The famous $5 preamp - everything you need to know
A few years ago, we published an interesting test of microphone preamplifiers. And, for your pleasure, here it is again...
Three mic preamps, one costing over $1500, another mid-price, another that cost just $5. Can *you* hear the difference?
Three mic preamps, one costing over $1500, another mid-price, another that cost just $5. Can you hear the difference? I'll admit straight away that this isn't a scientific test. It just kind of happened on the spur of the moment, hence the air conditioning noise in the background of these recordings.
However, I think you will find the recordings interesting. Three different microphone preamplifiers were used. One has a list price of well over $1500, another costs around $200, the third costs less than $5. Yes, five dollars.
The obvious question is, can you tell which is which?
I made three recordings using each preamp in turn, then three more similar recordings with a different microphone at a greater distance, allowing more reverberation to be picked up.
Let's label the mics A and B, the preamplifiers 1, 2 and 3. So here are the recordings, all in 16-bit .WAV format...
(Notice that the preamps are in the same order for both A and B mics.)
- Which is the most expensive preamplifier? 1, 2 or 3?
- Which is the least expensive preamplifier? 1, 2 or 3?
- Optional comments on the sound qualities you perceive.
Please post your answers in the comments section below. (If you're at all worried about getting the answers wrong, then you'd better give your name as 'anonymous'!)
This challenge is now closed. You can see the answers here...
That was the first article, and there were quite a number of responses. Here is the second article in the sequence...
A recent Audio Masterclass feature demonstrated three microphone preamplifiers costing from $5 up to $1500. Could Audio Masterclass visitors hear the difference? (Apparently not!)
Take a look here [The link in the original article referred to the previous test, the text of which is presented above] 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 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...
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|
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 [at the time the article was written] 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...
"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.
We're having a little trouble retrieving the comments from our old database, but when we have done that, we will include them here. In the meantime, here is the third article in the sequence...
Fresh from a comparison test against preamps costing $200 and $1500 - which it beat handsomely - the secrets of the $5 preamp are at last revealed.
If you're not up to speed on this topic, you need to read this article, and listen to the audio examples carefully. When you have made your judgment on which is the most expensive preamp, you can see the results here.
In summary however, significantly more people judged the $5 preamp to be sonically the most expensive sounding. To be fair, the test was limited, but even so, surely a $1500 preamp should have proven its mettle in comparison? Surely it should have blown away the $5 home-made one?
Since the tests took place, several requests have been received to see the schematic of the $5 preamp. Well it certainly isn't a secret. The preamp is based around a Texas Instruments INA217 integrated circuit, using the schematic provided on the manufacturer's data sheet. You can see the schematic right below.
But the $5 preamp doesn't even use the full circuit. R3 and its associated capacitor are intended to reduce any click when phantom power is switched on. The $5 preamp doesn't bother with that.
The four diodes you can see are protection for the IC against unexpectedly high input voltages. Omitted.
A2 is a secondary op-amp intended to eliminate any DC offset in the output. Well Rupert Neve didn't always bias the output of his push-pull stages to zero volts, so why should the $5 preamp do that either?
So basically the circuit is what's left. Not much is it? Oh, and the power supplies... the power for the IC was from four PP3 batteries, wired to give +18 and -18 volts, which is the maximum the INA217 is specified for.
Phantom power was supplied from five PP3 batteries wired in series to give 45 volts nominally. One commentator remarked that this "seriously under-powers the Neumann U87 microphone". This is not so. For one thing, new batteries will give higher than their rated voltage. Secondly, a microphone that couldn't operate on 45 volts instead of 48 simply wouldn't be up to the job of meeting real-world conditions. They're not that stupid at Neumann - they rate the U87 for 48 V +/- 4 V, and I suspect there is some margin beyond that.
It might be that it's the battery power supply that gives the $5 preamp the edge over the others. In my earlier tests, I found that I was spending an inordinate amount of effort getting a power supply derived from AC to be quiet enough, so using batteries eliminated that problem and perhaps produced a benefit.
One thing's for sure. The cat's among the pigeons and feathers are flying.
Would anyone care to repeat my test?
