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Given that we're starting to see more and more companies coming to the market with these digital amps I think it would be helpful for those in the know to help us understand what they're all about and why companies are moving to such designs. I won't pretend to know the answers to those questions but I thought I'd start the thread in hopes those that do know will step up and enlighten us.
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Digital amps are also known as Pulse Width Modulation (PWM) amps or Class D amps.
Basically they convert the analog signal into a stream of pulses. These pulses vary in width depending on the voltage level of the signal over time (a technique similar to DSD encoding used on SACDs, and also similar to the way 1-bit DACs work). These pulses are fed into a high-speed amplifier circuit (usually MOSFET design), and then are run through a low-pass filter which converts the amplified pulses back into an analog waveform, which is then sent to the speakers. In essence, a digital amp is a 1-bit ADC and a high-output 1-bit DAC.
The big advantage of digital amps are that they can generate more power efficiently with less heat than analog amps. Since the power switching is digital (full on/full off), the output transistors run cooler. This means a high-power digital amp can be much smaller and lighter than an equivalent analog amp. Another benefit is that a digital signal could theoretically be fed directly to a digital amp, eliminating an A/D-D/A step in the signal path.
As for drawbacks, proabably the biggest one would be the sound quality. I'm sure some high-end digital amps can sound great, but like comparing vinyl to CD, it's hard to make anything digital sound as pure as a good analog setup. Some earlier digital amps suffered from artifacts in the higher frequency ranges, making them suitable only for subwoofer use. I'm sure as the technology matures, digital amps will become more mainstream. Purists will no doubt still seek analog amps though. -
They still seek tubes for that matterPurists will no doubt still seek analog amps though.
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Is there not also a loss of quality as the signal is converted from analogue, to digital, and then back to analog?Originally posted by Kevin P
If that is so, and given that the major advantage of a digital amp (if I read Kevins post correctly) is that it is smaller and runs cooler than an equivalent analog amp - why would anyone but those absolutely squeezed for space buy one?
Trevor
Melbourne, AustraliaComment
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When Jon gets back from his current trip in route to Mininesota, we'll get him to comment. He built his first class D amp in the early 1980's, and published a AES paper about them as well. He was also directly involved with the design and development of the Crown K1/K2 series of amps.
I'm sure he can give everyone an ear full. I should point out that he doesn't use nor does he own any switching amps. That should serve as an indicator as to his views of them for high-end audio ...... :wink:
IB subwoofer FAQ page
"Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-BressonComment
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I too was a skeptic of digital amps untill this spring when we redecorated the master bedroom and I insisted that it was time to have HDTV there also. Since finances didn't allow my first choice, which was a plasma, we wound up with a Hitachi Ultravision 46" RPTV. To get to a decent height to watch from bed, we purchased an accessory stand that is 12" tall and contains 2 glass shelves for equipment. It soon became obvious that I wouldn't fit my Denon 3801, the satelite receiver, a vhs and a cd dvd player on these two tiny shelves. The first victim was the 3801. I first looked at the HK receiver with digi amps and rejected it because of both size and cost. I settled on a recently discontinued Panasonic XR25 100wpc 6.1 receiver. I honestly wasn't expecting very much.Originally posted by dermie999
I bought the receiver after reading a few user comments over at AVS forum, which seemed to have some glowing remarks. One even mentioned the sound being comparable to Krell. I honestly took them all with a grain of salt, figguring...how good could a $250 receiver from Panasonic, no less, sound THAT good????
I wound up having a very pleasant surprise...it sounds fantastic...clean, quiet, solid, sweet. It loves to drive the Klipsch RF15s I have for mains and the RCX4 center to ear splitting levels while remaining composed and never getting harsh. Our MBR is large, larger than most peoples listening rooms, and very dead. I say that not to brag but to illustrate the capabilities of this very small but mighty receiver.
If the potential new offering from Rotel can best the amps in this tiny Panny receiver, which it undoubtably shall, we are about to enter a whole new era in sound.Jerry RappaportComment
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Ladies and Gentlemen,
To put it succinctly, digital is the wave of the future, once it has gone through it's refinement processes (R&D).
My quick thoughts,
AzekeComment
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One of the early issues with digital amps was the noise generated from the high speed switching. This is why they first appeared in subwoofers as the noise could be easily removed by adding a high pass filter.
The technology is not new and Meridian have been using speakers that take a digital input from a preamp for a while. It is only recently however that they have started to see mainstream use.
And as to quality, due to the ability to remove alot of AD and DA from the network and effectively only have one DA (for CD) the quality is able to be higher. But like all analog versus digital arguments the outcome is highly subjective.Comment
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Although I don't actually like the any of the Class D amps I've heard, I would like to point out that most of what we are listening to is digital. The differences are at the point where the DA conversion takes place. For many, DA occurs near the source and often inside it. For others, it is at done at the pre/pro and for even more inside the receiver.
As I see it, the problem with Class D is not that most of them send PWM but that they are starting with a converted analog and re-converting it poorly. Now if the Burr-Brown division of TI were to make a high power A/D amplifier IC, I might go to the store and listen again. It would be even more interesting to see a speaker that actually had filters designed to match the signal of a Class D amp - in a way similar to the filters in a good D/A converter. Still, all of this has to occur at very high power levels.
Until then, I'll stick with Class A and AB. We have already mastered the amplification of low level analog signals and so far, it has proven to be easier and cheaper to have very clean conversion earlier in the chain.
ensen.
PS: Before we get into the usual A vs D, tube vs SS, discrete vs opamp arguments, let me remind everyone that each and every electron is a digital bit, that every vacuum tube is, in fact, a very high-resolution digital device.Those who claim to be making history are often the same ones repeating it...Comment
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Purportedly, the high quality sound of the Panasonic is attributed to keeping the signal in the digital domain until it's output to the speakers (eliminating any extraneous A/D and D/A transitions) except for source material that is analog. I don't know enough about the technology to evaluate it.
Both Panasonic and TACT use TI digital amp chips in their designs. I wonder if any other digital amp designs (based on different chip sets) process the signal in a similiar fashion, i.e. no extraneous D/A or A/D transitions.BruceComment
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As you illustrate, you lose the "ue". Some people barely notice it. :BOriginally posted by dermie999Comment
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I use a digital power for more then 2 years now the EarTwo and I'm very happy.
This is not a realy cheap amp 3500euro's. So I think digital amps good be good but it is true that there are also a lot of bad sounding amps.Comment
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