Salas hotrodded blue DCB1 build - Page 115 - diyAudio
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Old 26th June 2011, 03:54 PM   #1141
AndrewT is offline AndrewT  Scotland
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The anodised finish is very thin and the oxide is a very good thermal conductor.
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regards Andrew T.
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Old 26th June 2011, 10:56 PM   #1142
Salas is offline Salas  Greece
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Quote:
Originally Posted by Builder Brad View Post

I may revisit this and add a fan and improve the thermal interface between the MOSFETs and the chassis by removing the anodised finish where they are attached. I bet the lightly brushed anodised finish is less thermally conductive than dead flat aluminium.

Brad
It would be a self judged challenge to battle heat, if you actually felt enough subjective gains with 1R VS 2.7R. The question is, did you?
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Old 27th June 2011, 07:23 AM   #1143
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Cheers Andrew & Salas,

I did not really spend any time listening to the 1ohm setting.

It was hot here in the UK yesterday and the amp case got quite hot to the touch. Think I need to get an IR temperature probe

I also have a wood fired pizza over and have planned to get a IR temperature probe, so it will get well used.

Brad
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Old 28th June 2011, 07:44 AM   #1144
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Brad,

May I ask what is your heatsinking method?

I ask because I would like a reference for my set-up, planning 600mA (3.3ohm) stage.

I’m building a balanced version DCB1, 2 boards in the one chassis, each board sits on it’s own 111mm x 222mm 10mm thick anodised al blocks, the mosfets and diodes will be bolted to these, the blocks with then be bolted to a 453mm x 353mm 3mm thick anodised al panel, I’ll be putting thermal grease in between and ensuring I’ll have good thermal contact. Aiming for 600mA.

Hot Australian summers days can top 40

Last edited by johnwmclean; 28th June 2011 at 07:46 AM.
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Old 28th June 2011, 06:04 PM   #1145
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Hi John,

I have bolted the MOSFETS directly to my casework - sounds similar to yours - 12mm thick alu on the side and 3mm on the base. I am using silicone TO220 insulating washers which seem to do a pretty good job transferring the heat from the ICs.

I am thinking about dropping back to 5 Ohm current setting resistors as the casework has got pretty hot over the last few days - its been hot here in SE England for a change!

As its easy to change those resistors you can experiment and see how your build works during the hot Australian summer. The ambient temps really do dictate the efficiency of your heatsinking. i thought I was good to go for 1ohm resistors when I first fired up my B1 when the temps were in the 60s, but have had a rethink over the last few days.

I may add some switches that add additional parallel resistances to the 5 ohm resistor, so that I can run the super hot-rod version when I am critically listening, and then switch back for normal day-time entertainment, no point burning rubber when you don't need to, or cannot afford the fuel bills LOL.

Brad
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Old 28th June 2011, 07:53 PM   #1146
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Brad,

That’s a great help thank you, to clarify, have you bolted the IC’s to the 3mm base or 12mm sides?

BTW your the first person I’ve come across that’s had a stab at 1ohm circa, hat’s off to you sir!

John
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Old 28th June 2011, 08:20 PM   #1147
Marra is offline Marra  United Kingdom
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Man they must run hellish hot! I went as far as 5R but did'nt like the sound it seemed to harden up somehow so went back to 10R. Maybe I did;nt give it long enough. I'll follow your posts with interest; as you say its easy enough to change the resistors.
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Old 28th June 2011, 08:21 PM   #1148
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John,

the negative MOSFETS are bolted to the 3mm thick base plate and the + ones are ob the 12mm side, they seem to heat up to similar temps, although my hand is not a very accurate or scientific way of measuring this.

I thought that everyone tried 1ohm - mine was 0.909 ohms as I had a 10 and 1ohm in parallel. it did get quite hot, but at least I know it could work.

I like my idea of switched "boost"

Brad
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Old 28th June 2011, 09:39 PM   #1149
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Marra,

once I hit 2.7 ohms and below everything was hot. from what I remember how the case felt at 0.909 ohms, I think that I am now feeling similar temps with 2.7ohms, although the ambient temps are some 10 degrees C hotter - I know that at 5ohms there was a very slight warm feeling around the MOSFET positions.

As Salas mentioned a couple of pages back, your subjective experience with the higher current versions may not even make this worth it, as you may have found.
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Old 29th June 2011, 08:22 AM   #1150
Marra is offline Marra  United Kingdom
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Brad;

Yes I found that at 5R the temperature differance was minimal both on the resistors and mosfets which at the time were fastened to a piece of 10mm alluminium 300mmx135mm; no case. Its now cased up with the fets bolted to the base and the temp is just warm.

Marra
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