I finally got around to getting a new turntable to be housemate with the typewriter in Retro Corner. There has already been a lot of talk about the Vinyl Revival so I won’t bore you all with my take on the obvious visceral pleasure of dropping a needle on a record over selecting an mp3 from a menu. What I will talk about though (which is arguably even more boring unless you are facing the same problem), is the preamp required by turntables - even many modern ones.
I must confess that I didn’t really do my homework before purchasing my turntable, a Sherwood PM-9805. I did read the odd review and it generally rated quite well, particularly given its relatively affordable price; indeed my own experience so far has been that it is a well-made turntable, let down only slightly by a very tersely worded user manual. The area I needed to look deeper into was the output signal. Although it is true that some modern turntables now have built in preamplifiers allowing them to be plugged into any line-level input such as the garden-variety “Aux” or “CD” inputs we are all familiar with, the Sherwood does not. It is a traditional turntable and either needs to be plugged into a dedicated “Phono” input or first put through a Phono preamp.
Not too worry, I thought. My plan was always to run the turntable straight into my MOTU 828 audio interface and the two Mic/ Instrument channels on the front have preamplifiers built in. I dug out the cables I needed, plugged everything in and spun up a bit of Credence to mixed results. The preamps were working fine, I could get a good strong signal level out of them, but there was a very bad hum through the sound. Not the warm human crackle that I had turned to vinyl for, a loud and mostly unpleasant drone.
It’s about this point that I started to think a bit harder about what that little spade connector at each end of the cable that came with the turntable might be for. A ground to eliminate hum? Hmmm…
The advice I was given was to try attaching the ground to the PC case and make sure the turntable and PC are plugged into the same power circuit. I didn’t get to far down this track as with an iMac there isn’t an obvious way to attach the ground to the case (slip it under the foot? It’s all-metal after all), and the turntable only has a two pin plug, so it isn’t grounded to the circuit anyway.
On top of this hum problem, records need to have special equalisation applied to bring them back to “normal”. This is called the RIAA curve (http://en.wikipedia.org/wiki/RIAA_equalization) and wasn’t hard to replicate using the MOTU’s parametric equalisation.
While playing around with the settings on the MOTU I noticed that changing the phase of one of the channels (left or right, it didn’t matter) the hum was greatly reduced. Surprisingly, the rest of the sound didn’t seem to suffer too much at all so I finally had things working well enough to enjoy listening to those old records on the shelf.
Despite having things reasonably well sorted out, I ended up doing what any right-thinking man (or woman) would do and just buy a Phono preamp instead of trying to hack things together the hard way. I decided to go nuts and lash out the full $25 on this bad boy http://www.jaycar.com.au/productView.asp?ID=AC1662 and so far it has worked a treat. I now use the RCA cable that came with the turntable and I am able to connect the ground lead easily to the obvious spot on the preamp. The sound is good and the two channels on the MOTU with preamps are still free to use with mics and instruments as needed.
So, the moral of the story is that it is possible to get away without a dedicated Phono preamp, but for the sake of saving $25 why make life any harder than it needs to be?