• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

3 - 12AU7 Preamp. Is there such an animal?

cbj591

Member
2010-05-08 7:58 pm
Good evening everyone,

Question - just wondering, is there a schematic out there for a three 12AU7 pre-amp?

My chassis looks a little bare on the tube side compared to the toroidal on the PSU side. I've got the tubes, just didn't know is there was a decent design. Right now I had planned to build the Fore-Watt, but that extra tube would balance the aesthetics out.

I didnt want to just mount the 3rd tube without using it.

As always, thanks for the input.

Cheers
Brian
 
Brian,
I am from the form follows function school of design, so I can't really fathom your request.
But I can ask your goals. 50's romantic? Ultramodern low distortion?
How much gain do you want / need?
Do you "believe" in feedback?
What kind of loads do you want to drive?
What max output do you need?
Do you "believe" in followers?
Do you "believe" in transistor CSS?
Do you like transformers / autoformers / chokes in the signal path?

If 4 tubes would be even better, look at Aikido.

HTH

Doug
 

cbj591

Member
2010-05-08 7:58 pm
low distortion, I don't need a ton of gain.
as far as feedback. i dont really care. which ever sounds better.

I dont really have experience with design, so i dont know if i really believe in followers and transistor CSS.

I just look through the designs and look at peoples reviews and decide to build from there. I love audio and got into tubes because i wanted to see what all raves were about.

I think i do it more because love the build process, but dont want to build a piece of junk.

so, i will just rework how i was going to mount the tubes and maybe i'll add a decorative tube protector to balance the look.

cheers
Brian
 
Brian,

Do you need any gain, whatsoever? If your signal source(s) are 100% digital, a buffered volume control is most likely best. A (sic) single 12AU7 wired as 2X cathode followers, along with constant current sink (CCS) loading, will work quite well for that job.

Need a bit of gain? Pick a different tube, such as the 12B4. The 12AU7 is not especially linear and (μ = 20) yields a fair amount of gain.
 
:rofl:

Doug - you just throw ( at least) a year of reading at poor greenhorn .........

but - there is a hope for him , considering his avatar .........

:clown:

It's just I really dislike making assumptions.
The preamp he has chosen will probably drive a tube amp with normal sensitivity just fine.
A Firstwatt F4 that needs 20vpp from the preamp for full output, not so much. A typical SS amp with a 10K input Z, not so much.
If he is just using a CD, this preamp will give him about 20db of "empty" gain, which will result in higher noise and distortion.
Also people have many preconceptions about what they want to build.
I certainly do, LOL

Brian,

Enjoy your project, and good luck.

Doug
 

cbj591

Member
2010-05-08 7:58 pm
Good afternoon all,

I wasnt trying to sound rude about being asked all the questions, there are just so many options and designs and i just don't know the answer to them. At this point in time I just want a good sounding preamp, I dont care if it has 2 or 10 tubes....

Time to keep researching...
Cheers
Brian