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.
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.
Attachments
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.
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.
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
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
Your friend's circuit
I just want to point ou that your friend's circuit is not a SRPP, rather a mu follower. In my opinion the B+ for this mu follower circuit could be higher, at the moment those triodes aren't running in a very linear region (that's more of a guess, but I always see 6SN7 circuits with more b+).
About Brians comment: There was a recent thread where someone showed two schematics from a preamp with the 6SN7, both from Frank, one with coupling capacitor, the other without (both where 1st stage: anode follower, second stage: cathode follower). Try to search for it.
I just want to point ou that your friend's circuit is not a SRPP, rather a mu follower. In my opinion the B+ for this mu follower circuit could be higher, at the moment those triodes aren't running in a very linear region (that's more of a guess, but I always see 6SN7 circuits with more b+).
About Brians comment: There was a recent thread where someone showed two schematics from a preamp with the 6SN7, both from Frank, one with coupling capacitor, the other without (both where 1st stage: anode follower, second stage: cathode follower). Try to search for it.
Hi Carlos,
some questions:
1. Which tube did you prefer, the 6SN7, or the 6CG7?
2. Are you saying do not use a 1m resistor for a grid stopper? Then what value did you use?
3. Later on in this thread, there is a question about not using a coupling cap between stages? Did you end up removing that cap?
4. What is the output impedance of this preamp?
5. Since I am a blind person, can't see the pics, so does this schematic show the Power Supply too?
6. What transformer for the supply should I get? With the B+ and all of the correct voltages?
I think that is all for now. I was looking in to building a 12B4 preamp, but others have stated that there are better tubes out there like a 6n6p and so on. So back to the 6sn7/6cg7 tube.
Ray Bronk
Hi Ray ,
First of all , I'm talking about this schematic . A " U follower " .
A pre amp with 12AU7 , as I had said , my favorite , in the second place
I'd prefer the 6CG7 .
Suposing that you will follow me and use the 12AU7 , the answers are :
1 ) Neither one , I prefer the 12AU7
2 ) You can use the grid stopper resistor of 1000 ohms ( 1 K )
3 ) In this stage , U follower , the coupling capacitor is essential , and must
be polypropylene or oil , 0.022 uF x 400 V , the value of 0.22 uF x 250 V , is
not a good choice ( IMO ) because the time constant too high .
4 ) The output impedance is about 800 ohms ( with 12AU7 )
5 and 6 ) The power supply I use a transformer with an output of 270 V AC x 50 mA , bridge rectified , 150 uf as the first cap , a 10000 ohms ( 10 K ) x 3 W resistor , then a 180 uF x 400 V , then , 2 ( two ) 10000 0hms ( 10 K ) x 3 W resistors , each one feeding a 180 uf x 400 V capacitor , each one for each channel , this way the final voltage will be aprox. 265 - 270 Volts on the plates , that is the ideal value for the 12AU7 .
The resistors values on the table are correct , the only change I would do is
the cathode by-pass capacitor , 100 uF x 25 V instead 33 uF x 25 V .
Good Luck .
Hi, Just curious why did you use a 12BH7 as opposed to the 12AU7 or the 6SN7 or 6CG7 tube? I am not doubting your choice for the tube used. Have been looking around for a good tube preamp to build. Was interested in the 12B4, but people out there saying the 6H30 or even the old venerable 6SN7 or 6N1p is better. Anyway, just curious at this point.
Ray Bronk
Hi Carlos,
Thanks for your reply. So why is the 12AU7 your favorite? I have none. All of the reading around the web suggests the 6SN7 is more linear than the 12AU7, and might be more open too. Also, converting the 12AU7 to a 6CG7 is not difficult. Disconnect Pin 9 and make sure that whatever is connected on pin 5 is moved to pin 4, and move connection from pin 9 to pin 5. Also, the heter supply instead of 12 has to be 6 with the current draw rating twice as much for the 6.3 filament. There, essentially you shouldn't according to what I've read, have to change anything in the circuit for the 6CG7 to work. Anyhow, just curious why you like the 12AU7 tube. Again, no preference for me.
Ray
The original thread used the 12BH7, so I went with that. Although because of your comment, I just swapped out the 12BH7's with a pair of 12AU7's and I have to admit it opened things up quite a bit.
I rolled a ton of different tubes in my "Bijou" headphone amp...and the 6H30 by far is my favorite, followed by the 6N1P
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