Hum from decoder - Page 2

Eric · 16th March 2001, 01:53 PM

Pixie:

Here is the URL for the M.A.G.I.C. box. I personally don't have one, but lots of people over at the Home Theater Forum swear by them. They go for about $100

The Panamax line conditioner can be found here. It conditions AC wall power, as well as one CATV line. I use one of these with pretty good success. It also allows me to control power on/off to all of my components thru my preamp. These go for about $250

One other method I forgot about was to use a CATV signal amplifier, around 10-12dB. The process of injecting power into the signal also works to remove the hum. The one I used before I got from Radio Shack for about $15. May want to start with this one first - its one of the cheaper solutions.

By using these devices, you don't have to lose your ground connection from your equipment.

Let us know how it works out. Don't give up, many others have made their hum go away before!

GRollins · 16th March 2001, 04:31 PM

Pixie,
Forgot to say--in a pinch, an extension cord makes a dandy stand-in for a cheater plug. Try to scrounge up an old one that's got both blades the same size. This will give you the option of flipping the plug over to see if hum is lower one way than the other.
Incidentally, all my cheapter plugs are older ones that have two same-size blades. If you buy a new one and find that it's got a larger blade...take a file to it. You're not destroying some major, expensive piece of equipment, and I doubt you're going to lose sleep over 'voiding the warranty' on a $1.98 cheater plug.

Grey

pixie · 20th March 2001, 03:10 AM

OK. I talked to Randy Slone too. He told me several ways to get rid of hum problems in his design. The one major thing I did was run a huge wire from the center tap of the power transformer to the high quality ground. That cut it down to a tolerable level. I still haven't figured out a way to reconnect the earth ground. If I do, it doubles the noise. I'm going to try a 5 ohm resistor between my HQG and earth ground. We'll see what that does. That's something Nelson Pass suggests.

I tried disconnecting the cable TV. That's not the problem. It's somewhere else in the VCR. If I just connect the VCR output directly to the amp the noise is the same. So, it's just the VCR reacting with my amp. I removed the grounding wire between the VCR and the amp. That actually cut the noise down.

Any more suggestions?

Thanks,
pixie

GRollins · 20th March 2001, 04:22 AM

Pixie,
Does the VCR hum going straight into your McIntosh? I'm assuming that you would have mentioned it before if it were so, but I just wanted to double check.
Also, you might want to use something more than just a 1/4 or 1/2W resistor for that ground. You'd be surprised at some of the voltages that can run through a circuit in the ground loop.

Grey

cm961 · 18th June 2001, 03:09 PM

I think I have a simliar problem. When I run my VCR into my technics receiver, I get hum. However, this only occurs when the preamp is switched to something other than the VCR input. For instance, if the preamp is on CD, I get hum. If I unplug the cables from the VCR inputs it goes away. Like I said, there is no hum when the actual VCR input is selected on the preamp.

Could this be caused by the CATV connection to the VCR?

pixie · 18th June 2001, 03:53 PM

OK. I found the problem, I think.

The ground input of my amplifier was shorted to the case. It wasn't connected directly to the HQG.

I'm not sure why it was only a problem when the VCR was in the path, but now the only hum is comming from the transformer.

Does anyone have suggestions for how to get rid of the physical vibrations from the toriod transformer? Not likely, but I thought I'd ask.

Thanks,
pixie

phil · 18th June 2001, 06:17 PM

Pixie
I have known the LCD display on VCR's to radiate intiference. If you have access to another VCR try it.

16th March 2001, 01:53 PM	#11
Eric diyAudio Member Join Date: Nov 2000 Location: Central PA, USA	REmoving Hum Pixie: Here is the URL for the M.A.G.I.C. box. I personally don't have one, but lots of people over at the Home Theater Forum swear by them. They go for about $100 The Panamax line conditioner can be found here. It conditions AC wall power, as well as one CATV line. I use one of these with pretty good success. It also allows me to control power on/off to all of my components thru my preamp. These go for about $250 One other method I forgot about was to use a CATV signal amplifier, around 10-12dB. The process of injecting power into the signal also works to remove the hum. The one I used before I got from Radio Shack for about $15. May want to start with this one first - its one of the cheaper solutions. By using these devices, you don't have to lose your ground connection from your equipment. Let us know how it works out. Don't give up, many others have made their hum go away before!

18th June 2001, 03:53 PM	#16
pixie diyAudio Member Join Date: Oct 2000 Location: Austin, Texas, USA	Finally... OK. I found the problem, I think. The ground input of my amplifier was shorted to the case. It wasn't connected directly to the HQG. I'm not sure why it was only a problem when the VCR was in the path, but now the only hum is comming from the transformer. Does anyone have suggestions for how to get rid of the physical vibrations from the toriod transformer? Not likely, but I thought I'd ask. Thanks, pixie

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16th March 2001, 04:31 PM	#12
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Pixie, Forgot to say--in a pinch, an extension cord makes a dandy stand-in for a cheater plug. Try to scrounge up an old one that's got both blades the same size. This will give you the option of flipping the plug over to see if hum is lower one way than the other. Incidentally, all my cheapter plugs are older ones that have two same-size blades. If you buy a new one and find that it's got a larger blade...take a file to it. You're not destroying some major, expensive piece of equipment, and I doubt you're going to lose sleep over 'voiding the warranty' on a $1.98 cheater plug. Grey

20th March 2001, 03:10 AM	#13
pixie diyAudio Member Join Date: Oct 2000 Location: Austin, Texas, USA	OK. I talked to Randy Slone too. He told me several ways to get rid of hum problems in his design. The one major thing I did was run a huge wire from the center tap of the power transformer to the high quality ground. That cut it down to a tolerable level. I still haven't figured out a way to reconnect the earth ground. If I do, it doubles the noise. I'm going to try a 5 ohm resistor between my HQG and earth ground. We'll see what that does. That's something Nelson Pass suggests. I tried disconnecting the cable TV. That's not the problem. It's somewhere else in the VCR. If I just connect the VCR output directly to the amp the noise is the same. So, it's just the VCR reacting with my amp. I removed the grounding wire between the VCR and the amp. That actually cut the noise down. Any more suggestions? Thanks, pixie

20th March 2001, 04:22 AM	#14
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Pixie, Does the VCR hum going straight into your McIntosh? I'm assuming that you would have mentioned it before if it were so, but I just wanted to double check. Also, you might want to use something more than just a 1/4 or 1/2W resistor for that ground. You'd be surprised at some of the voltages that can run through a circuit in the ground loop. Grey

18th June 2001, 03:09 PM	#15
cm961 diyAudio Member Join Date: Jun 2001 Location: Peterborough, Ontario	I think I have a simliar problem. When I run my VCR into my technics receiver, I get hum. However, this only occurs when the preamp is switched to something other than the VCR input. For instance, if the preamp is on CD, I get hum. If I unplug the cables from the VCR inputs it goes away. Like I said, there is no hum when the actual VCR input is selected on the preamp. Could this be caused by the CATV connection to the VCR?

18th June 2001, 06:17 PM	#17
phil diyAudio Member Join Date: May 2001	Pixie I have known the LCD display on VCR's to radiate intiference. If you have access to another VCR try it.