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Old 10th January 2007, 08:18 AM   #1
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Default Wanted RIAA stage with 6SN7

I had made a phono amp with 5 5670/2C51 yet. however its hums....... i think its because the signal from power transf... I did not seperate them well and only use single solid line. I dont want to deal with it now maybe latter(its a little diffucult for me to re-built).
I still have some 6SN7 and 6J5 and this Time I want to try use them 1 6J5 1 6SN7 for 1 chl . I prefer RC for RIAA and If anyone had scheme or have any hint.
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Old 10th January 2007, 12:46 PM   #2
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6SN7/6J5 are not very suitable for input stages
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Old 10th January 2007, 01:27 PM   #3
smbrown is offline smbrown  United States
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The RCA Phono preamp schematic uses 12AX7's and you can sub in 6SL7's (can be microphonic, however), but not sub in 6SN7. I only suggest this as it keeps you in the octal tube family. Otherwise, I'd go for something like a 6DJ8 based design. Check out Vacuum State's web site for schematics of phono sections that are pretty darn good.
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Old 10th January 2007, 01:38 PM   #4
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6SN7 gain is too low to use as a phono stage - as pointed out above, the 6SL7 would be a better choice.

Someday I would like to build a pentode based phono stage...
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Old 10th January 2007, 05:26 PM   #5
cerrem is offline cerrem  United States
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I designed a 6SL7 phono stage with 6SN7 follower on the output of it.... I posted it in a folder on a NewGroup a number of years ago... It was in "Yahoo Groups" Some kind of tube group....it's been awhile and i forget exactly...
If you look in one of the schematic folders is should be there....
If I cab find it again..then I will post it here..

Chris
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Old 10th January 2007, 10:05 PM   #6
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Quote:
I designed a 6SL7 phono stage with 6SN7 follower on the output
Hey, me too!

www.hagtech.com/pdf/cornetoctal.pdf

jh
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Old 11th January 2007, 12:02 AM   #7
jayme is offline jayme  United States
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Quote:
Originally posted by hagtech


Hey, me too!

www.hagtech.com/pdf/cornetoctal.pdf

jh
Nice! I just found your website the other day, and was looking at the 9-pin version of the Cornet.

How would you describe the difference in sound between the 12AX7/12AU7 version and the 6SL7/6SN7 version?
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Old 11th January 2007, 12:59 AM   #8
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Quote:
Originally posted by hagtech


Hey, me too!

www.hagtech.com/pdf/cornetoctal.pdf

jh


Very interesting. I'm sort of a 6SL7 fan, and octals in general. Could you give us your impressions on the sound of this design? Thanks for sharing, Jay
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Old 11th January 2007, 01:08 AM   #9
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I found from tube CAD Journal

a single triode RIAA equalized preamp. Usually a cathode resistor is bypassed with a large valued capacitor, so as to ensure adequate low- frequency response. But if the bypass capacitor's value is reduced greatly, it introduces a shelving function, wherein the high-frequency gain is greater than the low-frequency gain, with the ratio being equal to the bypassed gain over the unbypassed gain or
1 .
Ratio = 1 + (mu + 1)Rk
Ra + rp
The transition frequencies are based on the capacitor's value and the time constants it forms with the triode's rp and its plate and cathode resistor values:
RkCk = 75S
[(Ra + rp)/(mu + 1) || Rk]Ck = 318S
Of course, one triode is not going to provide enough gain in most cases, so additional gain stages will be needed.
The overarching liability of this different path to RIAA equalization is the -12dB insertion loss beyond the expected losses, which brings it 1kHz insertion loss down to -32dB. With this equalization network, the near DC and subsonic frequencies are reduced by -12dB, whereas the traditional path retained all of the gain at the bottom of range. Now, -12dB is just too much to pay in most two-gain-stage phono preamps, but it is almost nothing in a three-gain-stage preamp, where the problem is usually having too much gain. Still the advantage of using a portion of the equalization network in double duty either, as a pseudo coupling capacitor or a partial cathode-bypass capacitor, is tempting.

how about it
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Old 11th January 2007, 01:09 AM   #10
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and this
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