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Old 23rd April 2003, 08:34 PM   #1
Kermit is offline Kermit  Norway
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Default Aleph3 to cold?

Hi, finally finished my aleph3 clone today! Worked pretty darn good on first power up. (some hum from the transformer that seems to find itís way to the speakers, or it might be my star grounding being far from perfect. But hey itís my first amp!) Pictures to come, just have to get them developed. The thing is however that I think itís running a bit too cold! (imagine that!). I donít have a suitable thermometer to check the temp on the sinks, but from touching the sinks (0,3c/w /channel) I guess itís a mere 45 deg. celsius after a few hours of playing music at a moderate level. I can hold my hands there without feeling any pain.
Now, I was a bit concerned about the moderately sized sinks so I did use thermal grease between all the chassis parts, but I donít think it ads up to that much. I can also touch the case of the transistors for a few seconds or so and itís slightly discomforting (hot, but not burning hot.) I have to admit Iím a bit concerned about the lifespan of the transistors, donít want them to go blowing up on me and causing my speakers to blow up or something.
So, you guys think Iím in the clear or what?
A bit about the setup if it helps:
600VA 2x18V transformer, 25,4 volts unloaded, lags down to 24,3 volts under load and seems to stabilize there.
22x4700uf caps
8xIRFP240 isolated with self adhesive silicone pads and thermal grease
Everything else is pretty much right out of the service manual.
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Old 23rd April 2003, 08:55 PM   #2
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wind two 2mh air core inductors out of 150 ft of #14 enamled wire and put them incorporate them with the filter caps, and I bet your hum will go away.
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Old 23rd April 2003, 09:24 PM   #3
Taco is offline Taco  Netherlands
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Good job, I have a question do you need to use thermal grease with silicon pads?
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Old 23rd April 2003, 09:32 PM   #4
Netlist is offline Netlist  Belgium
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Quote:
Posted by Nelson Pass on 01-22-2003 06:18 AM:

Well let's see if your temperature calibration nomenclature
matches mine:

Blimey hot is 10 seconds hands on = 45 deg C.
Crikey hot is 5 seconds = 50 deg C.
Bloody hot is 2 seconds = 55 deg C.
X*?@! is 60 deg C.

All of these are within an acceptable range, although
X*?@! is resrved for the more mature constructor.
This comes from the AlephX thread, but is a nice thumb rule for every amp.
What do I see...you live in Norway! Lucky you, in Africa they have to cool their heatsinks actively, or double their size.

Measure the current through the amp.
0.22 10Watt resistors or something, in place of the fuse.
Calculate the power consumption.
Say 150W * 0.3įC/W = 45įC + room temp.

One thing to consider: If memory serves, thermal grease and silpads shouldn't be applied together, but maybe Peter Daniel can tell you more about that. I could be wrong here.

/Hugo
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Old 24th April 2003, 02:52 PM   #5
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Default Re: Aleph3 to cold?

Quote:
[i]I guess itís a mere 45 deg. celsius after a few hours of playing music at a moderate level.[/B]
What is the ambient temperature, or more particularly, what is the rise of the heatsink above ambient?
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Old 24th April 2003, 04:59 PM   #6
Kermit is offline Kermit  Norway
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Tanks for replaying,
Lets see, circlotron: ambient was no more then 20, so rise is something like 25 deg. above ambient. According to my estimates it should be at least 35 above ambient if I take the chassis dissipation into account.
Netlist: I have searched and I believe you are right about the thermal grease, at least in the way that itís not necessary. But dos it make things worse?
Iíll try to measure the current drawn this weekend and post back. I read thru Rod Elliotís article about heatsinks and I think Iíll try to add a aluminium bar or something to help clamp the irfís better to the heatsink.
Audionut: Thanks for the suggestion , I will certainly consider it. The space is very limited so Iím unsure if I can manage to squeeze it in there. Any idea as to how many volts it will drop?
By the way how much hum would you consider acceptable from a brand new 600va toroid? The hum is audible from a couple meters away, no speakers or input connected, just the hum coming from the transformer.
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Old 24th April 2003, 05:20 PM   #7
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If you aren't using a pi (CLC) filter on the supply, it is highly recommended.

Also, if your amp is running cool, then you have a fine opportunity to crank the bias up some more. I would, as it improves the sound significantly.
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Old 24th April 2003, 05:35 PM   #8
Netlist is offline Netlist  Belgium
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Long ago, I read an article about the advantage or disadvantage of mica vs silpad.
I remember mica and grease is still the best way to transfer the heat, if well applied.
Wonder what Passlabs uses these days.
Nelson must be able to tell us what's best.
Of course grease can be messy.
The same article said that there could be degradation of the silpads over time when grease was used with them.
But it's too long ago and I can't find the article anymore, so I could be wrong here.
Not to scare you of course.

/Hugo
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Old 24th April 2003, 07:52 PM   #9
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With TO-3's we use Mica and Thermalloy grease. With
Plastics we use Silpads.
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Old 24th April 2003, 09:29 PM   #10
jleaman is offline jleaman  Belgium
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Quote:
Originally posted by audionut
wind two 2mh air core inductors out of 150 ft of #14 enamled wire and put them incorporate them with the filter caps, and I bet your hum will go away.

Could i also do this to my aleph 2 that is in progress. ? Would it bennifit me in any way. Im looking for all the improvements that i can do to my amps so that i have the best that i can build : O )
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