Sub Amp, what's wrong?

UNDERSTANDIN · 25th August 2006, 03:49 PM

When I turned on the receiver that morning, there was no bass sound and the sub amp was very hot. It didn't work at all that day. A few days later I tried it again, and there is sound. The only problem is that there is a initial "pop" sound from the speaker when it comes on. It seems like the amp is sending a larger than normal signal to the driver. The actual driver works fine with a different amp. I want to know what caused the malfunction, and what is wrong with it now? How can I fix the hard "turn on" and restore the soft "turn on"? Seems like a poly switch may have blown.

mrshow4u · 25th August 2006, 04:02 PM

It sounds like the front-end (op-amp, discrete differential stage) is a little "wiggley", or unstable. The pop might be a little DC offset. See if the cone pushes out, or sucks in. If so, I'd repair it pronto. You don't want the voice coil to sit there and dissipate the amp's wrong doing.

UNDERSTANDIN · 25th August 2006, 04:15 PM

Yes, the cone does push in and/or out. As you can tell, I'm not electronically inclined. Is it hard to repair or replace the op-amp?
I'm using another amp now, but would like to repair this amp. I have had it over a year, but it's been in use only a few months.

mrshow4u · 25th August 2006, 04:38 PM

It MIGHT be the op-amp, if it exist on that design. First place to start is getting some service information. A schematic would be really handy at this point. It sounds like this problem is intermittent. That's going to make it a little more tricky. Are there random noises coming out of the woofer at idle??? As it is intermittent, my gut feeling tells me it is the front-end (input stage) electronics. If it is an op-amp and is socketed, you could try to replace it. Mind your pin one. It'll be identified by a dot in the upper left corner of the IC. If there is no dot, look for a notch in the plastic package. Pin one will be left of that. If the above scenario takes place, DISCONNECT the speaker the first time you turn it on. Measure the speaker leads and check for DC. Anything under 50mV, or so is allright. Anything above (especially 5 ~ 60VDC) and you've still got work to do. Do not reconnect the speaker. If you get the service info, plenty of people will give you helpful information to to get your thumping back. Good luck

Jon

25th August 2006, 03:49 PM	#1
UNDERSTANDIN diyAudio Member Join Date: Apr 2005 Location: New Jersey	Sub Amp, what's wrong? When I turned on the receiver that morning, there was no bass sound and the sub amp was very hot. It didn't work at all that day. A few days later I tried it again, and there is sound. The only problem is that there is a initial "pop" sound from the speaker when it comes on. It seems like the amp is sending a larger than normal signal to the driver. The actual driver works fine with a different amp. I want to know what caused the malfunction, and what is wrong with it now? How can I fix the hard "turn on" and restore the soft "turn on"? Seems like a poly switch may have blown.

25th August 2006, 04:02 PM	#2
mrshow4u diyAudio Member Join Date: Jul 2006	It sounds like the front-end (op-amp, discrete differential stage) is a little "wiggley", or unstable. The pop might be a little DC offset. See if the cone pushes out, or sucks in. If so, I'd repair it pronto. You don't want the voice coil to sit there and dissipate the amp's wrong doing. __________________ ".........These go to eleven"

25th August 2006, 04:38 PM	#4
mrshow4u diyAudio Member Join Date: Jul 2006	It MIGHT be the op-amp, if it exist on that design. First place to start is getting some service information. A schematic would be really handy at this point. It sounds like this problem is intermittent. That's going to make it a little more tricky. Are there random noises coming out of the woofer at idle??? As it is intermittent, my gut feeling tells me it is the front-end (input stage) electronics. If it is an op-amp and is socketed, you could try to replace it. Mind your pin one. It'll be identified by a dot in the upper left corner of the IC. If there is no dot, look for a notch in the plastic package. Pin one will be left of that. If the above scenario takes place, DISCONNECT the speaker the first time you turn it on. Measure the speaker leads and check for DC. Anything under 50mV, or so is allright. Anything above (especially 5 ~ 60VDC) and you've still got work to do. Do not reconnect the speaker. If you get the service info, plenty of people will give you helpful information to to get your thumping back. Good luck Jon __________________ ".........These go to eleven"

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25th August 2006, 04:15 PM	#3
UNDERSTANDIN diyAudio Member Join Date: Apr 2005 Location: New Jersey	Yes, the cone does push in and/or out. As you can tell, I'm not electronically inclined. Is it hard to repair or replace the op-amp? I'm using another amp now, but would like to repair this amp. I have had it over a year, but it's been in use only a few months.

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