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Class ABDH
Don't make 'em to last. Supposed studio-grade ART amp, two models,
which I'm glad I didn't buy the more powerful of the two. It has a characteristic output heat difference: one channel's output transformers are hotter than the other. I noticed the heat discrepancy from day one, when I first plugged the unit in. Very basic sensory perceptions being not much more than a casual note, or why else would not I have returned or at least replaced it with another new unit. A perfectly respectable note from a repair or technician's standpoint, to point out sequential serial production models, any amp manufacturer may occasionally run into, which subsequently are prone to failure. Five years usage and the unit was never turned off, at least until the condition osculated and a heat-sensor disabled the channel with higher temperatures. Averages out to nickel, dime a day, or put another couple on the jukebox, unless compared to another of my Class A/B amps that has seen 10-times the usage of the ART. And so I've a Class D replacement slated, hopefully, which will fill a pro-grade bill, the caveat being for as little money as possible, or to cost close enough to my outlay on the ART unit. Class D being amps which can more or less respectably produce three times the power, over a former class of exclusive Class A/B amps, being Class D is now presented among serious technological advancements and offerings. And no doubt a wide one for characteristics between design intents. Three times the power, which I'll have, equates to the common assessment of a speaker at least twice more capable of handling that amount. Which I have: a speaker cabinet rated for 600 watts. A provision otherwise incredibly enough obtainable through the amp's firmware display for setting the amp in bridged mode. 600 watts for playing a bass guitar (from a DI impedance box) is not especially incredible. I have a 6-string guitar that's much bigger and uses huge strings. Other than being a guitar in all other respects, it's nevertheless called a bass guitar. I'll first have to turn on the new Class D amp. That will occur when I take possession, which will serve a purpose of effectively never turning it off. It idles at 18-watts, much as does a 52" ceiling-mounted fan left on at the lowest blade rotational speed. Even though the amp is equipped with a fan, it's Class D, and I don't expect the fan to run at idle wattage or slightly higher. Plugging in a bass guitar will be icing on the cake if it works as intended: twenty-four hour, low-wattage duty for longevity;- a relative occasional assessment for high-power usage. It's also an amp with an old name, going back further, older than the abovementioned amp, 10-times older than the failed ART amp. In fact the manufacturer of the Class D would hold public demonstrations to the strength of their amps by taking current from the output leads to weld together metal. I've some doubts, having used 100-watt vacuum tube amps for bass guitar, which accordingly are humbled among higher-wattage bass-designed amps. As I said, I'm out of it with today's Class A/B amps and the accompanying heat to an A/B's duty cycle. The Class D will be delivered and installed later today. The ART, being somewhat beautifully designed both inside and out, I suspect I'll lean up alongside a garbage can a little while for the contemporary sense of nostalgia it brings. |
#2
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Class ABDH & I
On Fri, 16 Mar 2018 02:01:13 -0400, Flasherly
wrote: As I said, I'm out of it with today's Class A/B amps... - The Harman Drive Core amplifier chip is a completely in-house design done through Crown engineering. The only thing we used TI for was their expertise in IC Chip manufacturing. There are several patents on the chip design, although the basic topology is a Class D output stage. The Drive Core technology is used in several places, including the Lexicon DD-8, and several Crown amplifiers. There are 2 chips, one is a complete amp on a chip that includes an output stage that is capable of delivering 75 - 150 watts into 8ohms (depending on power supply and application requirements) and is table to 2 ohms, and the only thing that is really needed is a power supply and an input stage. The first use of the technology was in the Lexus LFA supercar. The requirements were high output, small size, high efficiency (greater then 90%), and great sound. Moving the input and output stages onto a single IC allowed much tiger tolerances of the clock and triangle wave form generator that is the heart of all digital amp designs, and often the cause of the "Class D" sound some people don't like. There is also a version that is everything without the high output stage (the input, waveform generator, feedback circuit, etc...) that can me used to drive higher output stages either Class D or our patented Class I, where more then 150 watts is needed. Thanks for the interest, Todd Packer Harman Luxury Audio Group Field Application Engineer |
#3
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Class ABDH
Flasherly wrote:
