Ever wondered what a Phono Stage is actually for. Here's what it's all about.
It always used to be that when you purchased your new pride and joy amplifier, it came fitted with a Phono EQ stage (sometimes also known as an RIAA stage) already in it. That is to say that there was a dedicated input for you to plug in your turntable.
A cartridge has a very small output (moving magnet at around 5 milli-volt and moving coil at an even smaller 0.5 Milli-volts or 500 micro-volts), much smaller than the output of say your Tuner or CD Player which could be around 2 volts. Because of this your amplifier needs to bring this low level up to a standard line level amount like a tuner or CD Player to work with it. This is done by a pre-amplifier inside of your amp that pre-amplifies the signal and boosts it up before passing it on to the rest of the amplifier to use in a normal way.
It is also worth noting that it is not just a straight forward amplification stage. Because the frequency modulation of a bass note is much much greater than a high note your records are recorded with an EQ curve. If this wasn't the case then bass notes on your record would occupy so much space your record would only last a few minutes and the stylus would be thrown around the groove so much it couldn't stay put! On the flip side the high notes would have such a small modulation on the record that your stylus couldn't possibly pick it up. So in 1952 an industry standard was introduced by the Recording Industry Association of America called the RIAA Equalisation (or EQ) curve. This meant that records are recorded with an exaggerated high end and greatly reduced low end to fit it on the record and give you a reasonable time playing as well as making it possible for your stylus to track the groove. It also greatly increases the signal to noise level. The job of your Phono stage is then to turn this recording back the other way so that it is once again a neutral sound.
By the Late 80's the Compact Disc looked like taking over, and manufactures decided to stop fitting Phono stages in their amplifiers as it was deemed a waste of manufacturing costs. Vinyl looked like going the way of many good things. However, other manufacturers saw a space in the market for producing Phono stages in separate boxes that could then be plugged into any line level input on the back of amplifiers. Apart from meaning that people didn't have to worry about not being able to play there records any more it had one very big plus point. Many of the Phono stages that appeared offered significantly improved audio qualities over the the small IC chips (Integrated Circuits) that many amplifiers were using to run their built in Phono stages.
Up until this point there were very few separate devices to be found, and the sheer lack of number of them meant that they didn't really have much competition with each other. However as the separate Phono stage gained ground they slowly got better and better.
Then in the late 90's the unexpected happened. Vinyl, instead of retiring gracefully from the scene started to become more popular again. As time went by in fact, vinyl went from strength to strength and indeed is now a very popular format once again. This march forward has had the effect of dragging Phono stages along with it.
You now have a great choice of Phono stages to choose from, from the budget but excellent items like the Project Phono BoxS
right up to the incredibly revealing World of the Tom Evans MasterGroove
. An item that is capable of presenting more dynamics and detail than anything before it.