Either it is, like said,
too high bias current.
For some reason the setting has changed.
Usually this is set by a trim potentiometer in the circuit.
It is often not too far from big output transistors.
Or it can also be some form of oscillation.
If you put another pair of loudspeakers, does it still overheat?
Maybe you need a zobel filter at the output.
It is a cap in series with one resistor.
Can you measure the DC voltage and/or AC voltage
across the output terminals, with your speakers still attached?
With no signal both DC and AC should be close to 0.0 V.
Use the 2 volt range at your multimeter.
too high bias current.
For some reason the setting has changed.
Usually this is set by a trim potentiometer in the circuit.
It is often not too far from big output transistors.
Or it can also be some form of oscillation.
If you put another pair of loudspeakers, does it still overheat?
Maybe you need a zobel filter at the output.
It is a cap in series with one resistor.
Can you measure the DC voltage and/or AC voltage
across the output terminals, with your speakers still attached?
With no signal both DC and AC should be close to 0.0 V.
Use the 2 volt range at your multimeter.
Heatsink Size
Good Day,
I am building this stereo amplifier capable of of 60W RMS per channel into an 8-ohm load. I would like to know whether the heatsink that I am using for this amplifier I am building is sufficient for the output devices. My output devices are MJ15003 and MJ15004 made by ON Semiconductor. DC supply to the amplifiers is +/- 43 Volts.
The picture in the attachment is the output devices on the heatsink. Let me know if the heatsink is too small for my desired output power. Thank you.
Good Day,
I am building this stereo amplifier capable of of 60W RMS per channel into an 8-ohm load. I would like to know whether the heatsink that I am using for this amplifier I am building is sufficient for the output devices. My output devices are MJ15003 and MJ15004 made by ON Semiconductor. DC supply to the amplifiers is +/- 43 Volts.
The picture in the attachment is the output devices on the heatsink. Let me know if the heatsink is too small for my desired output power. Thank you.
Attachments
Hi 3Dgeek,
Check the bias setting by all means, but you may just have triggered an instability and that is the cause of the sudden heating. You need to put a CRO on it. A window to what's happening.
Hi Raveenvijendren,
You need to run you're amplifier under normal operation and feel - if the cases are too hot to touch you need a bigger heatsink. In your country, as in ours, ambient temps can be searing, si it's good for your amp to pamper it a little, by giving it a larger than minimal heatsink. It will return the favour with reliability.
Cheers,
greg
Check the bias setting by all means, but you may just have triggered an instability and that is the cause of the sudden heating. You need to put a CRO on it. A window to what's happening.
Hi Raveenvijendren,
You need to run you're amplifier under normal operation and feel - if the cases are too hot to touch you need a bigger heatsink. In your country, as in ours, ambient temps can be searing, si it's good for your amp to pamper it a little, by giving it a larger than minimal heatsink. It will return the favour with reliability.
Cheers,
greg
Raveenvijendren,
Afraid the heatsinks look too small also to me. Also, fins vertically placed would be slightly more efficient. As amplifierguru suggested do a test (can you measure temperature?) but if at all possible I would get bigger heatsinks. If not, could you try one per power transistor? (....which might get complicated, as I presume you have a heat sensing element somewhere on the heat sink for current compensation. In that case you will have to screw the 2 heatsinks together, with heat sensor in the middle.) My own 90W unit uses heat sinks almost twice the size (for 2 transistors).
Fans - I found them quite an advantage when matters came to the push: even a little air flow goes a long way.
Regards
Afraid the heatsinks look too small also to me. Also, fins vertically placed would be slightly more efficient. As amplifierguru suggested do a test (can you measure temperature?) but if at all possible I would get bigger heatsinks. If not, could you try one per power transistor? (....which might get complicated, as I presume you have a heat sensing element somewhere on the heat sink for current compensation. In that case you will have to screw the 2 heatsinks together, with heat sensor in the middle.) My own 90W unit uses heat sinks almost twice the size (for 2 transistors).
Fans - I found them quite an advantage when matters came to the push: even a little air flow goes a long way.
Regards
Good Day,
Thank you for the advice, Mr. Amplifierguru and Mr. Potgieter, for your views. I'll try to find a fan that fits since it is not possible for me to mount the heatsinks with fins vertically or seperate heatsinks for the output devices. However, the amplifier sounds very nice when the output devices are hot, that is, about 55 degrees centigrade(131 degrees Fahrenheit).
Mr. EchoWars, the whole heatsink is crawling with that white stuff which is only goes of your skin when brushed with a steel brush and industrial grade detergent.
Anyway, thank you very much, everybody, for your opinions.
Thank you for the advice, Mr. Amplifierguru and Mr. Potgieter, for your views. I'll try to find a fan that fits since it is not possible for me to mount the heatsinks with fins vertically or seperate heatsinks for the output devices. However, the amplifier sounds very nice when the output devices are hot, that is, about 55 degrees centigrade(131 degrees Fahrenheit).
Mr. EchoWars, the whole heatsink is crawling with that white stuff which is only goes of your skin when brushed with a steel brush and industrial grade detergent.
Anyway, thank you very much, everybody, for your opinions.
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