My Mini 12AU7 Tube Preamp

CrazzyAbtTubes · **Posted:** 09 Dec 2008 4:40 pm

I miteas-well post something since many people may have questions on the construction of the DIY 12AU7 Tube Preamplifier I built. I've gotten some mod ideas from my uncle that include building a docking bay into the preamp for my ipod. The plan is to remove the docking bay from a cheap boom box, use the analogue output and apply it to the preamp. I think I might build a second one to do this, since I would rather not dissect my functional preamp as it works just fine as is.

You may post any questions you wish and I will answer them when I get time.

Banditlead · **Posted:** 09 Dec 2008 9:53 pm

If you want to DIY the Ipod Dock, this fellow posted a schematic of his ipod dock that is also connected to is Mono Block Amp from S5:

http://kurtisb.awardspace.com/

And I have plenty of questions, but I will ask them when i have my work table set up.

CrazzyAbtTubes · **Posted:** 10 Dec 2008 4:57 pm

That is a neat system, I like his idea of using solid maple, the setup for the ipod dock is simpler than I was expecting, hopefully that applies to the newer second version of the nano, now I just need to get a plug for it.

Thanks for the info. :sing:

billnchristy · **Posted:** 02 Jan 2009 1:06 am

Do you have the part #s or location you got the transformers from?

Thanks.

CrazzyAbtTubes · **Posted:** 03 Jan 2009 12:49 pm

I go to partsconnection, but any other seller of Hammond transformers will do, all you need is 120V @25mA and 6.3V at 1A or so, or two 12V trannies back to back will also work.

Reed · **Joined:** 14 Nov 2008 9:09 am **Posts:** 21

Sorry for the newbie question -- but where is the volume potentiometer mounted on the preamp?
I really need a preamp for my tube amps and this looks like a great project!
Thanks!
Reed

CrazzyAbtTubes · **Posted:** 05 Jan 2009 3:48 pm

Oh, yes, on the original schematic there is a 100K pot at the input, in my case though, I decided it was not necessary to install a volume control because I used my ipod to control it, thus was able to make the preamp very compact. I should have made a pcb for mine because I barely had enough room to fit everything inside.

Feel free to ask any questions you like about construction and parts selection, that is what this post is for.

Attachment:

inside mini tube preamp(small).jpg

Attachment:

Inside mini tube preamp2(small).jpg

Reed · **Joined:** 14 Nov 2008 9:09 am **Posts:** 21

Hi Alan -
I'm going to try laying out the preamp circuit on a breadboard -- question for you:

are all resistors 1watt? (with the exception of the 1M pot)

In the upper left hand corner of your schem -- there is a 200k resistor -- there is a 330k resistor to the right of it -- they are joined with an arrow ie:

200k <--- 330k

what does LED adj refer to?

Thanks
Reed

CrazzyAbtTubes · **Posted:** 06 Jan 2009 6:09 pm

The resistors can all be 1/4 watt but 1/2 watt resistors would be more suited, and as for the led with the variable resistor, it is there to controls the brightness and is of no real importance, a single 100K resistor can be used instead.

zvarnell · **Joined:** 09 Jan 2009 5:28 pm **Posts:** 1

Quick newbie question sorry.

So is this a mono or stereo preamp? You said you were going to make it for a headphone amp, but that would require 3 tubes and they wouldn't fit. If it's just mono why are there 2 inputs and outputs in the picture? Also, if i were to build a stereo version of this preamp twice as big, how would the power supply be affected? Thanks!

My Mini 12AU7 Tube Preamp

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