Gain Without Pain: The Whys, Hows and Huhs? of Phono Preamps

On February 16th 2016 » By Ed Selley

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Part of the process of owning and listening to vinyl takes on the from of an incantation at times. Almost without thinking consciously about what we are saying, some phrases come almost pre loaded into our thoughts. There are a few of these commonly encountered anywhere where vinyl playback is being discussed, but none of them come close to the simple throwaway line- "you'll need a phono preamp." It is tacked onto any discussion of amplifiers or receivers almost as an afterthought, a back covering exercise to ensure we aren't blamed for something not working correctly.

This hurried little phrase does tend to mean that we also risk regarding phono preamps as a part of the system that is vital to it functioning but ultimately doing a process that is pretty simple like wheel nuts on a car. Sure, you're glad they are there and you don't want them removed but if you've bought a respectable set of nuts, that's all there is to it right? Well, as with a great many areas of analogue playback, it isn't quitethat simple.

What a phono preamp does is perform a process on a scale that almost no other part of the rest of the audio chain comes anywhere near matching. Rather than being a bolt on that ensures that a system works properly, it is shaping the performance of your turntable and how it works with the rest of your system to an extent that no other part of the vinyl replay chain can match.

So what is this process? Simply put, a phono stage adds gain to the output of a turntable so that it can then be received by an amplifier and the signal amplified for use for your speakers. Behind this one sentence explanation is a process that is one of the more intense engineering challenges in audio engineering. The reason for this is that the amount of gain being added to the signal by a phono stage is enormous and the process of doing this well is no small undertaking.

On any record player, electrical power is only applied to the process of spinning the platter. The tonearm might in some cases be moved on and off the record by electricity but the actual pointy end, the stylus of the cartridge is not the recipient of any of this power. The signal from a turntable is generated only by the movement of the stylus being converted into an electrical signal. And this signal is feeble. If we take the Ortofon OM5e- the cartridge fitted to most entry level Pro-Ject turntables and a great many other decks besides, you get an output of 4mv. When you consider a potato- that well known powerhouse of electrical generation- can produce 5 volts of electricity, you can see the numbers involved are on the low side.

A conventional phono stage would be looking to produce an output of 300mv for an amplifier to have a reasonable chance of producing a healthy level of output. In other words, the signal has to be amplified by seventy five times to be of any use to your amplifier. If you decide to go down the road of moving coil cartridges which have an output that is much lower than our example Ortofon, the situation is even more extreme. If you decide to buy an Audio Technica AT33- a very respectable and not too crazily expensive moving coil cartridge, your phono stage is going to have to amplify the signal by one thousand times to produce 300mv.

Roll that figure around your head for a moment. If we were to take a 4K ultra HD TV as an example, a moving coil phono stage would be creating a picture to fill 2360 lines of screen with less than two and a half lines of signal (or a generous 31.4 if you have a moving magnet cartridge). This is a signal boost on a scale that is absolutely enormous. And because the signal is so limited, the problems with creating that gain are substantial. If your phono preamp creates noise at the early stages of this gain creation, by the time it has finished, you will have an awful lot of noise with your signal to say nothing of extra noise being added at different stages the process.

As a result, a phono preamp should not be seen as a throwaway incantation but a seriously important part of your vinyl playback that has an enormous effect on how your turntable will perform. The good news is that a respectable phono preamp need not cost the earth. Standalone models from companies like Pro-Ject, Music Hall and Cambridge Audio start from around the $100 mark. By the simple dint of these phono stages being in their own chassis with their own power supplies, they can be quieter than the models built into affordable amps and turntables as the sources of interference and noise will be less.

Equally, as those back of an envelope gain calculations have hopefully shown, the benefits of more expensive models are unlikely to be purely theoretical. The improvements in signal to noise, channel separation and distortion are going to be clearly audible and hugely beneficial. The very best phono stages are uncannily quiet in operation and the effect they can have on vinyl replay is truly astounding. More advanced designs that can alter their input settings to more closely match the characteristics of your cartridge can also demonstrate eye opening performance.

On a more subjective level, even the most studiously engineered phono preamps tend to have a character all of their own because so much of the signal being received by the amplifier is down to them. This does mean that if you can get to listen to a phono preamp before you hand over the cash, you might be saving yourself a lot of grief in the long run as many people (myself included) find them second only to speakers in terms of subjective preference. I'll hopefully be making some recommendations for this blog in due course.

The phono preamp is an unsung hero that deserves consideration and care in choosing the right model to work for you rather than a little incantation to be uttered during system building. So, the next time you pop a record on, consider that part of your system is performing a minor miracle in order for you to hear what's in those grooves. They aren't generally very big but they're certainly very clever.

Happy listening.

Ed Selley

Ed Selley

Ed is a UK based journalist and consultant in the HiFi industry. He has an unhealthy obsession with nineties electronica and is skilled at removing plastic toys from speakers.

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