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  Believe the Hypex, class-D DIY amplifier 
 Date Written 
Brendan Falvey Dec 08, 2005, 04:04pm EST Report Abuse
Not withstanding your comments re 'digital' In my earlier days I did my electronic training in the transition from tubes to early IC components. About that timethere were Class D amps and as I recall and it was intended to overcome the deficiencies in power Transistor linearity. The view was that any class A/B or class B amp had the problem of a linear transition from one element to the other. As I recall the way around this was to (I cannot recall wheather it used Pulse width or pulse amplitude modulation) drive the amplifying element into saturation (yeah I know how linear is that) however the linearity was taken care of via the post processing. We really need to define the Class of operation clearly this process of hetrodyne mixing must be dependent on linearity (unless purely digital processing) and seems to be a new mode of operation perhaps a class E is appropriate but Class D has been clearly defined and around a long time (late 60 early 70s) and we should avoid ambiguity. The bibles for such definitions used to be books such as the Amplifier Handbook by O'Shea as I recall.

It worries me that people are redefining existing terminology as something else. I believe we must strive for improvement and this seems a very interesting approach it is only the class definition I have a problem with. Keep up the good work bring new technology and techniques to all us.

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DJ Dec 08, 2005, 11:06pm EST Report Abuse
>> Re: Believe the Hypex, class-D DIY amplifier
I agree with Brendan; I had experiences similar to his about ten years earlier when I was an undergraduate in EE. Class D amplification was known then but there were few if any applications for it; tubes were then the only active elements of adequate powerand they and their support were too expensive and lossy to make Class D economically practical. But two more generations of engineers appear to have made it practical, and I salute them!

Albert Crocker Dec 08, 2005, 11:14pm EST Report Abuse
>> Re: Believe the Hypex, class-D DIY amplifier
From "Class Act: The Pros and Cons of Amplifier Designs"

For convenience, engineers usually characterize amplifiers by circuit topology, the type of active components they use, load type, and even operating voltage: CLASS A, B, C, D, etc. Circuit topology describes how current is "steered," or controlled, within a power amplifier before it is delivered to a speaker load.

Class A is the simplest, most basic topology. Reproduction of music requires speaker motion both in and out. To do this, amplifiers must "source and sink" current. In a Class A amp only one direction of current control is used. To generate both directions of output flow, a constant current stage is subtracted from a variable current stage.

Pros: Since neither output stage ever turns off, device non-linearity and turn-on/turn-off time can be minimized or ignored, resulting in very low distortion designs.

Cons: As the maximum output is limited to the constant current stage, at idle this stage must put out full power and the variable stage must absorb this full power. Transformer, heat sink, and output stage must be sized for continuous duty at maximum power. Because of cost and the amount of waste heat generated by this approach, Class A only appeals to esoteric hi-fi designers, where lack of efficiency or price is no object.

Class B topology uses two variable output stages, one to source current and the other to sink current.

Pros: This topology overcomes the poor efficiency of pure Class A designs, only delivering power as needed. Transformer and heatsinks can be sized to match typical demands of music being reproduced.

Cons: Both output stages turn completely off, then on again, during each cycle of a waveform. Time delay and low-level non-linearities cause severe distortion, called "crossover distortion," during transition from source to sink output stages. This type of distortion is worst at low output levels. Pure Class B is only used in the lowest-cost, lowest-fidelity designs.

Class A/B topology, as you may have guessed, is a combination of Class A and Class B. Using two variable output stages like Class B but keeping them from ever completely turning off, you get near Class B efficiency with near Class A's low-distortion performance.

Class C topology combines active devices with resonant magnetic components for high efficiency at radio frequencies. This topology is not used in audio-frequency designs.

Class D topology uses source and sink output stages that consist of full-on or full-off switches. These output stages toggle from full sink to full source at a rate significantly higher than the highest audio frequency to be reproduced. The ratio of time sinking to time sourcing controls the audio output, with a 50% ratio delivering zero output.

Pros: Class D offers significantly higher efficiency than even Class B, which at 1/3 power is wasting more power inside the amplifier than it delivers to the load. Losses in Class D designs are limited to turn-on time of the switching devices and resistive losses in these devices and output filtering.

Cons: Class D amps require more complex circuit designs with extensive shielding and filtering.

Class G & Class H topologies are variations on Class B that use multiple source and sink output stages. Low-level signals are handled by one pair of output stages, while higher-level signals are handled by other pairs. Each pair is optimized for the power range it delivers.

