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Old 28th September 2010, 09:50 AM   #1
imagios is offline imagios  Czech Republic
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Default DIY Tube Mic

Hello,
after I have done some amps and speakers, I would like to make my first microphone, as Im not an expert in eclectronics I build most of my stuff from kits.
Can any one tell me what to expect from this kit?
DIY Vacuum Tube Condenser Microphone Kit

I will need two mic for stereo recording, mostly it will be pure solo instrument or two instruments, may be instrument + voice. Just for info I will conect the mic to a E-MU 0404 USB card and than to my loptop. I could buy some mic but doing it self is more fun and let say "unique"

What do you think of the kit? There is a 12AX7 tube unfortunately no mentioned which one. I hope its the russian not a China one.
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Old 28th September 2010, 11:49 AM   #2
banat is offline banat  Serbia
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Try this way:OTL

Aproven in praxis and sound good.

For balanced out(XLR) second half of ecc83 tube have to be rewired to form DC coupled Concertina phase Inverter,for Volume You have to use than double 100k Pot.
For even strictly standards You have to use Van Scoyoc phase inverter for balanced(XLR) output stage.

Good Luck
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Old 28th September 2010, 12:26 PM   #3
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If the output level is too high, you can use a 12AU7 tube.
I've built a similar microphone and used a NOS Telefunken 12AU7 tube rather than the supplied (chinese) 12AX7.
The Telefunken tube made all the difference in the world.
Good luck with the project.
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Old 28th September 2010, 04:46 PM   #4
imagios is offline imagios  Czech Republic
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Well Lookin at it closer I might exchange the 32mm diaphragm capsule, any suggestions for a reasonable priced one?
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Old 28th September 2010, 05:02 PM   #5
TheGimp is offline TheGimp  United States
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I think I'd be inclined to cut R7 by a factor of two, parallel the plates, grids and cathodes, and get lower noise and better output capability with that kit.

Tubes are cheap enough that you can change whatever you use as there are only one tube per mic.
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Old 28th September 2010, 05:59 PM   #6
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The kit is basically a knocked-down unfinished $200 Chinese tube mic.

Your E-MU 0404 has line inputs. You'll need a mic preamp between the mic and 0404 if you use a standard tube condenser microphone circuit, including the kit mic circuit.

There is a lot of DIY mic and mic pre action on Prodigy Pro DIY:

Meta-Meta: Look here for overview..

The schematic posted is very strange. I don't understand the floating cathode connection to the condenser capsule. How could this possibly work? Also no way a 100K pot will drive a standard 1600 ohm mic amp input. Even a little high for a guitar amp if you ask me...

Cheers,

Michael
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Old 28th September 2010, 06:27 PM   #7
imagios is offline imagios  Czech Republic
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Well, im not very knowlegeable about electronics therefore I can not say how good or bat it is just from the diagram... so far I read it seems not to be a good choice. Even thou a 200$ mic should not be bad at all...
I have no equipment to make my own PCBs thats why I use the kits so if there is a other kit some one can recommen im more than happy to take a look on it.
How much distortion it will have, what do you think?

As for the preamp I beliwe once to get a nice low noice kit there is a lot of them out there.
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Old 28th September 2010, 06:33 PM   #8
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The posted schematic calls for an FET capsule. I'm assuming that the cathode current will power the FET inside the capsule.
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Old 28th September 2010, 06:42 PM   #9
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Quote:
Originally Posted by imagios View Post
Well, im not very knowlegeable about electronics therefore I can not say how good or bat it is just from the diagram... so far I read it seems not to be a good choice. Even thou a 200$ mic should not be bad at all...
I have no equipment to make my own PCBs thats why I use the kits so if there is a other kit some one can recommen im more than happy to take a look on it.
How much distortion it will have, what do you think?

As for the preamp I beliwe once to get a nice low noice kit there is a lot of them out there.
Maybe you misunderstood slightly. I mean the schematic posted in this thread post #2 is strange.

I think the Auracle A5500 mic kit is probably a decent way to go and I may in fact spring for one myself just for grins. It may be hit or miss with the capsule but if you get a bad one they should exchange it for you. The circuit looks fine. Just getting the body and grill in a raw form is easier than gutting out a $50 FET mic and trying to retrofit a 5 or 6 pin XLR.

Word on the preamp. There are many good affordable kits out there.

Cheers and good luck!

Michael

I see they got some A5500 mic kits in on 9/27 and they're sold out today. Must be a popular item...
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Old 28th September 2010, 06:44 PM   #10
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Quote:
Originally Posted by Frank Berry View Post
The posted schematic calls for an FET capsule. I'm assuming that the cathode current will power the FET inside the capsule.
A "FET capsule"? With a FET circuit built in? So it makes a cascode or what? Please tell me more or point me to a part number?

Thanks!

Michael
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