Mackie power amp distorting

javey · 19th April 2005, 05:20 PM

Ch 1 works great,Ch 2 begins to distort immediately and gets worse by the minute to the point of total breakup. I have replaced all output transistors and drivers for this channel. I thought they were leaking while getting warmed up but this has not changed the symptons whatsoever. I cannot find any shorted diodes or open resistors. The power supply caps read within normal charge,but my tester doesn't have a leakage detecting feature. And i can't say for sure what they're doing while the amp is running.

What are the main causes of distortion in solid state amps,where it gets progressively worse?

The amps protection circuit does not come on and nothing is burning up smell wise. Its a 1400i if anyone is familiar with these things. They had a ribbon cable issue in the past,but they've all been replaced on mine. Like I said,right when you turn the unit on it mildly distorts with the ouput dial cranked and then gets worse and worse over the next thirty seconds. A minute or so later even if you turn the gain down its breaking up horribly. I also have gone over all connections and solder points without any change whatsoever.

javey · 20th April 2005, 02:31 AM

Is this thread too beginner for the forum? Any tips and advice would be greatly appreciated.
I just do basic solder work,but would love to learn more.

Enzo · 20th April 2005, 03:45 AM

It is not too beginner, I think no one has any particular insight into this. Ther is nothing inherent to SS amps we can point to. I hate working on Makie stuff myself, and I make a living running a pro audio repair facility.

I would bet an op amp is cooking or maybe a cap in the signal path is leaky.

Ny the way, I am down in Lansing at 517-882-2544, and in the shop weekday evenings after 6:30PM. You can call.

19th April 2005, 05:20 PM	#1
javey diyAudio Member Join Date: Apr 2005 Location: Saginaw,MI	Mackie power amp distorting Ch 1 works great,Ch 2 begins to distort immediately and gets worse by the minute to the point of total breakup. I have replaced all output transistors and drivers for this channel. I thought they were leaking while getting warmed up but this has not changed the symptons whatsoever. I cannot find any shorted diodes or open resistors. The power supply caps read within normal charge,but my tester doesn't have a leakage detecting feature. And i can't say for sure what they're doing while the amp is running. What are the main causes of distortion in solid state amps,where it gets progressively worse? The amps protection circuit does not come on and nothing is burning up smell wise. Its a 1400i if anyone is familiar with these things. They had a ribbon cable issue in the past,but they've all been replaced on mine. Like I said,right when you turn the unit on it mildly distorts with the ouput dial cranked and then gets worse and worse over the next thirty seconds. A minute or so later even if you turn the gain down its breaking up horribly. I also have gone over all connections and solder points without any change whatsoever.

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20th April 2005, 02:31 AM	#2
javey diyAudio Member Join Date: Apr 2005 Location: Saginaw,MI	Is this thread too beginner for the forum? Any tips and advice would be greatly appreciated. I just do basic solder work,but would love to learn more.

20th April 2005, 03:45 AM	#3
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	It is not too beginner, I think no one has any particular insight into this. Ther is nothing inherent to SS amps we can point to. I hate working on Makie stuff myself, and I make a living running a pro audio repair facility. I would bet an op amp is cooking or maybe a cap in the signal path is leaky. Ny the way, I am down in Lansing at 517-882-2544, and in the shop weekday evenings after 6:30PM. You can call.

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