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Class D Switching Power Amplifiers and Power D/A conversion

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Old 9th September 2004, 11:53 PM   #1
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Default At a loss...

I am at a loss. I read all this lingo about class D and I am not really sure what the purpose of class D is used for as an audio amplifier. I thought it was for high current fast switching maybe in power supplies or SMPS type circuits. Can someone explain why you would want to use class D for audio amp? Obviously it would be more power efficient. I know that, well for a BJT amp, when the load is matched to the output Z for maximum power transfere, the Thevenin equal circuit (simply a current source in series with two impeadences, Z out and Z load), the power to each impeadence is approxamatly equal. What would the Thevenin equal circuit look like for class D?

Is it just power efficiency?
What is a good bandwidth for class D?
What is the harmonic distortion of output, particularly symetric distortion? (relative to BJT or MOSFET amp)

Chris
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Old 10th September 2004, 07:16 AM   #2
rha61 is offline rha61  France
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hi Chris

you have just to listen to an UCD180 , for example , and you will be very surprised about classD

Alain
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Old 13th September 2004, 11:45 PM   #3
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Default ClassD

I build class-d amps because I need to develop a lot of power and I don't have a lot of space to do it in. Specially no room for heatsinks. However, we did not go class-d until the technology reached our high standards for sound quality. We found the ICE Power amplifers were the first Class D amps that reached this level.

The UcD amps also reach this goal and I have built a 180W per channel amp with them into a single rack space enclosure. The limiting factor was the power supply.
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Old 14th September 2004, 03:41 AM   #4
ghemink is offline ghemink  Netherlands
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Default Re: At a loss...

Quote:
Originally posted by cunningham
I am at a loss. I read all this lingo about class D and I am not really sure what the purpose of class D is used for as an audio amplifier. I thought it was for high current fast switching maybe in power supplies or SMPS type circuits. Can someone explain why you would want to use class D for audio amp? Obviously it would be more power efficient. I know that, well for a BJT amp, when the load is matched to the output Z for maximum power transfere, the Thevenin equal circuit (simply a current source in series with two impeadences, Z out and Z load), the power to each impeadence is approxamatly equal. What would the Thevenin equal circuit look like for class D?

Is it just power efficiency?
What is a good bandwidth for class D?
What is the harmonic distortion of output, particularly symetric distortion? (relative to BJT or MOSFET amp)

Chris

Hi Chris,

I agree with Alain. A well made Class D amp (like the UcD180) sounds better than a well made conventional amp (Accuphase E407) at a fraction of the cost. I have both amps (I also have a Tripath based amp). But the UcD180 very clearly outperforms both the Tripath and the Accuphase. Last year when I bought that Tripath based Marantz (4 channelsfor about $1000), I was really surprised that it ourperformed my far more expensive Accuphase. From that point on I became a Class D believer.

Just try and see (ear).

best regards

Gertjan
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Old 18th September 2004, 02:28 AM   #5
Konrad is offline Konrad  Norway
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Default Re: At a loss...

Quote:
Originally posted by cunningham
I am at a loss. I read all this lingo about class D and I am not really sure what the purpose of class D is used for as an audio amplifier. I thought it was for high current fast switching maybe in power supplies or SMPS type circuits. Can someone explain why you would want to use class D for audio amp? Obviously it would be more power efficient. I know that, well for a BJT amp, when the load is matched to the output Z for maximum power transfere, the Thevenin equal circuit (simply a current source in series with two impeadences, Z out and Z load), the power to each impeadence is approxamatly equal. What would the Thevenin equal circuit look like for class D?

Is it just power efficiency?
What is a good bandwidth for class D?
What is the harmonic distortion of output, particularly symetric distortion? (relative to BJT or MOSFET amp)

Chris
What would cach your attention to it ? Basicaly its nothing but designing better input stages, it may bee of little interest for some, but others; som know the importance of good design in input stages. Thiese stages can with ease also bee used as innput stages in normal amps. So If the innput- stages develop as for marked demand for it. The development is also there for "analog" amplifiers.

A snapshot from the "scetchboard", just a friday night idea, may i ask for a comment ?
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Old 18th September 2004, 02:36 AM   #6
sss is offline sss  Israel
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i see no reason making class d amp if u dont need high efficiency and if u dont need it to be compact
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Old 18th September 2004, 10:21 AM   #7
rha61 is offline rha61  France
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another reason is the cost
A Panasonic sa-xr45 is $300 for 6x80w and has a sonic presentation impossible to reach with analog stages at this cost

alain
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Old 18th September 2004, 03:11 PM   #8
ghemink is offline ghemink  Netherlands
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Quote:
Originally posted by sss
i see no reason making class d amp if u dont need high efficiency and if u dont need it to be compact

I see a very good reason: Sound quality.

A good Class D amp really sounds better than a conventional amp. The difference is very significant and very clearly audible even with my not extremely high-end B&W CDM9NT speakers. And as I said in my previous post, the conventional amp that I have is an Accuphase E407, it can`t compete with the UcD180 Class D modules.

Hearing is believing

Gertjan
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Old 19th September 2004, 11:13 AM   #9
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Wink Here's a good reason.....

I second Gertjan's reply and I would add: Great sound quality for less dosh .
(for a well-designed class D amp, of course).

Is that good enough?

Goliardo
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Old 21st September 2004, 02:16 PM   #10
Bakmeel is offline Bakmeel  Netherlands
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Default Commercial technology push

I see a different reason.

The quality criterium goes for all classes of amplifiers. A, AB, B, D, T, etcetera. One can build bad and good amps of all kinds, so forgte the criterium that "Class D" Amps sound better. I don't think that's valid.

Instead, look at the origin. Switchmode amps were originally designed for commercial purposes, as are all amps. Its us freak trying to copy and improve them. So the question is: why were class D amps developed in the first place? I see 3 explanations:

1) High Efficiency.
2) Compact.
3) CHEAP!

Because Switchmode amps can be integrated into one single chip, generating less heat and needing less power for the same output, large amps can be integrated into a single chip, with a minimum of external components. So all you need is a slab of silicium, which practically costs nothing. Large production quantities bring compact high-power amps to the public, and here is your money.

Why did they develop swithcmode amps? because there's money in them

Bouke
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