LP to CD recording-sudden hum apperas?

[corepaul]

I am recording vinyl LPs to CD using my PC sound card to record wave files
on my hard drive. I make the connection from my amplifier headphone jack to
my PC sound card line input using stereo jacks. The amplifier and PC are
across the room from one another and I don't leave them hooked up when I am
not recording something.

When I made the connection yesterday, I suddenly picked up a 60 cycle hum,
audible on the speakers attached to the amplifier. In all my previous
recording sessions, there was not even a hint of any hum.

I disconnected and cleaned every connection in the cable, including the
connection to the PC sound card and to the amplifier. I rerouted the cable
away from any power lines. The hum persisted.

Breaking the connection at any point stops the hum. With the cable
disconnected from the PC sound card, I can drag it across/along power cords
with no hint of a hum. As soon as I connect the cable to the PC sound card,
the hum starts (even with the cord away from power cords). To see if the PC
was generating the hum, I turned off the power strip, stopping all power to
the PC, and the hum still occurs (with no difference in magnitude or
frequency) as soon as I plug the cable into the PC sound card.

I had been having trouble with the sound-out connection on my PC sound card,
having to jiggle it occasionally to restore one stereo channel which had
dropped out. I thought that the plugs for the on-board sound card, several
years old!, might be the problem. I am doing a lot of vinyl to CD
transcriptions and decided it was time to upgrade to 24-bit audio.

I bought and installed a Soundblaster Live! 24-bit card. (I also disabled my
on-board audio card from CMOS) Everything works fine but when I connect the
amplifier output to the line-in/microphone connection on the new sound card,
the same hum occurs.

I am wondering what to do next.

I believe the most common cause of this problem is inadequate grounding but
I am unsure what to try. I haven't knowingly changed anything since
everything worked fine. From the symptoms, it seems the problem is in the PC
(not the amplifier). All power connections to the amplifier, the PC and
peripherals are through power strips - with three plug connections. The
turntable is grounded to the amplifier. There are no additional grounds
provided.

Is this likely something that can be fixed by providing a better ground to
the case of my PC or amplifier?

Or is this likely a problem with the PC power supply?

If my analysis is off base, please let me know. Any other ideas or tips will
be greatly appreciated.

Paul Core

 

[John McGaw]

I am recording vinyl LPs to CD using my PC sound card to record wave files
on my hard drive. I make the connection from my amplifier headphone jack to
my PC sound card line input using stereo jacks. The amplifier and PC are
across the room from one another and I don't leave them hooked up when I am
not recording something.

When I made the connection yesterday, I suddenly picked up a 60 cycle hum,
audible on the speakers attached to the amplifier. In all my previous
recording sessions, there was not even a hint of any hum.

I disconnected and cleaned every connection in the cable, including the
connection to the PC sound card and to the amplifier. I rerouted the cable
away from any power lines. The hum persisted.

Breaking the connection at any point stops the hum. With the cable
disconnected from the PC sound card, I can drag it across/along power cords
with no hint of a hum. As soon as I connect the cable to the PC sound card,
the hum starts (even with the cord away from power cords). To see if the PC
was generating the hum, I turned off the power strip, stopping all power to
the PC, and the hum still occurs (with no difference in magnitude or
frequency) as soon as I plug the cable into the PC sound card.

I had been having trouble with the sound-out connection on my PC sound card,
having to jiggle it occasionally to restore one stereo channel which had
dropped out. I thought that the plugs for the on-board sound card, several
years old!, might be the problem. I am doing a lot of vinyl to CD
transcriptions and decided it was time to upgrade to 24-bit audio.

I bought and installed a Soundblaster Live! 24-bit card. (I also disabled my
on-board audio card from CMOS) Everything works fine but when I connect the
amplifier output to the line-in/microphone connection on the new sound card,
the same hum occurs.

I am wondering what to do next.

I believe the most common cause of this problem is inadequate grounding but
I am unsure what to try. I haven't knowingly changed anything since
everything worked fine. From the symptoms, it seems the problem is in the PC
(not the amplifier). All power connections to the amplifier, the PC and
peripherals are through power strips - with three plug connections. The
turntable is grounded to the amplifier. There are no additional grounds
provided.

Is this likely something that can be fixed by providing a better ground to
the case of my PC or amplifier?

Or is this likely a problem with the PC power supply?

If my analysis is off base, please let me know. Any other ideas or tips will
be greatly appreciated.

Paul Core

If I were forced to make just one guess about the cause based on the
information you provided, I'd say "ground loop". Such problems can be
triggered by seemingly inconsequential actions such as increasing or
decreasing the electrical load on a circuit somewhere else in the house.
One way to minimize the possibility of ground loops is to ensure that
both pieces of equipment (stereo and pc in your case) are plugged into
the same outlet. If that is impossible, making sure that the equipment
is at least on the same branch circuit is a step in the right direction.

 

[corepaul]

If I were forced to make just one guess about the cause based on the
information you provided, I'd say "ground loop". Such problems can be
triggered by seemingly inconsequential actions such as increasing or
decreasing the electrical load on a circuit somewhere else in the house.
One way to minimize the possibility of ground loops is to ensure that
both pieces of equipment (stereo and pc in your case) are plugged into
the same outlet. If that is impossible, making sure that the equipment
is at least on the same branch circuit is a step in the right direction.

John,

How are things in Knoxville? I went to UT from 1966 to 1970. I live in Baton
Rouge, Louisiana now and really miss the mountains. But I digress...

Thanks for the comments. I lugged everything around to get the amplifier and
computer on the same electrical outlet (they were always on the same
circuit) but the problem persists. For the record, my house was completely
rewired several years ago and is up to the latest codes. Your statement;
"... triggered by seemingly inconsequential actions..." is frightening. It
implies that even if I finally find some combination of power source,
location, interconnection, etc. that works today, it might not work
tomorrow.

To increase my worries, I found an on line article on converting vinyl to
digital formats (mcp, wave, etc.) using a PC
(http://www.pcworld.com/howto/article/0,aid,117810,00.asp). The author,
testing two separate phono pre amplifiers (presumably connected on the same
power outlet) encountered ground loop hum with one. To correct it, he
connected the turntable ground to the computer case. The pre amplifier which
did not cause ground loop hum in the author's tests used a seperate 12 VDC
power supply.

This seems a more reliable/predictable/easy solution for me. I ordered a
seperate RIAA phono stereo preamplifier with adjustable output and a 12 VDC
power supply. Now I only have to move my turntable when I need to record
from vinyl. When I move it, I have to disconnect the turntable ground
connection from the amplifier. Grounding the turntable to the computer case
will be easy. The adjustable pre amplifier output will let me leave the
recording software input at 100% (for maximum dynamic range) without
overloading.

Unless you, or someone else, has additional comments or this doesn't work I
don't plan to post any further comments. Thanks again for your help.

Paul