restorer-john
Grand Contributor
No, they sit on the fence for a split second in between jumping over. Poor little MOSFETs, they must get all hot and bothered doing that all day huh?
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On Class D Amplifiers Measurements
- Thread starter pma
- Start date
No, they sit on the fence for a split second in between jumping over. Poor little MOSFETs, they must get all hot and bothered doing that all day huh?
Uh, I'm sorry, my mistake, your diagram is self explanatory, I yield the rest of my time to whoever wants it.
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I'm sorry, I know Class D does not mean digital. I was reading the Audio Precision page on using an AES-17 pre-analyzer filter and it mentions "digital amplifiers", and I typed digital without thinking. The issue, which I don't think is an issue in well-designed Class D amplifiers, is that you really need filters on the input and the output to have the similar bandpass characteristics (no high frequency noise) as non-switching amplifiers. A lot of people look at the AES-17 requirement and think there's a man behind a curtain somewhere.
https://www.ap.com/technical-librar...alyzer-filters-for-the-2700-series-analyzers/
I can understand both view points:
- As an EE I don't like a power amp to throw out stuff which has not been fed into it.
- As an objective audiophile I don't care about stuff I (or anybody else) can't hear, as long as the level is so low that it does not interfere with the audible band or heats up tweeters. Insofar chasing low THD is fine with me because it improves sound I can hear.
That's what I said. Read my post again. The content has to suit the amplifier or it all goes pear shaped. That's the difference, preamplifiers and power amplifiers were able to cope with anything up to low level RF and do what they should- amplify without adding or subtracting anything. There was no 'rubbish' going on up top to cause trouble in the baseband.
Take the 1978 Kenwood L07c. I used to use one on my bench for high level square waves in between my signal generator and attached device as it could swing another >30V more than my signal gen. Up to 100Khz the rise time barely suffered. It was amazing- like a instrumentation amplifier. It's matching power amps were insane. There's a Perreaux 2150B in my storeroom which runs out to 3MHz at unity gain- that's insanity.
So, why is it OK for Class D proponents to justify chasing ever decreasing levels of THD as their headline point of difference, well below the limits of audibility, and at the same time throw water on people justifying wide bandwidth amplification? Hint, it's not OK.
Read my post again, it's about the message and the justification sold to audiophiles and the attempt to subvert/divert and re-cast Class D in a different light by channeling the old UK amplifier designers of old where bandwidth limiting was the new black- until it wasn't.
Remember when CD-4 and other multichannel LP sources were devised? Bandwidths were expanded, capacitor coupling was thrown out and we got high speed diffused emitter, RETs, and the ability to do part time LW transmission with our power amps (kidding). Along came DC-Daylight for all things amplification related.
CD strawman nothwithstanding, is it OK to just say for once that Class D amplification does really, really well in the audible bandwidth and not outside it? Again, Class D doesn't have to be your own personal crusade, we already have one of them here (he's back).
But you are talking about this "message" as if it were a problem.
Audio has always been bandwidth limited. It doesn't matter if you put a 1Mhz BW 1970s amp in the middle. The mic in the studio was lucky to get to 30kHz, the analogue tape lucky to get to 35Khz, your record deck same again, and your speakers the same. We have had BW limited domestic digital for nearly 40 years now.
Your square waves have always been buggered up from the start of the chain. This is no strawman, its reality.
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CD strawman nothwithstanding, is it OK to just say for once that Class D amplification does really, really well in the audible bandwidth and not outside it? Again, Class D doesn't have to be your own personal crusade, we already have one of them here (he's back).
Again this is no crusade. I am debating technical points of fact. Disagreeing with you is not crusading.
IMO yes it is OK that class D does very well up to 50 to 60kHz. Having super wide BW amps only leaves you open to potential problems without audible benefit.
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Who are these people? Its not me. Bruno Putzeys stated that (paraphrasing) "we have asymptomatically approached perfect some years ago". In fact its usually class A A/B proponents saying that class D still doesnt reach the lowest levels that class A A/B can.
restorer-john
Grand Contributor
I'm sorry, but somebody has clearly bought up big on the 44 gallon drums of Class D Koolaid and is dutifully dishing it out, en-masse, to anyone and everyone. I've seen what mass consumption of Koolaid does, I'm old enough and remember the pictures. They weren't pretty.
What is tiresome is the constant attempts to hose-down valid discussions, threads and criticisms of what is a polarizing and paradigm shifting part of the high fidelity landscape, by simply telling people (over and over) that "these aren't the droids you're looking for". Whether that be overheating, premature shutdowns, out of band noise, reliability, power output claims etc. Notice, none of these are subjective criticisms, they are all (as you put it):
I'd rather have a ruler flat, wide-band amplifier in preference to a deliberately bandwidth limited amplifier that hides all its sins in HF noise.
I'd rather have a preamplifier and power stage that amplifies without fear or favor anything that is thrown at it to at least 5-10 times the highest frequency I can hear.
