How about using the phantom power from a mixer to power a 12au7 preamp for acc guit?

[Wynand]

ATTENTION PLEASE

Ok, i surrender the idea of a onboard tube unit drawing from phantom power. (i am cured)
An external unit seems like the answer. Guitar effects pedal type setup. i am not capable of designing my own circuit so is there anyone out there that will actually post a schematic on a simple tube preamp? Please remember, it is for acoustic guitars so i dont want an overdriven circuit. thanx for your time.

[Steve Conner]

How about the Alembic F2B? Doesn't get much simpler than that.

[Wynand]

How about the Alembic F2B? Doesn't get much simpler than that.

looks good, thanx

[J M Fahey]

wow, its getting hot in here, it seems like im rubbing you guys the wrong way.

Not really. On the contrary, most (all) guys here *will* try to give their best to help.
Of course, the answers may be diametrally opposite to what you previously imagined.
I was chiming in to suggest a classic "Fender first stage" but Steve beat me by suggesting an Alembic preamp which is about that.
Very clean and chimey, you'll love it.

[Wynand]

Not really. On the contrary, most (all) guys here *will* try to give their best to help.
Of course, the answers may be diametrally opposite to what you previously imagined.
I was chiming in to suggest a classic "Fender first stage" but Steve beat me by suggesting an Alembic preamp which is about that.
Very clean and chimey, you'll love it.

Awesome, i feel better.

thanx a million! would you mind if i ask some stupid questions as i build this project? im eager to learn. however ill only start building in a few months time as im recording soon. cant wait!

thanx once again!

[Guitarist]

I'm glad you brought that up, A+ reviews and a basicly a Fender pre, so two tubes are in order. More ubein the mix naturally.

[J M Fahey]

would you mind if i ask some stupid questions

As Enzo said and many others agree, there is not such a thing as a stupid question.
Anyway, a little previous research never hurts.

[Guitarist]

I tried at 18 volts but it sounds like it needs more B+ (no headroom?). PM with email me for more detail regarding kit. It was EASY to install, like 3 minutes. But this tube take @ 45V so mixer power would be perfect, if it can sound good.

[J M Fahey]

What did you actually build?
Because suggested Alembic or Fender classic preamps demand someting in the order of 200/250V.
18V *is* very low for tubes, unless you are building a distortion circuit.
Even 45V is iffy.

[Guitarist]

Mr Fahey,

Oops, I was referring to the subminiature tube here which was rated for 45V - from an Ozzy who made the pc board/pre. Those Alembic preamps get 9.5 ratings across the board, and yes they're basically just a Fender pre!

Sure would be nice to find a SMALL — as in 3" toroid — for one or two tube preamps.

[J M Fahey]

Mmmmmmmmmmmmmmmh , nice !!
Itching to see its schematic /(hint .... hint)

[Amp Kat]

I also agree that using the tube for warmth and sending 48 vdc to the plates won't be what you are looking for and would likely only produce odd order harmonics or very fundamental even order at best. What gives the rich tones of tubes as far as preamps are higher voltage on the plates however voicing can play a huge part on the final tone so it is possible to get a nice warm sound even with SS preamps and in this case with acoustics the name of the game is bigtime EQing and voicing. If you do use the tube and btw I also like Steve's suggestion but make sure you use a big input resistor like about 10M for the pickup impedance.

[exclamationmark]

48V on the plates of 12au7's sounds fine to my ears. Takes about 4v (a tad more) p-p to clip the input stage if centre biased, which is roughly equivalent to that of an 12ax7 at 250v B+. Don't know how it would react to an acoustic guitar however... it tends to amplify rather assymetrically unless you slap a big plate resistor on it (relatively speaking...), so it will probably do other horrible things to an acoustic guitars tone in addition to "adding warmth". Then again, it might be the best thing you ever heard.

I'd probably go for a single tube with 4xAA batteries for the heaters (or 4xRechargables... dunno about the lower heater voltage though), with 20k to 50k plate resistors and 1k to 4k cathode resistors bypassed by something largish. Probably a largish coupling cap in there too (0.022uf+). You also *might* want to put a trimpot between stages if you find it clips when you start strumming away, and of course a volume out (unless your mixer has the facilities to handle this). Should draw something like 1mA per triode half depending on the bias/plate resistors (phantom power should be able to source this, easy). Keep in mind, tube curves change a bit at lower voltages, so you may have to fudge some values. Sounds like a $20 weekend project to me!

On a side note, I'm fairly sure the 12U7 (a tube used for car radios at 12V) is actually just a specially selected 12AU7, because when you look at the inter-electrode capacitances from the same manufacturer, they are identical. Which might be a coincidence... But probably not.

[J M Fahey]

(or 4xRechargables... dunno about the lower heater voltage though)

Just use 5

[mnexsen]

I know it seems to be hype...

But I have used an ART Tube MP with a particularly "quacky" piezo and I thought it did a good job of taming the quack. The Tube MP uses a 9 volt power supply and a 12AX7; maybe it just compresses the leading edge of the signal enough to take out the quack. Whatever, I liked the way it sounded and it was a fairly cheap fix.