I don't have any first-hand experience with "class D" digital
amplifiers, but I saw an ad for a PowerAcoustik model that supposedly
puts out 2300W RMS into one ohm, and costs just a little over $300.
Even if they're wildly inflating the power numbers, that still sounds
like a hell of a deal. I paid almost that much for a Linear Power
2202IQ (about 375W RMS mono) in 1991, and $300 is about what I paid
for the used PPI A1200.2 (1200 WRMS mono) that I'm using now.

I know that digital amps are bandwidth-limited, making them
more suitable as subwoofer amps than as full-range amps, but are there
any other drawbacks to this design?

Scott Gardner

First, I know your calling them "digital" because thats the way they are
marketed. So I am not attacking your choice of words. But there is no such
thing as a "digital amplifier". Digital means 1s and 0s. You can't amplify
1s and 0s! You can convert an analog singal to digital, process the signal,
and convert it back to analog for amplifying. Hence "digital singal
processing".
I have no idea why they are called "digital", but it just bugs me....

To try and answer your question though, they are much more efficient than a
typical class A/B design. They take less space. Those are the major
advantages. I wont say "all" of them, because I dont know for sure, but
every one I have seen has a fairly poor damping factor, which means less
"control" of the sub, so it could sound sloppy (compared to a good Class
A/B). Overall they are not as good for sound quality as a Class A/B of equal
quality build. Class D (or Class T, or BD, or whatever) use a different type
switching which makes them useless for full range. They can't operate fast
enough for full range. Infinity used to make a Beta series amp (they even
had the words DIGITAL on the amps) that was supposed to be OK for full
range. Not sure how well they did it, but they were supposed to be capable
of it. I heard them used on subs, never on full range, so I can't say. So
with some exceptions, the basic rule is subwoofer use only.
If I were you, I would NOT get rid of that PPI A1200 for a PowerAcoustik
ANYTHING. Class D or not. But, that's just me.

--
John Spagnolo - teamROCS #016
Multi Media Xpress Car Audio www.mmxpress.com
"It's about the music stupid!" John "Batvette" Lucier 98'
R.A.C. FAQ: http://www.mobileaudio.com/rac-faq/
JL Audio Tech Section: http://www.jlaudio.com/tutorials
MMXpress Tech Section: http://www.mmxpress.com/technical/


"Scott Gardner" wrote in message
...
I don't have any first-hand experience with "class D" digital
amplifiers, but I saw an ad for a PowerAcoustik model that supposedly
puts out 2300W RMS into one ohm, and costs just a little over $300.
Even if they're wildly inflating the power numbers, that still sounds
like a hell of a deal. I paid almost that much for a Linear Power
2202IQ (about 375W RMS mono) in 1991, and $300 is about what I paid
for the used PPI A1200.2 (1200 WRMS mono) that I'm using now.

I know that digital amps are bandwidth-limited, making them
more suitable as subwoofer amps than as full-range amps, but are there
any other drawbacks to this design?

Scott Gardner

Oh, I'm not getting rid of my PPI amps for anything. I just came
across the PowerAcoustik model when I was researching some other stuff
for a friend. I don't know anything about that brand, I was just
using it as an example.

As for why they're called "digital", I believe it's in reference to
the power supply switching method. I know it's a marketing term,
that's why I put "class D" in quotes.

I wouldn't be too concerned about the low damping factor. The only
reason that class AB amps have such astronomical damping factors is
because damping factor is related to the amount of global negative
feedback in the amplifier design, and AB amps use a LOT of global
negative feedback. If you look at class A tube amplifiers for home
use, some of them have damping factors of 20 or even lower, and they
have no problems controlling subwoofer movement. Damping factor
turned into a marketing selling point for car amplifiers, but it's
really just a by-product of the feedback circuitry. I think you'd
probably be hard-pressed to tell the difference between a damping
factor of 50 or 500, all else being equal. Some of the best-sounding
pure class A tube amps have damping factors of less than 10. However,
these tend to be single-ended triode amps, and generally put out less
than 10 watts per channel, so driving huge subs isn't a priority with
these amps.

So, it sounds like if sound quality isn't your top priority, and
you're just using it to efficiently throw a LOT of power to a
subwoofer, a "class D" amplifier might be a good choice. Do you know
of any models that are accurately-rated as to their power output? I'm
still getting over that 2300W PowerAcoustik amp for $300, and I'd like
to find out if that kind of watts-per-dollar ratio is really possible
with a "digital" amp.

