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Rockmonton 3rd December 2004 03:44 AM

need a good low parts phono tube preamp schematic....
 
gotta make a christmas present there for my electronics mentor figured since he's got boxes and boxes of vinyl (around 5000) i'd finally make him a preamp, anyone got any good designs? i've got about 2 or 3 matched pairs of 12au7's i'd like to use up, i've looked on the net and am having trouble finding much..

Enzo 3rd December 2004 04:05 AM

Look in the back of the RCA tube manual. One of the sample circuits is a tube phono preamp with RIAA curve. it is based on one 7025. (12AX7) I would think the 12AU7 was a bit low gain for the application. Very simple circuit. You would need one per channel. SO two 12AX7 and a handful of small parts. You also need power supply.

You could probably make something with one 12AX7, but I don't see how you could get RIAA that way.

GeirW 3rd December 2004 01:02 PM

Gday.

Look at bonavolta page:
http://www.bonavolta.ch/hobby/en/aud...el.htm#Various


:)

pedroskova 3rd December 2004 01:37 PM

not exactly "low parts count" but worth it...

GeirW 3rd December 2004 03:17 PM

2 Attachment(s)
Gday.

Ohashi looks interesting,
with 3x12AX7/ECC83 and 12. res/log , 4. cap`s
it`s "low part". Haven`t a clue about the sound,
but i assume minimal use of passive components
can speak for quality. It shouldn`t sound worse than AR SP3
i reckon. Have you looked at the phono stage of the
Audio Innovation 500.




:)

ThorstenL 3rd December 2004 03:59 PM

Re: need a good low parts phono tube preamp schematic....
 
Konnichiwa,

Quote:

Originally posted by Rockmonton
gotta make a christmas present there for my electronics mentor figured since he's got boxes and boxes of vinyl (around 5000) i'd finally make him a preamp, anyone got any good designs? i've got about 2 or 3 matched pairs of 12au7's i'd like to use up, i've looked on the net and am having trouble finding much..
Well, the 12AU7 is not particulary useful in a Phonostage.

If you can scrounge up a single ECC83/12AX7 and a single ECC88/E88CC/6922 you could build the Phonostage I described here:

http://www.diyaudio.com/forums/showt...624#post335624

The thread following on has a lot of discussion on this, suitable PSU, implementation etc....

Sayonara

Geek 3rd December 2004 06:11 PM

2 Attachment(s)
Here's an active EQ phono stage from one of my more sucessful designs :)

planet10 4th December 2004 06:55 AM

2 Attachment(s)
Quote:

Originally posted by Enzo
Look in the back of the RCA tube manual. One of the sample circuits is a tube phono preamp with RIAA curve
It lacks the undocumented time-constant, but here it is

From the 1966 RCA Receiving Tube Manual.

dave

gmilitano 5th April 2005 12:27 AM

Quote:

Originally posted by planet10


It lacks the undocumented time-constant, but here it is

From the 1966 RCA Receiving Tube Manual.

dave


Are 12AX7 close enough to a 7025 for use with this schema? If not, is there an RIAA schematic for 12AX7? I'd be looking for a simple design, one 12AX7 per channel, no output transformer and about 30-40dB gain (for MM phono).

Any leads or info is always appreciated.
Gio.

planet10 5th April 2005 12:33 AM

Quote:

Originally posted by GG
Are 12AX7 close enough to a 7025 for use with this schema? If not, is there an RIAA schematic for 12AX7? I'd be looking for a simple design, one 12AX7 per channel, no output transformer and about 30-40dB gain (for MM phono).
A 7025 is a 12AX7 -- supposedly selected for higher performance, but in practise the variations are such that it is a no care.

dave


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