Hum in Hafler DH-500

Bogie · 1st March 2006, 11:36 AM

Any ideas on pinpointing/repair?

I've got just a _little_ hum in my #2 DH-500 (diagnostics: I pulled all the cables, switched all the cables to my other DH-500, etc., etc... so I'm pretty sure we're not talking ground loop). This one is running my rear speakers, and it really isn't noticeable unless you're standing right underneath one of 'em.

Bought #1 from AudioClassics, but this one got ebayed from a music store. I'm guessing it was used for gigging. It's got quarter inchers instead of RCAs, and the protection fuses aren't there anymore.

Sometime I'm thinking of tearing into it, and doing some fixups/replacements... back to RCAs, new caps, etc., etc... But for now, any ideas?

djk · 2nd March 2006, 01:41 AM

Use an ohm meter and check for continuity between the grounds f the 1/4" jacks and the speaker grounds. Early DH500 had a resistor that would open up.

Replace the ground strap between the main filter caps with a copper strap.

The caps could be drying up too.

freddymac406 · 5th March 2006, 12:03 AM

If your amp has pc-10 driver boards r-30 that connects the input and output grounds together may be open. They ranged in resistance from the factory. It will be either .5 ohm or 2.2 ohm.
Fred

djk · 5th March 2006, 03:56 AM

I told him how to check that in my post.

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1st March 2006, 11:36 AM	#1
Bogie diyAudio Member Join Date: Dec 2004 Location: St. Louis	Hum in Hafler DH-500 Any ideas on pinpointing/repair? I've got just a _little_ hum in my #2 DH-500 (diagnostics: I pulled all the cables, switched all the cables to my other DH-500, etc., etc... so I'm pretty sure we're not talking ground loop). This one is running my rear speakers, and it really isn't noticeable unless you're standing right underneath one of 'em. Bought #1 from AudioClassics, but this one got ebayed from a music store. I'm guessing it was used for gigging. It's got quarter inchers instead of RCAs, and the protection fuses aren't there anymore. Sometime I'm thinking of tearing into it, and doing some fixups/replacements... back to RCAs, new caps, etc., etc... But for now, any ideas?

2nd March 2006, 01:41 AM	#2
djk diyAudio Member Join Date: Feb 2001 Location: USA	Use an ohm meter and check for continuity between the grounds f the 1/4" jacks and the speaker grounds. Early DH500 had a resistor that would open up. Replace the ground strap between the main filter caps with a copper strap. The caps could be drying up too.

5th March 2006, 12:03 AM	#3
freddymac406 diyAudio Member Join Date: Jan 2005 Location: S.C.	If your amp has pc-10 driver boards r-30 that connects the input and output grounds together may be open. They ranged in resistance from the factory. It will be either .5 ohm or 2.2 ohm. Fred

5th March 2006, 03:56 AM	#4
djk diyAudio Member Join Date: Feb 2001 Location: USA	I told him how to check that in my post.

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