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
What's Wrong with the DC300A ?
Started by ●October 23, 2019
Reply by ●October 24, 20192019-10-24
Reply by ●October 24, 20192019-10-24
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
Reply by ●October 24, 20192019-10-24
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
Reply by ●October 24, 20192019-10-24
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
Reply by ●October 24, 20192019-10-24
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
Reply by ●October 24, 20192019-10-24
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
Reply by ●October 24, 20192019-10-24
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
Reply by ●October 24, 20192019-10-24
George Herold wrote: -------------------> > Not sure about amps,** Better leave it at that. You are just not for real. .... Phil
Reply by ●October 24, 20192019-10-24
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. > > > >..... PhilIt used a simple op amp? I used the simpler DC150. RL
Reply by ●October 24, 20192019-10-24
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
