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.
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
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.