Unity Gain Tube Stage

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beatpoet

Well-known member
Joined
Sep 19, 2006
Messages
334
Location
Michigan
Taking a break from reading about mics and filters, I thought I'd ask what everyone's idea of an ideal tube unity gain stage was.

The conditions:

1) Line Level
2) Transformerless
3) Flat freq. response & stability
4) Minimal or no passive padding
5) Single stage - well double if you have to
6) simple K followers are not usually unity gain

Here's an interesting idea from the HeadWize page:

C2348.gif


...And here's the thread

http://headwize.com/ubb/showpage.php?fnum=3&tid=6642

Here's some things at tubecad I've just started on:

http://www.tubecad.com/2006/06/blog0068.htm

http://www.tubecad.com/articles_2001/totem-pole_output_stage_psrr/
 
A gain of 0.9 isn't close enough to unity for you?

I'd just use a cathode follower--or a White cathode follower if I wanted to be able to drive truly low-Z loads. But if you're into needlessly complicated solutions to simple problems, then... go wild :razz:
 
i'd probably use a cathode follower.
and why not use a transformer?
i think tubes and transformers fit together.
for unity you could also use a tube with low gain and some feedback and then a proper step down say 15k:600.
there are many tubes that will drive that.
the feedback makes it quite lineair
it's simple and works.
you sure could use some extra current sources etc.... but then again whats the use of the tube then?
its just an opinion but recently i build an amp with an Long tailed pair. in the tail was a current source and you could perfectly adjust the current and you had gain enough.
now i removed it and used resistors to do the work.
much easier to work with and it works also. it sounds better also but that is subjectiv.
now i have a simple el84 pse amp playing and it doesn't have feedback, it has lundahl l1664 in the output and sounds really good.
the schematic is plain simple.
one little 5670 drives the el84's in triode.
so the kiss(keep it simple stupid) aproach works.
 
You need a unity voltage gain; what power gain do you need? I would start from this simple question, it is the basic one. And what kind of load are you going to drive. I.e. what is impedance, and how it depends on frequency.
 
[quote author="NewYorkDave"]A gain of 0.9 isn't close enough to unity for you?

I'd just use a cathode follower--or a White cathode follower if I wanted to be able to drive truly low-Z loads. But if you're into needlessly complicated solutions to simple problems, then... go wild :razz:[/quote]

Hey, that's a "MOSFet Sandwich" isn't it
icon_eek.gif
.

analag
 

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