6SN7 pre-amp

[Andersen]

I am going to build a 6SN7 pre-amp in accordance with the attached schematics in which I will use one kind of 6SN7 for the first stage (both channels) and a different type for the last stage. Can you please advise and comment on this project (any problems, changes to the schematics to be made, etc...) before I get started.

Thanks a lot.

 

[pengboon]

errr... where's the schematic?

 

[Cobra2]

The trouble with new members...

@ Andersen; do a few posts in the "Introductions" - section:
http://www.diyaudio.com/forums/forumdisplay.php?forumid=7
And your limitation will be lifted sooner...

Arne K

 

[Bandersnatch]

Hi,
If you don't understand what every piece is doing, or how it is interacting with the others, build it exactly as shown. Mixing two different 6SN7 won't give you any problems. Once you get a better feel for how the pre works, then you'll know better how to answer these questions( more likely, you'll just have different ones ). Questions are good, ask as many as you can, and keep asking until you understand the answer.
Cheers,
Douglas

 

[Apex Jr]

I've been wondering about the 6SN7's
And this thread brought it up again, SO,
What are the differences between them
GTA's and GTB's and others
I know the mil version 5642 is a great replacement
but why....

Steve @ Apex Jr

 

[dsavitsk]

I've been wondering about the 6SN7's

This will answer even the questions you didn't know you had about various 6sn7 varieties: http://www.head-fi.org/forums/showthread.php?t=119638

However, see this thread where it is argued, inter alia, that the 6sn7 is not all that great, at least in some places (it gets going around post #10 or so): http://www.diyaudio.com/forums/showthread.php?s=&threadid=42201&highlight=

 

[Andersen]

To Cobra2: noted with thanks! I've just made my introduction and still wonder when I can post the schematics.

To Bandersnatch: Thanks for your support. There would be quite a lot of questions when I can post the schematics.

I'm going to use 5692 RCA Red base at the first stage and 6SN7A Sylvania Metal base at the second stage.

 

[jeapel]

hi

maybe ?

-adjust for 300v B+ for ~ 150 to 200 v across 6sn7
-adjust for 6.1v heater for long life
-transfo is always a weak part why not a cathode follower
-in my 6sn7 i use a c4s ccs with good result

 

[EC8010]

Andersen: Frankly, that circuit is a very poor "design" and throwing exotic and expensive valves at it is not going to rescue it. What do you actually need to do? What is the sensitivity of your power amplifier? What output do your sources produce?

 

[Bandersnatch]

hey-Hey!!!,
I have a similar reaction to 801. I have not built like that, and prefer an all-tube active load on a single 6SN7 stage. The tube active load, made from a triode and pentode arranged as a cascode mu-follower has been very effective. It also lowers output Z to a level that lives comfortably driving 7k Ohms. It is the tube version of the MOSFET ccs as described by Gary Pimm.

IMO, fewer stages sound bettre than many. The PS also achieves its voltage output resistively. That's another thing I don't like doing. LC then a VR tube shunt regulator perhaps?

The single tube operating with a CCS load allows the sonic texture of the tube to show. I'd hate to wast such valves as you have on something that did not showcase them...
cheers,
Douglas

 

[plovati]

try 6BX7 WOT

I'm happy with a similar schematic preamp, but with 6BX7 power tube and 6SN7 driver.
OPT is a 6800/32 ohm very easy and cheap to build, is a 3 section EI54 M6 core.

Schematic is here:
http://www.audiofaidate.it/forum/uploaded/plovati/tuttuno_schema.JPG

here is driving 3V rms thru 600ohms load:

http://www.audiofaidate.it/forum/uploaded/plovati/spettro_3Vrms_out_6SN7_C_10k_lowres.JPG

it can be used as line preamp / headphone amp / and as 1W power amp too !
A real jolly, valid for every use (tuttuno in Italian means that)

 

[jeapel]

hi plovati

6sn7 with 10k plate load is not standard the minimum
in my book is 3 x ra = 3 x ~ 7k = ~ 21k and for me
with 5x or 10x you get more good triode sound and
the top is ccs with 100X and more

a good starting point for resistor on plate for 6sn7 is:

B+ =300v
bias=2ma
rl=47k
~200v across tube

 

[arnoldc]

The posted schematic was taken from the Sun Audio schematic for a 300B IIRC grafted to an output transformer. Doesn't it have too much gain for a preamp?

 

[Andersen]

Thanks all for your kind advice and comment.

I'm going to build this pre-amp to drive a Sun Audio 300BSE amp for mid and hi range (speakers: Altec Lansing 288B-16ohms, 311-60) and a Sun Audio 2A3SE amp for lo range (below 650hz, speakers: Altec Langsing 515B-16 ohms). Sensitivity of these speakers is more than 100dB.

Please advise what I should do now. Should I try the ultra-path pre-amp?

Thanks.

 

[SY]

What are your sources? If they're the usual 2V or thereabouts output, you really don't want or need much gain, maybe 6dB at the most. It doesn't need to be anything exotic unless you want exotic-for-exotic sake or want a preamp that alters the signal in some euphonic way.

 

[Andersen]

Currently, I connect directly from my CD player (TEAC VRDS-50) to 2 Sun Audio amps and have to adjust volume on these 2 amps. So I need a pre-amp not only to control the volume but also to control the soundstage. Is it possible?

 

[arnoldc]

I wonder how it sounds like with 300B and 2A3- two different character. Would they even get sync'ed with the music?

With speakers of such sensitivity, why bi-amp?

Obviously I'm curious as I have a speaker system based on Altec 406-8Y and I can't have party level volume with a pair of type 10 tube.

 

[plovati]

hi plovati

6sn7 with 10k plate load is not standard the minimum
in my book is 3 x ra = 3 x ~ 7k = ~ 21k and for me
with 5x or 10x you get more good triode sound and
the top is ccs with 100X and more

a good starting point for resistor on plate for 6sn7 is:

B+ =300v
bias=2ma
rl=47k
~200v across tube

What You said apply (if it applies, it is objectionable also in case of a single tube) only to a tranformer loaded single triode.
Is not the 6SN7 alone. Is the combination 6SN7 - 6BX7.
I tried different load for 6SN7, that can range from 6,8K to 22k, in order to have different distortion spectra and sonic result. 10K I found a good choice, not the best (id exist) but a good one.

Rules are made to be broken

 

[cerrem]

I will throw my 2 cents in...
When it comes to choosing plate loads....technically you can use whatever plate load you want....just as long as your happy with the results....and your not swinging the AC loadline way past max dissipation for most of the time.... ALso if you can back up your choice of plate load with distortion numbers....
Yes I know all the "rules of thumb" and the proper procedures...but there are cases when they do not always apply... I once made a pre-amp OPT, where the plate load was the same value of the plate resistance... i needed to do this to meet bandwidth requirements....
The other thing to keep in mind, is how much AC voltage swing will occur...In this case the AC voltage swing was tiny and was not ulilizing the entire load-line swing...it may have only used 10% of the full load-line swing...in this case the distortions were very small...

Chris

 

[jeapel]

my surprise was to see for the first time a 6sn7 with
10 k but if the sound is good very happy for you

my 6sn7 choice is a c4s ccs ( very high AC resistor equivalent)

but it s a interesting result because with 10k the
bandwidth will be very good

bye