I don't want massaged power output claims to suit someone chasing numbers on a data sheet. The only time an amplifier should shutdown is when it is broken.
I want 100% truth in specifications from component suppliers.
The manufacturers- who else? That has been (and continues to be) their only point of difference and the headline grabbing thing they plaster all over each and every datasheet, press release and marketing blurb.
This thread is interesting, the OP is investigating interactions with switching frequency and out of band content. Sure, he may have a vested interest in class AB amplifiers. We now he loves building them that's for sure.
But Class D can stand on its own without your blind allegiance, it really can.
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A potential source of ultrasounds can be DSD files converted to very high rate PCM ? Then you bypass the filter mandatory in SACD players just to deals with DSD ultrasonic noise .
Are not one of the current audio fads mucking with you own filters and upsample in your computer .
Was it not QUAD that continued to propose BW limited as the proper way to do stuff even when DC to GHZ amps was all the rage ?
Are not one of the current audio fads mucking with you own filters and upsample in your computer .
Was it not QUAD that continued to propose BW limited as the proper way to do stuff even when DC to GHZ amps was all the rage ?
I am sorry John but respectfully I think you need to cool down a bit.
Is there anything technically incorrect regarding my statements that audio is bandwidth limited right from the start?
The microphone
followed by the recording medium, analogue or digital
followed by the replay medium, analogue or digital.
Do you agree with this, yes or no?
Assuming yes, do you agree that your square wave example is not relevant as its harmonics have already been curtailed prior to it getting to the amp?
Assuming yes, can you explain what are you gaining by having an amp with 10 times that bandwidth?
John, you talk about narratives, but you clearly have your own which is negative towards class d. Its not my fault your points dont stand up to scrutiny.
So would you want an A/B amp with flat bandwidth so wide it picks up the local Taxi firms radio? No, you would filter the input. In your logic thats "hiding sins". That doesnt make any sense, its actually just correct design.
I have also posted videos of Class D amps happily passing the FTC power test.
Regarding using specs to market sell amps, ALL manufacturers do this. This is nothing exclusive to class D.
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Let's dial it down some folks.
On the point of OP, if we worry about AM radio stations, same signal can be demodulated by any amplifier and create an AM receiver. I am not sure if I worry more about a talk radio voice showing up in my music or a fixed tone from beat of class D carrier with the AM carrier.
On the point of OP, if we worry about AM radio stations, same signal can be demodulated by any amplifier and create an AM receiver. I am not sure if I worry more about a talk radio voice showing up in my music or a fixed tone from beat of class D carrier with the AM carrier.
restorer-john
Grand Contributor
It's rather difficult to address and reply to your posts @March Audio if you keep editing, adding, deleting and changing the content.
A cool tactic nonetheless- keep moving the goalposts...
A cool tactic nonetheless- keep moving the goalposts...
On the point of OP, if we worry about AM radio stations, same signal can be demodulated by any amplifier and create an AM receiver. I am not sure if I worry more about a talk radio voice showing up in my music or a fixed tone from beat of class D carrier with the AM carrier.
If you can hear AM radio coming out of an amplifier without a tuner, you should go and get yourself measured by the nearest doctor.
It's rather difficult to address and reply to your posts @March Audio if you keep editing, adding, deleting and changing the content.
A cool tactic nonetheless- keep moving the goalposts...
There is no goalpost shifting. The points have remained exactly the same.
Can you address the questions I have asked?
Let's dial it down some folks.
On the point of OP, if we worry about AM radio stations, same signal can be demodulated by any amplifier and create an AM receiver. I am not sure if I worry more about a talk radio voice showing up in my music or a fixed tone from beat of class D carrier with the AM carrier.
This is a point I have made numerous times. Input filtering is important for all Amplifier types.
Maybe, maybe not:If you can hear AM radio coming out of an amplifier without a tuner, you should go and get yourself measured by the nearest doctor.
Actually, having AM radio interference appear in the speakers has been fairly common over the years. It is fairly easily demodulated from the carrier (just takes a diode) and, if RFI suppression is not included or shielding inadequate, you can hear the results. I read an article some years back speculating that it was less common these days not necessarily because designs have improved but because the number of high-power AM stations has dwindled.
restorer-john
Grand Contributor
My father used to have "radio breakthrough" on various systems through the 1970s and when we first moved to Queensland, there was an AM radio station on 1197 with its main transmitter around 7km away. You'd could pick it up with a piece of wet string.
But as a little boy, a single germanium diode, a capacitor and a slug tuned coil, salt crystal earpiece would give me great reception with 20cm of wire. But only that station and in several places across my 'dial'. Even pocket transistor radios got overwhelmed...Most of the demod radio breakthrough he suffered, came via the speaker wires (NFB I guess) and/or the phono stages in his various 1970s pieces (they were brand new then). I've had zero trouble with it, ever, but as you point out Don, the AM stations are mostly gone and if they remain are running tiny fractions of the ERP they once were.
