Yes and yes. You pick an operating point that makes sense. The JC-1 gets hot after the 1/3 power test but doesn't blow up or catch fire. JA didn't measure the actual heatsink temp to say if it met or failed any regulations on that.
Point is that whilst you, and with undoubtedly valid reasons might chose a different thermal trade off, this case doesn't seem to be bad, just not how you would do it.
OT: Look at cars, they can't manage full output for very long at all before the cooling system is overwhelmed. Edge cases being things like the bugatti veyron which can dump thick end of 750KW out the rad for about 12 minutes till the fuel runs out.
Really OT: Ever seen a pre-class D vibration test jig for big things like cars. They often came with their own paddling pools for cooling water, which they could boil.
Agreed that thermal load is dependent on the Crest Factor of the signal among other things including the properties of the load.
A real world signal that is not a pure tone or something like it will have a minimum crest factor of about 8 dB, but that can go up to 20 dB.
Loudspeaker loads can have an average impedance of several times their minimum impedance or not.
YMMV!
If you use the 8 dB crest factor mentioned above, you will be pretty safe except for bench testing. Its more than doubling.
It was a worst case, based on a time long ago when the crest factor of music was not taken very seriously.
The heatsinks of the JC-1 size 16'' x 6'' x 2'', 38 ribs. Makes a thermal resistance of ~0.25C/W each.
Each heatsink has 9 output devices mounted straight to the heatsink, makes Rjs of an MT200 device some 0.9C/W
Means max dissipation level is some 700W at 25C ambient.
Largest contribution of the temperature rise is due to the heatsink, (9xRsa)/Rjs= 2.5
A heatsink at 60C is already too hot to the touch, junction temperature of the output device dies is still only at 75C in that condition.
you may recheck your calculations - 700W is too optimistic
Heat Sink Convection with Fins Calculator | Engineers Edge | www.engineersedge.com
Heat Sink Convection with Fins Calculator | Engineers Edge | www.engineersedge.com
The 1 hour test was in the original IHFM-A200 (1958)
http://www.americanradiohistory.com/Archive-Audio/50s/Audio-1959-Oct.pdf Page 26
"1.4. Operating Temperature
The amplifier shall be preconditioned by
operating at Va rated power output for at
least one hour in an ambient temperature
not less than 20° C. in still air, and in
normal operating position unless otherwise
specified (Reference 1.8.)."
The 30 minute test is a fairly recent (Year 1999) revision by the FTC:
https://www.ftc.gov/news-events/press-releases/2000/12/ftc-approves-amendments-amplifier-rule
"The Commission subsequently issued in the July 19, 1999 Federal Register a Notice of Proposed Rulemaking (NPR) that solicited public comment on specific proposed amendments to the Rule to:
reduce the power output requirement during the one-hour preconditioning period from one-third of rated output to one-eighth of rated output, and grant testers of self-powered subwoofers the discretion to choose the frequency of the test signal to be used during the preconditioning period;..."
About 40 years ago, I spoke with the guys who were on the panel that defined the 1/3 power test. They worked for a popular amp company that doesn't exist today. They told me that they DELIBERATELY made this absurd test level of 1/3 power, because they were making trouble for Phase Linear, a competitor, who also made large power amps but with inadequate heatsinking for the test. They did it on purpose, to rag a competitor. Finally, after some time, the FTC regulation apparently got changed to something more realistic FOR HOME USE.
My power amps are designed with a moderately high quiescent bias (as much as the heatsink can stand and stay at a comfortable temperature (usually for a cat) but when the amp used to extremes, a temperature sensor activates, and the amp disconnects from the load. Safety is important.
Now, fans are another question. I used my first airblown heatsink at Ampex Research in 1969 to make a 50V/50A motor drive amplifier and I used the most powerful and NOISIEST fan that would fit on the heatsink. It sounded like a vacuum cleaner in operation. Hardly practical for a home amp, or even a PA amp. That is the problem with fans. For PA use, a moderate fan, perhaps thermostatically controlled is almost mandatory, but it can be an inconvenience. For home use, hardly ever, but I have made a power amp that had 64W Class A, fully regulated supplies, and 250W Class AB using 3 airblown heatsinks with a 'whisper' (quiet boxer fan) on each. It pushed so much heat that we had to run a floor fan between listening sessions at CES because it overheated the room in LV with a winter snowstorm outside. Not very practical, but it did heat my customers garage for several years effectively. '-)
My power amps are designed with a moderately high quiescent bias (as much as the heatsink can stand and stay at a comfortable temperature (usually for a cat) but when the amp used to extremes, a temperature sensor activates, and the amp disconnects from the load. Safety is important.