Don't make 'em to last. Supposed studio-grade ART amp, two models, which I'm glad I didn't buy the more powerful of the two. It has a characteristic output heat difference: one channel's output transformers are hotter than the other. I noticed the heat discrepancy from day one, when I first plugged the unit in. Very basic sensory perceptions being not much more than a casual note, or why else would not I have returned or at least replaced it with another new unit. A perfectly respectable note from a repair or technician's standpoint, to point out sequential serial production models, any amp manufacturer may occasionally run into, which subsequently are prone to failure. Five years usage and the unit was never turned off, at least until the condition osculated and a heat-sensor disabled the channel with higher temperatures. Averages out to nickel, dime a day, or put another couple on the jukebox, unless compared to another of my Class A/B amps that has seen 10-times the usage of the ART. And so I've a Class D replacement slated, hopefully, which will fill a pro-grade bill, the caveat being for as little money as possible, or to cost close enough to my outlay on the ART unit. Class D being amps which can more or less respectably produce three times the power, over a former class of exclusive Class A/B amps, being Class D is now presented among serious technological advancements and offerings. And no doubt a wide one for characteristics between design intents. Three times the power, which I'll have, equates to the common assessment of a speaker at least twice more capable of handling that amount. Which I have: a speaker cabinet rated for 600 watts. A provision otherwise incredibly enough obtainable through the amp's firmware display for setting the amp in bridged mode. 600 watts for playing a bass guitar (from a DI impedance box) is not especially incredible. I have a 6-string guitar that's much bigger and uses huge strings. Other than being a guitar in all other respects, it's nevertheless called a bass guitar. I'll first have to turn on the new Class D amp. That will occur when I take possession, which will serve a purpose of effectively never turning it off. It idles at 18-watts, much as does a 52" ceiling-mounted fan left on at the lowest blade rotational speed. Even though the amp is equipped with a fan, it's Class D, and I don't expect the fan to run at idle wattage or slightly higher. Plugging in a bass guitar will be icing on the cake if it works as intended: twenty-four hour, low-wattage duty for longevity;- a relative occasional assessment for high-power usage. It's also an amp with an old name, going back further, older than the abovementioned amp, 10-times older than the failed ART amp. In fact the manufacturer of the Class D would hold public demonstrations to the strength of their amps by taking current from the output leads to weld together metal. I've some doubts, having used 100-watt vacuum tube amps for bass guitar, which accordingly are humbled among higher-wattage bass-designed amps. As I said, I'm out of it with today's Class A/B amps and the accompanying heat to an A/B's duty cycle. The Class D will be delivered and installed later today. The ART, being somewhat beautifully designed both inside and out, I suspect I'll lean up alongside a garbage can a little while for the contemporary sense of nostalgia it brings. On basic power transformers (not output transformers), a power transformer can overheat with no load whatsoever. I have such a transformer here, which I had just put into a home amplifier design, which overheated. Just plugging in the transformer with no load, it was overheating. This is caused by eddy current flow. The laminations in a regular power transformer (AC 110V to some lower AC output inside the equipment), those laminations are steel with a lacquer coating. The laminations are then sandwiched together. The purpose of the lacquer, is to prevent induced current flow from one lamination plate into the next. Now, as a transformer ages, or if a transformer is placed in a moist atmosphere, the steel in the laminations can rust and punch through the insulating coat. And when eddy currents flow from one lamination to another. This represents energy loss and consequent heating. A second failure mode for power transformers, is a short in some winding. Say there are multiple output windings, and an unused winding (a low power one) is shorted out for some reason. The transformer can overheat, with no apparent secondary side usage. ******* On output transformers, you don't want DC across them, as first of all, DC saturates the transformer core and prevents good passage of AC output. Transformers on output may be used on vacuum tube units, for impedance conversion purposes. A solid state design might not need them. ******* You might have contacted after-sales support, technical support, or warranty support when you received the defective amplifier and asked them if the situation was "normal" as far as they were concerned. There's plenty of junk on the market operating at high temperatures, such as the computer speaker 7.1 amplifiers situated inside the sub housing, with no decent cooling for any of the components. The air temperature inside the sub is warm enough, to "cook" the glue used to provide protection against vibrational failure. And the glue happens to conduct, once it's been cooked and breaks down chemically. The conductive glue then shorts out the power used to run the amp and makes the amp unreliable. All because cooling design was neglected. Paul |
#4
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Class ABDH
On Fri, 16 Mar 2018 04:26:50 -0400, Paul
