Class D come of age - Coherent amplification

[Mr. C]

It's only words so not really of any importance but...is there a solid definition of class d? People generally think of class d as denoting a digital amplifier when they are usually PWM. We can also think of "d" the as being a random letter which people then unfortunately ascribe to meaning digital. I think of class d as being predominantly PWM (switching) amps.

Clive

Wiki's answer to Class 'd'

The term "class D" is sometimes misunderstood as meaning a "digital" amplifier. While some class-D amps may indeed be controlled by digital circuits or include digital signal processing devices, the power stage deals with voltage and current as a function of non-quantized time. The smallest amount of noise, timing uncertainty, voltage ripple or any other non-ideality immediately results in an irreversible change of the output signal. The same errors in a digital system will only lead to incorrect results when they become so large that a signal representing a digit is distorted beyond recognition. Up to that point, non-idealities have no impact on the transmitted signal. Generally, digital signals are quantized in both amplitude and wavelength, while analog signals are quantized in one (e.g. PWM) or (usually) neither quantity.

[hornucopia]

....then you get to which speakers you are listening to the resulting sound on/with.
"—it’s amazing how well a superior single driver can perform' I just read (in a review of Nanotech cables!)
which I was agreeing with, as i was listening to my Ocellias for the first time in WEEKS!
We'd better not get started on the effects of cross-overs on the sound!

I agree with Geoff on power consumption, as my Pass F3 uses 250 watts -I think- to produce about 6 o/p!
on we go.

[George47]

Confusing guys. Class D was the next type of amplifier after Class A, Class B and class C etc. Any additional A/D converters are not necessary or really part of the Class D amplifier but just an additional stage. Class D can be PWM or pulse density modulation.

There has been a great deal of discussion on what the impact of the remnants of the switching frequency has on the audio and what happens to the mains due to the switching noise and the SMPS. Any measurements on distortion normally have to have a filter applied to remove the remnants of the switching otherwise the numberes can become nonsense. Some have argued that applying the output filters to remove the switching frequencies can impact the phase of the audio. A way around this problem has been the deployment of new GaN rather than Mosfets, which are operated at a much higher switching frequency. There are a few GaN amplifiers around and some have been very impressed with them. Bruno Putzeys was less impressed with GaN when I recently talked to him. Not needed.

Tony is this a GaN Class D amp?

[Mr. C]

Hi George

Something a little different, why not pop over and have a listen it may cause you to think somewhat it is. The evolution of the one we discussed at the show back in October

Tradition FET's even the new SIC types still have limitations and banks of FET's again gave there own issues in balancing, feed rail supplies, heat sink space etc

Remember the power supply on a pwm has to absorb a percentage of the output power (with a full bridge thats both rails)as one of its has traits along with aligning clock speeds along with particular null point in the switching spectrum that suits the particular module being used

The older t class used to switch around 1.2-1.4mhz and they used just one pair of FET's per channel to respectable effect

There is no black art here just common sense, and looking at the design from all aspects and taking your time to truly understand how and why each piece of puzzle has a direct effect on the soun. Also employing the services of an RFI engineer to help assess the impact of said design within the constraints of the what effect said interference has while also keeping within the boundaries of the CE regulations for such products

[Edward]

Sounds interesting.

I was convinced that PWM amps had a bright future when I heard the TAD PWM amps driving their speakers at a show about 3 years ago. The speed, openness, fluidity and detail was breathtaking (helped of course by the TAD speakers).


Tony I had a look at your website for more details of your PWM implementation, such as form, specs, price and pictures, but did not see anything. Any chance please of putting something up (here, on your website or directly to me) please?

Cheers
Edward

[montesquieu]

Sounds interesting.

I was convinced that PWM amps had a bright future when I heard the TAD PWM amps driving their speakers at a show about 3 years ago. The speed, openness, fluidity and detail was breathtaking (helped of course by the TAD speakers).


Tony I had a look at your website for more details of your PWM implementation, such as form, specs, price and pictures, but did not see anything. Any chance please of putting something up (here, on your website or directly to me) please?

Cheers
Edward

I had a Lyngdorf PWM power amp a few years back and thought it was pretty good with a Tannoys. I’m sure the technology has come a long way since that amp which was already an older model. Be interesting to see where this goes.

[Mr. C]

Edward

It is a brand new design currently testing with some respected beta testers in different systems across the uk, there are three amplifier designs currently. We have been testing the water for six months but these amplifiers have taken twelve years to come to fruition.

These will be 100% UK manufactured and built, the amps are called liquid music the clue is in the title I firmly believe we have now got so close to 2A3 fluidity without the draw backs it is worth bring to the attention of people.

Those that have listened to them have demonstrated immediate interest and the majority have been high quality valve owners, hence why we are taking this further.

It is not a magic bullet or will appeal to everyone, however those are are really interested in truer reproduction of recorded sounds will seek out an audition, whether they wish to take further will be a personal choice nothing more as with everything in audio your ears and sysyem will tell you if it is right for you and you alone.

I take it you were referring to the Windsor show a few years back Edward?

Tad speakers are superb, however you get what you put in and some amplifiers just do not deliver the results you would expect, a few well know pwm models among them.

We have a demonstration which maybe available for those interested in trying out these amps, I would suggest a pm rather than clogging up this thread

Edward
That particular amp was residing in a system very close to you up until a few weeks it is a shame you could have dropped in on that system and listened for yourself

[Edward]

Thanks Tony for your most comprehensive response. Yes it was at the Windsor show about 3 years ago and since then in Munich the TAD experience confirmed the view.

Edward

[Discopants]

I had a Lyngdorf PWM power amp a few years back and thought it was pretty good with a Tannoys. I’m sure the technology has come a long way since that amp which was already an older model. Be interesting to see where this goes.

I splurged on a black Friday deal TDAI3400 , its bloody brilliant bit of kit, very musical and the DSP is incredible. I only stream spotify and listen to you tube and TV via an apple TV. So its almost a one box solution. I cant detect any noise in the TV or the apple TV or the subwoofer from the switched mode power supply either audibly or visually.

[Edward]

So I have had on test for about a week now Tony's LM1 version of his PWM amp. In a short sentence the experience has been stunning - and highly disruptive.

Stunning in the liquidity, detail, speed it is able to perform. Disruptive in the sense it has taken me so far down the road as to what I thought an amp is able to do.

The amp Tony lent me is his smallest amp being 85w, the next ones up are a 125w and then 220w monos.

I have thrown everything I can at the amp and without fail it just gets on with the job. Absolutely sublime sound. I simply can't fault it.

Massive grip as well as stunning shimmering highs. The detail and speed are the major magic of the amps. But also the overall coherence, things are 'just right'.

I've had the amp driving Tannoy Eatons and Kudos Cardeas - both are handled magnificently by the LM1. The music is delivered perfectly. I've been listening to albums I know very well and hearing them in a radically new light. The detail that is extracted is so refined that one can almost visualise the instruments being played. Soundstage is deep, wide and high. Pinpoint accuracy. Totally non fatiguing. Highly emotional.

Tried various preamps and again the LM1 faithfully and honestly delivers the sound.

Adam (westlower) has heard this amp in an extended listening session as well. He can report on his views separately, but I did see a wide smile from him when he was listening.

Tony says he has some further 'tuning' he can do which will deliver 20% more. I can't imagine how it is possible.

Sadly the loan will end sometime this week.