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Kim Flint wrote: > probably the last I have to say about this, since it's getting off >topic.... Y'mean you're gonna let _me_ have the last word? ;-) OK: Hi, my name is John, and I'm a recovering tube amp addict... I agree that the minutiae of how a tube amp does its magic belongs in alt.guitar.amps... but we're all here, and I do think that the problem of getting a good guitar sound _and_ getting a good loop sound without lugging refrigerator-sized and expensive gear to gigs is pretty much on topic. Paolo, with his perpetual twin gifts for relevance and succintness, should have had the last word: Paolo Valladolid wrote: > > I've always liked the idea of getting a little tube amp for the >overdriven > sounds (e.g. the Mesa Boogie Subway Blues or the Ampeg ???Rocket or ??) > and using that in conjunction with the full range amplification setup. > Just mic the little tube amp and use your mixer to do whatever you want > to it (add effects, split it, just leave it dry, etc.). Sadly, I lack those gifts... ;-/ I also share your enthusiasm for tube amplifiers, to a point; while I've divested myself of most of mine, I still have a blackface Showman and a silverface Champ (still loaded with carefully-nurtured original Fender-branded tubes). And back when I was your age, and for quite a few years after that, I hauled my '72 Quad Reverb (which I hotrodded by rewiring the tremolo circuit into two extra signal-path gain stages) up and down many flights of stairs. But I must disagree with you about where the "bounce" comes from. If it were only input impedance, we'd all be happy with a simple, single 12AX7 preamp (and Stevie Ray Vaughan wouldn't have kept a Tube Screamer between his guitar and his Fender, Vox and Dumble amps). I contend that the tube magic comes from (a) the soft, curvaceous clipping which occurs in the grid/cathode diodes as the signal increases; much more musical than the harsh, square-kneed clipping in early solid state amplifiers, though current designs are mighty close; (b) the decrease in plate voltage (power supply sag) which takes place as the signal increases; much more noticeable with tube rectifiers, causing gentle compression, but having its greatest effect on the unregulated screen voltage of the output tubes, which in turn affects (c) the highly interactive output transformer/voice coil/cone/cabinet reactances, which vary wildly with signal strenth, frequency, and waveform; attempting to mimic this ain't easy, which is why good cabinet emulators are so expensive. But I contend that the input impedance of a 12AX7 is so nearly constant that the effect of variations on the pickup's frequency response are inaudible and un-feelable. First, I doubt that _any_ passive guitar pickup can drive the first stage hard enough to produce grid current flow. If it did, the resulting resistance (equal to the signal voltage squared divided by the grid dissipation) would be _tiny_, only slightly reducing the effective resistance of the typical one-megohm grid leak resistor. I further contend that active pickups actually _increase_ the dynamic effects available from a tube amp. I can plug my active pickup guitars into the aforementioned Showman and crank both guitar and amp wide open, with no risk of the horrid EMI (powerline noise, fluorescent buzz, etc.) which is all too likely with passive pickups. Also, the higher output might actually be enough to cause a little clipping in the input stage. But I cheerfully relinquish the virtues of the Showman and its attendant JBL-loaded 115 cabinet, in favor of a single rack space preamp with only two 12AX7s. I know what I'm missing; I just don't miss it very much-- certainly not enough to justify maintaining and transporting the Showman rig in addition to the PA. (At this point, I wouldn't be surprised if fred marshall popped in, gently tapped his water glass twice, and murmered, "Class... mmmmmmmmmm") John Troubador Tech (http://people.delphi.com/johnpollock/) Kim also wrote: > Another effect of the guitar/tube amp thing, and what I meant by the "amp > is half the instrument" comment, is that the input impedance of a tube > amplifier is not a constant thing. It changes as the current in the tube > changes. This means that the impedance will change a bit depending on the > signal. Guitar pickups are high output impedance devices, so the >impedance > of the input stage of an amplifier will have a strong affect on the > pickup's frequency response. So this means, as you pick a note, the tube > amp input will actually change the frequency response of your pickup over > the course of the note. I think most of this effect will occur during the > attack since you would have a large current change then, and that's where > most people hear it. > > For any other amplifier application, this is a serious flaw. But for > guitars it's a bit different. In that case, this strange affect becomes > something you use as a means of controlling timbre in your sound, >therefore > making it part of the "instrument". I don't think most people are real > conscious of what is going on, they just know that a big variation in >sound > happens depending on how they pick. It becomes an intuitive part of how >you > play. (Tube amp player's often refer to this as "bounce".) If you then >play > into a solid state input (by putting some pedals between guitar and amp, > using active pickups, or using a solid state amp), you notice that the > sound is less responsive. It seems lifeless. This is because the input > impedance is very stable, and that frequency respnse jiggle in the >pickups > is gone. (similar things happen between the output of a tube amp and the > speakers.) > > This doesn't have much to do with the character of the sound itself. It's > really about how the guitar/amp combination feels to the player. And that > of course, can inspire the player in creative ways. It also leads to >people > obsessing about amplifiers and they're signal chain. > > And as far as the response of "I've done it this way for years, and it > sounds fine to me", well, I been there! I had pedals and solid state >guitar > amps for the first 18 years of playing I did. And then I took that tube >amp > drug, and before long I was totally hooked. Once that bounce has gotten > worked into your playing, and you learn to control that aspect of the > sound, you'll be heading down to the corner tube pusher on a regular >basis, > mainlining EL-84's, doing 12AX7/6L6 speedballs....