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Old 30th May 2008, 03:45 PM   #1
SRITT3 is offline SRITT3  United States
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Default PPI a404 amp creating noise (squeal) on AM Band

My PPI a404 amp is creating noise (squeal) on AM Band can this be repaired? I have 3 of these and I would hate to lose one. Thanks in advance for any help
Steve
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Old 30th May 2008, 04:50 PM   #2
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Well there is a need for more info, that can only be gained by opening up the amp. In most cases I would tend to think by its age alone that your amps need servicing.
By servicing I mean that they need to be opened, inspected, and most probably many if not all the electrolytic caps replaced. I do this all the time on vintage amps like yours. The original SQ comes back, and they run cooler and more reliably.
Electrolytic caps die from age and use, and 15 year old amps need new ones installed just to stay functional.

I see old amps going for bank on e-bay and wonder why folks don't understand that electronics does not last forever, and amps this age need to be serviced badly, even if they seem to work perfectly thats just a rouse to the actual condition of whats inside. Even amps that show the inside visually are still misleading as good looks do not mean proper operation.

I would have the amp serviced by someone reputable. Service would consist of capacitors replacement from the 12 volt side to the secondary amp side, especially the lower rails caps they actually turn color and shrink the plastic covers on the caps bodies from excessive heat < very common situation on PPI >. The new silicon heatsink compound cause that stuff creeps till there is no thermal grease left under the power devices. Then a general alignment of DC offsets, and channel bias set points < this is a general service for a working amp this age.

This should solve you beat noise your getting from the amp. I am under the thought that this amp worked fine before, so this should get it back to spec. And if there is anything else wrong inside it would typically be found with a in-depth service like this... Hope this helps
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Old 30th May 2008, 05:41 PM   #3
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Quote:
Originally posted by 1moreamp
Well there is a need for more info, that can only be gained by opening up the amp. In most cases I would tend to think by its age alone that your amps need servicing.
By servicing I mean that they need to be opened, inspected, and most probably many if not all the electrolytic caps replaced. I do this all the time on vintage amps like yours. The original SQ comes back, and they run cooler and more reliably.
Electrolytic caps die from age and use, and 15 year old amps need new ones installed just to stay functional.

I see old amps going for bank on e-bay and wonder why folks don't understand that electronics does not last forever, and amps this age need to be serviced badly, even if they seem to work perfectly thats just a rouse to the actual condition of whats inside. Even amps that show the inside visually are still misleading as good looks do not mean proper operation.

I would have the amp serviced by someone reputable. Service would consist of capacitors replacement from the 12 volt side to the secondary amp side, especially the lower rails caps they actually turn color and shrink the plastic covers on the caps bodies from excessive heat < very common situation on PPI >. The new silicon heatsink compound cause that stuff creeps till there is no thermal grease left under the power devices. Then a general alignment of DC offsets, and channel bias set points < this is a general service for a working amp this age.

This should solve you beat noise your getting from the amp. I am under the thought that this amp worked fine before, so this should get it back to spec. And if there is anything else wrong inside it would typically be found with a in-depth service like this... Hope this helps

I agree 100% with this and it's not talked about often enough. The average cap Manufactured back then had a shelf life (keep in mind thats UNUSED shelflife) of 20 years. Most caps used even today only have an average USAGE life of 2000-3000 hours! Assuming an hour a day playtime during commutes @ 2000 lifespan cap thats only 5.5 years! Capacitors are fascinating and the whitepages you can find on them span great lengths. Much more to know about then other then 'storage device' which is what an average layman knows.

I usually test the caps with an in circuit tester I have and you would be surprised how many never vented or dried up that read bad anyways.

If you want to keep the amp for a long time and have several identical models as well, put in a bulk cap order to cover all of them. You will get them cheaper this way.

- Matt
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Old 30th May 2008, 08:58 PM   #4
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Quote:
Originally posted by 1moreamp
Well there is a need for more info, that can only be gained by opening up the amp. In most cases I would tend to think by its age alone that your amps need servicing.
By servicing I mean that they need to be opened, inspected, and most probably many if not all the electrolytic caps replaced. I do this all the time on vintage amps like yours. The original SQ comes back, and they run cooler and more reliably.
Electrolytic caps die from age and use, and 15 year old amps need new ones installed just to stay functional.

I see old amps going for bank on e-bay and wonder why folks don't understand that electronics does not last forever, and amps this age need to be serviced badly, even if they seem to work perfectly thats just a rouse to the actual condition of whats inside. Even amps that show the inside visually are still misleading as good looks do not mean proper operation.

I would have the amp serviced by someone reputable. Service would consist of capacitors replacement from the 12 volt side to the secondary amp side, especially the lower rails caps they actually turn color and shrink the plastic covers on the caps bodies from excessive heat < very common situation on PPI >. The new silicon heatsink compound cause that stuff creeps till there is no thermal grease left under the power devices. Then a general alignment of DC offsets, and channel bias set points < this is a general service for a working amp this age.

This should solve you beat noise your getting from the amp. I am under the thought that this amp worked fine before, so this should get it back to spec. And if there is anything else wrong inside it would typically be found with a in-depth service like this... Hope this helps
He wanted someone reputable and he called me.... I kid!

I didn't even see this thread, but I said the same sort of thing - capacitors. Also, a cooked toroid will produce severe leakage inductance and send huge spikes back through the primary switchers. Let's hope it's not that.
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Old 31st May 2008, 02:55 AM   #5
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