Hey guys and gals am I unreasonable in my expectations with documentation on commercial product?
Over the weekend I had a pair of Stereophile recommended power amplifiers on the bench. This particular amp is rated at 300 W output. (monoblock)
Sitting in my garage on a wire shelf (58 degrees F ambient) I could get over 300 watts short term, with no problem. Anything much over 60 watts long term (1/2 hour) would cause overheating and self protection.
Cyclotronguy
Over the weekend I had a pair of Stereophile recommended power amplifiers on the bench. This particular amp is rated at 300 W output. (monoblock)
Sitting in my garage on a wire shelf (58 degrees F ambient) I could get over 300 watts short term, with no problem. Anything much over 60 watts long term (1/2 hour) would cause overheating and self protection.
Cyclotronguy
Kind of a grey area...
Back in the mid-'60s you could find all-in-one record players that were advertised as "100 watts peak-instantaneous power". This rating was achieved by connecting the amplifier to a 1 ohm load, raising the line voltage to 140 VAC, and sending a single-cycle tone burst. They would increase the level of the test signal until the amp destroyed itself. In this way, they could take a 7 watt amp and rate it at 100 watts.
It was so out of control that the government (Federal Trade Commission) stepped in. The new rating system was very conservative. All channels had to be driven, and the load, the bandwidth, and the distortion levels all had to be specified. This makes sense, but they also added a "pre-heat" requirement of 33% of rated power for 1 hour, which caused all kinds of problems as this happens to be pretty much the point of maximum dissipation for a class AB output stage.
It sounds like the unit in question has somewhat undersized heatsinks as far as the FTC rating goes, so in that regard it is probably somewhat "under engineered". But I would be highly surprised if you had any problems in the real world when playing music.
So the question becomes rather fuzzy. Does it make sense for the federal government to demand an over-engineered heatsink that will significantly raise the price of a product without any direct benefit to the consumer? If you answer "yes" to this question, then should the federal government also mandate that no capacitor should ever be run at more than 75% of its rated voltage? Where do you draw the line?
I don't know....
Back in the mid-'60s you could find all-in-one record players that were advertised as "100 watts peak-instantaneous power". This rating was achieved by connecting the amplifier to a 1 ohm load, raising the line voltage to 140 VAC, and sending a single-cycle tone burst. They would increase the level of the test signal until the amp destroyed itself. In this way, they could take a 7 watt amp and rate it at 100 watts.
It was so out of control that the government (Federal Trade Commission) stepped in. The new rating system was very conservative. All channels had to be driven, and the load, the bandwidth, and the distortion levels all had to be specified. This makes sense, but they also added a "pre-heat" requirement of 33% of rated power for 1 hour, which caused all kinds of problems as this happens to be pretty much the point of maximum dissipation for a class AB output stage.
It sounds like the unit in question has somewhat undersized heatsinks as far as the FTC rating goes, so in that regard it is probably somewhat "under engineered". But I would be highly surprised if you had any problems in the real world when playing music.
So the question becomes rather fuzzy. Does it make sense for the federal government to demand an over-engineered heatsink that will significantly raise the price of a product without any direct benefit to the consumer? If you answer "yes" to this question, then should the federal government also mandate that no capacitor should ever be run at more than 75% of its rated voltage? Where do you draw the line?
I don't know....
Amplifiers need to be tested appropriately for their intended application, otherwise the world will be building VASTLY OVERBUILT products consuming excessive raw materials and wasting resources - which should a crime in this polluted/climate change world!
Also it pushes the cost out of the reach of many just for some inappropriate testing regime.
A power amplifier intended for general audio use would be appropriately tested with the already defined 20:1 toneburst signal.
A recent commercial design of mine used one 300W toroid for 150W/channel with 2dB dynamic headroom - so it clips like a 240W/ch amplifier with a stiff supply. It had 5inch square heatsinks with 1.25 inch fins and ran quite warm with high power operation but cool inside with open chassis ventilation and 105C caps.
It was small and efficient and reviewed as a giant killer. Also a fraction of the cost of it's competition.
Also it pushes the cost out of the reach of many just for some inappropriate testing regime.
A power amplifier intended for general audio use would be appropriately tested with the already defined 20:1 toneburst signal.
A recent commercial design of mine used one 300W toroid for 150W/channel with 2dB dynamic headroom - so it clips like a 240W/ch amplifier with a stiff supply. It had 5inch square heatsinks with 1.25 inch fins and ran quite warm with high power operation but cool inside with open chassis ventilation and 105C caps.
It was small and efficient and reviewed as a giant killer. Also a fraction of the cost of it's competition.
sadly Charles the Eidetic amp/preamp never made it to the US. I produced it in Australia in 1989-94 and exported some to Singapore while some were privately taken to the UK and Canada.
