John Curl's Blowtorch preamplifier

[hitsware]

It is not? How do you know, is that your personal belief or can you back that up with anything?

I consider it common knowledge, but evedently? I'm wrong.
I know from personal listening experiences that it
would seem true based on the excellent and similar
(but granted not identical) specs of many SS amplifiers
(with attendent disimularities in sound).
However, at one time Carver purportedly ran a clinic wherein
he could make any amp emulate any other by (I think) adjusting
the squarewave response at the input.
So it's personal belief based on personal experience enhanced
by the consenses .... Since I didn't go to the Carver clinic

 

[KBK]

"noise from 400 Hz on up"

Yes, yes..interesting point, there..isn't it. The most incredible things can hide in plain sight.

 

[jcx]

has anyone looked at Lovoltech power jfet noise? - maybe moot due to unavailability?
I assume they don't pay any attention to processing controls with respect to noise performance

a few lower noise fet and cmos op amp noise plots - none competive with discrete
http://www.diyaudio.com/forums/showthread.php?postid=843381#post843381

 

[jan.didden]

I consider it common knowledge, but evedently? I'm wrong.
I know from personal listening experiences that it
would seem true based on the excellent and similar
(but granted not identical) specs of many SS amplifiers
(with attendent disimularities in sound).
However, at one time Carver purportedly ran a clinic wherein
he could make any amp emulate any other by (I think) adjusting
the squarewave response at the input.
So it's personal belief based on personal experience enhanced
by the consenses .... Since I didn't go to the Carver clinic

I think Carver adjusted the Zout of his amp to make it indistinguisable (in sound) from a specific tube amp. Successfully.

From Richard Dawkins' letter to his daughter on the occasion of her 10th (!) birthday:

"Three bad reasons to believe anything:

- tradition (also called 'common knowledge');
- revelation;
- authority".

Jan Didden

 

[hitsware]

>I assume they don't pay any attention
>to processing controls with respect to
>noise performance

Part of my point. Just because a device is not
designed for low noise, does not mean that it
is not (accidently) quiet.

 

[SY]

At John's request, the Right Way to get noise measurements.

 

[john curl]

What are you trying to say KBK?

 

[Nelson Pass]

has anyone looked at Lovoltech power jfet noise? - maybe moot due to unavailability?
I assume they don't pay any attention to processing controls with respect to noise performance

Probably a good assumption. I did check them out for noise, and while
I didn't gather numerical data, I can tell you that they were unimpressive.

Are they unavailable? I'll bet they have some inventory.

 

[hitsware]

>"Three bad reasons to believe anything:

>- tradition (also called 'common knowledge');
>- revelation;
>- authority".

If we add the vagaries of perception to that list, we're not left
with much ......

 

[john curl]

Do you believe in measurement? Especially when it comes to noise?

 

[hitsware]

>Then please specify these 'other things'
>otherwise you are using a fallacious
>argument to try and present your point.

'Magic' by it's essence cannot be 'specified'

However, one thing I have found to make
a big differance in sound is slew rate ....
even if the signal to be passed does not
even approach the limit.

And one must remember that the magic
of one generation may become the science
of the next.

 

[scott wurcer]

At John's request, the Right Way to get noise measurements.

You could recreate one with a little work and a good sound card. No unobtainium inside, just a lot of old bakelite PC boards (I have a set of the schematics). Clever bias control allows setting operating point and a calibration of gain right to the input. The digital ones are no fun though.

No need to get into that discussion or we'll be back to 40 years ago....

 

[SY]

Actually, I think that the HP 3581 that John loaned me could work for that. It's pretty darn quiet.

 

[hitsware]

Probably a good assumption. I did check them out for noise, and while
I didn't gather numerical data, I can tell you that they were unimpressive.

Nelson,
Out of curiousity, have you ever measured the noise
performance of one of your hunky power mosfets ?
At a reasonable current and (for the moment) disregarding
the input capacitance.

 

[syn08]

Brodersen and Emmons from TI research in Dallas did it, there's a slew of papers published in IEEE Transactions on Electron Devices 1975-1977. Example:
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1478391

Notice date on reference below 1977, but I can't find the products now. Of course there are no discreets or never were any and I think only one flavor of MOSFET was super quiet.

 

[john curl]

Not easy to make a QuanTech equivalent, but possible. A friend of mine has done it in the Bay Area. SY, I could introduce him to you. He knows as much as I do on the subject, BUT his expertise is ultra low 1/f noise. We use essentially the same parts.
Better to use a FFT based analyzer as the readout, because it is faster.
For the record, I still work consistently at 2.5 times LESS noise than the AD797, so Scott has a lot of catching up to do. All done thanks to QuanTech.

 

[jan.didden]

>"Three bad reasons to believe anything:

>- tradition (also called 'common knowledge');
>- revelation;
>- authority".

If we add the vagaries of perception to that list, we're not left
with much ......

Nope. We're on our own. As always

Jan Didden

 

[KBK]

Of course there are no discreets or never were any and I think only one flavor of MOSFET was super quiet.

And what exact alloys did it employ? How were they arranged?

What did the published curves look like?

What was their fabrication process, and what was their reject rate at? What did the reject curves look like?

 

[scott wurcer]

For the record, I still work consistently at 2.5 times LESS noise than the AD797, so Scott has a lot of catching up to do. All done thanks to QuanTech.

I'm working at .25nV where have you been? There's no commercial products there just lab stuff. I asked a while back,"How would you make a useful .1nV amplifier". I still don't have an answer.

 

[Onvinyl]

This is for just ONE fet, but I almost always use them in parallel, and at high current, so my typical input voltage noise for a Vendetta is 0.4nV / rt.Hz at 1kHz.

Hi John,
for which inout impedance or range of impedances do you get this (0.4nV/rtHz) number?

Rüdiger