Scott Gardner


On Sun, 21 Dec 2003 12:35:06 GMT, "John Spagnolo MMXpress.com"
wrote:

First, I know your calling them "digital" because thats the way they are
marketed. So I am not attacking your choice of words. But there is no such
thing as a "digital amplifier". Digital means 1s and 0s. You can't amplify
1s and 0s! You can convert an analog singal to digital, process the signal,
and convert it back to analog for amplifying. Hence "digital singal
processing".
I have no idea why they are called "digital", but it just bugs me....

To try and answer your question though, they are much more efficient than a
typical class A/B design. They take less space. Those are the major
advantages. I wont say "all" of them, because I dont know for sure, but
every one I have seen has a fairly poor damping factor, which means less
"control" of the sub, so it could sound sloppy (compared to a good Class
A/B). Overall they are not as good for sound quality as a Class A/B of equal
quality build. Class D (or Class T, or BD, or whatever) use a different type
switching which makes them useless for full range. They can't operate fast
enough for full range. Infinity used to make a Beta series amp (they even
had the words DIGITAL on the amps) that was supposed to be OK for full
range. Not sure how well they did it, but they were supposed to be capable
of it. I heard them used on subs, never on full range, so I can't say. So
with some exceptions, the basic rule is subwoofer use only.
If I were you, I would NOT get rid of that PPI A1200 for a PowerAcoustik
ANYTHING. Class D or not. But, that's just me.

--
John Spagnolo - teamROCS #016
Multi Media Xpress Car Audio www.mmxpress.com
"It's about the music stupid!" John "Batvette" Lucier 98'
R.A.C. FAQ: http://www.mobileaudio.com/rac-faq/
JL Audio Tech Section: http://www.jlaudio.com/tutorials
MMXpress Tech Section: http://www.mmxpress.com/technical/


"Scott Gardner" wrote in message
...
I don't have any first-hand experience with "class D" digital
amplifiers, but I saw an ad for a PowerAcoustik model that supposedly
puts out 2300W RMS into one ohm, and costs just a little over $300.
Even if they're wildly inflating the power numbers, that still sounds
like a hell of a deal. I paid almost that much for a Linear Power
2202IQ (about 375W RMS mono) in 1991, and $300 is about what I paid
for the used PPI A1200.2 (1200 WRMS mono) that I'm using now.

I know that digital amps are bandwidth-limited, making them
more suitable as subwoofer amps than as full-range amps, but are there
any other drawbacks to this design?

Scott Gardner

There's nothing wrong with the sound quality of a class D amp.

Also, a good discussion on damping factor can be found he
http://www.diyspeakers.net/Articles/...G%20FACTOR.pdf

"Scott Gardner" wrote in message
...
Oh, I'm not getting rid of my PPI amps for anything. I just came
across the PowerAcoustik model when I was researching some other stuff
for a friend. I don't know anything about that brand, I was just
using it as an example.

As for why they're called "digital", I believe it's in reference to
the power supply switching method. I know it's a marketing term,
that's why I put "class D" in quotes.

I wouldn't be too concerned about the low damping factor. The only
reason that class AB amps have such astronomical damping factors is
because damping factor is related to the amount of global negative
feedback in the amplifier design, and AB amps use a LOT of global
negative feedback. If you look at class A tube amplifiers for home
use, some of them have damping factors of 20 or even lower, and they
have no problems controlling subwoofer movement. Damping factor
turned into a marketing selling point for car amplifiers, but it's
really just a by-product of the feedback circuitry. I think you'd
probably be hard-pressed to tell the difference between a damping
factor of 50 or 500, all else being equal. Some of the best-sounding
pure class A tube amps have damping factors of less than 10. However,
these tend to be single-ended triode amps, and generally put out less
than 10 watts per channel, so driving huge subs isn't a priority with
these amps.

So, it sounds like if sound quality isn't your top priority, and
you're just using it to efficiently throw a LOT of power to a
subwoofer, a "class D" amplifier might be a good choice. Do you know
of any models that are accurately-rated as to their power output? I'm
still getting over that 2300W PowerAcoustik amp for $300, and I'd like
to find out if that kind of watts-per-dollar ratio is really possible
with a "digital" amp.

Scott Gardner


On Sun, 21 Dec 2003 12:35:06 GMT, "John Spagnolo MMXpress.com"
wrote:

First, I know your calling them "digital" because thats the way they are
marketed. So I am not attacking your choice of words. But there is no
such
thing as a "digital amplifier". Digital means 1s and 0s. You can't
amplify
1s and 0s! You can convert an analog singal to digital, process the
signal,
and convert it back to analog for amplifying. Hence "digital singal
processing".
I have no idea why they are called "digital", but it just bugs me....