A while later we reprised the $5 preamp...
Is it really possible to get a state-of-the-art mic preamp for just $5. Possibly it is. So why would anyone pay $1500 or more?
The Audio Masterclass website has been going for quite some time now. And certain articles from the archive keep on raising interest and questions. And none more so than the ones about the famous $5 preamp. A giant-killer in miniature.
One story I didn't tell at the time was about the 'boutique' 8-channel preamp I once owned. The reason I owned it is because I had it for review, it worked fine and I needed an 8-channel preamp, so I made an offer.
That preamp normally sold for somewhere around a thousand UK pounds. That's around 1500 Euros or $2000 US dollars. Not cheap therefore.
Unfortunately it eventually developed a fault. I'm not recommending you do this yourself, but I thought it might be a good idea to take the lid off and see if there was something simple and obvious that was wrong.
I was astonished...
There was hardly anything inside. In fact the 'boutique' preamp was nothing more than a few integrated circuits, resistors and capacitors. And the main integrated circuit for each channel was the SSM2017 chip which you could shortly before that time buy for around $3 in small quantities.
It was in fact this chip that had failed on seven of the eight channels. This happened after several months of only using one channel, and then suddenly having the need to use all eight.
Since this chip had by that time gone out of production, I replaced it with the INA217, which is the successor to the SSM2017 and is the same chip as used in the $5 preamp. It worked fine.
Shortly after that, the unit received a 'drop test' and sustained serious damage, so I scrapped it.
Always ready to learn lessons, I noted two things from this...
Firstly, an expensive preamp might be nothing more than inexpensive components in a fancy box.
Secondly, the SSM2017 and INA217 sound damn good!
Oh and thirdly, don't drop a $2000 preamp.
So, over to you. Everyone is entitled to their opinion on preamps and there are no rights nor wrongs.
What do you think about preamps based on cheap chips? And are expensive 'boutique' preamps really all that much better?
Following this, we received some messages by e-mail...
In response to Is it time for the $5 preamp to make a comeback?, H.C.D. Studios writes...
While it may be true that you can find a great sounding chip in most cases pres that are based around a chip sound kinda blah. Over time transistors repalced tubes as gain blocks, then ic's were developed to make things smaller and cheeper. I have used every mic pre from $40 tube pre (with ic) boxes to avalon, real vintage Neve, 610 tube, SCA handmade, amek, crane song and the list goes on.
The thing is that all those pre's have a sound of their own. If you open up a behringer box you see lots of chips. While they are functional they sound like shi* compared to say, any of the ones listed above. If you have ever built a SCA (or other kit) pre you can see what goes into a discrete circut.
There is a reason that you pay so much for classic circuts. They have lots of componants and many are hand wired. This whole discussion could go round in circles till we all drop dead. F the gear if the song aint great even a $4500 mic pre won't help. A C12 won't make a great singer it just captures what you put in front of it.
In response to Is it time for the $5 preamp to make a comeback?, Chris writes...
Hello Audio Masterclass,
I love the $5 preamp story. One question, I understand that you had some difficulties powering the unit, hence went with batteries. Do you have any new insight into powering it so I can build one without obtaining an EE degree?
Audio Masterclass's response: We used the batteries to solve an immediate problem and in doing so removed a potential variable. You don't need a degree to understand voltage stabilizers followed by heavy capacitative and inductive filtering. It's outside the range of topics of this site for now, but the topic is normally covered in basic electronics text books.
In response to Giant-killing $5 mic preamp - its secrets revealed, Antti writes...
Thanks for the great point-out to these pre-amp schematics. I've got one rather stupid question, though. How are the four 9V batteries supposed to be wired to give both +18V and -18V? Can't you just use two and connect them together to give 18V, and then connect the + and - ends to the suitable connection points provided by the schematics. Or if I use four batteries, where am I connecting the extra + or - ends that I'm left with, when I connect two and two together?
Audio Masterclass's response: If you connect them all in series, then the midway point becomes the 0 volts reference and the two ends are +18 and -18 volts respectively.
So there you have it, the full story of the amazing $5 preamp!