J-fet VS Vaccuum tube mic preamp.

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Bob wrote
>Is there any significant difference in noise performance between a j-fet and
>a vaccuum tube mic preamp, besides nostalgia.

Here's a link to a search I did, "Tubes Vs Transistors", you can find lots of
yes or no's. It really all depends on what kind of sound you want to get.

http://aolsearch.aol.com/aol/searc [...] %2Faol%2Fj
sp%2Fsearch.jsp&query=transisters+vs+tubes&x=26&y=11

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On Mon, 06 Sep 2004 23:21:43 GMT, "sycochkn" <sycochkn@earthlink.net>
wrote:

>Is there any significant difference in noise performance between a j-fet and
>a vaccuum tube mic preamp, besides nostalgia.

Because a JFET operates at room temperature it has a factor
of 2.5 lower equivalent noise resistance for the same
transconductance. It's also easier to get larger transconductances
affordably.

JFET's are made in both genders, and a complimentary input
circuit parallels the devices for noise.

OTOH, an ordinary 12AX7 triode is amazingly linear and has a
huge dynamic range. JFET's are square-law devices and must be
matched and operated in push-pull (or push-push) for linearity.

Both are noise-matched at very high impedances, but that's
not really significant.

Chris Hornbeck

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In article <bi6%c.9320$w%6.2277@newsread1.news.pas.earthlink.net> sycochkn@earthlink.net writes:

> Is there any significant difference in noise performance between a j-fet and
> a vaccuum tube mic preamp, besides nostalgia.

A lot of newsgroup noise, for sure.

What's the hangup with noise all of a sudden? Are people having
problems with preamp noise?

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

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<< What's the hangup with noise all of a sudden? Are people having
problems with preamp noise? >>

It was never a problem for me until I got a ribbon mic in my collection. Now
it's a problem.


Scott Fraser

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In article <20040907110553.17257.00000158@mb-m25.aol.com> scotfraser@aol.com writes:

> It was never a problem for me until I got a ribbon mic in my collection. Now
> it's a problem.

Noise was never a problem for me either when I had good ol' analog
recorders that ran at a nominal operating level of +4 dBu and you
didn't want to push them to more than 10 dB higher than that most of
the time. Now that we want to light all the lights on our nominal
+4 dBu digital recorders, we need 10 dB more gain out of our preamps
in order to get there. Or else we just need to move the mic closer.
<g>



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

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"Phil Allison" <philallison@tpg.com.au> wrote in message
news:2q6rpiFrd8idU1@uni-berlin.de...
>
> "Paul Stamler"
>
> > >
> > > > Is there any significant difference in noise performance between a
> j-fet
> > and a vaccuum tube mic preamp, besides nostalgia.
> >
> > Not if they're both well-designed. You can make a very quiet preamp
using
> > j-fets, tubes or bipolar transistors, if you dot all the I's and cross
all
> > the T's.
>
>
> ** With a tube pre-amp an input matching transformer is essential for
low
> noise.
>
> Not so for a transistor mic pre-amp.
>
>
>
>
> ............ Phil
>
>
>
>

Archived from groups: rec.audio.pro (More info?)

"sycochkn" = top posting wanker.

> The best I ever did with a j-fet input op amp and a transformer
was -139dbm.


** Not with a 150 ohm source you did not.


> It would be nice to get rid of the transformer since a good one costs 40
or
> 50 dollars.


** Lose the op-amp.




........... Phil

Archived from groups: rec.audio.pro (More info?)

In article <vMr%c.731$xA1.111@newsread3.news.pas.earthlink.net> sycochkn@earthlink.net writes:

> The best I ever did with a j-fet input op amp and a transformer was -139dbm.
> It would be nice to get rid of the transformer since a good one costs 40 or
> 50 dollars.

That's the same thing that every manufacturer of a transformerless
preamp has said.

On the other hand, a good transformer imparts a color that isn't easy
to achieve without one. Theorists say "good riddance" but a lot of
engineers and producers like the coloration you get from a good
transformer (though most would rather have no transformer than a bad
one).



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

Archived from groups: rec.audio.pro (More info?)

Monte McGuire <monte.mcguire@verizon.net> wrote:
>In article
> "Paul Stamler" <pstamlerhell@pobox.com> wrote:
>> Yes, it'd be nice to get rid of the transformer for reasons of cost, space
>> and weight (I'd put the price more like 70 dollars). To do so, as Phil said,
>> you need to use bipolar transistor inputs. If you want to use FETs or tubes,
>> then transformers are part of the design if you want low noise.
>
>Don't some of the large geometry JFETs like the 2SK170 have extremely
>low voltage noise, on par with 30-70 ohm sources? You'd need no input
>transformer using devices like that.

The numbers are good but still not anywhere near as good as the large area
bipolars (like the THAT arrays). There's a Marshall Leach article in the
JAES from around 1990 which goes through the math with various devices and
input configurations. The thermal noise of a typical transformer is a
problem and means the transformer is only a win on tube and FET input stages.

But, there are some very quiet transformerless FET and tube devices out there.
The Forssell preamps come to mind.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."