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Old 22nd October 2009, 10:17 PM   #1
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Default Looking for a good valve preamp

Hello all,

I have just some parts in my bin (three 6922 tubes, power transformer, etc...), I need only need a line stage preamp. Any idea for a good schematic?

I found interesting the Vacuum State FVP5 / FVP5A projetc. Anyone know/built it?

Thanks in advance!

Andrea
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Old 22nd October 2009, 10:34 PM   #2
Glowbug is offline Glowbug  United States
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Three 6922s...maybe a grounded grid? I'm not sure if the 6922s would work for that though, I've just seen it done with 6SN7s and 12AU7s, of course.
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Old 22nd October 2009, 10:37 PM   #3
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Hi Jim,
I can by another one...or use only 2 :-)
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Old 22nd October 2009, 10:50 PM   #4
DougL is offline DougL  United States
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Question one. How much gain do you need?
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Old 23rd October 2009, 02:24 PM   #5
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Hi DougL,

I think not too much, I use only cd player and digital sources like pc...
The amps are diytube.com :: View topic - diytube Ike docs & mods *UPDATE 10/11/06*
(el34 push pull)

thank you
Andrea
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Old 23rd October 2009, 05:03 PM   #6
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Quote:
Originally Posted by DougL View Post
Question one. How much gain do you need?
Doug,

Still new to all this. So how do you determine how much gain you need?

Alan
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Old 23rd October 2009, 05:52 PM   #7
DougL is offline DougL  United States
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Quote:
Originally Posted by booangler View Post
Doug,

Still new to all this. So how do you determine how much gain you need?

Alan
This is much harder if you still have a phonograph.

If you only have CD, The CD player usually has a maximum output specification. This is usually about 2 Vrms
The amp also has an input sensitivity spec, usually under 2 Vrms. for full power. In this case, you do not need gain.

The Heretical is a good example of a tube Preamp without gain. The B1 from Firstwatt is a solid state example.

Does this help?

Doug
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Old 23rd October 2009, 07:29 PM   #8
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Three 6922's will make you a nice version of the FVP5. I had a thread describing the evolution of my design version of the FVP5 some time ago using three ECC88's. The secret is to substitute MOSFETS for the top triode in the original. This worked very well and I still have it now. I rebuilt it using ECF80's which sounds marginally better. Short of going balanced I cannot see me building another preamp.

Do a search on FVP5 and shoog and you might get a bit of inspiration.

Shoog
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Old 23rd October 2009, 07:56 PM   #9
45 is offline 45  Italy
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Quote:
Originally Posted by DougL View Post
This is much harder if you still have a phonograph.

If you only have CD, The CD player usually has a maximum output specification. This is usually about 2 Vrms
The amp also has an input sensitivity spec, usually under 2 Vrms. for full power. In this case, you do not need gain.

The Heretical is a good example of a tube Preamp without gain. The B1 from Firstwatt is a solid state example.

Does this help?

Doug

Actually, the average output from a CD player is much lower than the maximum output.
I think it is not a good idea to determine the gain from that number.
In my experience a 0.2-0.3 Vrms sensitivity for a integrated amp (i.e. 1W output) or 0.1-0.2 Vrms for a preamp (i.e. 1Vrms output) work better.

Cheers,
45

Last edited by 45; 23rd October 2009 at 08:00 PM.
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