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Digital noise, vintage equipment

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Posted on July 14, 2016 at 20:54:06
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 Laptop with SSD, USB DAC, updated PAS 3, Fisher console amplifier also updated. Over time, began to hear a whine between songs or very quite passages, that builds, stops, rebuilds. Soft, but annoying. I don't have a spectrum analyser, my guess is the noise is in the 3 - 5KHz range.

Unplug laptop, so it is running on battery, dead quiet. So I figure it is AC conducted noise. Not much space so I filtered with Furman AC-215, it attenuated the noise about 50%. I turn off preamp, noise also halves so probably picked up through preamp and amplifier.

Replaced with Sherwood 5000, no noise. I would like to go back to the PAS and Fisher. Could sure use some insight/suggestions as to how the Sherwood is filtering the noise and apply it to the PAS and Fisher. Thank-you in advance.

 

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RE: Digital noise, vintage equipment, posted on July 14, 2016 at 21:18:44
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 are you running a digital signal with a HDMI cable or digital USB to a DAC. You are not using analog out?

Check to see if you have dolby switched on or off. Should be off.

charles

 

RE: Digital noise, vintage equipment, posted on July 14, 2016 at 21:21:29
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 USB DAC, dolby off. The problem is a bit worse using analog out.

 

Here is what you can do., posted on July 14, 2016 at 23:30:47
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 One option is a balanced power conditioner..The other option is to plug the dynaco or fisher into a separate socket on a different circuit and see what happens.Which Sherwood S5000 version do you have? The 7189 version is the real nice amp.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Here is what you can do., posted on July 15, 2016 at 11:44:37
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 The laptop should be a three prong plug. However one of the vintage pieces may be using a hot leg as ground?????

Any chance of reversing the plug and see if that helps?

 

RE: Here is what you can do., posted on July 15, 2016 at 14:56:53
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 Actually it is the 7591 version, which I went out of my way to find. This goes back a while, I tried every amplifier I could get my hands on for ESL-63 speakers. On that system I listen primarily to low/medium volume classical, and I found there were characteristics of 7591 amplifiers that I really liked. Although the Sherwood has proven to be a bit of a disappointment, hence its temporary use on the other system that drives outdoor B&W speakers. But the Sherwood sure is noise immune.

So back to the problem, still curious of what in the Sherwood circuit is filtering the noise, but it sure seems like it is the switcher laptop supply that is beating with something causing it. And yes, plug that laptop into another circuit as far away from the analog amplification and it solves the problem, but not a wife friendly solution. And not enough room in the cabinet for a filter larger than the Furman.

 

RE: Here is what you can do., posted on July 15, 2016 at 14:59:15
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 All the tube stuff has been converted to three prong, but I understand where you are going with this, good suggestion. Some kind of ground loop is definitely a possibility.

 

RE: Here is what you can do., posted on July 15, 2016 at 15:52:37
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 old gear uses the ground AC line AS a ground. Even with the three prong plug it still may be reversed but you are not aware of it. if a different outlet worked out I would say this is your problem is reversed +/- line on your Sherwood.

 

RE: Here is what you can do., posted on July 15, 2016 at 17:15:47
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 Did you mean to write neutral? I thought that was a UL violation, even back then, but what the heck I can try it, not a big deal to swap them. I will let you know the results.

 

RE: Here is what you can do., posted on July 16, 2016 at 10:20:35
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 The old plugs didn't have a real hot/neg leg. You could put the old plug in any polarity. Besides how do you know if your outlet was wired correctly. I was an electrician and found MANY outlets wired in reverse. It made very little difference in the old days. Old stereos used the ground to the outlet AS the chassis ground. Hench hum issues when mixed with new gear.

Sounds like you got yourself the classic ground loop.

Play with the plugs.

charles

 

RE: Here is what you can do., posted on July 16, 2016 at 14:26:15
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 Sorry this took me a bit of time, with two pieces of equipment, preamp and amp, had 4 combinations, tried them all. There were combinations that added a bit of hum, no combination eliminated the beating switcher noise. Also checked the outlets, all wired ok. Didn't pop any breakers so none of the neutrals were tied to chassis. But thanks for the suggestion it was worth a shot.

 

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