LM4780 and cooling

[john_lenfr]

Put an ammeter in line with the V+ supply (disconnect the v+ lead from the supply, connect one ammeter lead to the wire and the other to the supply where it ws removed) and measure the current - if over 175 mA you have something wrong.

Why I did not think of it before? I'll try to do this of course...

 

[peranders]

you are right, running those sinks hot would be dangerous.

I don't think so. Those IC's have temperature protection but in the long run it's not wise to run them at max temp. I'll suspect that the lifetime will be better to run them cooler, besides you can get more intermittent power out of the chips.

 

[BobEllis]

P-A - Hot is also slang for electrically live, as in not isolating the chip from the sink, so that the sink is at V-.

I am usually better at using proper terminology, sorry.

 

[peranders]

Sorry, I didn't read too carefully but "hot" to me is dangerous voltages and 40 volts isn't especially "hot" for me but having 40 volts metal parts outside a box isn't very wise if this would have been case.

 

[SpittinLLama]

John, what is the voltage of the supply when on but no signal and then with a signal that is at a level you normally listen too? +/-38V driving 6 ohms is running above what National recommends for the LM4780. You can normally get away with running audio signals higher than what National recommends since they test with 20Hz sine waves at max Pd, worst case testing. But they also test at 25C.

-SL

 

[john_lenfr]

OK, so:



@ Russ White : you said "I also have a LM4780 amp that powers my mains, and for added safety just to be sure I never hit the SPIKE protection I added a 12V fan, which is powered by about 4V so it runs very slow, it keeps the chips very cool, and is silient.
"

=> I also think of that. But I want to make a very tiny amp.

@ jackinnj : you said "route at right angle away from the input RCA jacks"

=> I did, so thanks

@ slackman : thanks for your advices (V-, heatsink...)

@ peranders : you said " The speaker cable is very near the 230 mains area. Keep all wiring neat and tidy, that's a good thing and keep all 230 V things apart from the rest."

=> I tried but my box is very small (of course because I want that!). So it is very difficult to keep 230V appart from the rest.


@ macboy : you said "Your amp is definitely, absolutely oscillating.. Without any doubt whatsover. When attached to a heatsink, and with no signal present, the amps should not get warm. The fact that they are getting warm indicates that they are not just sitting there idle. They are doing something. They are oscillating. You need to fix that, not your heatsink. Your heatsink is fine."

=> now with no signal I am at the temperature of my room. (so 22 to 30).

@ BobEllis :you said "I tend to agree with Macboy. At idle the 4780 typically draws 110 mA, or around 8W with your rails. With that sink you should notice that the chip is warmer than ambient, but barely with no signal."

=> It's true. I measured 110 to 112mA. (between GND and V+)


@ SpittinLLama : you said "what is the voltage of the supply"

=>I measured:
+-38V when on but no signal.
+-34 to 36 V with a signal. At max level.





Finally, I found! It was the screws! They connected the package to the heatsink. So I replaced them. (But it is strange because
normally the FI should switch power down).

Now it is better.

SO, THANKS FOR ALL OF YOUR ADVICES!

 

[john_lenfr]

I measured also:

temperature of my room: 31°C

->27°C without signal on the heatsink.
->up to 65°C at max signal and level on the heatsink.

 

[jackinnj]

How New Zealanders cool their GC's

jet propelled P4 and beer cooler:

http://www.asciimation.co.nz/beer/