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Old 15th January 2006, 05:12 PM   #1
chrisvw is offline chrisvw  South Africa
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Default Which 6SN7 preamp should I build?

Hi Everyone,

I'm about to build a 6SN7 preamp for use with my SS amp. I have found two schematics that look promising.

One is a schematic by Frank:
http://www.diyaudio.com/forums/atta...tamp=1092149935

The other I got from a friend. My friend's circuit is SRPP, and having just read an article on tubecad.com, http://www.tubecad.com/may2000/ where it says...

"It [SRPP] is often misused as a line stage amplifier (where the load impedance is not predefined) or as a driver stage (where the load impedance is far too high). Preloading the output overcomes much of the mismatching problems. Preloading means adding a fixed resistor to the output a value slightly higher than optimal, so that when an external high impedance load is added, the combined paralleled impedance will prove optimal. Still the question remains: if the load to be driven is a high impedance one, why bother with a push-pull output stage? If high gain and a good PSRR figure are needed, use a current source loaded Grounded Cathode amplifier instead. If low output impedance is needed, use a White Cathode Follower, Plate Follower, Cathode Follower, or even a lower rp triode instead. It is often misused as a line stage amplifier (where the load impedance is not predefined) or as a driver stage (where the load impedance is far too high)."

I have my doubts. Frank's schematic seems the way to go. The problem is that I'm listening to my friends line-stage as I type this, and it sounds very good.

What would you reccomend?

Thanks, Chris.
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Old 15th January 2006, 05:39 PM   #2
chrisvw is offline chrisvw  South Africa
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Default Frank's Schematic

Sorry about the broken link. Here's a picture of Frank's schematic:
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Old 15th January 2006, 07:52 PM   #3
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chrisvw


I built Frank's preamp and I am very pleased with the outcome. It is far superior to anything using 6SN7's that is pre built. I have built a number of different circuits using the 6SN7 some of which claim to be the best. Go with Frank's line stage and go the extra mile with a regulated power supply. You won't be sorry.
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Old 15th January 2006, 10:02 PM   #4
arnoldc is offline arnoldc  Philippines
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burnedfingers, have you built the VTV 6SN7 linestage? can you comment on that vs. frank's 6SN7 (i'm also planning to build)
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Old 15th January 2006, 10:14 PM   #5
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Build Frank's and you will be grinning from ear to ear.
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Old 16th January 2006, 06:57 PM   #6
chrisvw is offline chrisvw  South Africa
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Default Bump

Any comments about the hand dawn schematic?
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Old 15th February 2006, 03:26 AM   #7
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Hi ,

This schematic is my favorite , it sounds great , has a low output impedance and is simple to build .

I built the version using 6SN7 , the version using 6CG7 , and the
best ( my favorite ) using 12AU7 / ECC82.

Try to build , don't using the 1K grid stopper resistors , all others
values are OK .

You will be very satisfied with the results

Regards

Carlos
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Old 15th February 2006, 03:28 AM   #8
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Sorry , my mistake .

Only one correction : You have to use 220 uf x 25 V for C1

Regards

Carlos
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Old 15th February 2006, 03:56 AM   #9
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Default Stage can be simplified

Regarding Frank's preamp schematic above, why not direct couple the cathode follower to the first stage? Minor resistor adjustments might be needed. Thus remove the coupling cap.
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Old 15th February 2006, 04:50 AM   #10
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Brian,

It the stages were direct coupled, would the 220K resistor have to go too?

Thanks
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