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Discussion Starter #1
I'm working on a 4 channel class a amplifier with hopefully 30 to 60 watts per channel. unlike the other things that I have made I won't be designing everything. I'm making all the chassis components but I have ordered amplifier boards and power supply boards. I should hopefully learn a lot from this.
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Not enough heat sink for 4 channels of that
Agreed.

OP,

Have you performed any thermal transfer calculations? You'll need a fin stack 4x more dense than that plus taller. You can get by with a smaller fin stack if you use forced air. Have you looked into other aluminum extrusion options? Perhaps a box section?
 
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Discussion Starter #7
I'm either going to use some sort of liquid cooling and or a lot of copper it's not on my drawing yet.
 

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60WPC int 4ohm? Assuming this is a push-pull design, that's 5.5A current through each output device. At +/-30-odd volts supply (which you would need for 60w into 8 ohm) that is going to be... 330watts heat dissipation per channel. 4ch, 1.33kw. That is like an electric heater. Or nearly 2bhp, for a car specific reference.

I like class A for home audio. But I don't think it's realistic in a car. There are a thousand acoustic challenges in a car that deserve attention, before looking at dissipating 1.3kw of heat from class A amps...

Thought I'd add - this 1ft square heatsink from RS:
dissipates at 0.29˚C/W. So that is still approx 100˚C above ambient with 1 per channel. Not going to work. Even 2 per channel would be pushing the limits of the device temperature, I'd guess. And that's 8 sq.ft of heatsink. So liquid cooling with exterior radiator is the only possible viable option!
 

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I'm either going to use some sort of liquid cooling and or a lot of copper it's not on my drawing yet.
How about commercially available PC liquid coolers? That would be cool. They also run on 12 and 5 volt.
 

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Generic water cooler blocks are available. But cooling the water is still an issue, probably requiring an external radiator. Maybe you could reappropriate an aftermarket oil cooler behind the front bumper?
 

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Discussion Starter #12
How about commercially available PC liquid coolers? That would be cool. They also run on 12 and 5 volt.
Actually that's what I've been looking at. but I'm having delivery issues with some of the things that I've ordered that's aggravating me and stressing me out a little bit.
 

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60WPC int 4ohm? Assuming this is a push-pull design, that's 5.5A current through each output device. At +/-30-odd volts supply (which you would need for 60w into 8 ohm) that is going to be... 330watts heat dissipation per channel. 4ch, 1.33kw. That is like an electric heater. Or nearly 2bhp, for a car specific reference.

I like class A for home audio. But I don't think it's realistic in a car. There are a thousand acoustic challenges in a car that deserve attention, before looking at dissipating 1.3kw of heat from class A amps...

Thought I'd add - this 1ft square heatsink from RS:
dissipates at 0.29˚C/W. So that is still approx 100˚C above ambient with 1 per channel. Not going to work. Even 2 per channel would be pushing the limits of the device temperature, I'd guess. And that's 8 sq.ft of heatsink. So liquid cooling with exterior radiator is the only possible viable option!
Ignoring ^the math*, what are your thought's on the wattage?
(I could see 10-20W for tweeter and MR respectively.)
 

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Man class A in a car in my opinion is a total waste of time and money , the background noise of the vehicle when moving will defeat any benefits you would get from running class A.

Class A is for home use when you have a completely quiet environment to enjoy the benefits of class A even then it's small.

With the quality of class D now , I would just get a quality 4 channel class D amp , I was a bit hesitant using class D for the tweets (Alpine PDX-F6) but after doing the install over a year ago I have been extremely impressed and can't tell the difference to a quality class A/B from previous years.
 

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Discussion Starter #16
Man class A in a car in my opinion is a total waste of time and money , the background noise of the vehicle when moving will defeat any benefits you would get from running class A.

Class A is for home use when you have a completely quiet environment to enjoy the benefits of class A even then it's small.

With the quality of class D now , I would just get a quality 4 channel class D amp , I was a bit hesitant using class D for the tweets (Alpine PDX-F6) but after doing the install over a year ago I have been extremely impressed and can't tell the difference to a quality class A/B from previous years.
Well it might be a waste of time but I'll find out as for the money it's not going to be that bad compared to the class a car amps currently available. I'm doing this more for the fun of it. if it fails that will be ok if it doesn't fail that will be great.
 

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I'm hope for maybe 30 watts per channel at 4 ohms
What does hope have to do with it?
(One pretty much knows what it will do before building it.)

The power supply determines the rail voltage and the current available determines the impedence of speakers it can push.

Why not go for 8 ohm speakers? And run higher rail voltage?
And what SPL requires 30W RMS?
 

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What does hope have to do with it?
(One pretty much knows what it will do before building it.)

The power supply determines the rail voltage and the current available determines the impedence of speakers it can push.

Why not go for 8 ohm speakers? And run higher rail voltage?
And what SPL requires 30W RMS?
The OP said he ordered prepopulated amplifier and power supply boards. I'm not certain he has the ability to make adjustments.

Even if he could raise the voltage rails on the power supply, he should be mindful of the voltage rating of capacitor bank and the amplifier board.
 

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The OP said he ordered prepopulated amplifier and power supply boards. I'm not certain he has the ability to make adjustments.
...
Yeah - so if they are a kit board then they must have a rating?
(I assume that A30 might be 30W.)


...
Even if he could raise the voltage rails on the power supply, he should be mindful of the voltage rating of capacitor bank and the amplifier board.
  • If he was going to change things, then a reason to get to 60W (from 30W) would be good to know the reasoning behind it.
  • If the OP only needs 10W, then it may be be easier to lower the rail voltage than it would be to raise it?
 

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I'd probably go for ~15W - that's ~300/350W to dissipate which is much more manageable. If this is driving Mids/Tweeters from ~300Hz, that is more than enough. Assuming a house curve rising +10dB down from there, that means that it would be balanced with a woofer/sub taking 150W. That is a pretty decent listening level. Also, it won't clip or run out of power at that point. Up to the power limited by the supply rails, beyond the class A power limited by the bias current, it will transition to class AB (and you won't notice any difference :) ) - for 30v rails, this would be about 100W.

The class A bias current is surely adjustable. Assuming a push-pull design and not just relying on an output cap for DC blocking, there must be some variable resistor in a potential divider setting the MOSFET gate voltage. Without this, the + rail and - rail MOSFETs will not be in balance - it is a fine adjustment. With this, you can set the bias current to be what you want and thus the Class A power level.
 
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