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Old 13th June 2006, 11:44 AM   #1
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Default Phono preamp

Thought I might dig out the turn table and so I will need a tube phono preamp stage.

I have some 6SL7's and 6SN7's tubes. Can anyone think of some good circuits to try. I have the normal shoe box full of 12AX7's but I would like to make something with an octal tube to stay with my linestage theme. Am I correct in assuming that I can take the output of the phono preamp and input it into my Aikido 6SN7 linestage?
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Old 13th June 2006, 04:47 PM   #2
kevinkr is offline kevinkr  United States
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Yes you definitely can, and the 6SL7 is a pretty good choice for a phono pre-amplifier tube, my next one is planned to use these.

Keep an eye on the miller capacitance though, high output MC highly recommended or a MM type that likes input capacitance.

I'd go with passive EQ, and I'm also thinking about trying a cascode input stage, lots of gain and lowered miller capacitance due to the low effective gain of the tube in the lower section of the cascode, and not as noisy as a pentode. I'll probably use a CF to get low source Z to drive a low impedance passive network. We'll see.

If you're interested pm me and I'll work out the details if you don't mind being a bit of a guinea pig..
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Old 13th June 2006, 11:51 PM   #3
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The "classic" RCA passive circuit works as is using 6SL7s instead of 12AX7s. AAMOF, RIAA EQ accuracy is slightly better.

Buffer the preamp's O/Ps with 6SN7 cathode followers.
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Old 14th June 2006, 12:58 AM   #4
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Anyone have a schematic?
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Old 14th June 2006, 01:02 AM   #5
cerrem is offline cerrem  United States
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I would caution using a 6SL7 in place of a 12AX7, since you will fall short on the low frequency response due to reduction in mu....
The RCA phono stages are pretty high in distortion and were not intended for Hi-Fi...and also have major RIAA errors...
I design a few 6SL7 phono stages... the 6SL7 can be a great tube..
I posted the schematic on a Yahoo group for tubes... I will dig it up and send it to you...

Chris
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Old 14th June 2006, 01:12 AM   #6
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Bob Danielak's phono pre uses 6(12)SN7 and 6(12)SL7:
http://www.geocities.com/bobdanielak/phono.html
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Old 14th June 2006, 02:29 AM   #7
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I built Thorsten's phono pre and I think it's great. Here's a looooooooong thread about the build (I came in half-way). I ask lots of dumb questions and people get p1ssed at me and stuff-- standard Kofi post.

Anyway, you might want to check that one out. It really sounds nice and was pretty cheapt to build. Also, Thorsten (Kuei Yeng Wang) gives me some pretty detailed advice on the grounding scheme that just killed the hum completely.

Good luck. Let us know what you decide to build and update us on your progess.

Kofi
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Old 14th June 2006, 02:39 AM   #8
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Actually, here's the thread relatted to the grounding for the phono stage. This really saved my tookas. It's dead quiet now.

Kofi
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Old 14th June 2006, 02:46 AM   #9
SY is offline SY  United States
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Quote:
Originally posted by Kofi Annan
This really saved my tookas. It's dead quiet now.

Kofi
Good thing. A noisy tookas is a thing to be dreaded. Ask Mrs. Y.
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Old 14th June 2006, 10:40 AM   #10
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You grounded your tookas to the phono stage?
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