Mezmerize DCB1 Building Thread - Page 21 - diyAudio
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Old 2nd February 2011, 04:43 PM   #201
ramallo is offline ramallo  Europe
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Quote:
Originally Posted by JBdV View Post
I guess 8 W of heat just "dissapears" on such a big metal bottom plate.
Its a sign that the (9)240's are making great thermal contact.

Measuring locally with a "temp gun" could reveal whats really happening

@Ram, why didn't you put the toroid together with the other stuff in one enclosure?

Jan
Hi Jan,

The toroid is too big (50VA) and if I did the mechanizing the IEC connector, the fuse and the power switch, the toroid was too close to the output RCA and the mosfets (just touch one), and I was very afraid of the bad influence of the mosfet's heat and noise induction on the rca.

Just I put the transformer in a small box and I connect it with a 3 conductor wire and Lemo connectors (I have a bunch of old Lemo).
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Old 8th February 2011, 06:10 PM   #202
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My DCB1 is still running happily. I put 10R and 8R resistors in to give me ~200ma on each channel, it warms the case quite a bit but I wouldn't describe it as "hot." You can hold your hand on the case or the mosfets directly indefinitely.

Now I'm tempted to put the 3.3R resistors in there to see what I can get away with. The mosfets are bolted directly to the chassis, but I'm using an old ethernet switch as a case. It's made of pretty thin metal, and I think it's steel rather than aluminum. It's basically the same thickness and material as a PC case. Is a proper heatsink a necessity for 600ma, or can I wing it? If it gets 3 times as hot as it does with 200ma, it'll get pretty darn hot but I don't think I'll be in egg-frying territory.
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Old 8th February 2011, 06:19 PM   #203
Salas is online now Salas  Greece
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Try resistors and go up to a comfortable heat level in the specific box step by step, provided you hear some appreciable subjective gain, I would say.
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Old 8th February 2011, 06:32 PM   #204
AndrewT is offline AndrewT  Scotland
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It's not just the Tj of the FETs you need to consider.

If you heat up the floor of the chassis then you are cooking all the components in the frying pan you have created.
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Old 8th February 2011, 06:34 PM   #205
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Okay, I'll give it a try. If it runs too hot, I'll just use it as a preamp for my Phase Linear 400 and let them race to see which one turns into a slag heap first
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Old 8th February 2011, 06:58 PM   #206
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what is the VA of tranny?
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Old 8th February 2011, 07:19 PM   #207
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I believe 50VA, but I'll have to check. It's a toroid from Antek

Antek - AS-0512
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Old 9th February 2011, 09:14 PM   #208
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Popped the 3R3 resistors in, powered it up, and let it sit for about 15 minutes. It's running much hotter now, but I can still hold my hand on the case directly next to the mosfets for 5 seconds. I can handle 8 seconds tops. I'll let it sit for an hour or so and see if it still passes the 5 seconds test.
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Old 10th February 2011, 09:40 AM   #209
AndrewT is offline AndrewT  Scotland
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Try turning the mains input voltage up to max tolerance (Variac)
and test temperature of your capacitors.
Then short your output and check the temperature of the CCS FET.
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Old 10th February 2011, 09:28 PM   #210
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I don't have a variac or any way of measuring the temperature of the mosfets, so I decided to just plug it in to my system and see what happens. It sounds much better than going straight from my PC to the amp, of course, and I think it sounds better than it did with less current. Wider sound stage, better detail, all that good stuff. More detail comes through at low volume, which is really nice.

However, after being on for 20 minutes or so, it's not passing the 5 second test anymore. I can do 3 or 4 seconds tops. I might have to throttle back a little or find a larger heat sink.
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