wrote: On basic power transformers (not output transformers), a power transformer can overheat with no load whatsoever. I have such a transformer here, which I had just put into a home amplifier design, which overheated. Just plugging in the transformer with no load, it was overheating. This is caused by eddy current flow. The laminations in a regular power transformer (AC 110V to some lower AC output inside the equipment), those laminations are steel with a lacquer coating. The laminations are then sandwiched together. The purpose of the lacquer, is to prevent induced current flow from one lamination plate into the next. Now, as a transformer ages, or if a transformer is placed in a moist atmosphere, the steel in the laminations can rust and punch through the insulating coat. And when eddy currents flow from one lamination to another. This represents energy loss and consequent heating. A second failure mode for power transformers, is a short in some winding. Say there are multiple output windings, and an unused winding (a low power one) is shorted out for some reason. The transformer can overheat, with no apparent secondary side usage. ******* On output transformers, you don't want DC across them, as first of all, DC saturates the transformer core and prevents good passage of AC output. Transformers on output may be used on vacuum tube units, for impedance conversion purposes. A solid state design might not need them. ******* You might have contacted after-sales support, technical support, or warranty support when you received the defective amplifier and asked them if the situation was "normal" as far as they were concerned. There's plenty of junk on the market operating at high temperatures, such as the computer speaker 7.1 amplifiers situated inside the sub housing, with no decent cooling for any of the components. The air temperature inside the sub is warm enough, to "cook" the glue used to provide protection against vibrational failure. And the glue happens to conduct, once it's been cooked and breaks down chemically. The conductive glue then shorts out the power used to run the amp and makes the amp unreliable. All because cooling design was neglected. Paul The temperature discrepancies occur on the left side of the amp, and may be easily felt from both hands placed on the heatsink fins. Facing from the front the left side is always hotter, somewhat to the rear side. There are four transistors directly mounted to the side panel-heatsink assembly. Might correspond to the higher "left channel" bias current.* And, yep, I lose the left channel, the orange "clip" light faults to an on condition, shuts down. It works. I even pulled the top case panel, but it still overheats at a left hinksink near uncomfortably hot to touch. Eventually in a matter of time, and this part of the year isn't anywhere near summertime hot yet. One side note: I put a vacuum tube buffer preamp between a mixer and input channels about a month ago: - J61 classic tube design, optimization line. Size: 95x100x32mm/3.7x4x1.3 inch Power: DC12V 1A Frequency Response: 20HZ (-0.2DB) ~ 20KHZ (-0.2DB) SNR: 100DB Input Sensitivity: 300 ~ 2000MV Output: 3000MV THD: 1000MV 0.1% Should be immaterial. As I said the amp has been slightly, to now definitely hotter from day one, from first unpacking the unit. Yeppers...should'a but didn't contact tech;- highly, very, reviewed. And then, sigh, who'd have expected. And only two years out of warranty. So much for art and ART (Applied Research and Technology) as defined in Rochester, New York. Now I know. btw- side-by-sdie & its replacement https://www.amazon.com/ART-SLA2-200W.../dp/B0009GWNOG Ah, yes,...this is It...the good life, pictures, the beauty, everything imaginable and hard-core... * "These biasing current was found to be 47mA in the left channel and 32mA in the right channel. The input side to the darlington consists of a complimentary pair made up of 2SC3421/2SA1358 devices (10W, Vceo=120V, 1A, ft=120 MHz)." http://gnu.295.ca/peak/audio/sla-1.html 1.3 SLA-1 Innards The SLA-1 is based upon two large printed circuit boards to the left and right of the centrally mounted toroidal transformer, a front panel PCB and a small board behind the transformer used for the IEC connector/fan regulator/ground lift switch. The power supply and most of the weight is due to a centrally mounted toroidal power supply with a center tapped 76V output (i.e. 38-0-38) and a secondary 13V RMS output consisting of two green wires. This is used to power fan section that gets a 1/2 way rectified DC 7808 8V regulated DC. I can detect a faint hum coming from the transformer. The full wave rectifier bridge (unmarked) is heatsinked to the left channel...updating this to soft recovery types may be more difficult unless one uses higher rated parts and no heat sinking. The main power supply uses 4700 uF 63V (Metacon) units for the positive and negative supply (mounted on left channel output board). These provide +/-50V rails. For 100W output into 8 ohms, the outputs need to generate a 40V peak. The input, volume section and pre-driver section are powered off +/-15V derived from zener diodes off the +/-50V main DC supply. The remaining 20 electrolytics (for each channel)are made by Tocon (whom I have not heard of) consist of about 4 x 220uF units, 1 x 100uF unit and a ton of 10uF 50V units. There are some green film units (about four of them) are used in various parts of the amplifier with values of 0.1uF and 0.001uF. The 1/4 watt resistors are 5% units. Larger 1 watt units are found for the 10 