What's Wrong with the DC300A ?

[Phil Allison]

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

 

[Phil Allison]

Rick C wrote:

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

Anyone know what that flaw is ?

No schem searching is needed.

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.

** 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

 

[Rick C]

On Wednesday, October 23, 2019 at 4:22:51 PM UTC-4, Phil Allison 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.

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.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[mpm]

On Wednesday, October 23, 2019 at 4:22:51 PM UTC-4, Phil Allison wrote:

> Anyone know what that flaw is ?

Easy: It weighs too much!

 

[John Larkin]

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

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

 

[Phil Allison]

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

 

mpm <mpmillard@aol.com> wrote in
news:f1de3688-6314-498a-9a8d-56ba36e8fc98@googlegroups.com:

On Wednesday, October 23, 2019 at 4:22:51 PM UTC-4, Phil Allison
wrote:

Anyone know what that flaw is ?

Easy: It weighs too much!

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

 

[Allan Herriman]

On Wed, 23 Oct 2019 13:22:47 -0700, Phil Allison 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.

"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

 

[Rick C]

On Thursday, October 24, 2019 at 8:49:20 AM UTC-4, Allan Herriman wrote:

On Wed, 23 Oct 2019 13:22:47 -0700, Phil Allison 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.


"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

How about outrush limiting?

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

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.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

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.

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Wednesday, October 23, 2019 at 4:22:51 PM UTC-4, Phil Allison 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.

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.

..... Phil

 

[Winfield Hill]

Allan Herriman wrote...

On 23 Oct 2019, Phil Allison wrote:

However, the DC300A has a simple flaw that renders it
unsuitable for many professional audio uses.
No schem searching is needed.

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

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

 

[George Herold]

On Wednesday, October 23, 2019 at 4:22:51 PM UTC-4, Phil Allison 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.

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.

..... Phil

 

[John Larkin]

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.

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

 

[Phil Allison]

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

 

[Phil Allison]

Winfield Hill wrote:

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

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.

** 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.

And the spec
says it requires 500 watts to deliver 300 watts.

** Impressive for class B.


I'm

a fan of the Hafler P3000,

** 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

 

[Phil Allison]

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.




...... Phil

 

[Phil Allison]

George Herold wrote:

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

Not sure about amps,

** Better leave it at that.

You are just not for real.


..... Phil

 

[legg]

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