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
What's Wrong with the DC300A ?
Started by ●October 23, 2019
Reply by ●October 23, 20192019-10-23
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
Reply by ●October 23, 20192019-10-23
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
Reply by ●October 23, 20192019-10-23
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! :)
Reply by ●October 23, 20192019-10-23
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. > > > >..... PhilThe 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
Reply by ●October 23, 20192019-10-23
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
Reply by ●October 24, 20192019-10-24
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
Reply by ●October 24, 20192019-10-24
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.
Reply by ●October 24, 20192019-10-24
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
Reply by ●October 24, 20192019-10-24
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. > > AllanHow about outrush limiting? -- Rick C. + Get 1,000 miles of free Supercharging + Tesla referral code - https://ts.la/richard11209