It was an OPA627/637 driven nested feedback MOSFET design. It had an impedance plug for 4/8 or 1/2 ohms by series or paralleling the 4 secondary windings for 68V or 34V.
It was an OPA627/637 driven nested feedback MOSFET design. It had an impedance plug for 4/8 or 1/2 ohms by series or paralleling the 4 secondary windings for 68V or 34V.
I agree that it can be considered wastefull to build and amp that can run at the maximum (either power or thermal) indefinately, but 60W is only 20% of the rated power and 58 deg F (14 deg C) is quite chilly. I don't think you are unreasonable to raise an eyebrow.
I too am curious regarding the make and model. Sounds like an example of Self's Law of High-end Audio Pricing : "MSRP and performance are inversely related". (Myo wmn paraphrasing.)
I too am curious regarding the make and model. Sounds like an example of Self's Law of High-end Audio Pricing : "MSRP and performance are inversely related". (Myo wmn paraphrasing.)
It was very simple really. The input stage was an OPA627/637 feeding a normal discrete amplifier with complementary bipolar diff pairs feeding a symettrical Vas stage then 3 output pairs of Toshiba MOSFETS with a local feedback loop bcah to the diff pair and a global loop back to the 627 inputs. No capacitors in the circuit and DC offset adjustment with a trimpot on the 627s dedicated pins. Power Supply had 16x 3300uF 80V caps for low Z.
The trick was in the compensation to ensure absolute stability. In addition it was tailored to be -3dB at 100KHz with a 160K input filter and matching feedback rolloff.
2uF and 10K square wave had only a small ripple and no overshoot. THD 0.002% at 20KHz 100W and 90dB channel separation from a common supply. Each channel was complete on a 3x5 inch heatsink mounted board with fitted gold RCA in.
The trick was in the compensation to ensure absolute stability. In addition it was tailored to be -3dB at 100KHz with a 160K input filter and matching feedback rolloff.
2uF and 10K square wave had only a small ripple and no overshoot. THD 0.002% at 20KHz 100W and 90dB channel separation from a common supply. Each channel was complete on a 3x5 inch heatsink mounted board with fitted gold RCA in.
Charles Hansen said:
I wouldn't be too averse to that 75% rule for filter caps (although that's a tad too specific for the FTC) after I saw my neighbour lose two P**k subwoofers in a row when they nuked their supplies. Post-rectifier voltage: 36 V. Caps: 35V. Oops. They actually lasted a surprisingly long time, considering there were only two tiny little high-ESR guys tasked to filter 100 watts of ripple.
As far as the heat sink issue goes, users put stereo gear in all kinds of poorly ventilated places. What might seem over-engineered on the bench could be just adequate when stuck in a glass-fronted cabinet.
Francois.
I prefered the Marantz method and spec for continuous power.
They might not have been the cleanest watts, but they were honest.
Amplifierguru , I recall your amp designs well, they were ahead of their time, your active crossover article in Aust HiFi was also a hit.
Didnt you work for Krell or ML at one point?
Have you thought about the rebirth of a design or a diy project?
Macka
They might not have been the cleanest watts, but they were honest.
Amplifierguru , I recall your amp designs well, they were ahead of their time, your active crossover article in Aust HiFi was also a hit.
Didnt you work for Krell or ML at one point?
Have you thought about the rebirth of a design or a diy project?
Macka
Thanks Macka for the compliment. Yes I worked for Madrigal as a consultant designer for 4 months when they stuffed up the immigration/green card and I pulled the plug.
Jacco, Eidetic means (of visual or auditory images) Exceptionally vivid allowing detailed recall of something previously perceived.
See attachment for picture.
Back to the topic. Sam9, 60W is really only 7dB below rated power and it's unlikely to be averaging that level on normal program, even band limited, without considerable clipping distortion - encouraging lowering the volume.
Jacco, Eidetic means (of visual or auditory images) Exceptionally vivid allowing detailed recall of something previously perceived.
See attachment for picture.
Back to the topic. Sam9, 60W is really only 7dB below rated power and it's unlikely to be averaging that level on normal program, even band limited, without considerable clipping distortion - encouraging lowering the volume.
Forgot the brochure attachment. It's 600K jpeg won't post.
I used to love sitting my little 7kG 150W/ch Eidetic on top of a Levinson or Krell and watch their jaws drop as we compared.
By the way I prototyped a 250W/ch 8ohm version - I have it right here. As soon as I get my FFT analyser/CRO up I'll post some pics.
I used to love sitting my little 7kG 150W/ch Eidetic on top of a Levinson or Krell and watch their jaws drop as we compared.
By the way I prototyped a 250W/ch 8ohm version - I have it right here. As soon as I get my FFT analyser/CRO up I'll post some pics.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.