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Class D Switching Power Amplifiers and Power D/A conversion

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Old 9th November 2008, 06:11 AM   #11
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A simple high quality triangle generator can be made with a crystal oscillator (11.2896MHz crystal and 74HCT4060 oscillator divider) feeding into an integrator (fet opamp, +in grounded 1M and 47p in parallel from out to in- and 6K8 from oscillator to in -)
depending on the rail-rail operation of the opam the 6k8 be trimmed to get maximum swing with lowest top distortion.
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Old 9th November 2008, 08:30 AM   #12
Pafi is offline Pafi  Hungary
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Quote:
Has anyone heard birds chirping in their speakers when running multiple self-oscillating Class D?
Yes, I have, at about -80 dB, but only as long as the onboard supply decoupling capacitors were 1 uF, and sw. freq was only 200 kHz, and 2 channels were on the same PCB, and supply rails were directly paralelled.

Official UcD must be free from this problem.
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Old 9th November 2008, 01:43 PM   #13
fredos is offline fredos  Canada
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I heard a lot of Icepower multi channel amplifier beating. Most of the time people did'nt notice, they think it was the noise floor or some white noise...To be honnest, I never hear more than 2 channel of ice power that didnt do beating..Maybe you just didnt realize that is that.

Fredos
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Old 9th November 2008, 04:53 PM   #14
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Quote:
Originally posted by fredos
I heard a lot of Icepower multi channel amplifier beating. Most of the time people did'nt notice, they think it was the noise floor or some white noise...To be honnest, I never hear more than 2 channel of ice power that didnt do beating..Maybe you just didnt realize that is that.

Fredos

As with many class d caveats you have to know to listen for it, it can sneak by at lower levels of intrusion and particularly for certain types of music, or while using lower efficiency speakers.

I likely coined the term "birds chirping" as it's quite descriptive over beat frequencies, whistling or heterodyning. Non the less it's largely a question of EMI, and I think if you can't handle a simpler, more robust self oscillating amp without it occuring at problematic levels, a similar clocked based amp you'd handle no better.

Synching them doensn't alleviate EMI. You have to fix it at the root of the cause and not through trickery as synched clocks that might only half work.

Higher levels of EMI will also show up in ways that might make you think sounds good but really doesn't if you know what you're hearing and how to listen. IcePower is not the most advanced or best executed example of self oscillating technology. I could name others that also completely don't pass the grade, far worse than IcePower, or I could name a few that do. UcD is of course one worth mentioning that has no such issues, and it's both by design and implementation.

In terms of free lunch you don't get the same level of performance with a clocked amp as you can with self oscillating without resorting to additional complexity that can amount to reduced reliability, and more board space to pollute your control signals with, but I guess it's OK for PA

You've still got jitter with your clock, any induced noise on the line or circuitry that powers it will add to it. Let's not pretend that the best measuring and sounding class d amps in the world are all self oscillating by design, some of which are in fact used in multi channel home theatre or cinema setups and go beyond UcD.

Putting down proven technology that's on the cutting edge is a poor business model if you ignore the facts, but fear it if you must.
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Old 9th November 2008, 07:39 PM   #15
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Quote:
Originally posted by bwaslo
My tweeters don't respond at all at 300kHz+ and I doubt that yours do either!
I would say, if your tweeters roll off at 16 kHz, then they might respond at 300kHz with approx. -50db.
And this -50db are referencing to the HF-ripple of the amp output, not to the max power output.
That's why I say, this effect is not loud.
Also our personal perception regarding such effects seems to be very individual.
For some people, this is making magic.
For others it is messing up the entire sound stage.
I was listening to UCD (UCD400 if I remember correctly) only once and we compared it to a shameless priced Mark Levinson and to my both class AB Rookies and one R&D prototype of a friend. The speakers were ESL.
My Ranking:
1. Both Rookies and the other R&D proto ( I feel quite guilty... subjective ignorant idiot I am... )
The Rookies and the other R&D proto all had their own signature, but for my ears they were playing on the same level.
2. UcD. For my ears the UcD sound did NOT appear as obviously birding. Even if I was aware of the theoretical backgroung before the listening test. For me the UcD was not overwhelming magic, but basically OK and not tiring.
3. Mark Levinson. Some call it neutral. And if this is really correct, then I do not like correct neutral amps.
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Old 9th November 2008, 09:05 PM   #16
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Quote:
A simple high quality triangle generator can be made with a crystal oscillator (11.2896MHz crystal and 74HCT4060 oscillator divider) feeding into an integrator (fet opamp, +in grounded 1M and 47p in parallel from out to in- and 6K8 from oscillator to in -)
Why a fet opamp?
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Old 9th November 2008, 09:08 PM   #17
fredos is offline fredos  Canada
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Quote:
Originally posted by classdphile



As with many class d caveats you have to know to listen for it, it can sneak by at lower levels of intrusion and particularly for certain types of music, or while using lower efficiency speakers.

