2b is/was and you may find the Alembic scheme online (it has been around and I'm trying to find it) You could use a bridged LM3886 amp (about 160w into 8) in an "active enclosue" with a single 15/12 or 10. I've rebuilt Polytone amps with the 2x3886 amp and they work amazingly well. Add the Fender preamp on top as a head, you can build more powered speakers if you need more level. This would be super cheap to build and sound great.

[nobody special]

I would recommend using a regulated supply for the preamp stage. It should make it easier to get the low frequency roll off down to an approprate cut off point without motorboating. You may want to watch out for guitar amp designs as they often have a very high low frequency rolloff, which you don't want for bass. If it were me, I would consider using a mosfet front end (possibly jfet input stage for lower noise). Put a tube somewhere in the gain path for a little character (split the gain path off to the tube, and make it so you can blend it in... that would be cool). You could probably get away with running it at a low voltage, since you want the harmonic distortion in this case, so you could use the same power supply as the mosfets.
As far as IC amps go.... yeah, it's easy and cheap, but when they "hit the wall", it's really ugly. And, they WILL hit the wall often with a bass guitar! It require a lot of power. A soft clipping circuit would help things out tremendously on a lower powered amp. Why not an A/B Mosfet push pull? adapt one of Aussieamps designs, or something similar. To build it right either way, the majority of the $$$ will be spent on the power supply, so why bother with IC amps?
It all depends on what you want to do with it, of course. If it's a practice amp, and you won't be competing with loud guitars, drums, etc. or in big rooms, then the criteria changes.
Oh, and BTW, consider using multiple drivers to increase the efficiency- free SPL (kind of).
Hope this helps.
-NS