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Thebrain 10th August 2008 06:36 AM

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 is just too much of a hassle :bawling:
if someone here can help with a link or something i would be really really happy:D

mississippi 10th August 2008 02:16 PM

2 Attachment(s)
Here a schematic diagram of a mic_amp with the EF86.

Moke 10th August 2008 02:39 PM


very highly regarded, and, available in kit form.

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.

Thebrain 13th August 2008 02:10 PM


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?:clown:

im pretty noobish at this stuff what power supply should i use for this

mississippi 13th August 2008 04:23 PM

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.

Thebrain 13th August 2008 09:27 PM

sweet thanks!:)

kevinkr 14th August 2008 04:02 AM

Better design here:

and here:

Hugh 14th August 2008 04:20 AM

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.

mississippi 14th August 2008 04:27 PM

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.

Hugh 14th August 2008 11:43 PM

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.



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