I likely coined the term "birds chirping" as it's quite descriptive over beat frequencies, whistling or heterodyning. Non the less it's largely a question of EMI, and I think if you can't handle a simpler, more robust self oscillating amp without it occuring at problematic levels, a similar clocked based amp you'd handle no better.

Synching them doensn't alleviate EMI. You have to fix it at the root of the cause and not through trickery as synched clocks that might only half work.

Higher levels of EMI will also show up in ways that might make you think sounds good but really doesn't if you know what you're hearing and how to listen. IcePower is not the most advanced or best executed example of self oscillating technology. I could name others that also completely don't pass the grade, far worse than IcePower, or I could name a few that do. UcD is of course one worth mentioning that has no such issues, and it's both by design and implementation.

In terms of free lunch you don't get the same level of performance with a clocked amp as you can with self oscillating without resorting to additional complexity that can amount to reduced reliability, and more board space to pollute your control signals with, but I guess it's OK for PA

You've still got jitter with your clock, any induced noise on the line or circuitry that powers it will add to it. Let's not pretend that the best measuring and sounding class d amps in the world are all self oscillating by design, some of which are in fact used in multi channel home theatre or cinema setups and go beyond UcD.

Putting down proven technology that's on the cutting edge is a poor business model if you ignore the facts, but fear it if you must.
I did'nt say thatself oscilating are bad...I just a matter of thinking...I dont like ''uncontroled'' design. If a parts change value (you heard about tolerance of parts?), switching performance\frequency can change...In a clocked design, with proper feedback this should not happen. I agree that clocked design need more parts, but anyway, in pro audio you need lot more for stupid guy. Exemple: short protection, thermal proteck, clipping limiter, under\over voltage protection, turn-on\turn-off muting, HF oscilation protection for drivers, DC protection, etc...

Other hand, you can optomize dead time, implement variable dead time in function of power to increase effiency, use zobel for power limiting, etc...All this need predictable performance, not easily achievable with self oscilating...

EMI by the way cause same probleme in clocked and self oscilating design...So dont say that that's the cause of beating of self osc amp...A badly designed clocked design will do same if EMI are not properly managed. Just use a 2'' compression drivers with 110db on any self osc and you will know what I talk about...

Fredos
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Old 10th November 2008, 02:08 AM   #18
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Hi,

So you're saying you prefer clocked as you fear the uncontrolled aspect of controlled chaos? So long as we agree that doesn't make it inferior.

You had stated your preferred method to form the clock was with a simple RC. Perhaps you can explain to me how that's immune to this phenomena of tolerancing and stability you speak of, I'm pretty sure it isn't.

In self oscillating the frequency may change wrt to such things, but it's as an intrinsic corrective measure since they're already a part of the control loop. In a simple clocked case a global loop ignores it, hence a requirement for additional measures.

The protections mentioned can be seen as transparent to the actual methodology for the most part, falling outside of the control structure. They're used because things aren't always predictable either. I don't view that as being any more involved for one variety than the other.

Quote:
Other hand, you can optomize dead time, implement variable dead time in function of power to increase effiency, use zobel for power limiting, etc...All this need predictable performance, not easily achievable with self oscilating...
Much of that too can be seen as transparent to methodology, mostly, they switch the same in either case. Variable deadtime is better sensed and not predicted per se. The use of a zobel is something of a bandaid with drawbacks of its own, and some amps don't need it. In fact it's proven itself a common part to burn up and may require additional protection just for itself, you know, for mr. stupid of which there's no shortage.

Quote:
EMI by the way cause same probleme in clocked and self oscilating design...So dont say that that's the cause of beating of self osc amp...A badly designed clocked design will do same if EMI are not properly managed. Just use a 2'' compression drivers with 110db on any self osc and you will know what I talk about...
EMI wreaks havoc in a variety of ways. I am saying heterodyning is caused by unoptimal EMI since even non fixed frequency self oscillating amps that don't suffer heterodyning solved it through optimal EMI alone.

Try running multiple clocked amps off the same supply and don't synchronize anything. If you hear the birds it's because EMI could be optimized further. Synchronizing them is a common trick to make it robust against less than perfect EMI performance in some respect or other. If lowest EMI is always superior, which amp is then best, one that relies on synchronizing, or one that gets away without 99% of the time?

I think your amp remains one of the best examples of a clocked amp around here anyway.
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Old 10th November 2008, 05:45 AM   #19
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Default why fet opamp?

Fet op amps have a much higher input impedance and from experience give much less distortion than the 5532 bipolar types
part I use in this case is TS272 from SGS
http://www.st.com/stonline/products/...2303/ts272.pdf
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Old 10th November 2008, 12:01 PM   #20
fredos is offline fredos  Canada
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They are more sensitive to noise, EMI and glitch too...Just dont forget to drive them with low impedance source...
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