Adventures In Audio with Audio Masterclass

Well, could *you* hear the difference? Could you??


Take a look here and you will find audio examples of three microphone preamplifiers. One costing over $1500, another around $200, and a third a mere $5. Audio Masterclass (prior to our migration to Auralize) visitors were asked to identify which preamp was the most expensive, and which preamp was the cheapest of the three. Well the results are in, and here are the votes cast as of Jan 13 2006…

Microphone A, by the way, was the humble Shure SM57. Microphone B was the Neumann U87 Ai. Each set of three tests used the same mic at the same distance.

Most Expensive Least Expensive
Preamp A 8 19
Preamp B 28 7
Preamp C 18 24

The clear winner is Preamp B, which I will tell you more about shortly. In second place is Preamp C, which is the Universal Audio LA-610 Classic Tube Recording Channel – a single channel preamplifier costing around $1500 and therefore the most expensive. Yet it didn't win. In third place is Preamp A, which is the infamous Behringer Ultragain Pro MIC2200, complete with LEDs to make the tube appear to glow. Most people identified this as the cheapest sounding preamp, yet it is not the cheapest – it just, apparently, sounds cheapest.

So – shock news headline – by a margin of 28 to 18, it is the five dollar preamp that people feel sounds the most expensive. And here it is…

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“What on earth is that?”, I hear you say. Let me tell you the story…

In September 2005 I was working with students in Audio Electronics classes. The object of the classes wasn't to turn them into electronic designers, but to give them a feel for the inner workings of the tools of the Sound Engineer's profession. So we made some audio circuits and tested them, objectively and subjectively. And this is one of the circuits we made. I say 'we', but the students did the making and I did the checking of connections to make sure not too many components got fried.

This preamp has at its heart a Texas Instruments INA217 mic preamp integrated circuit, which is widely regarded as state-of-the-art, even though it is inexpensive. The circuit was constructed according to the data sheet, with a few features left out for simplicity. You can see two IC's on the circuit board above. The lower one is actually a completely different amplifier that we had constructed on the same board. In the photo above, and in the test, it was totally disconnected. The power supply consists of the four PP3 batteries you can see to the right of the picture.

Once assembled, the first test was with the Shure SM57 microphone, recorded into Pro Tools using the Digidesign 888/24 interface. The results seemed promising, so at that point I decided to make comparison recordings with the other two preamps, which just happened to be to hand. I played these recordings to an associate who commented that I should try similar recordings with a U87 mic. To do this, we had to add phantom power to the preamp, which is provided by the five PP3 batteries to the left of the photo.

After the tests were recorded, it seemed like a good idea to upload the files to Audio Masterclass for your enjoyment. To make the circuit simpler to construct, a fixed gain of 50 dB was set. This proved to be too much for the U87, which has a higher output than the SM57 and clipped the audio interface, so I stood a little further away. This accounts for the increase in room ambience, and for the lower LF content because of the reduced proximity effect. I could have clicked in the pad on the mic, but in the moment I chose not to. The change in microphone does not affect the preamp test. For each set of preamp recordings, the mic and distance were the same.

So in conclusion, well at least my conclusion because I am sure you will have your own too, it says a lot that a preamp assembled from $5 worth of components and not even mounted in a box can compare favorably against a preamp costing $200, and another costing $1500!

Your comments will be very welcome.

David Mellor

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David Mellor



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