What's Wrong with the DC300A ?

The DC coupling? If you connect a signal source with a small DC offset it will produce a huge DC offset in the output that may fry speakers.

--

  Rick C. 

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** Though possible, that was never an issue in practice.

Fitting a 1uF film cap is series with the gain pot removed any possibility.

I did that mod to a few of them.

..... Phil

Easy: It weighs too much! :)

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.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

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

So yours was 37 dB quieter - eh ??

1.5uV.

Pigs can fly....

..... Phil

page=4#manual

"The power supply features a 1kW transformer and large computer-grade filter capacitors giving over 48 joules of energy storage."

I hope they remembered to add some sort of inrush limiting.

Allan

mpm wrote in news: snipped-for-privacy@googlegroups.com:

Big rack mount design. Instant on might blow a driver.

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.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

How about outrush limiting?

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  Rick C. 

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My attention was attracted to its power consumption. Standby is spec'd at 40W, but could be higher, as a function of the class AB bias setting. And the spec says it requires 500 watts to deliver 300 watts. I'm a fan of the Hafler P3000, because, although it wasn't shipped as a DC amplifier, bypassing the input cap made it into one, good as a 300 watt laboratory amplifier. They were also readily available on eBay. But they did generate a lot of heat. Too much for comfortable studio HVAC, with a few racks of P3000's running. So I think they were replaced with a little less power hungry amps.

--
 Thanks, 
    - Win

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?

George H.

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?

George H.

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.

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

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** The output stage operates in pure class B - there is no forward bias current in the output transistors.

Unusual at the time, but done so well that x-over distortion is virtually non existent.

** Impressive for class B.

I'm

** A 90s home hi-fi design using Hitachi flat Pak lateral mosfets.

Skimped on output devices, no current limiting, no even rail fuses.

POS.

..... Phil

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** Go look up a schem you lazy shit.

..... Phil

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** Better leave it at that.

You are just not for real.

.... Phil

It used a simple op amp?

I used the simpler DC150.

RL

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** Not a bad thing.

** 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