What's Wrong with the DC300A ?

Winfield Hill wrote:

---------------------
Phil Allison wrote...

FYI:
The D150A II has the lowest THD I have ever tested.
Under 0.002% at rated power and all lower levels at 1kHz.


You might enjoy measuring my AMP-70A, as modified by
a team in Germany. It was about 10x better, 2ppm,
even at 20kHz. Bet then it goes from DC to 10MHz.
Click to expand...

** No, I would not waste my time.

The D150A is a low cost, readily available, consumer stereo amplifier for driving loudspeakers at home, in a small studio or cinema.

Your contraption is none of the above.


...... Phil
 
Phil Allison wrote...
FYI:
The D150A II has the lowest THD I have ever tested.
Under 0.002% at rated power and all lower levels at 1kHz.
Click to expand...

You might enjoy measuring my AMP-70A, as modified by
a team in Germany. It was about 10x better, 2ppm,
even at 20kHz. Bet then it goes from DC to 10MHz.


--
Thanks,
- Win
 
On Thursday, October 24, 2019 at 2:37:25 PM UTC-4, John Larkin wrote:
On Thu, 24 Oct 2019 10:19:13 -0700 (PDT), George Herold
ggherold@gmail.com> wrote:

On Thursday, October 24, 2019 at 11:04:39 AM UTC-4, jla...@highlandsniptechnology.com wrote:
On Wed, 23 Oct 2019 17:05:13 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

John Larkin wrote:

-------------------


The probably-same Crown amps were used as NMR gradient amplifiers at
Varian, until they asked us to design a custom replacement. A
voltage-output amp is not ideal to drive a gradient coil; we designed
a current-output amp.

Our s/n in that application was 70x better than the Crown.


** The DC300A is speced at 110dB s/n unweighted 20Hz to 20kHz or 0.1mV

https://www.manualslib.com/manual/225257/Crown-Dc-300a.html?page=6#manual

So yours was 37 dB quieter - eh ??

1.5uV.

Pigs can fly....



..... Phil



Crown converted their big audio amp into a gradient coil driver by
running the low side of the load into a shunt to ground, and doing
some feedback to make it a current output amp. 50 millivolt shunt I
recall. It think they had ground loops.

NMR is insanely sensitive to any noise on the z-axis field, parts per
billion resolution. About the worst thing a system can have is 60 or
120 Hz sidelobes on a resonant peak, the marketing equivalent of a rat
in the soup.

Not sure about amps, but commercial power supplies are much too noisy
for 'fine' magnetic control.

George H.

We sold a lot of gradient drivers to Varian, until Agilent acquired
Varian and killed the NMR and FTMS operations.

We made our own current shunts and amps and stuff.
Click to expand...
Nice.. I was much lower end. Who makes the nmr stuff now?
Japan? China? Germany?
George H.

With a good, properly shimmed magnet, the hydrogen line Q is around
1e9, and the frequency is linear on the mag field.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Click to expand...
 
On Thursday, October 24, 2019 at 3:05:20 PM UTC-4, Phil Allison wrote:
George Herold wrote:

-------------------


No schem searching is needed.

No idea, But I wonder how the various grounds were connected?
Did each channel 'float' from the other and did they float compared
to the chassis ground?



** Go look up a schem you lazy shit.
Click to expand...
Oh thanks, I thought you said no schematic searching is needed?
George H.
..... Phil
Click to expand...
 
On Thu, 24 Oct 2019 21:17:42 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

On Thursday, October 24, 2019 at 2:37:25 PM UTC-4, John Larkin wrote:
On Thu, 24 Oct 2019 10:19:13 -0700 (PDT), George Herold
ggherold@gmail.com> wrote:

On Thursday, October 24, 2019 at 11:04:39 AM UTC-4, jla...@highlandsniptechnology.com wrote:
On Wed, 23 Oct 2019 17:05:13 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

John Larkin wrote:

-------------------


The probably-same Crown amps were used as NMR gradient amplifiers at
Varian, until they asked us to design a custom replacement. A
voltage-output amp is not ideal to drive a gradient coil; we designed
a current-output amp.

Our s/n in that application was 70x better than the Crown.


** The DC300A is speced at 110dB s/n unweighted 20Hz to 20kHz or 0.1mV

https://www.manualslib.com/manual/225257/Crown-Dc-300a.html?page=6#manual

So yours was 37 dB quieter - eh ??

1.5uV.

Pigs can fly....



..... Phil



Crown converted their big audio amp into a gradient coil driver by
running the low side of the load into a shunt to ground, and doing
some feedback to make it a current output amp. 50 millivolt shunt I
recall. It think they had ground loops.

NMR is insanely sensitive to any noise on the z-axis field, parts per
billion resolution. About the worst thing a system can have is 60 or
120 Hz sidelobes on a resonant peak, the marketing equivalent of a rat
in the soup.

Not sure about amps, but commercial power supplies are much too noisy
for 'fine' magnetic control.

George H.

We sold a lot of gradient drivers to Varian, until Agilent acquired
Varian and killed the NMR and FTMS operations.

We made our own current shunts and amps and stuff.
Nice.. I was much lower end. Who makes the nmr stuff now?
Japan? China? Germany?
Click to expand...

I think the only big NMR operation left is Bruker, a German company
with a big US NMR operation.

I think NMR is fading away as an analytical chemistry technology. It's
too expensive to run those big magnets.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 25 Oct 2019 07:53:25 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

jlarkin@highlandsniptechnology.com wrote...

I think NMR is fading away as an analytical chemistry
technology. It's too expensive to run those big magnets.

Dunno about fading, but when our chemist retired, we gave
away our NMR machine, which was in excellent condition,
and in steady use right up to the end. It didn't have
the highest magnetic field, but had many good features.
Click to expand...

I have been to labs that had a high-field magnet in the corner, warm
and collecting dust. It's really expensive to keep one charged with
liquid helium.

My many MRIs were done on a machine with a reliquifier in the next
room, gently chugging away. And an MRI makes $1000 an hour or
something like that.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
jlarkin@highlandsniptechnology.com wrote...
I think NMR is fading away as an analytical chemistry
technology. It's too expensive to run those big magnets.
Click to expand...

Dunno about fading, but when our chemist retired, we gave
away our NMR machine, which was in excellent condition,
and in steady use right up to the end. It didn't have
the highest magnetic field, but had many good features.


--
Thanks,
- Win
 
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