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Power Amp Hum Causes


TJIann

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A ground loop isolator cost a fortune at $6-12. Get one and have no doubt that you are safe.

I'd rather not use a component like that with my amp and high end cables. Worried about the affect on tone/sound quality with the thin RCA cables, etc.

Edited by TJIann
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A ground loop isolator cost a fortune at $6-12. Get one and have no doubt that you are safe.

I'd rather not use a component like that with my amp and high end cables. Worried about the affect on tone/sound quality with the thin RCA cables, etc.

 

Agree but it's a good tool to isolate the offending component.

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"I'd rather not use a component like that with my amp and high end cables. Worried about the affect on tone/sound quality with the thin RCA cables, etc."

 

Then buy a higher quality transformer.

 

Edcor makes very good ones starting at about $30, or if you want the best, go Jensen, about $200.

 

1) Transformers break ground loops. Since the transformer’s primary and secondary aren’t electrically connected, no ground loop currents can flow. Hair- pulling, aggravating ground loop related hum and noise problems disappear.

 

2) Transformers have ultra-high common mode input impedances (inputs-to-ground), unrivaled by active differential circuits. This is also a result of the galvanic isolation provided by the insulated, shielded primary windings. Direct connection to a differential (balanced) amplifier’s inputs doesn’t guarantee perfectly balanced operation – transformers do.

 

The majority of Jeff Rowland's new products are equipped with line-level input transformers.

 

http://www.stereophile.com/solidpreamps/999rowland/index.html

Edited by djk
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Do as djk suggests. with an isolation transformer. They are extremely effective. There are some here who know what they are talking about; he is one of them.

3-to-2 prong cheater plugs are great as diagnostic tools, but IMO perhaps not the best choice for a permanent solution for breaking a ground loop. Break down of power transformer insulation and/or other wiring on the AC side of power supplies in modern equipment is highly unlikely, but it's really not a bad idea to maintain a safety path to ground in the improbable (but not impossible) event of a suddenly "live" chassis. It can and has happened.

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Some great suggestions on here, as usual. I actually had this issue with some mono blocks, tired the usual troubleshooting, cheeter, plugs, etc. One you could hear slightly from 5' away. The othwr was dead quiet.

I finally called Craig and he had me try a couple of things, nothing, and then he had me swap the amps connections at back of preamp and I was doing that and felt slight amount of juice through the IC and he said, "remove the bottom plate and I will have you look for some things." I said "no way B+ and I don't mix they are on the way to you, let me know."

Long story short, there was a cold solder joint of a wire that tied to ground. He couldn't believe that it was that it wasn't screaming hum because it did when he hooked it up to his speaker. I was running it through power conditioner on an isolated line, so I may have help on that.

I would have never found and it would have driven me crazy. Craig sent it back "no charge."

Sometimes it is the equipment, I admire the guys here that know enough on how to figure that out. Several people had hum problems with DX 38s and a "patch" was finally developed for that after more than two or three people were experiencing the same thing.

I hopes yours is a simple and easy solution.

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You can make one for about 1/10 the the normal cost.

 

well, maybe you can.. some of us are mere mortals. :P

 

I thought about building one (there are a few good YouTube videos from guys who built larger versions in outlet boxes), but there is no way I could make one in a nice compact plastic enclosure with a light to tell me it's engaged.  The cost was worth it for me as I only needed one for the power amp in my system and wanted something that did not take up much space in my already cluttered cables/surge protector area behind the cabinet.  I may build a couple of the versions in standard electrical outlet boxes for my guitar amps.  They can be built for ~$10 in parts.

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The Hum_X is a ground lift with a pair of inverse-parallel 6A diodes connecting the ground.

 

You can make one for about 1/10 the the normal cost.

 

  Not in that nice clean neat little package you can't... I'm sure they do make them for less then $10 each with labor. But they are most likely buying the custom made package in the 1000's count.. they have to market it...sell it at wholesale price then the retailer has to make a buck...

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6. Are there any ham radio operators near your house?

 

my listening room is a former HAM radio room, which is precisely why I don't have any ground loops. That equipment is just as sensitive, if not more so, and the previous owner went to great lengths to remove any potential issues, including a dedicated circuit physically isolated from the house. 

 

Just jumped in to give Thad his 1000th "Like"......

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The Hum_X is a ground lift with a pair of inverse-parallel 6A diodes connecting the ground.

 

You can make one for about 1/10 the the normal cost.

 

  Not in that nice clean neat little package you can't... I'm sure they do make them for less then $10 each with labor. But they are most likely buying the custom made package in the 1000's count.. they have to market it...sell it at wholesale price then the retailer has to make a buck...

 

Yea but $80 for two diodes. C'MON

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I'd rather not use a component like that with my amp and high end cables. Worried about the affect on tone/sound quality with the thin RCA cables, etc.

 

I use mine on subwoofers so no real problem with SQ: actually improved without the backgroud hum.  I measure the sub and there was no major chang in distortion levels at higher volumes to get pass the hum.

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"Yea but $80 for two diodes. C'MON"

 

The diodes are less than $0.50 in small quantity, a fiberglass box and cover about $2, a duplex outlet about $1.

 

It all depends on what your time is worth.

 

DCblock.gif

 

Note how Bryston has the diodes inside the amp.
 

Edited by djk
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