John Curl's Blowtorch preamplifier part II - Page 3768 - diyAudio
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Old 4th April 2013, 12:43 AM   #37671
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> (=creating more disorder elsewhere)

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Old 4th April 2013, 12:52 AM   #37672
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Originally Posted by gk7 View Post
Just want to note that Toshiba still makes low noise FETs (only n-channel and smd though): 2SK880, 2SK208, 2SK209. And they are cheap...
Thanks for that, Georg. I only use N channel and ain't skeered of surface mount.

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Old 4th April 2013, 09:38 AM   #37673
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About the advantages of SMPS two remarks.

First look at where the market turns for sensitive applications. I understand AP switched to switch mode because no linear PS could deliver the same clean power. Linn uses it. The reason is because it provides benefits.

As seen from the technology itself, what I mean with the added layer of intelligence is that a first stage of recitification, followed by a oscillator circuit that creates AC of precisely defined properties, followed by an optimized transformer operating at high frequency, removes much of the low end hash you never seem to get completely rid of with linear power supplies. Filtering out the high frequency components from the rectified output is obviously much easier than filtering out 50 or 60 Hz and low frequency harmonics from a linear supply.

And I am not even talking about the benefit of having a regulated PS.

Last edited by vacuphile; 4th April 2013 at 09:40 AM.
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Old 4th April 2013, 10:10 AM   #37674
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Smaller magnetics, can even use PCB based planar transformer, which is easier to screen, and easier to screen against capacitive coupling in the transformer.
Smaller footprint for a given power rating, smaller loop area. Better thermal management.
Smaller capacitors (no electrolytics in some cases).
Noise way above the audio spectrum.

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metal can transistors (dissipation)
Surface mount devices are far superior for heat dissipation...
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Old 4th April 2013, 11:47 AM   #37675
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Originally Posted by marce View Post
Surface mount devices are far superior for heat dissipation...
Dual output stage on an Al2O3 board, face to face with the 'heatsink' panel.
Attached Images
File Type: jpg SMDissipation.jpg (104.4 KB, 165 views)
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Old 4th April 2013, 12:55 PM   #37676
qusp is offline qusp  Australia
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Jacco, marce is likely talking about devices that expose the die/substrate to a pad on the underside, rather than the pretty high impedance of the epoxy body, when trying to pull the heat through the top, like you have there.

using these devices means 2 thermal interfaces are cut out of the thermal impedance calculation.

even something as simple as the LME49726 opamp in a MSOP8 powerpad package, allows a small opamp that will put out 300mA at 5v output. I havent even picked the highest, just one i'm looking at today.

yep, the audio cliches for numbers of things nolonger hold true, but that wont stop many people hanging on to them until they have no options left.

Last edited by qusp; 4th April 2013 at 01:00 PM.
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Old 4th April 2013, 01:26 PM   #37677
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Originally Posted by simon7000 View Post
These are fancy breakers that monitor the current and combine into an energy management system. So either they set the trip point switch incorrectly or didn't mount them in the panel correctly.

Balancing the phases "fixed" the problem and no one wants to send me a failed breaker, so I suspect installation was the actual issue.
Was the panel fed delta or wye? Excessive neutral pull could cause overvoltages. Given the waveform shown with the dead just in front of zero crossing, I'd first look at the neutral currents.

Reminds me of Zsa Zsa trying to add single digit numbers so she doesn't blow the generator out.

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Originally Posted by qusp View Post
Jacco, marce is likely talking about devices that expose the die/substrate to a pad on the underside, rather than the pretty high impedance of the epoxy body, when trying to pull the heat through the top, like you have there.
Smt packages will generally have one or more of the leadframe coppers being used to remove heat from the die. That is done by bonding the die backside directly on the copper, heat transports through metal to the external solder pads of the board. Any lead which is not chip backside will have a very tiny wire bonded chip to pad, they are not direct heat transport mechanisms, there will be a little due to side conduction of the encapsulation epoxy.

It's the exact same with the big 247 and TO-3 cases. The chip is bonded to the metal, and heat exits that way.

I do like that Al2O3 board, it's a great heat spreader.

jn

Last edited by jneutron; 4th April 2013 at 01:40 PM.
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Old 4th April 2013, 02:07 PM   #37678
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that depends what you are talking about, i'm working with some passivated GaN Die parts that have a pretty much direct connection, just a solder bump in the way. nothing wrong with the pic above, as you mention its pretty neat indeed, but heatsinking from the top of the package is always quite a bit worse than a metal on metal connection. same with the bottom as long as its the epoxy rather than soldered, still rather neat, but i'm pretty sure its not what marce had in mind.

edit:actually reading my wording in the above post you are correct, my mistake. I didnt mean to say die for the msop, rather the leadframe.

Last edited by qusp; 4th April 2013 at 02:15 PM.
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Old 4th April 2013, 02:12 PM   #37679
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Originally Posted by qusp View Post
like you have there.
The SMT's have their large collector lead soldered to pads at the underside.
Contact surface of an SOT-223 larger lead is 0.01 in2 , each pad is part of a 0.1 in2 area of the output lane.

Each half of the board image manages 20A peak in 1 Ohm, aka ~2.2A per output device.
Hence the 9 Allen bolts to clamp the board to the front panel.
(each of the SOT-223 can do 15A peak, from a 1/30 in2 size body, btw)
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Last edited by jacco vermeulen; 4th April 2013 at 02:18 PM.
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Old 4th April 2013, 02:18 PM   #37680
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aah sorry Jacco, I misunderstood the photo, I took the exposed board as being the same as the other 2 ie. lots of tiny sot232, but without the heatsink to illustrate what was underneath.

looking at it again now thats stupid, the connections would foul on the heatsink :redface:

Last edited by qusp; 4th April 2013 at 02:21 PM.
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