the simplest tube preamp

[thomas2]

hi. i've asked about this same thing before a couple of days ago, but i was under a different subject so..
if anyone knows some super simple tube preamp circuit using one 12AX7, please let me know.. the only requirements are that it needs to be with just one tube and absolutely no controls whatsoever + it needs to use a 12V adapter for power source.. there was a very very simple tube preamp building instruction on a finnish music magazine a wile back, but it used a EF86 tube and i didn't/don't have one. and i don't have much money either.

any help is appreciated!

cheers
Thomas

[sir_modulus]

Heres all the tube pedals i can find. If you want no controls (i can't seem to see any with none), then just put a fixed resistance instead of a control.
http://amps.zugster.net/articles/tube-pedals/
there you go.
Hope it helps!

[Brian Marshall]

I'm not sure you will have much luck with a 12ax7 at 12 volts.

Ive never built anything with tubes in it, but if i remember right at 12 volts a 12ax7 has verry little headroom.

I'd definitely look for another tube.

[bobbletrox]

http://users.bigpond.net.au/styrowfoam/rubyboost.gif

The Ruby Tuby Preamp perhaps?  You could replace the pots with trimmers or resistors.

p.s. if anyone has made a pcb or perf layout for this let me know!

[sir_modulus]

If you want real nice tube tone with sustain, buy/build a EH blackfinger.
If you want just tube pre, I can't really help you.
For tube preamp with added dist (twin channel tube preamp(both channels have tubes)), get a matchless hotbox. I'ts got contols though.

[Paul Marossy]

This preamp that you want, do you want a clean sound or like an overdrive sound? The only thing that I have built that can give you a clean sound with a single 12AX7 is the Real McTube II. It uses a pair of 120V/12.6V transformers in a back to back configuration, and has a B+ voltage of about 150V. Anyhow, I can get some real nice clean tones with this circuit. You can get some nice distortion sounds with it, too. The Matchless HotBox uses a similar B+ voltage.

If you want a tube overdrive, my suggestion is to build the Shaka Tube.

[sir_modulus]

Hey good thinking Paul. Forgot about the Rea McTube. My link will have a nice layout for that. For a more complicated build, go for the Matchless hotbox (in my link), but remeber tis is more like a real tube amp, so it needs either two EH torodial transformers, or a hammond power transformer to operate at that sort of B+ voltage (2 12AX7's may push the back to back transformer setup a bit, same with the single torodial setup.
http://www1.korksoft.com/~schem/newamps/matchless_hotbox.pdf
thats the hotbox.

Hope that helps,

[brett]

Here's a kit.  Might be interesting for you.
http://www1.jaycar.com.au/productView.asp?ID=KC5370&CATID=&keywords=valve&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=
cheers

[cd]

If you're only going to run the tube at 12V (without a 12V>240V transformer) don't bother.  It'll sound horrible.

[toneman]

there's always the PAIA StackInABox(SIAB)
one 12AX7 run from a 12V wallwart.
onboard 4069based dc/dc takes 12V to 40VDC.
very cute.
U can get a kit, just pcb, &/or just frontpanel.
i got just the pcb...great 2 experiment with.
then do the gain mods @ Frank Clarke's pages.
PAIA also makes a TubeMicPreamp.
www.paia.com  
afn
tone

[Alpha579]

you could try making a preamp by following Slajuene's idea of using 12v tubes, he's had great results, search for some of the sopht amp threads...take a look at //www.sopht.ca

Alex

[Paul Marossy]

If you're only going to run the tube at 12V (without a 12V>240V transformer) don't bother. It'll sound horrible.

I agree and I disagree. If it were just a tube at 12V, it would probably lack headroom. But, in a circuit like a Shaka Tube where the tube is "driven" by a JFET opamp, I think it sounds great. It's all in the execution...

[thomas2]

wow thanks!  :lol:  .. so many replies!
i guess i should forget the 12AX7 then. i need a clean sounding tube pre. i'll have to see if i can get some other tubes from somewhere. or the other chance is that i start messing around with the 230V which is something i'm afraid of..

[Mike Burgundy]

Nothing wrong with a 12AX7 - it's a mainstay! The problem lies in the B+ voltage - any high-voltage tube run at low voltage will sound flat and dirty.
Pristine clears and headroom can only be gotten with plenty of B+. Being afraid of high voltage is a good thing.
Perhaps try something a little easier first, before you start playing with high voltage?

[thomas2]

what about the ruby tuby amp? it uses an 12V adapter and has a 12AX7 in it.. can't i simply build one without the 386 amp part? sorry again if i'm
asking stupid questions. i'm still learning.

[Mike Burgundy]

that's what the forum is for.
It definitely needs a kick in the pants, which is provided by the opamp. Same thing goes for the shaka tube, Tube Driver, Red Box, etc.
I wouldn't go for just low-voltage tubes - that will sound crappy. Using a low-voltage tube driven really hard and/or rounding off the rough edges of previously generated distortion can work well though.
Keep in mind this will never sound exactly like a HV-tube circuit, but it's an interesting different way of generating distortion, anyway...
hih

[petemoore]

Well for a super kwik to try tube circuit, I did a [actually 2] Shaka Tube, 2nd halves...no OA...because I have many already.
 9vdc WW for the heater supply.
  30vdc printer WW for the circuit supply.
 THis makes it very easy and kwik, though 'gangly' with all the power cables/WW's.
 I think the Shaka sounds really good. Not very distortey by itself, and a rather medium amount of boost. The thing I like most about it is the way it drives an otherwise sterile sounding amp into  much more 'animated' tones, and the way it gets driven by any booster or Fuzz or OD.
 Besides the Power Supply, the circuit is no more difficult [well the tube pin connections must be made right], than wiring a couple booster transistors.
 It definitely sounds like a tube.

[bobbletrox]

what about the ruby tuby amp? it uses an 12V adapter and has a 12AX7 in it.. can't i simply build one without the 386 amp part? sorry again if i'm
asking stupid questions. i'm still learning.

That's what the Ruby Tuby Preamp is.

[thomas2]

i know. but woudn't it work as a stand alone preamp? i can't see why not

[sir_modulus]

That's what it is. There is no power amp attached to it.