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My Mini 12AU7 Tube Preamp
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Author:  CrazzyAbtTubes [ 09 Dec 2008, 16:40 ]
Post subject:  My Mini 12AU7 Tube Preamp

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.

Author:  Banditlead [ 09 Dec 2008, 21:53 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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:

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

Author:  CrazzyAbtTubes [ 10 Dec 2008, 16:57 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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:

Author:  billnchristy [ 02 Jan 2009, 01:06 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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


Author:  CrazzyAbtTubes [ 03 Jan 2009, 12:49 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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.

Author:  Reed [ 04 Jan 2009, 22:00 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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!

Author:  CrazzyAbtTubes [ 05 Jan 2009, 15:48 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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.
inside mini tube preamp(small).jpg
Inside mini tube preamp2(small).jpg

Author:  Reed [ 06 Jan 2009, 11:03 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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?


Author:  CrazzyAbtTubes [ 06 Jan 2009, 18:09 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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.

Author:  zvarnell [ 09 Jan 2009, 17:33 ]
Post subject:  Re: My Mini 12AU7 Tube Preamp

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!

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