SE bass amp?

[mresistor]

Just wondering if anyone here has either built a single ended bass guitar amp, or has seen one, or has some ideas that could be implemented to build one. Like a single channel bassman with a single ended power section and PI.

[bigdaddy]

I was going to do that with a KT-88 and Hammond transformers, I have the transformers. I was going to use a different preamp, more based on the Ampeg B-15 and with 6SL7 preamp tubes. One triode of the 6SL7 into a James/baxandall tone stack the the other triode then the KT-88. Simple but it really should sound great with the proper bass speaker and cab.

I was also thinking about adding another preamp stage with an active EQ. I got the idea from the Webervst kits. Also looking at some sound city bass amps with there complex arrangements.

But I did finally decide to keep it simple, I just never built it.....I think the original arraignment with the 6SL7 would probably sound the best. I found that the baxandall tone stack is very easy to adjust and you can add switches to change the frequency points/shelving much easier then a Fender TS. That to me is important with bass to find the sweet spot with the speaker you're using, almost like having a parametric EQ.

[mresistor]

Thanks for the reply bigdaddy - I might have some questions for you when I've had some time to investigate the information you have provided. I was actually studying an Ampeg Jet earlier today, a J-12A.  Looking at the tone stack.
http://www.schematicheaven.com/ampegamps/j12a_jet.pdf

[bigdaddy]

Many will disagree with me but I have experimented with SE amps for a few years now. One thing I have noticed is that they don't like cathode driven tone stacks directly into the power tube. They like a high gain higher impedance signal for best tone and sound, IMO.

For guitar I really like the simple fender tone stack it works for me. I experimented with the baxandall and I see the amazing potential for tone shaping but not for guitar again IMO.

Another way to help create the tone mojo for an SE bass amp might be using a cascode 6SN7GT as the first stage then into a 6SL7GT. The 6SN7 is a low Mu/gain tube that the Hi-Fi guys seem to like. There is no doubt in my mind that those octal preamp tubes deliver more fidelity in terms of a wider bandwidth then the small triodes. That is what will help a bass guitar, low gain and wide range of frequencies being produced and then shaping them.

Because of the what I call 4 string guitar players real BASS guitar has been forgotten in many respects. It has made a comeback with the superior bass players and the addition of the 5th string for those who know how to use it. But I'm a P/J bass kind of guy plugged into any good amp, tube or even SS. If you know how to set up your rig even a GK amp can be made to sound fantastic. Add a tube pre and a compressor to an RB 400 and a good cab and the sound will be amazing. With bass more then anything it's about the cabinet and speaker being tuned for the head and it's limitations not to be gone beyond. Once you do that your sound turns to crap.

[PRR]

> single ended bass guitar amp

SE guitar amps are "usually" not adequate for stage use without PA (and may be marginal even with PA if stage-level is high). The Champ is a dandy practice amp and studio amp, but Fender did not intend it for paying gigs.

The OT and PT for an SE amp are bigger than for a P-P amp of the same power. Or conversely: the 14 Watt P-P early DeLuxe uses the same PT as the 5 Watt SE Champ, and the DeLuxe OT is not bigger than the SE Champ's OT.

You can use a bigger SE tube + OT + PT to get double the power, but that isn't a lot louder.

That's all for guitar. BASS needs bigger speaker or more Watts just to keep up with guitar. In most modern genres the bass is actually higher SPL than guitar, so that its mellower lower tone can keep up with the midrange scream of guitar.

While I know of bass-amps in the 12W-18W range, and have seen them used for small jazz, "serious" bass amps run 25 watts and up and up and up.

Also the OT size (weight, cost) goes up as frequency goes down. 42Hz needs at least twice the iron and copper as 82Hz.

So pencil a "minimal" 25W bass amp. SE tube efficiency won't be better than 40%, and the amplifier must idle without melting. Therefore the idle dissipation is 62 Watts. No single common tube will dissipate this much for long. Even two 6L6GC is dubious. So we are into two 6550 or one transmitter tube.

At 42Hz we can't use Hammond's "Universal" SE OTs rated for 150Hz. We find Hammond's 1627SE will work: 11 pounds and $128-$160. This is twice the weight and 150% the price of a Fender P-P 100W OT.

Power requirement is roughly 450V 180mA. This requires something like a Fender Bassman PT, 8 pounds $90-$140.

With nearly 20 pounds of PT+OT to support, the chassis won't be lightweight.

Power caps are now cheap and light, but the high power demand and the poor ripple rejection of SE means the cap-bank won't be small or light.

So by the time you have an SE bass-amp big enough to take anywhere, it's awful heavy and may not do the bigger gigs.

And as BD says: "even a GK amp can be made to sound fantastic". Bass is (should be) a DIFFERENT instrument from guitar.

[bigdaddy]

To me it was more of a can it be done and sound good rather then SHOULD it be done....

I have taken a champ amp and put it through a good bass cab and it sounded great by the way. It all has to do with the efficiency of the speaker cab especially below 100hz down to 40 were the E string lives.

