Modding an amp: cicuitry question

[nealric]

I have a kenwood A/V reciever that has a thermal protect feature that turns the amp off when it gets too hot.

The problem is, Im having a party or somthng, when its constantly loud- it will only last 30min or so before turning itself off.

Solution: OVERCLOCK IT

I want to put some quiet case fans on the heatsink and on either side to create some airflow inside the amp. I was going to find a small power supply and itegrate it into the amp casing to power the fans.

The only thing: to make it truly classy I want it to have a switch that responds to a thermal diode- so the fans only come on when they are needed. IT would be annoying to have fans going when im listeining to quiet music.

Any ideas where I could get such a switch?

Also under consideration- cold cathodes

 

[clocker2]

Perhaps you are overthinking this project.
Most 80mm fans with 7 blades or less are dead silent when running on 5v. Especially when the intake isn't restricted (stamped holes or grillwork...you would want dust screening). If you wait till the part gets too hot then the fan won't be able to keep up with the thermal load, better to nip the problem in the bud and run the fans constantly.

I would think.

 

[nealric]

Well, they were going to be restricted (I was going to make a grill for them)- In my experience there is usually some noise.

The circuit would actually be turning on the psu- so that would avoid having to turn it on every time i turned the amp on.

If it was a variable circuit- I could play with the tolerace so it could keep up.

 

[DaWiper]

I agree with 'clocker2'. Don't make things harder than they have to be. You can even try to get hold of the blueprints of your kenwood and try to locate a suitable voltage output. This can be risky. MAKE SURE you don't DISTURBE/CHANGE any of the internal voltages in your amp. The fan should of course be directed towards the heat sink in the amp...

 

[clocker2]

Okay then.
Maybe you could tie the switch directly into your volume control knob. It would kick in at a specified volume level ( hence load). This could probably be done mechanically, without the need for any sort of circuitry...

 

[nealric]

Hmm- what you are suggesting sounds more difficult.

I dont want to touch the actual amp circuitry- thats why I am putting in a seperate power supply for the fans.

I found a few sites that offer switches- but only ones that break the circuit- not ones that connect one.

Im sure such a thing exists- Its the same thing that power supplys with switching fans use.

 

[clocker2]

I was thinking along the lines of a bomb timer ( like you see on TV...I have never built a bomb ) where the hour hand completes a circuit.
If the volume knob, say at level 4, completed the ground circuit for the fans maybe?

 

[nealric]

Hmm- what you are suggesting sounds more difficult.

I dont want to touch the actual amp circuitry- thats why I am putting in a seperate power supply for the fans.

I found a few sites that offer switches- but only ones that break the circuit- not ones that connect one.

Im sure such a thing exists- Its the same thing that power supplys with switching fans use.

 

[Cyrix_2k]

I know of a switch you could use. It's actually on lawn mowers as a safety cut-out switch. The one on our tractor completes a circut when on. BTW, i agree with clocker2.

also, why don't you just mount a larger heatsink on the hot parts of amp and use some AS3 w/superglue in the corners?

 

[nealric]

The heatsink is HUGE

like 2in by 8 in.

So I cant really just mod that.

 

[clocker2]

Something doesn't compute here.

Most modern electronic equipment should be able to run at it's rated maximum for hours, not just 30 minutes.
In it's present location does it get good access to fresh air and is there airflow around it's case?
If it's crammed into a restrictive area with lots of other heat producing equipment that could be the problem right there.

 

[nealric]

Nope its pretty open.

Ive read up on it and apparently these amps tend to have that problem. They just can run at more than 50-70% volume without overheating.

I could move the amp to a window- but thats only a temporary solution as long as winter is here.

 

[clocker2]

Does that Kenwood have an audio out port?

You might be better off just running the audio to an amp that CAN handle the load without cutting out.
If the problem is a widely known design flaw I'm wondering if any "band-aid" fixes that you could apply would really do much good.

 

[nealric]

WEll, it works fine if there is a house fan blowing on it- housefans just arent a good day to day solution.

I dont want a seperate amp- a better amp than what is built in would cost more than the the reciever itself.

 

[skahtul]

I want to put some quiet case fans on the heatsink and on either side to create some airflow inside the amp.

Just install a switch in the back. You don't need "quiet" fans if they are only going to be on when the AMP is hot. There is no way you could hear them over the volume of the system. Just turn them on when you need them.

Another idea, just use thermally controlled fans like those from Thermaltake. You can dig out the thermal couple and place it in an area where they would not get direct heat from the mosfets. I know if the fan was to close, they would be on all the time because of the heat even under zero load can get pretty hot. But if you placed them a little distance away it may work.

 

[Cyrix_2k]

I like /\ his /\ idea. You just need some basic soldering skils.

 

[pby5cat]

this power supply should work well. it has 12 and 5 volts, and should be able to power 3 fans on each voltage. also this would work is u just want 12v. as for power for both PS, both need eather 110VAC or 240VAC, and usually, the wires comming from the recievers wall plug connect to the reciever PS by exposed polls. Or if u want to get more complicated, u could trace where the riecievers power button goes, most likely a relay in the PS, and connect there.

 

[ZachM]

If you are just wanting to use normal 80mm case fans, those can't be heard even with quiet music. You could wire up a little knob that looks nice on the front hooked up to a potentiometer to control your fans. That way you can turn the fans up when you turn the volume up since the knobs are right next to each other. That wouldn't be too inconvinient. It would be best if you wired up the power supply so that it turns on with the receiver though. That shouldn't be too difficult.

 

[johnny5c]

You could skip the power supply and just use 110 volt fans. I have 2 of these mounted behind my amp, blowing out of the amp rack.

http://www.partsexpress.com/pe/show...St3=-57075305&DS_ID=3&Product_ID=117425&DID=7

 

[cack01]

You could skip the power supply and just use 110 volt fans. I have 2 of these mounted behind my amp, blowing out of the amp rack.

This is what my roomate did. He used the 110VAC remote out on the back of his reciever so the fan would turn on when the reciever turn on. All he had to do was plug the fan into the back.

The only problem, is the fan is easily 5x louder than a tornado when its just resting on top of the amp's grills. He finally cut a hole in the top and mounted the fan correctly. Now its bareable.

I think thats your best bet if you don't want to solder anything.

The second choice is to just get a 12V 80mm fan (probably a vantec stealth) and slice it into a 5V line someplace on the amps board. I bet the amp has wires and possibly a few molex connectors runningh around inside, so a simple multimeter reading will find you a 5V or 12V line you can solder the fan to.

I do not think you need to use a switch or variable resistor to control the speed (with the 80mm route). You are not going to hear the fan, and if you do its b/c you trying to hear it. They are not loud and will not distract you from what ever you plan to do.