So I picked up a Craigslist special......a JL audio 300/4 amp with an issue.
I just hooked it up to a 10A bench supply with the following results:
All of the driver board LEDs are illuminated.
Both front and rear left channels behave the same, and appear to be acting normally.
For both left channels, as I crank up the function generator, the output appears to behave as expected...I'm assuming the clipping shown is typical.
The first picture is the left channel output....second picture is left channel clipping
For both front and rear right channels, at higher outputs the signal looks like the last picture.......
Third picture is right channel at lower output, and the last pic is right channel when cranked up.
Where do I start?
Thanks!
Bias
LF 3.1ma
RF 2.7ma
RR 1.5ma
LR 3.0ma
I just hooked it up to a 10A bench supply with the following results:
All of the driver board LEDs are illuminated.
Both front and rear left channels behave the same, and appear to be acting normally.
For both left channels, as I crank up the function generator, the output appears to behave as expected...I'm assuming the clipping shown is typical.
The first picture is the left channel output....second picture is left channel clipping
For both front and rear right channels, at higher outputs the signal looks like the last picture.......
Third picture is right channel at lower output, and the last pic is right channel when cranked up.
Where do I start?
Thanks!
Bias
LF 3.1ma
RF 2.7ma
RR 1.5ma
LR 3.0ma
Attachments
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The scope negative is connected to each speaker output negative....
I haven't listened to the amp..
..I was assuming that the amp had a problem based on the hazy description the seller gave me.....he sold it "for parts or repair" but was unclear on what the issue was. He wasn't happy with the stereo shop where he purchased the amp and went to another shop where they replaced the amp.I will hook it up to some cheap speakers and give it a listen...
Perry: Do you suspect that I may have an issue with the test setup? I can re-test as well....
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Thanks Perry....I'll try that. They have signal on them because...??? Something to do with bridging channels?
Yes. The right signal is inverted and therefore has to be on the negative terminal so the left and right channels will be in phase in stereo configuration.
Bridgeable Amplifiers
Bridgeable Amplifiers
I just connected the scope -ve to the power supply ground and got zero signal....for the right front channel.
I just read your "bridged amp" page.......can I just put the negative scope probe on the right channel positive and the positive scope probe on the right channel negative or will bad things happen?
I just read your "bridged amp" page.......can I just put the negative scope probe on the right channel positive and the positive scope probe on the right channel negative or will bad things happen?
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D'oh! ..... I'll do that now..... based on your website it's no wonder that I saw zero signal!
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With scope probe on the right channel negatives and the scope ground on PS ground, the right channels look fine......thanks Perry!
I'll let the amp warm up and set the bias for all of the channels to 3ma. Should I also consider solder sucker and re-solder the 473R's next to the LEDs on the driver boards? ...it's a 300/4 V3...if that makes any difference.
I'll let the amp warm up and set the bias for all of the channels to 3ma. Should I also consider solder sucker and re-solder the 473R's next to the LEDs on the driver boards? ...it's a 300/4 V3...if that makes any difference.
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