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A warning to those that use Class D amps


Bass is the place
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I had issues with my Laney Nexus Tube head at a Fake Fest earlier this year. Intermittent buzzing and crackling, early distortion. All of this was seemingly random and by some quick root cause analysis could only be attributed to the power supply.

The issue could not be reproduced later the same day at home and has not happened since.

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  • 2 weeks later...

[quote name='Count Bassy' timestamp='1499774865' post='3333489']

So where did "Class H" come from?

And I agree with your other point. Class D is digital in that the output has two states, on or off. However there have been very long threads regarding this before, so best not open that particular can of worms again!
[/quote]Class H is just the latest class to be defined. It is an improvement on Class G. Classes E and F are not useful for Audio

Audio Classes are A,B, AB, D,G and H.

The reason Class D amps switching amps but are not digital. Audio in the digital world is sampled and in Class D the audio is modulated. It is really more akin to a power modem.

Edited by Chienmortbb
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[quote name='Chienmortbb' timestamp='1501148368' post='3342792']
Class H is just the latest class to be defined. It is an improvement on Class G. Classes E and F are not useful for Audio

Audio Classes are A,B, AB, D,G and H.

The reason Class D amps switching amps but are not digital. Audio in the digital world is sampled and in Class D the audio is modulated. It is really more akin to a power modem.
[/quote]

Ah, I always thought that Class H preceded class D, based on when the the Marshall DBS series was around, but I guess not.

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[color=#282828][font=helvetica, arial, sans-serif]"I played the Ealing Beer Festival a few years back, using my Matamp all-valve head. At 11pm they wanted all the punters to start going home so they turned on all the floodlights. The sudden draw on the (huge) generator caused my amp to cut out instantly and it was over a minute before I could get it back up and running."[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]I did Henley Regatta for ten years or so with OrangeMatamp (valve) kit - on a generator which supplied the 'commercial' bank (Fawley Meadows) - never had a single issue in all that time, apart from a genny going down one year.........[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif] [/font][/color][color=#282828][font=helvetica, arial, sans-serif] :)[/font][/color]

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So did it still work when you got home? Or did the genset kill it dead :¬(

Speaking as an electrical engineer (day job) I'd be surprised if a Class-D was more sensitive to low voltages than a class anything else, it just depends on what electronics are in there. I'm guessing more modern kit with more built in protection rather than anything fundamentally more damageable.

And the "D" does mean digital btw (it has power devices that are ON or OFF = digits; whereas A, B, C, H use transistors that are "partly" on = analogue. Class H is a Class C with a variable power supply rail voltage - the QSC 3200PLX I use at work is one of those, always a bit of a glitch as it switches from one power level to another - fantastic amp tho). It's just handy that D came after C.

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  • 5 weeks later...

[quote name='NickA' timestamp='1501941112' post='3348366']
So did it still work when you got home? Or did the genset kill it dead :¬(

Speaking as an electrical engineer (day job) I'd be surprised if a Class-D was more sensitive to low voltages than a class anything else, it just depends on what electronics are in there. I'm guessing more modern kit with more built in protection rather than anything fundamentally more damageable.

And the "D" does mean digital btw (it has power devices that are ON or OFF = digits; whereas A, B, C, H use transistors that are "partly" on = analogue. Class H is a Class C with a variable power supply rail voltage - the QSC 3200PLX I use at work is one of those, always a bit of a glitch as it switches from one power level to another - fantastic amp tho). It's just handy that D came after C.
[/quote]No it is not digital it is PWM. If it were digital, signal would be converted to a binary or octal number (digit) before power amplification. With PWM it is the width or frequency of the pulse that changes. It is like having a closed circuit radio system where the transmitter and receiver are in the same box. Yes it is valid to call Class D a switching amplifier class, but Digital is wrong. Even if the modulation is digitally controlled, the amp is not digital.

Edited by Chienmortbb
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