Now, fans are another question. I used my first airblown heatsink at Ampex Research in 1969 to make a 50V/50A motor drive amplifier and I used the most powerful and NOISIEST fan that would fit on the heatsink. It sounded like a vacuum cleaner in operation. Hardly practical for a home amp, or even a PA amp. That is the problem with fans. For PA use, a moderate fan, perhaps thermostatically controlled is almost mandatory, but it can be an inconvenience. For home use, hardly ever, but I have made a power amp that had 64W Class A, fully regulated supplies, and 250W Class AB using 3 airblown heatsinks with a 'whisper' (quiet boxer fan) on each. It pushed so much heat that we had to run a floor fan between listening sessions at CES because it overheated the room in LV with a winter snowstorm outside. Not very practical, but it did heat my customers garage for several years effectively. '-)
The 1/3 power test is still the one to use if you want to be sure all is good with the temps.
But the teeth have been pulled out of that test with 1/8 and the new wording.... now a worthless test only suitable for boom-box and cheap receiver mfrg. Which i guess is a large market.
I would still use the 1/3 test conditions for really 'serious' amp design/building.
-RNM
But the teeth have been pulled out of that test with 1/8 and the new wording.... now a worthless test only suitable for boom-box and cheap receiver mfrg. Which i guess is a large market.
I would still use the 1/3 test conditions for really 'serious' amp design/building.
-RNM
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I don't follow. A 0.25C/W heat sink with 9 devices each with 0.9C/w junction to heat sink (very optimistic, IMHO, since it sums both the Rth junction-case and case-heat sink) makes a total of 0.35C/W. For an 150C of junction temperature, this comes to 150/0.35=428W and the heat sink temperature will be around 100C up from the ambient. I would not touch that...
Of these 428W, the idle power takes 90V (rail voltage) * 1.35A (idle bias current according to Mr. Curl)=121W, leaving room for some 300W for dissipation.
In the worst case of 1/3 max power test, the total dissipated power is 2*Vc^2/(PI^2*Rload). The net result for 600W (since we have two halfs) is Vc=54V, enough for some 200W into 8ohm
From this point, you may want to consider the 12dB crest factor and yes, likely the heat balance would probably be ok (also considering the thermal shut down that Mr. Curl mentioned).
However, the amp is specified at 400W/8ohm and 800W/4ohm. I don't think this could survive the 1/3 power test without thermal shutdown, in particular at 4 ohm load. Don't forget that at 150C junction temperature the output devices SOA is minuscule due to the power derating.
I'm not saying the JC-1 amp is a bad amp, only wondering how close to the edge are these high power audio designs or, if you prefer, how overinflated the output power specification may be.
P.S. Only the idle dissipation of 121W leads to a 40C heat sink temperature. A cat would indeed probably enjoy that.
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He he. Very often, our suppliers were coming in my recording studio to propose new power amps to test. My first step procedure was very simple: Eliminate any amp using fans ;-)
Even if they are very quiet, at the end of the day ... they add fatigue...
And fans are not long lasting, they are more and more noisy with time, untill they fail, and they ask frequent cleanings.
On the contrary, when i was running this big PA system, it was a requisite (Flight cases with 4 or 5 power amps + active filter inside ;-). The noise they produce is not an issue here (Noise of the public, close miking, very high SPL ) and safety, in this activity, is a requisite.
Not that the market would sensibly bear this suggestion (nor the aesthetic), but with all the effort placed into making computers quiet, there are some awfully nice, quiet fans out there that can move enough air to really help with heat dissipation. Especially if the fan runs off a PWM. E.g something like Noctua's 120mm/140mm fans run push/pull through a tunnel heatsink would only be audible if one put his/her ear next to the inlet/outlet.
