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Old 22nd March 2004, 12:48 PM   #211
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Default It Works, 100W AlephX Monolith

Finally got One of Two channels working last night. Will finish the second this week.

Absolute DC Offset +/- 20mV (floats)
+39mV offset + to - on terminals (haven't played with diff pair yet)

Standard 10mA diff pair bias but will increase at a later date.

Running 22.8Volt rails total bias of 11.6 amps.

After 3 hours of running the amp is hot. Much hotter than expected especially the rectifiers. FET Mount plate temp is around 60 - 65C. I used the Avid Thermal Tick recomended earlier in this thread. Once the stuff melts it works great. As of right now I can see that the outer plates hav'nt melted the grease yet. ( Can't use the oven since its too big and I don't even want to think about the WAF)

Sound is very good even with only one channel in operation. Definatly worth the effort.

Regards
Scott
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Old 22nd March 2004, 02:22 PM   #212
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Those heat sinks look a bit scant. I can't tell from the picture how the heat is transferred from the inside fins to the outside ones; it takes a lot of meat to get the heat from point A to point B. Is there plenty of gap underneath so that air can enter from the bottom?
That said, it's clearly a massive hunk o' amp. Hope it serves you well.
And yes, the DC offset will tend to drift a bit. Won't hurt anything.

Grey
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Old 22nd March 2004, 02:48 PM   #213
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Default Another Photo

Please forgive me for previously not giving credit where credit is do. Thanks to Nelson, Grey, HiFiZen, and everyone else for the dedication and willingness to share their ideas and knowledge for the benefit of the DIY community. Without you this stuff would be impossible.

The heat sinks were calculated to remove 500W of power per side at 30C temp rise. I de-rated them 50% for loss at metal to metal interface. This seems to be about right as the sinks are being asked to dissipate about 260Watts as it is operating now and the mounting plate is rising about 30-35C.

Grey as you said, the limiting factor for this design is the heat transfer from plate to plate. To improve this, I am seriously considering increasing the width of the spacers from .5x.5 inch to .75x.5 inch. This should significantly improve the effectivness.

The plate are cut at an angle on the bottom to promote better air flow.
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Old 22nd March 2004, 09:08 PM   #214
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Quote:
Originally posted by BDP
Do you have a good ground to the PCB? If you measure from PCB ground to cathode of D1a you should have positive rail voltage. What is the voltage from PCB ground to junction of D1a and R17.

>> I have no idea... i'm using a variable dc psu for testing psu, then i'll build one for this ax... so the varaible psu doesnt have ground output... how shoud i do that? do i need to?
>> i get 0 volts from the cathode of d1a... and 0 at the anode

Is J1a in. Resolder your connections.

>> j1a is in, continuity is checked, soldered is redone

BDP
thanks
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Old 24th March 2004, 01:24 AM   #215
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Scott,
If all else fails, you can still try forced air cooling, though that would mess up your esthetics.

Grey
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Old 24th March 2004, 02:41 AM   #216
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You could also add more plates of stacked alumnium to each side to increase the radiating area. That wouldn't screw things up a bit. If you force air them consider some slick ductwork that would be added to the back of each heatsink assy to make it look like part of the amp.

Mark
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Old 25th March 2004, 12:37 AM   #217
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Thanks for the insight. I took some measurements today. With the room temperature of 20C the mounting plate runs 58C, outer plate runs 47C. This was after 4 hours of operation. I certanly will have to do something with it for the summer. I think Grey was right that there isn't enough mass between the plates to conduct the heat properly, or the aluminum that I used has a lower heat conductivity than my calculations.

Right now my biggest concern is the rectifier. It is running around 68C after 4 hours. In the previous photos you can see the rectifier assembly sitting on top of the transformer housing in the back center.

Temperature aside, this amp sounds sweet even on only one channel.

I should finish the second amp by this weekend

Thanks Again

Scott
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Old 25th March 2004, 12:45 AM   #218
Magura is offline Magura  Denmark
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Throw in a copper bar for the rectifiers to work as a heat spreader, a copper bar would also do the trick to get the heat to the heatsinks. You can make heat travel far and fast with the right copper bar.

Im working on a SOZ and the box for that is including more than 10 kilograms (20 pounds) of copper per monoblock.


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Old 25th March 2004, 01:05 AM   #219
jwb is offline jwb  United States
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Is 58C a problem in your design? I missed how much power each device is dissipating. I think the thermal designs on this site are restrictively conservative. I've designed my new amp for 68C on the sink and 100C+ on the die.
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Old 25th March 2004, 01:38 AM   #220
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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.

I have a couple of extra sets of matched 244's as spares but it is a pain in the you know what to open the box up a replace them. The hardest part would be stuffing my woofer back in its frame.

Correct me if I am wrong but in a failure mode this circuit would drive one side to rail voltage. I would think it would take a while before the fuse blew given the size of the power supply.

I am currently using a 6amp sloblo which is marginal for long term operation. (I've allready blown one) In reality once I feel nice and secure (dangerous place to be) I'll raise it to 8 amps. Just the output devices will pull 5 amps on the line not including the losses in the power supply.

Scott
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