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Old 27th October 2014, 03:21 PM   #1
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Default Heatsink dilemma, reduce Vcc or Iq

due to a the heatsinks i bought being mislabeled.... Grrr.
i've got working PLH Monoblocks that run just a bit too warm.
.
they currently run ~40v @2A each channel.
the heatsinks are 2x 0.7 deg/W each monoblock

this gives 28degrees C above ambient, which might be ok if i was back in the UK, but i'm working in China where the ambient with AC is ~30degrees.

currently i've blue-tacked fans on top, but this has low WAF and is a little noisy,

options are reduce Vcc a couple of volts, or reduce Bias.
in the PSU i have CRCRCRC the R's are currently 0.1 or 0.05 i could easily up the first R to 1-2R to drop a few volts,
or would i be better to drop Bias by a similar amount?

advice appreciated
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Old 27th October 2014, 03:39 PM   #2
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Just about all electronics are rated for 85c or better, 58c shouldn't be a problem.

If your amp is properly set up, think about new heatsinks instead of electrical changes.
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Old 27th October 2014, 03:46 PM   #3
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Pluss 1. 58c should be okei. Reducing voltage by up the R in the PSU is not a good idea. That will kill dynamics.
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Old 27th October 2014, 03:54 PM   #4
Maousse is offline Maousse  France
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As long as your heatsinks are below 60C, there is no risk of skin burn.
This is why 60C is the maximum allowable temperature that something that can be touched may reach.
For the components themselves, my fellows did already answered.

BTW, power supply current is constant in A class amps, so raising R is not a problem, except for the R itself (heat). But again, no need to do that.
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Old 27th October 2014, 04:16 PM   #5
Mooly is offline Mooly  United Kingdom
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Or use both options together. A couple of volts less and say setting Iq to 1.8 amps would bring the dissipation down by 12 watts or so.
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Old 27th October 2014, 05:06 PM   #6
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i'm thinking about 10deg less heat, so around 12w
the amps reach 60+ deg. depending on ambient.
i fitted 60 or maybe 70 degree thermal switches inside, and these tripped without the fans. i need to check if they were 60 or 70.
i'd rather not run the amps so hot, it's not great for component life.
as mist speakers are nearer 4 ohm than 8 in reality, i guess losing a couple of volts would be best.
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Old 27th October 2014, 10:19 PM   #7
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Depends on if you need 40V rails for your speaker load.

A slightly naughty option is to wind on extra windings onto the secondaries in the opposite direction to drop V, but that adds heat, which is already a problem for you....
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Old 27th October 2014, 10:59 PM   #8
Zen Mod is offline Zen Mod  Serbia
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or fans

either on heatsinks , or in form of Babysitter
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Old 28th October 2014, 01:51 PM   #9
Maousse is offline Maousse  France
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gbullimore : pictures of your amps may help give advice
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Old 28th October 2014, 03:59 PM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Maousse View Post
BTW, power supply current is constant in A class amps, so raising R is not a problem, except for the R itself (heat). But again, no need to do that.
Shame you added a btw!
You are wrong.
Most ClassA amplifiers are NOT constant current !
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