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On tube preamps...


Gruuve

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Hey folks:

 

I read some interesting stuff on the web about tube preamps and tube power amps the other (I'm sorry, but I didn't save the link...I'll have to try to find it again).

 

Anyway, the gist of the discussion was that the "tube amp sound" (that rubbery, spongy kind of dynamic response) comes primarily from over-biasing the power tube section, not so much from the over-biasing the preamp tube section. Interesting...I never knew that. Along the same lines, the discussion on tube distortion was that preamp distortion is "fuzz" or "buzz" for the most part...the guitar (and bass) distortion that we all know and love again comes from overdriving the power tubes rather than preamp section.

 

At about this point, I was starting to wonder why folks buy expensive tube preamps.

 

As I read further, they noted that in order to get a preamp to output the sound kind of sound that you get from a tube power amp, you essentially have to build a mini-power amp into the preamp section. Very interesting. Essentially, the original preamp tube essentially raises the voltage to the right level, then it's output goes into a mini-power tube (which could actually be the same type of the voltage gain tube), and it's wired to amplify power. Only, rather than producing watts, this mini-power tube is chosen with the characteristics that allow it to produce milli-watts or so. So, essentially, you get the same characteristic rubbbery, spongy output out of this second tube, and that output then goes to your solid state power amp of choice. Really interesting.

 

Now, (can you anticipate my question?) what bass guitar tube preamps are designed this way? I know my SWR is not (single preamp tube). It's obviously narrowed down to the list of bass preamps that have two preamp tubes. Does anyone know that list? I'm just curious...this article peaked my curiosity... :rolleyes:

 

L8r,

Dave

Old bass players never die, they just buy lighter rigs.

- Tom Capasso, 11/9/2006

 

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Actually a lot of that sounds more specific to guitar use, and not all bass players are going to find that level of nonlinearity musically useful for BASS playing, where the premium is on dynamic range and transients. Most tube preamps for bass don't have a single cascading gain level in them - let alone a quasi power stage. If they can even overdrive distort a little, it is pretty mild stuff indeed - gritty and dirty rather than sweet and smooth and supersustaining - but also closer to sounds classicly associated with the Bass in rock history.

 

Interestingly, the device used to provide overdrive for Randy Bachman's guitar in AMERICAN WOMAN was indeed a mini tube pre and power stage that put oput just enpough wattage that it could severely overload the input stage of the then-not-so-flexible tube guitar amps of the day... For the past decade and more such a device would not be needed as many guitar amps hgave very wide amounts of pregain avaialble in their stock format.

 

Any[guess]Who...

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Oh, Dave, BTW -

 

The Ampeg SVP-Pro leads the way in tube count at prices mere mortals can justify: five for some, and I think they even had seven in there for ahwile. But those tubes are not supplying cascading gain or a quasi power stage. After the initial gain stage they are providing EQ and effects loop, if I recall my schematics properly. But this puppy sounds a lot more tubey than most of what else is out there.

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Oh, I'm with you guys...the article was someone's opinion (although perhaps a more educated opinion than mine). Although the article mentioned guitar a few times, it was concerned with tube amplification in generaly (home stereo, guitar, you name it.) Agreed on the Ampeg SVT. I'm happy with my SWR, even though it only has one lowly tube. :) However, I do recall once hearing a live group up close and bassist was playing through an old (and big) tube amp...I believe it was a Sunn Coliseum if I'm remember correctly. The rubbery sound really caught my attention. That said, it's probably a little too rubbery for slap...sure sounded good with finger-picking though. Of course, sometimes the memory is sweeter than the reality... :freak:

 

L8r,

Dave

Old bass players never die, they just buy lighter rigs.

- Tom Capasso, 11/9/2006

 

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You don't even WANT to open the home entertainment can of snakes. People in that sector who can afford to buy cables that bend spacetime quanta by dint of pyramid-shaped things near the connectors, and if it wasn't for their status-backed-baby buying power they'd be wearing tin foil hats.
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Dave,

 

The Sunn Coliseum Bass:

 

http://www.dangpow.com/~sunn/colibass/colibass.jpg

 

There's not a single tube in that beast; all solid state, all the time. ;)

 

GB,

 

Television is dead. Talk radio lives on.

 

And one of the partners I work for owns home speakers that cost more than an average car. When you spend $3k on cabling so you can critically listen to a mindless sitcom... oiy. ;)

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Actually some of the cool bass overdrive comes from solid state. I'm thinking that Sunn, the Acoustic stuff, my Peavey Max when switched to its SS channel etc. It's all in the quality of the engineers ; }
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I have a friend who recorded and plays live with an Orange re-issue put out by Sound City I believe. Added a custom shop J-bass to it and got a great sound for his 70's rock style. Kinda what Geddy gets now. More of that top end bell dirt than the run and grit on the old albums like "Farewell To Kings" Speaking of a player who gets quite a bit of grit into his tone. Though I know he's used some SVT's in the studio, for at least the past 15 years Geddy hasn't used much tube stuff. All the Tech 21 stuff. I think before that he was doing Trace Elliot.

Mike Bear

 

Artisan-Vocals/Bass

Instructor

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BigDaddyFromMowtown,

 

When I mention "distortion" of tube stuff, as I have often done on these forums, I am also often talking of clean tones as well. Because it is intrinsic for a tube amp NOT to be linear ie output waveform does not resemble input waveform. That's the audio definition of distortion, and not the "effect" version (unfortunate that the same word came to represent two ends of the spectrum perhaps).

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Dave,

 

Part of your question was about why people pay big money for tube preamps. Many people like the "tube shaped sound", and some builders have adopted this over solid state. These guys have invested in getting the sound they want, and often back it up with construction methods that make the unit solid. I'm thinking Alembic and Read Custom, but greenboy probably knows tons of other examples.

 

That in no way means that other preamps (tube or solid state) are inferior, but the hand wiring and solid materials of these units are an understandable chunk of the cost (not just because they have a tube).

 

Tom

www.stoneflyrocks.com

Acoustic Color

 

Be practical as well as generous in your ideals. Keep your eyes on the stars and keep your feet on the ground. - Theodore Roosevelt

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Originally posted by getz76:

[QB]Dave,

 

The Sunn Coliseum Bass:

 

http://www.dangpow.com/~sunn/colibass/colibass.jpg

 

There's not a single tube in that beast; all solid state, all the time. ;)

 

/QB]

Before Sunn Was bought by Fender (or maybe after)they had an all tube Colisium amp, which is now the Fender Bassman 300. I saw Susan Tedeschi a few years ago and her bass player was using one.

"Start listening to music!".

-Jeremy C

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Sunn had that BEFORE FENDER.

 

EDIT: Not that the fairly modern/recent piece has much to do with the antedeluvian design picture you quoted from Geztman other than a brand name id. In fact I think SUNN was a resurrected brand, with some down time before new owners went for it.

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