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Old 3rd March 2011, 01:31 AM   #1
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Default Hum in Crate guitar amp

I have a Crate CR-160 guitar amp that has a low hum with all level controls all the way down. The hum does get louder as I in crease the volume levels somewhat.

It has two 4700 mfd 35 volt filter caps in place but before I go removing those I was wondering what other conditions may cause the hum other than the caps?

Thanks!
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Old 3rd March 2011, 02:07 AM   #2
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Is the suspect hum around 120 Hertz??? If so, yes by all means change out those 4700uF caps.....if the power supply board is of an "open" type & there is room, bump the voltage up to 50V, this will increase the lifetime of these caps.....keep the value the same at 4700 tho'.
These large caps dry out pretty consistently, changing the values ..your unit was made around 1983 & who knows how much it's been used...assuming your not the original owner of course.

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Old 3rd March 2011, 02:38 AM   #3
eyoung is offline eyoung  United States
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Rick is right, replace the electrolytics in the p/s. modern caps are going to be smaller for a given value so going to a higher voltage typically will result in the same physical dimension. Newark, Mouser, or Digikey are good sources for parts.
or ck the swap meet forum

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Old 5th March 2011, 06:24 PM   #4
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Im not a good judge on pitch so I cant say for sure what hertz it counld be.

If the O.D. of a 50v cap is larger would be a problem to install the way this unit is assembled. Whats the advantage of increasing the volt value of the cap?
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Old 7th March 2011, 01:33 AM   #5
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I found some caps of the same value but rated for 50 volt in a scrap unit I hold on to and temporarily installed in the amp. The hum was not present at initial power up but after a few minutes it began to hum. This is with all level controls at full off.

I then put the original caps back in to have the same result as mentioned above.
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Old 19th March 2011, 09:06 PM   #6
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OK.It seems the caps are OK at this point. You need to start trouble-shooting this unit. Has the unit allways had this hum? If not when and under what circumstances did the hum "start".
First off you want to make a very comprehensive visual inspection.......the very first step in troubleshooting. Make some room where you can eyeball the unit, have some very good bright lighting, find yourself a magnifying glass (preferred) ...your looking at all the solder joints thruout the circuit board.....your looking for poor connections & hairline cracks on the joints.
A typical joint looks like a "Hershey Kiss", silver in color of course, A typical crack will be a hairline crack all the way around said joint...circular. Further you are looking for burn't components, and evidence of overheated components (Discoloration) discoloration of the board too. Look extremely close....We are trying to solve your problems......by taking the first steps..........Granted we all have our "favorite" failures........and sometimes it works out just fine skipping right to it, but there is no replacement for a full "investigation" here.
Recent designs in engineering of amps & such are very poor in design & we all here can upgrade & improve the performance, reliability & function of you unit. I've seen the schematic of this particular amp & I'd bet real money it can be improved.

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Old 19th March 2011, 11:12 PM   #7
llwhtt is offline llwhtt  United States
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Check the 15 VDC zenered supplies, the parts run hot in that area. Check all components mounted on the PCB that extent thru the front panel, look for cracked/bad solder joints. Since the hum gets worse after time sounds like a heat issue, zener supplies.

Craig
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Old 19th March 2011, 11:17 PM   #8
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IMO, I would call the factory and tell them to fix it! jer

Last edited by geraldfryjr; 19th March 2011 at 11:26 PM.
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Old 19th March 2011, 11:51 PM   #9
llwhtt is offline llwhtt  United States
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This thing is 30 years old, I don't think the factory will have anything to do with it.

Craig
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Old 20th March 2011, 12:01 AM   #10
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Okay , my bad. jer
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