Paul's Posts — 03 August 2012
By Paul McGowan
In the last couple of days I’ve been writing about the end of the analog preamp era and the beginnings of the digital preamp era. That’s sparked a lot of controversy and there are calls for me to either be lynched or certainly sent to my room for a few days. In my defense let me suggest I am NOT suggesting ANALOG is dead – it can’t be and never will be because you have to get to analog somehow to listen to it.
Here’s the thing: none of us should feel threatened by what I am writing. Why? Because reporting about what’s coming isn’t going to change anything other than your awareness. It won’t change the inevitable just because I write about it. I think I now have a clearer understanding of the poor soul who first wrote that airplanes would be replacing trains – or horses replaced by cars. He was probably hated. Isn’t there a saying about shooting a messenger or something? :)
To keep things in perspective, this tipping point we’re a part of in the history of high-end audio is a transition phase which every era change goes through. That means we’re not fully in either paradigm yet – we’re in the crossover period where much remains of one and the growth is seen in the other. This perspective is important to point out because of course there are many use cases where the old is still needed and the new doesn’t yet fill the gap. That’s normal. When photography transitioned from film to digital there was tons of film available everywhere – now it’s harder and harder to find until within a few more years it will no longer exist. That’s the nature of change.
Today let’s cover the output stage of our preamplifiers and note how similar they are and why that matters.
Yesterday I pointed out that all analog preamps have three main elements: input selector, volume/balance control, output stage. Digital preamps also have three main elements: input selector, digital to analog conversion+volume balance, output stage. I lumped together D to A conversion and volume/balance control because in fact they are integral to each other – a subject which I will cover in depth in this series.
So essentially analog and digital preamps are the same, certainly when it comes to the output stage. In both cases the output stage is a voltage amplifier – in many cases a simple op amp (something we covered many posts ago in a 9 part series). I promised many of you I wouldn’t get so technical on you in future posts so let’s keep this simple. A voltage amplifier simply makes a little voltage at its input a bigger voltage at its output.
Perhaps the biggest point to this post is this: a properly designed output stage on an analog preamp SHOULD be identical to the same on a digital preamplifier or DAC. It certainly is on any PS Audio design and it is on any well designed DAC I have ever seen. So why does that matter? Because it means from the perspective of the interconnect cable between the preamp and the amplifier and from the amplifier’s viewpoint, there isn’t any difference between an analog preamp and a DAC/digital preamp.
That’s a very important point to think about because if, from the viewpoint of the power amplifier, there isn’t any difference between an analog preamp and a digital preamp/DAC, then all we are left with is the other two elements in the chain, the volume control/conversion stage and the input selector.
Certainly simplifies things eh? More tomorrow. Now, let me go find that bulletproof vest.
Forward to a friend and help us engage more readers
Related Articles
Share
About Author
(5) Readers Comments
Leave a Reply
You must be logged in to post a comment.
Terry Franklin
From what I have read, you have given us a presentation of the future direction of audio. I see no reason for trepidation.
paulsquirrel
I totally agree Paul, but I would like to have the perspectice of thinking future a little bit enlarged. Why not thinking of a digital preamp with internal room correction and crosstalk cancellation algorithms feeding the data wireless (without the restrictions/limitations of SPDIF) to a digital power amp or active speaker?
For the volume control solution in the digital domain there are high end designs from Meitner and TacT. And wouldn’t it be straightforward having a most precise masterclock in the preamp feeding the sources and power amps?
However you are provoking new ideas that could lead to a renaissance of an active preamp. Actually I was convinced that having a cutting edge passive preamp (see MF audio) there is no need anymore for an active preamp at least when having the phono preamp as a stand alone unit sitting nearest to the tonearm.
Undilutedigital
Yesterday, I argued that Paul wasn’t being bold enough in his digital preamp vision. I argued that the real future is the all-digital amplifier where there is NO analog in the signal path before hitting the speaker terminals. Like Paul, I was misunderstood and probably just increased the flack he took. Analog isn’t going away any time soon, and I still spend many delightful hours enjoying my Rega turntable with its sitll-working Shure V-15. It’s just that that’s not the future. Let’s all agree that the first couple decades of digital recording produced mostly crap, as was nicely detailed in a recent TAS. Those days are (mostly) over, thankfully.
Interestingly, the all-digital amplifier could potentiallly be the BEST WAY to listen to vinyl. You just need a good A/D converter to take advantage of it. NAD claims (I haven’t heard it) that they do autoranging with their phono A/D module for their M2 to optimize SNR. Doing RIAA equalization in the digital doman has distinct advantagnes. One company — can’t remember the name — even compensates for non-linearities in the analog signal chain, including turntable and cartridge, in the digital doman. Analog through an all-digital amp COULD be the best way to appreciate vinyl.
straylight
Yes, as long as we are going blue-sky and thinking big how about a digital control unit (avoiding the term preamp here) that welcomes any analogue signal and is smart enough to detect and irradicate analogue noise, 60 Hz hum, buzzes, even clicks and pops in LP’s. I would consider such a a smart digital device to be a very useful addition to my equipment if it could improve any analogue signal it receives.
oliver T. Finch
As far as audio is concerned it’s all about the quality of sound .A DAC may do all that an analogue preamp does but that does not make them the same. A DAC converts a digital signal to an analogue signal. An analogue preamp does no such thing. It is simply a voltage amplifier. A DAC adds distortion in the process of converting signals in addition to the other shortcomings of digital. These are clearly audible. Saying that since both amplify signals therefore they are the same is incorrect. It’s like saying that since a dog and a cat both .have four legs therefore they are one and the same. We can’t compare apples and oranges.DACs may sell well but it will never be the same as an analogue preamp. They are simply not the same and never will be. Also they will never sound the same simply because they are based on different principals.Regards/