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Old 10th August 2008, 06:36 AM   #1
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Default DIY tube microphone preamp

i've been googling forever trying to find a site or some kind of thread
telling you where you can get a full tube microphone preamp kit.
(and a good one!)
all i find is threads and sites giving you instruction what to buy and how to make your pcb.it is just too much of a hassle
if someone here can help with a link or something i would be really really happy
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Old 10th August 2008, 02:16 PM   #2
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Here a schematic diagram of a mic_amp with the EF86.
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File Type: jpg mic_amp.jpg (48.1 KB, 1373 views)
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Old 10th August 2008, 02:39 PM   #3
Moke is offline Moke  United States
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hamptone:
http://www.hamptone.com/

very highly regarded, and, available in kit form.

edit:
click the www link below my signature line. Its a link to a recording forum where we discuss mics / preamps / recording, endlessly, 24/7/365. You can get some good info, and probably some good leads there, as well.
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Old 13th August 2008, 02:10 PM   #4
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Quote:
Originally posted by mississippi
Here a schematic diagram of a mic_amp with the EF86.

thanks man this one looks really really simple does it work?

im pretty noobish at this stuff what power supply should i use for this
one?
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Old 13th August 2008, 04:23 PM   #5
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You will need a transformer with the right mains winding (120 or 230V)
Then sec. 6,3 V 200mA or more.
And a sec voltage of 145 V 5 mA or more.
Then you need a rectifier bridge with can stand 400V or more, a few elco's (2 x 50uF 250V) and some resistor to bring the voltage at 200V.
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Old 13th August 2008, 09:27 PM   #6
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sweet thanks!
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Old 14th August 2008, 04:02 AM   #7
kevinkr is offline kevinkr  United States
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Better design here:
http://www.frontiernet.net/~jff/pult...onePreamp.html

and here: http://www.recording.org/users/kev/G9_tube_micpre.htm
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Old 14th August 2008, 04:20 AM   #8
Hugh is offline Hugh  Australia
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Mississippi
wouldnt that unloaded mic transformer create a peaky audio response?? 10M load on the EF86 grid to me should be more like 50K to load the transformer properly, presuming a 200 ohm to 50k typical transformer.
...Hugh
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Old 14th August 2008, 04:27 PM   #9
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Without micr. transformer you use a micr of 5 mV and 1Mohm impedance.
There are 2 transformers for this design.
the EL6805/01 50/25000 ohm
the EL6807/00 500/500 ohm.
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Old 14th August 2008, 11:43 PM   #10
Hugh is offline Hugh  Australia
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The circuit above must be not quite complete. Whatever transformer 500 Ohm or 25k secondary to me should have that as a load impedance, not 10M as shown on circuit. Circuit would be fine for HiZ mics & no Tx.

Whatever.

Hugh
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