Pros: More efficient amplifiers can deliver the same output power with smaller transformers and less heat sink.

Cons: Circuit complexity increases, which adds cost. Switching distortion similar to Class B's crossover distortion occurs at each output level transition.

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Brendan Falvey Dec 09, 2005, 03:24pm EST Report Abuse
>> Re: Believe the Hypex, class-D DIY amplifier
Time flies obviously there has been many developments over the intervening years. As noted the Class D used the off or saturated mode to allow significant power handling, way above the analogue characteristics of solid state devices, that simple switching provided. The hard part was the filtering the output to recover the amplified signal with some degree of fidelity. As I recall there were two models that I was aware of one was by Sinclair (Clive Sinclair) the fellow who developed the first small Personal Organiser/PC the other I seem to recall was a magazine developed amp in one of the Australian electronic mags of the 70s and issued as a kit could be wrong here though.

As an observation the Class D development pointed the way for later digital developments such as the CD and the problems it would have to overcome to meet reasonable fidelity criteria.

arlen nelson Dec 09, 2005, 07:34pm EST Report Abuse
>> Re: Believe the Hypex, class-D DIY amplifier
some of you EE types seem pretty on this stuff...

do any of you know of a public domain design for that i may be able to use one of these amps in a automotive application?

a powersupply that can cleanly step 12-15vDC upto about 40vAC with a peak of about 10A?

or as least provide me with enough evidence to drop the idea?


Brendan Falvey Dec 09, 2005, 09:49pm EST Report Abuse
>> Re: Believe the Hypex, class-D DIY amplifier
Since you are looking at a automotive application (Mobile 12v assumed). While others may suggest otherwise the rule of thumb here would be do not bother. I will presume you are looking for maximum grunt from the loudspeakers.

At my mechanics recently another customer had installed a large audio system with no consideration for the available power. Result a burned out alternator and a tow home until a new higher capacity alternator is found. a standard 40-50 amp alternator will not cut the mustard and this is where we will start. I will assume you will have istalled something like an 80amp alternator giving something like a 1kW peak (80x12=960) the rest comes from then battery. If we look at the issue of stepping up from 12 Vdc to 40V ac (rms) 112v pk-pk will incur a loss. Typical efficiencies for a switched mode type of supply are about 85% for a steady load and drops for a variable load say 75% this means that after all that effort you can only contribute about 750W to usefully apply to the amplifier.

Put the effort into designing a good amp that operates off 12 volts. There are some designs around that have a form of capacitor dump to provide a peak boost that switches in as the signal level exceeds a design threashold but this is quite sophisticated but may be worth your investigation.

In many parts of this forum about computer many result from poor power supplies the same can be said for any electronic equipment make sure the power is there and do not waste it on changing levels that while initially look like a good idea and if connect to themains not a problem but when mobile you want the most you can get from what you put in and any loss cannot be recovered.

andrew kairis Dec 29, 2005, 09:05am EST Report Abuse
>> Re: Believe the Hypex, class-D DIY amplifier
you obviously know your stuff brendan
40-50 amp alternator?

I'm no car guy but I've never seen anything under 65. I've seen VW's with 90 amp alternators from the factory.

I have a 65amp in my corolla and the 4 channel 40watt rms per channel (320watt total peak) blew up my alternator.... by my math i needed closer to a 135 amp. (JBL rates the max/peak draw at 43amps ) they only leave like 15% spare amperage for upgrades to the radio and such. (although I've seen people with much more power hungry systems running off of less powerful alternators..the headlights just dim)

Randy Knutson Jan 08, 2006, 11:40am EST Report Abuse
>> Re: Believe the Hypex, class-D DIY amplifier
Very excellent and beautiful work with the implementation of those Hypex modules! Keep up all the hard work!

[ member ]

Ramon Betancourt Sep 19, 2006, 12:14am EDT Report Abuse
>> Re: Believe the Hypex, class-D DIY amplifier
Mr. Sassen,

You did a beautiful job with the 2-channel UcD400 amplifier. I'm planning to build two amplifiers: a 2-channel similar to yours and a 4-channel using the UcD180. Could you provide information on where to get a nice enclosure like yours for a reasonable cost? Also, what potentiometers did you use? Has the UcD400 proven to be reliable?

My amps will have balanced and unbalanced inputs and maybe Speakon connectors for the outputs.

Thanks for a well written article on the UcD400 being used.




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