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Post subject: Question regarding bass amp hum
Posted: Sun Feb 02, 2014 3:42 pm
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I have 3 amps, and the small 10 inch speaker amp has a hum when it is powered up..Makes no difference if an instrument is plugged in or not, and none of the controls have any effect..Works fine otherwise, just a little annoying. I tried a 2 prong plug adapter, so I do not believe it is a ground loop problem.. I pulled the chassis and powered it up and tapped on some of the components as one person suggested...Any suggestions or knowledge of the problem would be greatly appreciated...Thank you..Forgot to mention..It is all solid state..


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Post subject: Re: Question regarding bass amp hum
Posted: Sun Feb 02, 2014 4:06 pm
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Is the hum low frequency (around 60 hz) or higher than that?

If it is near 60 hz, then it MAY be a power supply filter capacitor going bad OR has become unsoldered from it's mounting location. In any event - unless you are well versed in electrical repairs, don't go in there yourself. There are dangerous voltages in there in the primary (120 volt) side of the power supply.

If the hum is higher than 60 hz, then a audio circuit grounding issue may be present. Either way, this is probably a task for a technician with proper test equipment.


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Post subject: Re: Question regarding bass amp hum
Posted: Mon Feb 03, 2014 7:08 am
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Thank you for the reply.. I guess I would call it a low frequency hum, and I am not a real expert on electronics, but pretty good on others..The amp is $179 new , and I paid $60 for it used, so I guess it probably would cost more than I paid for it, so will have to hope it works as is for a while..Thanks again


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Post subject: Re: Question regarding bass amp hum
Posted: Tue Feb 04, 2014 2:38 am
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Sure sounds like a filter cap.


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Post subject: Re: Question regarding bass amp hum
Posted: Tue Feb 04, 2014 4:41 am
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brotherdave wrote:
Sure sounds like a filter cap.


Dave - sure does... It is one of the most common power supply failures - because the electrolytic capacitors have a little weight to them and transporting combo amps that get bumped around can loosen up the cap solder on the circuit board very easily. They also have a significant internal failure rate when the cap's dry out with age internally and become "resistors" rather than caps.

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Post subject: Re: Question regarding bass amp hum
Posted: Tue Feb 04, 2014 8:06 am
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Thank you all..I took the circuit board completely out where I could really inspect everything, and it all looks good. I did re solder the connections on the tall capacitors with no effect. You will think I am nuts , but as this is just a practice amp for very limited use, I put some padding inside the speaker grill and it really muffles the hum and sounds fine. I did talk to one repair shop and the guy was very honest and told me it would probably be better to just purchase a new amp, as it would cost just as much in labor...Lesson learned in buying from Craigslist..Always plug it in and try it before you buy it instead of meeting the guy to save a few miles..Thanks again for the replies..


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