ohm stabilization network, 2 x 1 kohm unit, 2 x 470 ohm units, a 100 ohm, and 2 x 47 ohm units, unit. 1.3.1 Input Stage The quad op-amp Matsu****a AN6554 uses two of the units for left and right channel in differential to single ended gain configuration providing 3.52 dB gain (1.5x) for single ended inputs. The 14 pin package uses pins 8,9 and 10 for the left channel and pins 5,6 and 7 for the right channel. A 22K and 33k feedback resistor set the gain for this stage. A second pair of these is needed for handling the balanced inputs. Two input DC blocking caps and and output cap complete the circuit. The phono plugs TRS (tip ring sleeve) provide IN+, IN- and ground connections for differential inputs. Single ended Phono plugs will short IN- to the sleeve/ground and provide single input via the TIP portion of the plug. Both the XLR and Phone plug inputs provide for balanced inputs. It should be possible to flip the phase of the amplifier by feeding a input to the "RING/IN-" input and grounding the "TIP/IN+" to ground/sleeve. 1.3.2 Volume Control Section The outputs from the input stage go to a 9 pin header and connect to the front panel PCB. A third op-amp (of the four in the AN6554) provides a Unity Gain buffer from the volume control before going to amplifier section. The fourth op-amp is provide for phase inversion in bridge mode. 1.3.3 Amplifer Section The output stage is a complimentary Darlington configuration with about 10% local feedback. The output side of the Darlington are two pairs of 60 Mhz output transistors: 2SC2837 (NPN) and 2SA1186(PNP) complimentary bipolar transistors are used for each channel and arranged in common emitter configuration . These biasing current was found to be 47mA in the left channel and 32mA in the right channel. The input side to the darlington consists of a complimentary pair made up of 2SC3421/2SA1358 devices (10W, Vceo=120V, 1A, ft=120 MHz). This is driven by 1/2 of the 4558 opamp. Feedback components set the gain to about 25 dB (18.3x). Signals coming in are both high and low pass filtered. The output stage contains a classic zobel network to stabilize the amplifier. There is no DC servo control so large caps are needed to provide for high pass filter that limits the amplification of subsonic signals. A generic 812H relay provides a delayed connection to the speakers and instantaneous disconnect to them during power on and power off , respectively. This means that there is not turn on transient or turn off transient. The same relay disconnects the output in the event of overheating and shorted outputs.A second sourced UPC1237HA chip is used to sense when to open the relay breaker and protect the chip. One is used per channel. Two small signal transistors (Q19 and Q20) are 50V/150mA 2SC945 NPN devices (ft=300Mhz) and 2SA1015 PNP devices(ft=80 Mhz) make up a current sense circuit to feed into pin 1 of the protection IC. These general purpose transistors are also used near the bottom of the left channel board and in the front panel board. My guess is that they provide for compare functions for the green signal LED, red clip LED and the overload LED. |
#5
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Class ABDH & I
On Fri, 16 Mar 2018 03:34:23 -0400, Flasherly
wrote: Todd Packer Harman Luxury Audio Group Field Application Engineer Installed the Crown Class D. Huge difference in engineering between Crown and ART. The ART is engineered along its case as a massive heatsink with a 2-speed, dinky-butted piece-of-junk fan for a decorative engineering afterthought. Dunno about promercial amps, QVS or Crown's approach similarly in a Class A/B application models, but my new D Class series shows a wider regard for Crown's approach to heat: Crown doesn't mess around, and the outside casing is all about airflow and accountable heat-dissipation. Not that it necessarily need be, I'd imagine, being a Class D is inherently cool. It's nonetheless still equipped with one big, honkin' fan for cooling contingencies. That's cool for business terminology, but what's cooler is the fan never need be run within modest operational characteristics. There's even firmware logic for a LCD to display sensors to the output stage's operating heat. Also nifty, although I'd trade the whole LCD shebang for a 50-year warranty in a minute. Provisionally and traditionally from promerical grade. Whereas these new Crown designs are also making headway into the A/V prosummer circuit. Especially for those whom can't directly state to an high-end Class A amp ownership, exactly why they really can, or cannot, tell a difference between their Class D and a $5000 Class A amplifier. Or it may be just simpler with split encoded signals provided by Hollywood entertainment, for those who like that sort of thing, to use such as the amp's firmware, also provided, for bandpassing from a low-shelf notch to appropriate dedicated speakers. Some might then call it OK for mere low-frequency Class D operation. (Certainly less bother with transients or Mid/Side, a likes to stereo signal encoding, marginally absent in a lower frequency range.) I can't go there. I know how the ART and I know now how the Crown sounds. And that's good enough for me. After a few hours of music listening, my soul may have been soothed. I somehow feel lighter now, so much less dissatisfied with the ART, being it's out of sight, stacked up next to the garbage can. |
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