Hi again,
I have built a Gainclone based on this schematic: http://diyaudioprojects.com/Chip/LM3886_CA/LM3886_CA.htm
The heatsinks get quite hot, and I was thinking about putting a fan on the inside that sucks air out, and drill holes around the chips, so that most of the air is sucked in from that area.
But how can I design the fan circuit? I thought about having 9 to 12 V on the fan, and I tried to put a 220k in series with a 470k, parallell to the +32V. But I guess the fan acts like an inductor, because when I put the fan across the 220k, the voltage across the resistor fell to 1V and the fan did not work.
Does anyone have any ideas to how I can get it to work?
I have built a Gainclone based on this schematic: http://diyaudioprojects.com/Chip/LM3886_CA/LM3886_CA.htm
The heatsinks get quite hot, and I was thinking about putting a fan on the inside that sucks air out, and drill holes around the chips, so that most of the air is sucked in from that area.
But how can I design the fan circuit? I thought about having 9 to 12 V on the fan, and I tried to put a 220k in series with a 470k, parallell to the +32V. But I guess the fan acts like an inductor, because when I put the fan across the 220k, the voltage across the resistor fell to 1V and the fan did not work.
Does anyone have any ideas to how I can get it to work?
Hi,
do not run the fan off an audio PSU.
Supply it from a separate PSU, either from a separate winding off the transformer or from a separate transformer.
Select the Vac to suit the fan motor.
Arrange for some kind of temperature control. Off when cold. Medium speed when warm and fast +warning light when hot.
Be careful to ensure it starts when on medium speed.
It might need a kick to overcome friction and then slow to medium speed.
I would also fit a high temp mains switch to the sink in case of failure of the fan/control circuit.
do not run the fan off an audio PSU.
Supply it from a separate PSU, either from a separate winding off the transformer or from a separate transformer.
Select the Vac to suit the fan motor.
Arrange for some kind of temperature control. Off when cold. Medium speed when warm and fast +warning light when hot.
Be careful to ensure it starts when on medium speed.
It might need a kick to overcome friction and then slow to medium speed.
I would also fit a high temp mains switch to the sink in case of failure of the fan/control circuit.
Thanks! I think I'll skip the fan then. I have added a couple of heatsinks on the chassis instead. That helped a bit.
But is there no easy way to run it from the audio PSU?
BTW, the amp sounds great! I'm very happy with the result.
But is there no easy way to run it from the audio PSU?
BTW, the amp sounds great! I'm very happy with the result.
I once had a transformer made, with an extra secondary for a fan... sadly I could never get rid of the noise the fan made elctricaly, tried filters etc... then gave up and got proper heatsinks....
A good heatsink for a chipamp should cost no more than $5 to $10 (if you are feeling fancy) per channel.
A good heatsink for a chipamp should cost no more than $5 to $10 (if you are feeling fancy) per channel.
I have run a fan off the main amp PSU with just a resistor to slow it down and there was no audio noise. I have also done it with lots of audio noise. For no noise it requires maybe some shielding and good PSU PCB design. I had to shield the input wires and the fan wires. You can also get a 12V fixed regulator to run off the main PSU lines. This helps with isolation of the electrical noise on the PSU lines. The best option is to not use a fan at all.
-SL
-SL
Thanks for the answers! I dropped the fan, and hope that it won't be too hot. It hasn't failed yet at least.
Here's the final result:
http://folk.ntnu.no/espenta/bilder/hifi/DSC_0022.jpg
Here's the final result:
http://folk.ntnu.no/espenta/bilder/hifi/DSC_0022.jpg
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