Bass Guitar Tube Amp

[Charles BL]

Hello and hello,
I sure am enjoying the conversation! I've got very little DIY experience, (tweaks to my ST70) and some Pass Labs stuff, but I would like to build a smallish tube amp for my son's bass. He want some good warm tone. I do have access to a machine shop for the physical construction, but would probably not attempt trannies. Are there any suggestions for a relative first timer? Should I copy a known commercial amp?
Thanks,
Charles BL

[Colt45]

how much power do you need?

once we get that done I can start rattling off some ideas

If you want <20w, we could probably put something decent together for cheap, especially if you can scrounge parts from the junk bin.

more power and we'd have to jump the cost some (mostly because of the larger output tranny required..)

[Joel]

Originally posted by Charles BL
Should I copy a known commercial amp?

Yes. Except I don't think 'tubes' is the right forum, since all of the bass players I know seem to prefer solid state amps. Increased headroom, bass, etc.
I have heard that the Fender "Dual Showman" is a classic circuit. That's tubed.

[Magnetmaz]

I'm actually a jazz bass performance major....

I have a tubed '70 fender bassman that i really like, but tube amps tend to be for a more round, warm, retro sound. If you want slap'n'pop kind of bass playing, the amps i really enjoyed playing through were solid state: AMPEG, mesa boogie, SWR...coupled with a decent compressor, i think these were more suited to my playing style.

I suppose if it's just a practice amp, it doesnt matter much....but if you told me what style music, and what kind of bass he has, i could give you an ideal amp model and we could dig up the schematics.

[nobody special]

WHAT HE SAID (Magnetmaz)...

Although, I have heard an amp with multiple pairs of 6550's built for bass (I think it was an ampeg). It had a good dynamic sound, even though it did lean toward the warm side.
What about a hybrid? Tube front end, solid state output stage. Could be the best of both worlds, if done right.
-NS

[Magnetmaz]

I could be mistaken, but Ashdown (think that's their name) have gained much fame in the last couple years for building outstanding amps and cabinets. They are big bucks, though. I believe they are tube front end and solid state back end, ....they have huge analog VU meters on the display, and they look like something out of a WWII bomber.

I've played them, and they were a 'best of both worlds' sort of solution....but i dismissed them as too expensive.

[nobody special]

Magnetmaz,
Do you find most of the amps these days are using a switching type output stage, or is someone out there still using class B/ AB? Just curious- haven't kept up with the bass amps as of late.
BTW, do you use a seperate compressor, or is it built in to your amp?
-NS

[Magnetmaz]

Alright...my knowledge of electronics is pretty limited to what i've learned on this board in the last month. I'm not quite sure the difference between class B and A/B amp types, nor am i familiar then with what class a bass amp typically uses. Enlighten me, please...

as far as the question i CAN answer : i use a seperate, rack mount DBX 166 stereo comp/limiter/gate. I have my bass gear plugged into one channel for compression, and my Marshall full stack plugged into the other and am using it as a noise gate.

[phase_accurate]

or is someone out there still using class B/ AB?

Most solid-state bass amps are AB. There are although some people using the Crown K-type PA amplifiers together with a bass preamp.

Most bass (pre) amps have built-in limiters. I have even seen a schematic of an earlier Trace-Elliott bass combo where they used zener diodes in the feedback network of the power-amp section to achieve some kind of soft clipping !!

Regards

Charles

[nobody special]

Thanks for the replies. I would have thought that a lot more manufacturers would switch to a "digital" type amp, but I know it wouldn't be good for tone.

As far as amp classes go, here's a basic run down-
It all has to do with how the output stage operates:

Class A- Output devices (tubes or transistors, or whatever) are on all the time- always conduct current.
These can use just 1 output device, or two (or more), pushing and pulling against each other. They will always be turned on and conducting though.

Class B- Uses two devices (or multiples of 2, in pairs). One device turns on and conducts for half of the wav, the other picks up the other half. This boosts efficiency. Because it is impossible to really match up the waveforms exactly, there is always a little overlap, where each device conducts a little more than half. This is called class AB (which, really all push pull amps that aren't class A are). Most people call the amps that are really close to being "perfect" b types b, and the ones that conduct a little more, class AB. I haven't ever seen a set-in-stone cutoff point for B to AB... maybe someone else can define that.

switching output stages- turn on and off at a high frequency to approximate the signal. when you filter the high frequency out, it averages out to an audio signal. Very efficient.

BTW, dbx compressors have always been my favorite...
Have you ever heard Doug Pinnick from King's X? he biamps, and runs the lows through a bass amp, and the highs through a fender guitar stack. Very unique sound.

-NS