Not necessarily. The needle on a turntable is connected to the rca jacks by some incredibly thin wires. It also produces some seriously low voltages, which is why we need to use the preamp/receiver/whatever to connect the turntable to your computer.
Your turntable probably plugs into the wall... as such, it needs to run through a transformer to step the voltage down from 120 (or 220 in Europe) to a voltage that the motor in your turntable can use. Our lines here in America are AC... at around 60 Hz (50 in Europe.) When the voltage is stepped down by the transformer, the transformer can transmit LOTS of noise to the little wires if they are not protected by... drum roll here... a grounded shield. If you looked at the frequency of the hum, you'd find that it's right around 60 or 120 Hz. The power plug doesn't have to have 3 pins because the AC that you get from the wall has nothing to do with the output from your turntable... it just drives the main motor and the motors that drive the return mechanism on the tonearm. This diagram might help (been a long time since I did ascii art... please bear with me: ----------------------------- Shield ============================= Left wires ============================= Right wires ----------------------------- Shield This is the wire in the tonearm/headshell which shields the wires coming from the cartridge (the thing that holds the needle.) The pair of wires for each channel contains a "ground" wire and a "hot" wire. Music is an AC event, so there really isn't a "ground" and "hot", rather it's the center connector (or connectors) and the outside connector. Once it gets out of the turntable, it goes like this: ----------------------------- Shield (to ground on amp) ============================= Left wires ============================= Right wires Typical RCA cable wiring has a center connector with a connector connected to the "shield". It's cheaper that way, but not always the best alternative. Higher end cables have a pair of conductors down the middle of the wire with a shield that connects at one end so that the ground doesn't pick up too much junk. hope this helps. smiles, Jamie On 3/25/02 7:59 PM, Tom Baker <[EMAIL PROTECTED]> typed: >At 6:03 PM -0800 3/25/02, Jamie Pruden wrote: >>Many do... however, it's usually got some sort of terminal on the end to >>tie in to a ground on the back of the receiver/preamp/whatever. >> >>The hum is the give away... open ground. >> >>smiles, >>Jamie >> >>On 3/25/02 5:39 PM, Tom Baker <[EMAIL PROTECTED]> typed: >> >>>Could it be that the cord from the turntable that plugs into the amp has a >>>ground built into it, so it's actually already grounded? > >But if the hum in the speaker outputs and the headphone jack is from an >open ground, wouldn't the output-to-tape port also hum? Like I said before, >that port doesn't hum, and I can get a clear (humless) recording into the >Mac from it, but because the volume is so loud the music on the recording >ends up clipped. There's where the adjustable preamp could fix things--by >allowing me to turn down the volume. > >This audio stuff is mysterious! -- G-List is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | -- We have Apple Refurbished Monitors in stock! | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> G-List list info: <http://lowendmac.com/lists/g-list.shtml> Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/g-list%40mail.maclaunch.com/> Using a Macintosh? Get free email and more at Applelinks! <http://www.applelinks.com>
