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Old 18th November 2012, 07:14 AM   #7611
dvv is offline dvv  Serbia
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Originally Posted by a.wayne View Post
Just make sure it can drive this ......
Wayne, good buddy, that's my new reference standard for evil loads.

That's no loudspeaker, it might just as well be a welding machine. In my case, your minimum of say 1.3 Ohms is 6.5 Ohms, I quite simply do not need what you obviously need.

It will not be able to drive that loudspeaker on a continuous steady state basis; it could be done, of course, add two more pairs and watch it go, but I'd also have to beef up just abut everything, and especially heat sinking.

However, if we come back to Earth, and recognize that we simply cannot run a power amp at full rated steady state power all of the time, as we must provide at least some headroom for transients, assuming we leave just 6 dB of headroom, then it should be able to drive them, bless your cotton socks.

As for those transients, remember that the protection will stay dormant for about 40 mS, so even larger peaks can be accommodated. Meaning you wouldn't have to settle for whisper level sound only.

Where DID you find those speakers, anyway?
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Old 18th November 2012, 07:29 AM   #7612
dvv is offline dvv  Serbia
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All this talk reminds me of 1975 or 1976. A good friend had a pair of loudspeakers which were also bad news for many amps, especially in those days.

Then he bought a Studer/reVox A740 power amp. It was rated at 100/175W into 8/4 Ohms, and used three pairs of custom Motorola 250W devices per side, mounted on a VERY hefty heat sink. 2 x 33,000 uF caps per side. Big transformer, discrete high power diodes as rectifiers, ona separate heat sink running all the way from left to right. Said to be a low TIM level design. See it here: Prospekt Revox A 740

And suddenly, all his problems with both micro and macro dynamics were gone. Nada, just music. Thankfully, his speakers (I forgot the manufacturer's name, it wasn't a big name, and that was like 37 years ago) were fairly effcient, if memory serves something like 93 or 94 dB/2.83V/1m.

This was the case that gave me on object lesson of what drive capability is all about.

The case was sealed by a Harman/Kardon receiver, I think it was a model 930 (a alter evolution model of this one: http://wegavision.pytalhost.com/harman76/hk1.jpg ), nominally just 45 W/8 Ohms per side, but in a true dual mono topology, two big (for the power) transformers, two rectifiers, 2 x 2 capacitors, etc. 45 WPC is hardly ane exciting power level, nor was it exciting even then, but that receiver somehow managed to sound way bigger than it really was. And it refused to be caught out by any transient thrown at it. A fine machine I wouldn't mind owning even today.
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Last edited by dvv; 18th November 2012 at 07:32 AM.
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Old 18th November 2012, 10:13 AM   #7613
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I once thought of placing the output transistors in water . It might work if the contamination was kept low ( water filter element from a filter jug ? ) . The specific heat capacity of water from memory is 4.2 KJ / KgK . Deal with the heat as we do in motorcars . Oil might be more practical although not as good a transporter of heat . Water is a poor conductor of heat . Not a problem if it is kept on the move . I suspect even convection circulation might work . Anyone ever built a heat pipe ? We accept water in motorcars , why not in amplifiers ? It only has to be as well safeguarded as a central heating system . DF 96 says he likes facts . Here are some to chew over .
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Old 18th November 2012, 01:09 PM   #7614
dvv is offline dvv  Serbia
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I once thought of placing the output transistors in water . It might work if the contamination was kept low ( water filter element from a filter jug ? ) . The specific heat capacity of water from memory is 4.2 KJ / KgK . Deal with the heat as we do in motorcars . Oil might be more practical although not as good a transporter of heat . Water is a poor conductor of heat . Not a problem if it is kept on the move . I suspect even convection circulation might work . Anyone ever built a heat pipe ? We accept water in motorcars , why not in amplifiers ? It only has to be as well safeguarded as a central heating system . DF 96 says he likes facts . Here are some to chew over .
The way you put it, Nige, it might appear you need some waterproof transistors.

Not "in water", but "use water cooling". We sort of had something like that with Sony's now dead in the water heat pipe, which used gasses much more efficient than water. It was all the rage in the early eighties, but now, nobody is using it as far as I know.

It was lighter than classic aluminium, true, but was in fact not really smaller, rather more compact in length rather than depth.

Also, it was hardly practical. If there was a leak, you were done for, you had next to nothing cooling and of course, had to dish out the dosh for a new one, only to discover that pricewise, it may as well have been made of a platinum and titanium alloy, bound together by uranium.

Not that it had to be so, of course, just the good, old Ford logic, accepted without question in Japan and revered more than the Emperor - sell the basic product as cheaply as you can, and then skin them alive in service and price parts.

I'll stick to my caveman aluminium fin heat sinks, thank you velly much.
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Last edited by dvv; 18th November 2012 at 01:11 PM.
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Old 18th November 2012, 01:24 PM   #7615
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Water cooled heat sinks have been used in industry to cool both tubes and transistors for multiple decades. It is a hassle, BECAUSE you have to used d-ionized water that you buy at significant cost and you still need a radiator the size of an auto, to dissipate the waste heat. We used to use one at Humphrey Instruments to cool a huge control amp for a strobe that we designed.
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Old 18th November 2012, 01:46 PM   #7616
a.wayne is offline a.wayne  United States
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Love that revox , power meters and all, i still dont get it, why do designers keep leaving them out .....

POWER METERS = REAL AMPLIFIER !!!!!!


DVV , yeah...madness load coupled with 80db/M/2.83v, it would be easy if the sound was evil , but far from it , yeah they work me , most amplfiers loathe them ....


John !!! Power meters would look fantastic on the JC-1 ..
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Old 18th November 2012, 02:21 PM   #7617
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Water cooled heat sinks have been used in industry to cool both tubes and transistors for multiple decades.
Water cooled film gates were common in very high power movie projectors, such as those used at drive-ins. It was the only way to keep the gate and the film cool. Normal water was used, IIRC.

I haven't seen a water cooled digital project yet, but with the huge increases in brightness, they may not be far away.
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Old 18th November 2012, 02:26 PM   #7618
SY is offline SY  United States
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Lots of hotrodders water cool their CPU, so I suppose you could call that a digital project. I'd use a more nonreactive thermal transfer fluid if I were going to do this.
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Old 18th November 2012, 04:17 PM   #7619
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In did think of TO3 with heads into the water . The PNP and NPN kept apart by a plastic bit , the pipe could be all plastic although daft not to use copper . Getting the water in close seems ideal . The problem with non reactive fluid is heat capacity , water is a very remarkable liquid . I suspect TO3 in water would outperform totally enclosed in oil . As luck would have it where water fails transistors also . I could well beleive transistors could be run hotter if direct liquid cooled , albeit slightly .
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Old 18th November 2012, 04:24 PM   #7620
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the manufacturer's already give ridiculous power ratings on the datasheet for Tc=25C - presumably they do it with water cooled copper cold plate

Cold plates, heat pipe-assisted, embedded, vacuum-brazed and liquid cooled, Thermacore Inc.

somewhere I've seen a pic of a R_TH_jc test done in fluorinert

Last edited by jcx; 18th November 2012 at 04:45 PM.
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