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6n1p simpl(ish) design

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Hi tube-nuts! I have spent endless hours looking for simple but good line-amp designs, preferably using 6N1P tubes. All I have to show for it so far is gigabytes of downloads and a massive telephone bill. (And a fair amount of confusion!)
Can anyone suggest something not too difficult? I am a newbie to tubes, but I know without any doubt this is the way I want to go. Gain can be anything from unity to about 5x. I am replacing my passive pre and I have just enough gain with it at the moment, but a bit more would also be okay.
 
diyAudio Senior Member
Joined 2002
Hi,

6N1P are beautiful in mu-follower or Loftin-White CF stages

Hmmmm...
Too much gain from the mu-follower probably and unity gain from the WCF.

Somewhere inbetween there's that nice SRPP circuit which will do nicely provided you build it a nice PS and don't use too long and too capacitive interconnects. Never too bright an idea anyway.

Make sure you look at the correct datasheet for the 6N1-P. There's quite a bit of rubbish being spread over the net about that one....

Cheers,;)
 
hihopes,

Is there any particular reason why you want to use the 6N1P?

A simple grounded cathode circuit with a low-mu triode like the 12B4 is reputed to sound good. If you are willing to use transformer-coupling (which is of course more expensive because of the transformer), olden-day 1930s triodes like the 56, 76 etc are also reputed to be good-sounding.

I don't mean to confuse, but there are many other options out there...
 
audiousername said:
hihopes,

Is there any particular reason why you want to use the 6N1P?

A simple grounded cathode circuit with a low-mu triode like the 12B4 is reputed to sound good.
The 12B4A is a great option and will give the specified performance at modest cost, cheaper than the OPT option. I've posted my variation on that theme several times before on this board. Using such a high mu triode (6N1P) to try to get a stage with a 0-5x gain is not the best choice imo/ime.
If you are willing to use transformer-coupling (which is of course more expensive because of the transformer), olden-day 1930s triodes like the 56, 76 etc are also reputed to be good-sounding.
There are also other more modern options such as the ECC99 that are less finicky than some of the vintage triodes.
I don't mean to confuse, but there are many other options out there...
You raise good points, and there are of course a lot of other options. The 6N1P is a decent tube, but this is not where I'd use it.
 
Nothing wrong with a 6n1p. If you don't need more gain..just go for a 6n1p in cathode follower mode.

Cheers,
Bas

http://www.decware.com/linestage/zp1.htm

I've added a little example of what you could try. It's not tried and tested...just a ballpark 6n1p cathode follower..Build it and tell us what it's like...

One more thing you should ground the filament both sides with a little 100R resistor.
 

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Wow! Thanks for all the input guys. Comments:-
1) I do not want to use a design with an output transformer. Here in good 'ol sunny RSA such hardware is impossible to find and very expensive to import (as are chokes).
2) It seems to me that really simple designs require really quiet power supplies to do them justice, which in turn require really big ironware. Thus, the simplicity and low cost of the design is overshadowed by costly PS complications. That is why I asked for suggestions for a siml(ish) design.
I would love nothing better than to be able to build a 1 or 2 tube design as my first project, as in my experience, less is often more, (and I must say, Bas, that circuit diagram does look very tempting,) but I would hate to have to spend the time and money I should have/could have spent on tweaking/tuning the amp on trying to sort out PS noise. Don't get me wrong - I am aware of how much difference a good PS can make (I have a 90kva E-core TRF with 10000uF Panasonic reservoir caps just to run an OPA627/Buf634p design) but it is impractical for me to go overboard with massive chokes etc.
3) The 6n1p is a preference, because I know a bit about it and it is also one of the few tubes I have heard in a pre, but it is by no means cast in stone. However, if I were to show no preference at all, I would probably be inundated with so much stuff I would not be able to breathe!
4) I have downloaded 3 6n1p spec-sheets (2 of them Russian and English side by side). How do I know which are the correct specs?
Please keep the suggestions coming. If anyone has a proven design that is really working well and not too difficult to build, I would really like to know about it. Also, if someone can tell me categorically (from experience) that another tube (5687; 9622; 6h30 or whatever) is generally better, or would work synergisyically with a 6n1p, then please don't hold back!
Thanks again,
William.
PS If a whole series of replies is posted without any input from me, that is not becuse I have lost interest in the thread, but because I often don't have a lot of opportunity to go online.
 
diyAudio Senior Member
Joined 2002
Hi,

Why would you want a crap SRPP? Awful sounding things.

I wouldn't generalize that much.
It's fairly easy to make any circuit sound awful, it's the other way around that's a little harder.:D

Anyhow, with a high gm tube such as the 6N1-P and a stiff PS you have a very good chance to build a nice preamp that has the potential of being outstanding without the intrinsic limitations of an OPT.

For this SRRP I'd suggest a series regulated PS of 250 VDC.
The upper triodes require a dedicated heater supply which must be biased upwards by about 100V to prevent heater to cathode insulation breakdown.

If money is no object a higher raw B+ can be used in conjunction with a VR shunt regulated supply or even series + shunt.

One of the advantages of the SRPP topology is that a fair amount of voltage swing can be had from this relatively simple circuit.
If later on a 6922 or similar valve is substituted for the 6N1-P, even lower Zout is possible, promising even better cable drive capabilities.

Cheers,;)
 
hihopes said:
Wow! Thanks for all the input guys. Comments:-
1) I do not want to use a design with an output transformer. Here in good 'ol sunny RSA such hardware is impossible to find and very expensive to import (as are chokes).
2) It seems to me that really simple designs require really quiet power supplies to do them justice, which in turn require really big ironware. Thus, the simplicity and low cost of the design is overshadowed by costly PS complications. That is why I asked for suggestions for a siml(ish) design.

You don't need expensive transformers or huge chokes for a small preamp design. You could use two ordinary mains transformers (cheap, but not so cheap that they will burn your house down :) ) with the secondaries the correct voltage for the valve heaters, and connect the other one backwards (i.e. using its secondary as primary) to get the high voltage for B+. I have heard of people doing this, but I have not done this myself. Wait for someone more experienced to comment on safety concerns!

Also, for low-ripple from the power supply, there is the brute-force method of large caps and chokes, or you could use something like a CRC filter (which would result in rather high ripple) then pass it through a regulator. The regulator needn't be complex, something could be made with a dissimilar triode like a 6EM7 and a gas voltage reference, or even simpler would be to knock something up with an LM317 or similar. Some may object to this because signal currents travel through the power supply, and hence through the regulator as well - possibly altering the sound.


My personal recommendation would be for Brett's 12B4 circuit. I reckon it would work (and sound) a treat with a good power supply! (unless of course you have power amps which can't stand the 900 ohm source Z, which since you were using a passive attenuator, I assume you don't)

Also, this might be of interest. http://www.diyaudio.com/forums/showthread.php?s=&threadid=12042&perpage=10&highlight=&pagenumber=1
It's an old thread for a preamp design by fdegrove, and includes a regulated PS.
 
Thanks for the tip about the thread. I have downloaded it and will go through it at leisure.
Guys, the diagram GIFs are most welcome, but they are illegible when I enlarge them. Where can I find the originals, or can you post them in a different format?
Thanks,
William.
 
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