Hi there, I have a NAD T742 where i'd like to connect a turntable. I also have a NAD preamp, but i can't find the aux connection. Where should i connect the preamp? Thank you!

Everything you need to know about hooking up a vintage turntable First things first - the simple setup: If you're hooking your vintage turntable to a stereo receiver or amplifier that has jacks on the back marked "PHONO," it's easy: Plug the matching cables coming from your turntable in the phono jacks. Most likely (but not always) there's also a skinny single wire coming from the turntable. This is called the ground wire. Attach it to a post or a screw (usually labeled "GROUND") on your stereo (more on that below). Plug in the turntable's power cord, set the function on the stereo to "phono," and you're ready to go. Just be sure not to put the turntable too close to your speakers! (More on that below, too.)
If you DON'T have a phono input on your stereo, or if you're just hooking your turntable up to powered speakers, headphones or a sound input on your computer, the rest of this document is for you. (Note that I'm NOT going to discuss turntables with USB outputs because those aren't vintage.)
Unlike most audio sources you connect to a stereo (DVD/CD players, iPhones, etc.), the output from the cartridge on a vintage turntable is MUCH lower. It requires additional amplification and some EQ to bring it up to a proper signal. This additional amplification is called a phono preamp. Phono preamps are built-in to older receivers and amps(see above). Some preamps are even built into some models of inexpensive (plastic) modern turntables (check the manual). In general, newer stereo gear, including most mini-systems, Bluetooth speakers, home theatre units, etc. don't have phono inputs. To use a vintage turntable with these newer units or to play through a computer, powered speakers or headphones, the turntable signal must pass through an external phono preamp. You'll then plug the output from the phono preamp into line-level inputs on your gear (these may be marked Aux, Tape, Line, Video, CD, etc).
Note: If the input on your speakers or stereo is a stereo mini-plug jack (like the headphone jack on an iPod), you'll also need a 3.5mm Mini Plug to RCA stereo cable. These are inexpensive and very common, typically used for connecting iPods or smartphones to stereos with two RCA plug (left and right) inputs.
Which external phono preamp should I buy?External phono preamps range from under $20 to thousands of dollars. For the casual user, you don't need to spend a lot to get decent sound. The units below are listed roughly in order of increasing quality:
Pyle PP999 (~$15) - Bargain basement basic unit
Behringer Microphono Pp400 (~$25) - Basic unit with both RCA and ¼" stereo outputs
ART Pro Audio DJPRE II (~$49) - Higher quality basic unit * Best deal here!
ART USB Phono Plus (~$79) - Same as above with USB output
TCC TC-750 or TCC TC-750LC (~$44 and ~$50) - Other high quality units in this price range.
Remember - any stereo unit that has a "PHONO" input has the phono preamp built in already! You don't need to buy a separate unit. And even an old stereo unit that is "broken" may still be usable as an external phono preamp. If the unit powers on, try plugging the turntable into the "Phono" jacks and take the output from the "Tape Out" jacks, then plug those into an input on another system.
What do I do with the skinny wire and/or why is there a buzz?
Most turntables have a thin "ground" wire alongside the phono cables. Not connecting the ground wire will result in an unpleasant buzzing. If no ground wire is present on your turntable, you may not need to worry about it, but always look to make sure no one's amputated or unplugged it. Older stereos have a marked connection point for this wire. Some external phono preamps have one too. This is the best place to connect the ground wire, especially if using with a computer sound input. Some inexpensive preamps have no dedicated ground terminal; try connecting the wire to the preamp's metal back plate using any means available. You'll know when you've connected the ground wire because the buzzing will stop.
Why is my stereo marking a horrible noise when I play the turntable above a certain level?
The cartridge on a turntable is very sensitive to vibrations (it's supposed to be - that's how it extracts the music from the grooves). If your speakers are close enough to the turntable, the cartridge will pick up the low frequencies and you'll get a very unpleasant form of acoustic feedback. It can ruin your records, your needle, and even your speakers if it gets out of control. The solution is to make sure that the speakers and turntable have a good bit of distance between them, and they shouldn't be on the same surface. Another handy hint - the more stable the surface, the better your turntable will sound.
Okay, how do I set it up to play properly? What's with the numbers on the dials and/or the weight at the back of the tonearm? What is anti-skate and how do I set it?
There are no easy, cut-and-dried answers to these questions. While many turntables have fairly simple and standard adjustments, there are endless variations and some have no adjustments at all. Your best bet is to go to the Library at Vinyl Engine (you will need to create an account) and download the users manual for your turntable model. You will also need to know information for your particular cartridge/stylus, specifically the tracking force (VTF). Most cartridges have an entry in the Cartridge Database at Vinyl Engine.
As a general rule of thumb, a "safe" default tracking force is between 1.5 and 2 grams for most hi-fi cartridges. Ones specifically made for DJs track a bit heavier, around 2 to 4 grams. Anti-skate (force that helps the stylus stay centered in the groove, sometime called "bias") is usually set the same as the tracking force.
How do I record digital files (MP3s, FLACs, etc) from my records?
This operation is also referred to as a "needle drop." From an old receiver: hook the tape out jacks to the sound input on your computer. From an external preamp: hook the preamp outputs to a computer input. Use audio editing software (Audacity is an example, and is freeware) to record. Try Google for more details.

Connections 3 or 4 on preamp. Turntable requires pre amp out from preamp to amp.