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.

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.

 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

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? 

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 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. 
Oh thanks, I thought you said no schematic searching is needed? 
George H.  
> 
>   
> 
> 
> .....  Phil

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? 
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

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.
> 

** 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.

 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

legg wrote:

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

> 
> It used a simple op amp?
> 

 ** Not a bad thing. 

> I used the simpler DC150.

** No such amp. 

 You must mean the D150A. 

 It does not suffer from the same problem the DC300A does. 

FYI:

The D150A II has the lowest THD I have ever tested. 

Under 0.002% at rated power and all lower levels at 1kHz.

Much better than speced. 

.....  Phil

On Wed, 23 Oct 2019 13:22:47 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>
>Hi to all my fans, 
>--------------------
>
>see pic of possibly the most famous stereo power amplifier ever made.
>
>https://cdn11.bigcommerce.com/s-6naz0isypk/images/stencil/2048x2048/products/3247/20471/5569873-7432-5__81144.1510738289.jpg?c=2
>
>The Crown DC300A was first released in the early 1970s and sold in large numbers, world wide. The letters "DC" refer to the fact it has response down to DC. 
>
>https://www.manualslib.com/manual/225257/Crown-Dc-300a.html?page=4#manual
>
>Though ostensibly designed as a "laboratory  amplifier" it was immediately adopted by the professional audio world for studio and live sound plus by many audiophiles for home stereo use. IOW to drive loudspeakers. 
>
>It was beautifully engineered inside and exceptionally reliable, I have only had to repair a small number for minor faults - never seen a blown up one. 
>
>However, the DC300A has a simple flaw that renders it unsuitable for many professional audio uses.
>
>Anyone know what that flaw is ? 
>
>No schem searching is needed.
>
>
>
>.....  Phil  

It used a simple op amp?

I used the simpler DC150.

RL