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09-25-2009, 12:55 AM
| #1 |
| Member Join Date: Jun 2009
Posts: 45
| ampeg ba210sp bass amp
It hisses. I just had one in the shop and it did not hiss. I plugged in to the headphone and xlr line out and there is no hiss. I am assuming it would be in the output section. Suggestions on what to be looking for?? Could not find any loose grounds and bad solder connections. Resoldered cold joints on all pots and jacks. I have attached a schematic.
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09-25-2009, 02:11 AM
| #2 |
| Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA
Posts: 10,366
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Reasonable to assume it is from the power amp. Hiss is usually associated with gain, so the first suspect is the IC. Replace the 5532, U3. Scope the circuit. The hiss ought to be visible on pin7 of U3. Is it on pin 1 as well? One of those JFETs could be noisy.
__________________ Education is what you're left with after you have forgotten what you have learned. |
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09-25-2009, 08:44 PM
| #3 |
| Member Join Date: Jun 2009
Posts: 45
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I am seeing the noise on both pin 1 and pin 7. I need to place an order for the chips. Would it be wise to order the transistors aswell (Q1-Q8) or just the FETS?
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09-26-2009, 04:27 AM
| #4 |
| Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA
Posts: 10,366
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It is only my opinion. I doubt that hiss is coming from your output transistors, especially since you find the noise on pin1 of the IC.
__________________ Education is what you're left with after you have forgotten what you have learned. |
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10-01-2009, 09:24 PM
| #5 |
| Member Join Date: Jun 2009
Posts: 45
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So it seems that the ground noise on pin 1 of U3 was caused by choosing a poor ground for my scope probe. The noise is definitely visible on pin 7 and not on pin 1. I replaced U3 and the output FETS and still see noise.
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10-01-2009, 10:10 PM
| #6 |
| Member Join Date: Jun 2009
Posts: 45
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Yup im a newbie for sure. I replaced Q1 and Q4. Problem solved. Thanks for the help as allways enzo
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10-02-2009, 03:23 AM
| #7 |
| Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA
Posts: 10,366
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I can't take much credit, I didn;t steer you towards those drivers. Glad you got it straightened out.
__________________ Education is what you're left with after you have forgotten what you have learned. |
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