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FDP Forum / Amp Mods, Repairs, and Projects / Crate Amp has 60 cycle hum

Jake
Contributing Member
**********
******

West Chester PA

Wait, what?
Feb 6th, 2018 11:55 AM   Edit   Profile   Print Topic   Search Topic

Started out where if I put the guitar in the stand it would slowly develop a buzz. Now, it's present with both channel volumes to zero and no instrument or cord plugged in. For a while if I turned it off overnight say and tried it the next day it would be OK, and maybe I wouldn't have the problem for some days, now it's a solid failure.

Anything come to mind short of opening it up and visually inspecting everything? Did some component gradually fail? Grounding problem? I am trained in electronics but haven't really dome any in decades.

It's a POS and I have no particular attachment to it after 18 plus years. Would just as soon buy something else or use some of my POS back ups. Might donate it as is to the school of rock and see if their handy people can repair it and use it.

Leftee
Contributing Member
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VA

Life makes a man tired.
Feb 6th, 2018 01:09 PM   Edit   Profile   Print Topic   Search Topic

What amp?

pdf64

UK

Feb 7th, 2018 03:12 AM   Edit   Profile   Print Topic   Search Topic

If it's a tube amp, maybe the issue is that a tube has gone bad.
It is expected that tube amp users have a 'known good' spare tube for each type used in their amp.
Then the spare can be swapped into each socket in turn, as appropriate.
When the tubes have been eliminated as the cause, then a failing power supply ecap is the next most likely cause.
Also may be a bad connection to the chassis, so re-establish all electrical connections to the chassis, eg pots, jacks, fasteners for solder eyelets.
That means slacken the fastener off, rotate the star washer a little so that it makes a fresh cut into the chassis metal, and re-tighten.

(This message was last edited by pdf64 at 05:15 AM, Feb 7th, 2018)

Jake
Contributing Member
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West Chester PA

Wait, what?
Feb 7th, 2018 06:19 AM   Edit   Profile   Print Topic   Search Topic

It's a solid state, 30W "stereo" combo with two eight inch speakers. It's in the GX line I think. Not in front of me, I'm at work.

Steve Dallman

Merrill, Wisconsin

Age is just a number...mine is big
Feb 7th, 2018 08:28 AM   Edit   Profile   Print Topic   Search Topic

I have a G-40-C that hums for a moment when I turn it on. The power supply filter caps need replacing.

willie
Contributing Member
********

Too Near Atlanta GA

Amp Tech Emeritus
Feb 7th, 2018 09:35 AM   Edit   Profile   Print Topic   Search Topic

In addition to bad caps...Crate amps of this era were notorious for having bad solder issues...often very tiny cracks at points of inertial stress such as radial cap cans.

w

Jake
Contributing Member
**********
******

West Chester PA

Wait, what?
Feb 7th, 2018 11:24 AM   Edit   Profile   Print Topic   Search Topic

Thanks for the responses so far. Would the hum off of a full wave bridge rectifier with a bad cap be 120 cycles? My old training suggests so.

pdf64

UK

Feb 8th, 2018 04:44 AM   Edit   Profile   Print Topic   Search Topic

Yes, full wave rectification results in a ripple frequency twice that of the ac input frequency.
Have you measured the frequency of the noise?
Is it a hum or a buzz?

Jake
Contributing Member
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******

West Chester PA

Wait, what?
Feb 8th, 2018 06:37 AM   Edit   Profile   Print Topic   Search Topic

"Is it a hum or a buzz?" A little of both I guess.

Te 52

Laws of Physics

strictly enforced
Feb 8th, 2018 10:13 AM   Edit   Profile   Print Topic   Search Topic

120 Hz is right in between Bb2 and B2 (A string 1st fret and A string 2nd fret).

(This message was last edited by Te 52 at 12:22 PM, Feb 8th, 2018)

Leftee
Contributing Member
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VA

Life makes a man tired.
Feb 8th, 2018 10:14 AM   Edit   Profile   Print Topic   Search Topic

If you had a failed leg in a bridge rectifier, would a SS amp even work?

pdf64

UK

Feb 10th, 2018 03:02 AM   Edit   Profile   Print Topic   Search Topic

Might do if it failed open circuit.
Diodes usually fail short circuit though, which should draw fault current and blow the fuse.

Jake
Contributing Member
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******

West Chester PA

Wait, what?
Feb 25th, 2018 01:54 PM   Edit   Profile   Print Topic   Search Topic

The filter cap isn't a leg of the rectifier I don't think. :)

I may donate it as is to the school of rock in philly.

willie
Contributing Member
********

Too Near Atlanta GA

Amp Tech Emeritus
Feb 25th, 2018 02:23 PM   Edit   Profile   Print Topic   Search Topic

Exactly what model Crate amp is it?

w

FDP Forum / Amp Mods, Repairs, and Projects / Crate Amp has 60 cycle hum




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