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Old 3rd April 2013, 08:49 PM   #501
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Quote:
Originally Posted by danny_66 View Post
Thanks, I think I'll attach the regulators to the alu frontplate, it's 10mm thick and 45x18cm large.
If that's not enough I can always add some cooling fins on the frontplate (inside the case).
Not enough...

Last edited by permaneder; 3rd April 2013 at 08:51 PM.
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Old 3rd April 2013, 09:47 PM   #502
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Quote:
Not enough...
Yeah, I was afraid so... if I look at the heatsinks of my current F5.
How much C/W does the heatsink needs to be for one regulator (20w) ?
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Old 3rd April 2013, 09:54 PM   #503
NicMac is offline NicMac  Italy
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I was thinking to build it in a case LIKE THIS (that I already have) and I think it will be just fine
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Old 4th April 2013, 12:24 AM   #504
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Danny,
You might want to rethink the amount of heat going into that front plate - each Reg is dropping a minimum of 10 volts (4.6V for the Fet, 5+ for Reg margin) so, as Georg says, multiply this by the current and you get a minimum of 12W ea Reg/Rail if amp is biased at 1.2A, and if amp is biased about 1.5A, like mine, then 2 x 15W extra heat per channel (= 30W, or 60W total into that front panel - 80W if using 2A bias, as per above post).

To keep the Fets temp down to maybe a similar 25*C temp rise, will need heatsink about 08*C/W (25*C/30W) for each channel (or 0.4*c/W for the both channels) - in other words, you'll need a dedicated heatsink similar to each amplifiers side heatsinks for the extra Regulators and not just the flat front plate.

However, it seems your heatsinks are huge with 400mm long, 180 high and 10mm fins, if I got that right, so the thermal efficiency might just be good enough to handle this extra 30 watts per channel - Need to check this (the *C/W efficiency of your heatsink)

For example - if your amp is biased to 1.5A, and rails are now +/- 25 volts, dissipation is about 75 watts and if the thermal efficiency of that big heatsink is anywhere near 0.25 *C/W (= temp rise about 18*C), then the extra 30 watts will still only push the heatsiink temp up about another 8*C (= about a 26*C temp rise above room temp) and this is pretty much ideal operating temp, altho appears much higher than the usual operating temp of about 45*C (finger touch test).

Anyway, perhaps this might be useful about your front panel ...
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Old 4th April 2013, 07:15 AM   #505
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Hi James,
Thanks for the explanation, it's clear now.

I'm thinking of using 4 pairs per channel instead of 3 pairs.
My speakers have a dip to 3ohm in the bass, so 4 pairs should be better.
Biased at 0.4A that gives me 3.2A *22v=70w per channel.

The frontpanel will not do it, it is just 10mm thick without fins.
My case is from hifi2000, the 4U 400*435 model.
Each heatsink has a thermal resistance of 0.23C/W, more than enough for the output mosfets of each channel.

I think I'll add this heatsink from velleman. Cut it in pieces of 15cm and use 2 pieces back to back for each regulator.
The whole heatsink is 0.19C/W, so that should do it.
Regards,
Danny
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Old 4th April 2013, 07:54 AM   #506
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Quote:
Originally Posted by danny_66 View Post
Hi James,
Thanks for the explanation, it's clear now.

I'm thinking of using 4 pairs per channel instead of 3 pairs.
My speakers have a dip to 3ohm in the bass, so 4 pairs should be better.
Biased at 0.4A that gives me 3.2A *22v=70w per channel.

The frontpanel will not do it, it is just 10mm thick without fins.
My case is from hifi2000, the 4U 400*435 model.
Each heatsink has a thermal resistance of 0.23C/W, more than enough for the output mosfets of each channel.

I think I'll add this heatsink from velleman. Cut it in pieces of 15cm and use 2 pieces back to back for each regulator.
The whole heatsink is 0.19C/W, so that should do it.
Regards,
Danny

Your configuration will dissipate ~ 100W per channel. So there is no mandatory need for additional heat sinks for the regulators.
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Old 4th April 2013, 08:00 AM   #507
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Big buggers - at 0.23*C/W, you could just hanh the regulator Fets off the same sink - at 1.6A, and assume 20V rails, thus about 30 from C-R-C gives a power consumption of about 30 x 2 x 1.6 which is near enough to 100 watts that'll create a temp rise of 23*C -

I'd go with that, before going nuts with extra fins and stuff - maybe add some extra cooling vents on bottom and top lids - I usually leave a 10 - 15mm gap each side on the bottom, clear of the heatsinks, for extra cooling breeze and open mesh on the top - the diodes will need a separate heatsink as these need to be kept as cool as possible, unlike the power fets.

On a really hot day, just a small cooling fan will keep the temperature down to reasonable - I try to keep my heatsinks up in the mid 50's as the amp sounds quite a lot smoother & better detail when "quite warm" - not everyone comfortable with amps running this hot but with plenty of internal air flow and sensible thermal layout, not a problem.
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Old 4th April 2013, 09:07 AM   #508
tinitus is offline tinitus  Europe
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regarding where/how best to mount/place the regs, I would also consider wires/connections, etc

without having thougt too much about it, my guess is the best place would be at the bottom,somewhere in the middle
but as said, only 'early thoughts, and by far not conclusive in any way

supply schematic/layout ?
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Old 4th April 2013, 04:57 PM   #509
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Thx Georg, James !
Nice that I don't need any additional heatsinks for the regulators
So I have more place inside for capacitors, CLC, softstart, ... cases tend to be always a little too small on the inside

The HiFi2000 case already has ventilation holes in the top and the bottom, so that's OK.
Each diode will get its own small heatsink, like I did in my "regular" F5 build.

I got the case, enough heatsinks, most parts,... the build can start !

Regards,
Danny
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Old 4th April 2013, 07:42 PM   #510
Anchan is offline Anchan  United States
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Default Output protection

I am gathering the parts to build this amp. I plan on using 2 switchers to get the +/- 20V. I'm not interested in getting into the switch vs linear debate. I'll let you know how it sounds

But I am concerned about what happens if one of the rails gives way. It is sure to destroy the speakers.

So I was thinking about some very crude speaker protection.
Basically a 48V relay sits between the output of the amp and the speaker. The coil needs to see near 40V to turn on. So if a rail blows, the relay coil de-energizes and disconnects signal to speaker.
Thoughts?
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