Which 6SN7 preamp should I build?

chrisvw · 15th January 2006, 05:12 PM

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.

chrisvw · 15th January 2006, 05:39 PM

Sorry about the broken link. Here's a picture of Frank's schematic:

Original Burnedfingers · 15th January 2006, 07:52 PM

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.

arnoldc · 15th January 2006, 10:02 PM

burnedfingers, have you built the VTV 6SN7 linestage? can you comment on that vs. frank's 6SN7 (i'm also planning to build)

Original Burnedfingers · 15th January 2006, 10:14 PM

Build Frank's and you will be grinning from ear to ear.

chrisvw · 16th January 2006, 06:57 PM

Any comments about the hand dawn schematic?

refference · 15th February 2006, 03:26 AM

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

refference · 15th February 2006, 03:28 AM

Sorry , my mistake .

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

Regards

Carlos

Brian Beck · 15th February 2006, 03:56 AM

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.

Looneytunes · 15th February 2006, 04:50 AM

Brian,

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

Thanks

15th February 2006, 03:56 AM	#9
Brian Beck diyAudio Member Join Date: Dec 2004 Location: South Florida, USA	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. __________________ Brian

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15th January 2006, 07:52 PM	#3
Original Burnedfingers diyAudio Member Join Date: Nov 2002	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.

15th January 2006, 10:02 PM	#4
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	burnedfingers, have you built the VTV 6SN7 linestage? can you comment on that vs. frank's 6SN7 (i'm also planning to build)

15th January 2006, 10:14 PM	#5
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Build Frank's and you will be grinning from ear to ear.

15th February 2006, 03:26 AM	#7
refference diyAudio Member Join Date: Jan 2006 Location: SAO PAULO - SP	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

15th February 2006, 03:28 AM	#8
refference diyAudio Member Join Date: Jan 2006 Location: SAO PAULO - SP	Sorry , my mistake . Only one correction : You have to use 220 uf x 25 V for C1 Regards Carlos

15th February 2006, 04:50 AM	#10
Looneytunes diyAudio Member Join Date: Oct 2005	Brian, It the stages were direct coupled, would the 220K resistor have to go too? Thanks

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