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Preamps: multiple tubes vs. single tube


_Sweet Willie_

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OK, a question for some of the tech-heads on the board. I have become a fan of hybrid amps, whether as separates (tube preamp + solid state power amp) or as a single head (w/ tube preamp section + solid state power section). I like the tone coming from the tube preamps and the lighter-weight, higher power from the solid state power amps.

 

That said, I have started to notice a subtle preference of my own for preamps with multiple tubes vs. preamps with single tubes. For example, I think that the Kern preamp (3 tubes) is fantastic and that really nice sound can be had from a head like the Ampeg SVT-3Pro (multiple preamp tubes). I have an SWR Super Redhead, w/ a single tube preamp, and while the sound is really nice (no doubt about it), it lacks some of the sweetness and fatness I hear in multiple tube preamps. Certainly some of this is a function of the ways the difference manufacturers build their amps (SWR and Ampeg, for example, I think are aiming for different tonal ideals), but even when I try out a variety of amplification in music stores, I'm finding myself gravitating towards preamps w/ more than one tube.

 

So, finally, the question: Any technical explanations for why I'm hearing a sweeter, warmer sound from multiple tube preamps vs. single tube preamps? Am I crazy, or do the tubes actually interact in a way that satisfies my personal tonal tastes more fully than single tubes? What's the science behind this? (robb.? others?)

 

Some partial answers to this question have been given in other threads, but not as directly as I'm looking for.

 

Peace.

spreadluv

 

Fanboy? Why, yes! Nordstrand Pickups and Guitars.

Messiaen knew how to parlay the funk.

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it has to do with the total approach, although how the EQ section is engineered plays a role, too.

 

you'll notice, for example, that an alembic F1-X is both "all-tube" and also "very clean and glassy". it gets the fat tube sound. it also gets the clean, precise reproduction that one is not (but should be) accustomed to associating with tubes. that is because the entire signal path is tubes. they're not designed in specifically for tube color along the way, they're the entire signal path. tubes can be very precise and very accurate (hence, "clean and glassy"), but they also overdrive very well and give us the "warm" character that is most often associated with tubes.

when the preamp is hybrid, as in the ampeg svp-bsp billy sheehan signature preamp that i own, where the tube is at the front end of the signal chain, it is designed so that it cannot be missed sonically. it is there to provide color, a specific sound, before the signal is sent through solid state EQ and control. the tube adds warmth, thickness, whatever words you want to use. it adds energy to the signal like a tube always does (especially when it's a single-ended triode circuit, a la 12AX7A): in the low-order harmonic distortion. we like the way they sound enough to use them as an effect, even if not as replacement for a transistor or op-amp.

 

they sound different, because they're designed differently. when it's all tube, and not just "tube-colored", the tubes are used differently, more like transistors. they're biased less toward the overdrive side of things and more toward getting a clean, precise, accurate reproduction of the source.

 

as far as EQ, tube EQ is a lot different to design than an op-amp EQ. that is another reason why some preamps are hybrid. it is typically prohibitively expensive and difficult to design a tube graphic EQ in the face of proven, low-cost, good-souding, easy to build op-amp graphic EQs. that is why all-tube units are bass, mid, treble (with knobs that go zero to ten, instead of -15dB to +15dB). the way the circuit alters the sound is different, so it sounds different and is approached, design-wise, differenly.

 

tubes are real devices, not just a "sound" to be added when needed (although there's nothing wrong with using them that way, either). sometimes they're used as a sound (hybrid preamps), and sometimes they replace, altogether, solid state devices (all-tube preamps).

 

robb.

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While there may be something with the tubes, it's probably all of the circuitry combined. SWR has a certain sound (in general), Ampeg has a sound, Kern has a sound, SansAmp, Demeter, Epifani, Ashdown.....

 

Maybe it's the lessons causing you to be more discerning...

 

Now I'll step aside and let knowledgable people post...

 

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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Dunno about any other pre but my ashdown tends to run in the "tube colored" pre. The tube is used to get warm distortion instead of a clean sound. Even with the knob fully on clean it still has a twinge of warm distortion

 

Dave

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Thanks, Bass Brothers!

 

From what you've written so far, it seems like the design of the whole preamp probably impacts the sound overall moreso than the number of tubes. It's more about how the tubes are used than about how many there are.

 

That said, I think that some of the preamps that use tubes for sound coloration, do it with better success than others, or else have user interfaces that allow us to do more with those tube colors than others.

 

In the end, as always, it comes down to carting the trusty bass to the store and playing a bunch of amps/preamps to see what sounds we can pull out of them.

 

Anyone wanna comment more on this issue of multiple tube vs. single tube preamps? Or, better yet, those of you with tube preamps or tube preamps stages in your amp heads or combos, wanna comment about what kinds of sonic shaping you've been able to do taking advantage of those tubes?

 

Peace.

spreadluv

 

Fanboy? Why, yes! Nordstrand Pickups and Guitars.

Messiaen knew how to parlay the funk.

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Please forgive this minor diversion. On TBL, they've had some discussions about how you know when a tube goes bad. Jack Read was working too late one night, and posted a funny bit that deserves to be seen. Thanks Jack!!

 

- - - - - - - - - - - - - - - - - - - - - -

"When Good Tubes Go Bad, Tonight on Fox Television". ;

 

Top Ten Signs That Your Tube Has Gone Bad:

 

10. It doesn't know its cathode from its anode

9. You see it on the Jerry Springer Show saying it identifies more with being a transistor and is undergoing solid state reassignment surgery

8. It's got a permanent seat on Hollywood Squares

7. It's microphonic (funny ringing noises, squeals, pops, clangs)

6. It won't stop humming

5. Your gain just isn't what it used to be

4. You turn on your amp and all you hear is... nothing, and there's no little orange glow inside the tube

3. It looks like someone is taking flash photography inside your amp

2. It glows blue when running, indicating that air is leaking into the tube

 

And the number one sign that your tube has gone bad:

1. It announces its engagement to Jennifer Lopez

 

[Yes, it's been really busy lately so I end up working till Letterman comes on. And for all those of you whose basses I am building right now, this email only took me 5 minutes, and I'm going right back to work!]

 

Jack Read- Read Custom Instruments, Inc.

 

- - - - - - - - - - - - - - - - - - - - - -

 

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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