1 - An MT200 power device has a larger mounting area than a TO-3. A TO-3 with mica insulator does an Rcs of 0.3C/W (Rjs of a Sanken power device with a Keratherm insulator is a lot lower than 0.9)
2 - The usable temperature range is not 150C, but 125. (150C minus 25C ambient)
3 - a monaural power amp has 2 heatsinks
=> http://www.monacoav.com/audio-video...ds/2014/06/5-2Parasound-JC1-JC2-Monaco-AV.jpg
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Pulling rabbits out of hat doesn't work.
- MJE15022 (TO3) has Rthj-c=0.7C/W. A mica TO3 has 0.3C/W plus the interfaces (grease, etc... to another 0.1C/W at least) so that adds up to 1.1C/W. I have not seen any hard data about a Keratherm TO3 and its interfaces (case-Keratherm, Keratherm-heatsink) but I somehow doubt that adds up to only 0.2C/W to meet your 0.9C/W estimate.
- If you have any precise information about the MT200 Rth's, please come up with. I doubt it's much better than a TO3, in particular because the area of the metallic plate on the back doesn't seem to be much larger (and is likely thinner) than a TO3. The TO3 is also able to radiate (being fully in metal), something I doubt the plastic MT200 efficiently can.
- 125 degrees of "excursion" actually only makes things worse from a thermal perspective.
- Already considered two heat sinks, if you bother to read again.
P.S. I don't do equipment photo porn.
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Richard, try Koh Samui - out of the way but you will need to fly there. Its good from about March through to end August/September IIRC - after that the rain comes. However, its a small island, so you'll need to fly there.
I love Bangkok - hired a driver for $100 who took my wife and me around all the temples a few years ago - fascinating.
Have you tried Angkor Wat? We stayed at a fabulous French Colonial hotel there for a few days while we explored the place. I have some pictures up on flickr (type 'Andrew C Russell Flickr' and you should find my travel pics)
JC,
Back when I was still rather young we used the first Phase Linear amps in PA applications in outdoor events. I still remember having to add forced air fans on those 700's to help keep them alive. Many of them went up in smoke, they were very early prototype amps so perhaps they improved on the temperature handling but they were marginal to failure prone under hard working conditions. They did sound pretty good though before they failed!
Back when I was still rather young we used the first Phase Linear amps in PA applications in outdoor events. I still remember having to add forced air fans on those 700's to help keep them alive. Many of them went up in smoke, they were very early prototype amps so perhaps they improved on the temperature handling but they were marginal to failure prone under hard working conditions. They did sound pretty good though before they failed!
Ever been to the Samui art party? Ten Stars Samui Art Party
I've seen the work of a Thai artist that paints only with coffee, quite interesting.
Kindhornman, of course the Phase Linear amps required fans for PA use! We all agree with this. For the record, I hung out for a couple of months in London in 1972 with the PA company, Kelsey and Morris, who did the sound for Pink Floyd, at the time. They also used Phase Linear 700's and did extensive rework on them before putting them in service. The Phase Linear 700 had lots of voltage swing, lots of xover distortion, and very little sustained power available.
Waly, it has been almost 15 years since I designed the JC-1, and I would hope to not have to go back to my original calculations and parts choices to justify my design, but IT DOES WORK!
For the record, you are correct that it was never designed for sustained loads of 2 ohms or less. A different type of design would be more appropriate. The 2 ohm loading figure of 1200W, was never derived or tried by me, and I would recommend adding a couple of whisper fans to the amp for some nut who uses a 2 ohm load load and wants to reproduce hard rock all day.
Waly, your assessments are barely adequate, nonetheless.
Waly, it has been almost 15 years since I designed the JC-1, and I would hope to not have to go back to my original calculations and parts choices to justify my design, but IT DOES WORK!
For the record, you are correct that it was never designed for sustained loads of 2 ohms or less. A different type of design would be more appropriate. The 2 ohm loading figure of 1200W, was never derived or tried by me, and I would recommend adding a couple of whisper fans to the amp for some nut who uses a 2 ohm load load and wants to reproduce hard rock all day.
Waly, your assessments are barely adequate, nonetheless.
We used to sell the 400's at a store where I worked.
I always thought the U metal sinks were a joke.
And they did have a high failure rate. It was always
amazing to me that such dubious amplifiers got
Carver off to such a flying career .........
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