I can't tell you how many bass players and others look at me like I'm an alien when I would tell them to get a tube microphone preamp, a 15 band EQ like a Rane and a DBX 166 compressor and hook it up to any quality power amp for a sound system and you'll have a great bass amp with the right speaker cab. You could even use the a Universal Audio rack unit with a SOLO 610 and compressor or a lot of the mic channel strips on the market now. I'd say put it in a small rack which makes it very easy to carry and run the power amp on bridged mono with an 8 ohm load, put that on top of any 4-10, 2-15 or 2-12 cab and you'll make everybody cry "turn it down!!!!!!", you won't need a lot of wattage becuase it's extremley effeicent, much more so then any so called bass amp from companies like Ampeg, GK, Mesa, Fender and whatever. For S&G (sheets and giggles) add an X-over with a mix of 10s and 18s or a pair of Eden 4-10XLT cabs with a good old Crown or Crest power amp and watch the paint peel off the walls. The rack will be about the weight of a V-4B and the system will basically make your bass into a symphony of sound.

But most bass players are too cheap and lazy, they would rather get a $100 POS amp and some lightweight 2-10 cab and then wonder why they can't cover a whole band and their amp distorts so much. That's been my experience with bass players. A beat up old P bass that needs a ton of work on it , an old cable from 10 years ago that has so much capacitance it passes no highs and some mismatched head and cab that is lucky to make it through the gig let alone sound good.

[6G6]

Even in P-P, it's hard to have enough power for most modern bass amps with tubes.
It can be done, but you end up with something like an SVT.
That's 80 pounds + a 180 pound speaker cabinet (or two).
Not a bad amp, but not something you'd want to move every night, either.

To get to that power range in SE, you'd probably need big tranmitter tubes
or banks of KT88s and a seperate PS chassis.

If you want a smaller amp for practice or a studio, sure go ahead.
I just can't see building a SE bass amp to play out anywhere.

[mresistor]

If you want a smaller amp for practice or a studio, sure go ahead.

This is what I was thinking when I posted, sorry I didn't mention it, but a great discussion none-the-less...  :-)

[bigdaddy]

My idea was just to make a 10+ watt SE bass amp and use a good 10" bass speaker. I was thinking about the Eminence BP-102 in a well designed cabinet. Not for volume sake but for tone to record with. What i was thinking was to use 3 inputs, one direct, one with an SM57 on the speakers cone and one with a kick drum mic on the shelve or port. Having 3 specific recorded sounds I would best be able to use each one in different ways. My idea was to have the bass audible without it filling all the holes and making the music sound muddy and indistinguishable.

I wanted to be able to control the aspects of bass guitar that were pleasant and made the music better. That would be to have the notes have some ability to be heard yet not interfere with the melody of the song, actually add to it. Yet be able to use some of the lowend thump that drives the groove and can live in the world of the kick drum and floor toms. It's easy to get a good sound until you do a mix down and find that things interfere with each other and you have to drop certain frequencies to fit the vocals in for instance. Everything can sound great individually but it's the sum. That's the art of the mix down. The idea was to be able to record at a low volume a great sounding bass guitar and be able to use what the instrument had to offer to the music as efficiently as possible.

When I did sound, I had a pretty big sound system that was a portable as possible for me. It had a 1-18 reflex bin on each side and a 1-15 w/horn on a pole for the front system, it was tri-amped and I did not use passive x overs. It was loud and clean.....but a strange phenomenon would happen, when I got a good kick sound and a good bass guitar sound separately it would not work when they were put together. In reality I needed 2-18s per side for the subs. One speaker could not handle the pulse from both the bass and drums. The speaker would literally freeze and that would cancel out the ability to define each instrument, you would get the movement of air but without distinguishable notes/tones/sounds, just garbled thumps.

[mresistor]

So, what about using one 6SL7 for the preamp and drive one 7591A or 6L6 or similar? Kind of like a bass Champ. Then run it to a highly efficient 10" driver, or could just build this in a head cab and then the bass player could use one of his cabs for it. But a 10" driver sounds like a good idea. My thought was for strictly a bass "practice/low power" amp that a player could use at home and be able to turn the vol knob past 1 or 2 and still keep the rest of the family reasonably happy.

[bluesbear]

"My thought was for strictly a bass "practice/low power" amp that a player could use at home and be able to turn the vol knob past 1 or 2 and still keep the rest of the family reasonably happy."

For that, an AA764 Vibro-Champ preamp, minus the vibro and change the 10k mid resistor to a 25k mid pot, with a 6L6 and SS rectification would be fine. I'd use a 10" speaker... 8" won't cut it.
Dave

[bigdaddy]

Yeah that's the idea, it will work but I would add a bigger OT and some more filtering.

[panhead]

I once built a SE KT66 bass head for a friend who just wanted to noodle around in his kitchen. Started with a 5F2A type design, and increased the voltages for more headroom and added variable NFB. It worked out pretty well for what it was designed to do, but as PRR says, for stage use you'll never get enough volume. Most bass players I know are running 300 watt heads turned down.

[EW57]

I've often toyed with the idea of going SE and low power with the intention of running it in front of a big poweramp. Low enough power to get some power tube overdrive while keeping the iron costs down..... Never got past the dreaming phase though....

Didnt one of the SWR amps/preamps have a (small) powertube section?  I thought hughes & kettner did so also in the late 80's/early 90's....