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Old 25th March 2004, 03:09 AM   #221
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At the rate you guys are going, I think I'd better go long on some metals companies. Let's see, Phelps Dodge closed at $77.77, Freeport-McMoRan at...

Grey
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Old 25th March 2004, 03:14 AM   #222
Magura is offline Magura  Denmark
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Loads of copper for even distribution and loads of heatsinksjust makes things so much easier, especially in the summertime

The last amp i made had all the heat distribution problems i could ever ask for....this time ive done the footwork and actually calculated the heat distribution for the box.

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Old 25th March 2004, 03:30 AM   #223
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Quote:
Originally posted by SGregory
So far 58C hasn't been a problem. In the summer 58C will become 65C which may or may not be a problem. Output per device is 32Watts per the WIKI spreadsheet.

I am using the IRFP244 chips and don't have the spec sheet in front of me. I will measure the chip temps to see if I am still safely within operatin specs with derating.
Sounds pretty conservative to me. You are probably getting something in the range of 1.2-1.5 Rθjs, and the part is rated for 150°C operation. Yours are operating at less than 120°C, which sounds high but isn't. With a decent thermal interface (e.g. Bergquist Sil-Pad K10), it will be closer to 105°C.

If you want more headroom, use the IRFP044, rated to 175°C
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Old 25th March 2004, 04:26 AM   #224
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Grey,

I have an advantage, I work in the metal making industry. I have seen a few other "large" chassis here so maybe an increase in production is in order.


jwb,
Thanks for the input. I feel a little better about operating the chips at this temperature. It will be interesting to measure them to see in reality how hot they are actually running. Since it is hard to measure the actual interface temperature, how accurate is it to measure the case tempeature?

Switching Gears (Un related to improved power handling)
I think it would be interesting to listen to the difference between the 044 and the 244 chips. In the Aleph 5 circuit I found the 044 to be more on the dark side compared to the 244. Would the X circuit improve this?

Scott
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Old 25th March 2004, 04:37 AM   #225
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Magura,

I like copper to but it is more difficult for me to obtain cheaply. It is also harder to cut with a table saw and router. A nice endmill would solve that problem, but, I like being married.

Where I errored in my calculations is with either the junction resistance between the spacer and plates or a lower thermal conductivity of the spacers themselves. The latter is easy to fix with either wider spacers for more surface contact area or as you said copper. Junction resistance on the other hand becomes a little more tedious as it will require better thermal compounds and/or much improved surface flatness.

If jwb is right, and I have no reason to doubt it, then I might not have a problem at all. I like this possibility.

Scott
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Old 25th March 2004, 04:49 AM   #226
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Scott,
Metal working, eh? Must be nice. I'm only set up to do wood, although I can handle about anything I'll ever need to do there. Metal working isn't a common need around this town; there's no such thing as industry these days.
You can get into debates about heat vs. transconductance, but I prefer something that runs a little cooler--just 'cause I'm getting silly in my old age. For the Alephs, I went water cooled. It's cumbersome, but works like a charm. The rig I've got can dissipate enough spare heat to run an old-fashioned steam locomotive. The Aleph-Xs are air cooled.
All things being equal, I imagine that the '044 will pretty much tend to sound darker than the '244. I haven't done a direct comparison between the devices and the topologies as my Alephs use the IRF644 (a TO-220 casing) and the Aleph-Xs are filled with '044s. Shooting from the hip, I'd say that the Aleph-X might be a bit brighter than the regular Aleph assuming the same devices, and the 'pure' X a bit brighter still. Nelson is likely the only person who's had enough of these things sitting around that he could do side-by-side comparisons with different output devices.

Grey
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Old 25th March 2004, 05:23 AM   #227
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Funny you should mention...

The 044's are doped (and who knows what else) differently than
say a 240 or 244, but we do see that they have lower Vds rating,
higher tranconductance and higher capacitance. The latter two
are the interestings specs. The higher transconductance means
that open loop gain will be higher, particularly at lower
frequencies, while the nonlinearity of the Cdg capacitance will
be likely higher.

This corresponds to the experience of sound that you mention.
The 044's tip the spectral balance toward the bottom end, where
they have more punch and lower distortion, but at the same time
they have a "darker" characteristic (darker being the opposite
of brighter, is not necessarily a negative). Conversely the higher
voltage versions (244 and such, tip the spectral balance
in the other direction and are brighter at the top end (all other
things being equal). If you are bi-amping or tri-amping (and so
on) the choices are easy.

The one way to get the best of both is to cascode an 044 with
a 244 (or even an 044). The distortion due to Cdg pretty much
disappears here, and the results are well worth the effort.

Of course one of the remaining Zen Variations will address this
issue (always saving the best for last... )
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Old 25th March 2004, 05:40 AM   #228
jwb is offline jwb  United States
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I don't really pretend to hear the difference between FETs, but to a practical fellow like myself, the thermals of the 044 are more advantageous than those of the 140, 240, 244, or even the 044N. One wonders why.
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Old 25th March 2004, 06:01 AM   #229
jwb is offline jwb  United States
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For example:

IRFP044,140: Rθjc: .83, max Tj: 175°C, max Pd @ Tc=70°C: 126W
IRFP240,244: Rθjc: .83, max Tj: 150°C, max Pd @ Tc=70°C: 96W
IRFP044N: Rθjc: 1.3, max Tj: 150°C, max Pd @ Tc=70°C: 85W

But if power dissipation is your prime design concern, there is always the unholy IRFP260N:

IRFP260N: Rθjc: .50, max Tj: 175°C, max Pd @ Tc=70°C: 210W

Yeehaw. And a nice 5000pF input capacitance, also
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Old 25th March 2004, 02:00 PM   #230
Coulomb is offline Coulomb  England
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What about the IRFP054(N) and IRFP064(N)? The 064 device is a 200 watt device with an RDS of .008! are these devices not popular for audio use because of price or availability?

Regards

Anthony
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