New Posts New Posts RSS Feed - Class D Amplification
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Welcome to the Graham Slee Audio Products Owners Club

 

Open to all owners plus those contemplating the purchase of a Graham Slee audio product wishing to use our loaner program: join here
Subscribe to our newsletter here (Rules on posting can be found here)


Class D Amplification

 Post Reply Post Reply Page  12>
Author
Bags View Drop Down
Regular
Regular


Joined: 14 Apr 2018
Status: Offline
Points: 43
Post Options Post Options   Thanks (0) Thanks(0)   Quote Bags Quote  Post ReplyReply Direct Link To This Post Topic: Class D Amplification
    Posted: 30 Apr 2021 at 7:52am
Given how trendy class D seems to be coming, I'd be interested to hear Graham's thoughts on the subject.  Big power numbers don't interest me but efficiency should interest us all these days.

Apologies if there is already a thread on this topic, but because of understandable limitations with the forum Search I failed to find it.
Back to Top
Sylvain View Drop Down
Senior Member
Senior Member


Joined: 18 Jan 2010
Status: Offline
Points: 193
Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2021 at 11:04am
Yes and I have been trying same for some time .

You can't avoid it...portable and programable and realistic but is it audiophile ......for me my ears are tuned at Acoustic instruments, natural musicality  and D' class cannot cut it ...

Graham, Proprius analogue transistor allows portability and small enprint.. 

i recall T, Z class in late 1990's to 2005 with overwhelming bass but that is all.  
Back to Top
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Telling it as it is

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 10802
Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2021 at 6:01pm
Pulse width modulation is one way of shying away from tackling thermal runaway. So is current dumping.

Whatever the pulse rate, it always produces noise. Take charge-pulse DC to DC converters as an example. For audio, it has to be above our hearing, so if generating a 9V rail from a 5V rail (as in the Voyager), a low rate can be heard as a high pitched whistle, so we take it beyond the audible range.

However, once it becomes a fundamental part of the audio signal, which will be 'inconveniently' subjected to transients, you have a variable and choppy interference generator. Left without output filtering, it will transmit via the speakers and cables as interference. To remove as much as possible, magnetics (ferrite cored inductors) are used to filter the HF noise. They can only go so far, and there will always be a residue. However, the interference remains inside the amplifier circuit (and power supply) and must result in some signal deterioration.

Like aliasing distortion, sum and difference frequencies are inevitable, and although the residue might be in fractions of a volt, domestic listening levels aren't much higher. Beat frequencies occur inside the audible range, which is no part of the original signal and will coincide with elements of the music, leading to fatigue.

Class T reduces fatigue by sweeping the pulse rate up and down within the limits of the magnetic filters to avoid repetitive beat frequencies and reduce listening fatigue.

Nevertheless, there are always beat frequencies (heterodyning), which can never be classed as high fidelity. Class D serves a purpose for arena and stadium sound, where the emphasis is on loud energy, but it isn't high fidelity. For quality public entertainment, a suitably biased class B amp will always produce a better atmosphere and lead to greater audience satisfaction.

Obviously, with no quiescent current flowing in the output stage, class D will consume less energy than class B. However, the pulse generator and comparators consume current of their own unless they can be shut down in 'standby'. If conventionally powered, there will be little comparative energy saving. A switched-mode power supply is required to save idling energy, but there will be little difference in wasted energy between class D and class B when so powered.

With care, class B can be designed not to go into thermal runaway, and in a 100% up-time (always on) design, that's imperative. The 70's amp now idles, consuming about 12 watts per channel with minimal quiescent voltage drift.

Not simple enough for Google-Bot to understand...
Back to Top
peterb View Drop Down
Senior Member
Senior Member
Avatar

Joined: 02 Feb 2017
Location: Cornwall
Status: Offline
Points: 196
Post Options Post Options   Thanks (0) Thanks(0)   Quote peterb Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2021 at 7:33pm
I have used a purchased 200W Class D Amp for a small, homemade sub-woofer, worked out to be a successful application. I only use it for watching Films so it is not 'always on', just when it can add to the atmosphere/feelBig smile of what we are watching.

Peter
---------------------------------------
Dual 505-1, Cyrus CD T, DIY 80W MosFet amp and PreAmp, 2xKEF 103.2
Back to Top
Sylvain View Drop Down
Senior Member
Senior Member


Joined: 18 Jan 2010
Status: Offline
Points: 193
Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 01 May 2021 at 9:34am
If '' Technical expertise allow
For my lay man head ...I dream of a 8 to 12 Watts of Pure Analogue  Class A for High Mid frequencies perhaps with a Valvee flavour  and a Class D digital for Bass and sub bass .

Could also need an electronic Cross over ....to integrate the frequencies and environmental acoustics dispersion 
Back to Top
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Telling it as it is

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 10802
Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 5:34am
Twenty years ago, I couldn't get any sense out of Ferranti regarding their Zetex class D chip and magnetics set. They gave me the class D board to assemble into a giant "ghetto blaster", which was being built by a theatrical model maker in Sheffield. I was working sub-contract to my friend Darryl who was managing Farranti's USA exhibition.

My part of the job was designing and making the RS232 multiple relay interface to operate the "ghetto blaster" driven by a simple MS Basic sequencing program. Additionally, they wanted a random lamp driver with a stop button to achieve a similar effect as the "Catchphrase" TV quiz screen - it being used to emphasize the marketing bullet points about class D.

I'd attended meetings with the engineers and marketing people in the Oldham factory. All the manufacturing labs had been mothballed, so I assumed the engineers were the designers - after all, the random lamp exhibit boasted far-east production. I'd expected them to send the class D amps as some form of ready to use module to the theatrical model makers, who were to combine it and my control electronics into the "ghetto blaster".

A small board assembly was delivered to my address - no covering letter or datasheet - just the board assembly, to my surprise and horror. It turned out to be the prototype sent from the far east, and Ferranti expected me to produce the amplifier module, probably by ESP!

Darryl and I took turns phoning the Ferranti "engineers" to obtain sufficient data to power the thing up, give it an input, and figure out how to connect the speakers. I think the word I'm searching for is 'clueless' in describing what followed. "Oh yes, the chief engineer will be able to tell you, but he's on leave." Eventually, one of the engineering bods phoned and talked me through the pinout and suggested I try X volts and Y amps and "hope for the best."

It was an educated best guess, and it did work, producing an impressive sound from such a small far-east PCB assembly - that is with a linear power supply several times its size - made in England by me!
Not simple enough for Google-Bot to understand...
Back to Top
Sylvain View Drop Down
Senior Member
Senior Member


Joined: 18 Jan 2010
Status: Offline
Points: 193
Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 9:06am
I have been building a speaker from a 'Falcon Acoustic' KIT ...and whilst they are do ' Cross overs '', DIY is an opportunity to input personal investigation and development. 
Class D is here to stay but true acoustic reproduction can only be achieved with volume of air in a hollow cavity box and bass and sub needs air volume. Mid and high need diaphram needs a very controlled enclosure. 
The technology is far apart..... BUT if an Amp circuit assembly incorporating D and A class with a suitable power supply is KITTED OUT ........there may well be a PRODUCT  for a niche audiophile Market. Graham is testily that it can be done and Britain may need to adopt some of that ''far east '' enterpreneurnial strategy and tactics .....We need to be bold and NEWTON, SHAKEPEAR and  Dysan and Virgin Atlantic .....
Back to Top
 Post Reply Post Reply Page  12>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 0.094 seconds.