To try and answer your question though, they are much more efficient than
a
typical class A/B design. They take less space. Those are the major
advantages. I wont say "all" of them, because I dont know for sure, but
every one I have seen has a fairly poor damping factor, which means less
"control" of the sub, so it could sound sloppy (compared to a good Class
A/B). Overall they are not as good for sound quality as a Class A/B of
equal
quality build. Class D (or Class T, or BD, or whatever) use a different
type
switching which makes them useless for full range. They can't operate
fast
enough for full range. Infinity used to make a Beta series amp (they even
had the words DIGITAL on the amps) that was supposed to be OK for full
range. Not sure how well they did it, but they were supposed to be
capable
of it. I heard them used on subs, never on full range, so I can't say. So
with some exceptions, the basic rule is subwoofer use only.
If I were you, I would NOT get rid of that PPI A1200 for a PowerAcoustik
ANYTHING. Class D or not. But, that's just me.

--
John Spagnolo - teamROCS #016
Multi Media Xpress Car Audio www.mmxpress.com
"It's about the music stupid!" John "Batvette" Lucier 98'
R.A.C. FAQ: http://www.mobileaudio.com/rac-faq/
JL Audio Tech Section: http://www.jlaudio.com/tutorials
MMXpress Tech Section: http://www.mmxpress.com/technical/


"Scott Gardner" wrote in message
...
I don't have any first-hand experience with "class D" digital
amplifiers, but I saw an ad for a PowerAcoustik model that supposedly
puts out 2300W RMS into one ohm, and costs just a little over $300.
Even if they're wildly inflating the power numbers, that still sounds
like a hell of a deal. I paid almost that much for a Linear Power
2202IQ (about 375W RMS mono) in 1991, and $300 is about what I paid
for the used PPI A1200.2 (1200 WRMS mono) that I'm using now.

I know that digital amps are bandwidth-limited, making them
more suitable as subwoofer amps than as full-range amps, but are there
any other drawbacks to this design?

Scott Gardner

So, it sounds like if sound quality isn't your top priority, and
you're just using it to efficiently throw a LOT of power to a
subwoofer, a "class D" amplifier might be a good choice. Do you know
of any models that are accurately-rated as to their power output? I'm
still getting over that 2300W PowerAcoustik amp for $300, and I'd like
to find out if that kind of watts-per-dollar ratio is really possible
with a "digital" amp.

I was looking at getting a pair of Kenwood KAC-810D's a while ago. They
go for abouy $750 CDN each, and IIRC they are rated for 800W into 2
ohms, or 1600W into 1 ohm.

I'd be a little warry of a $300 USD amp that claims 2300 watts but I
dunno...

Aaron

On Sun, 21 Dec 2003 10:37:44 -0500, "Mark Zarella"
wrote:

There's nothing wrong with the sound quality of a class D amp.

Also, a good discussion on damping factor can be found he
http://www.diyspeakers.net/Articles/...G%20FACTOR.pdf

I've already read that article, and it says basically what I posted,
that high damping factors are a by-product of feedback, and that
higher numbers really don't buy you anything. Actually, Pierce goes
as far to say that differences in damping factor are inaudible over
20. I at least went as high as 50.

Scott Gardner



"Scott Gardner" wrote in message
...
Oh, I'm not getting rid of my PPI amps for anything. I just came
across the PowerAcoustik model when I was researching some other stuff
for a friend. I don't know anything about that brand, I was just
using it as an example.

As for why they're called "digital", I believe it's in reference to
the power supply switching method. I know it's a marketing term,
that's why I put "class D" in quotes.

I wouldn't be too concerned about the low damping factor. The only
reason that class AB amps have such astronomical damping factors is
because damping factor is related to the amount of global negative
feedback in the amplifier design, and AB amps use a LOT of global
negative feedback. If you look at class A tube amplifiers for home
use, some of them have damping factors of 20 or even lower, and they
have no problems controlling subwoofer movement. Damping factor
turned into a marketing selling point for car amplifiers, but it's
really just a by-product of the feedback circuitry. I think you'd
probably be hard-pressed to tell the difference between a damping
factor of 50 or 500, all else being equal. Some of the best-sounding
pure class A tube amps have damping factors of less than 10. However,
these tend to be single-ended triode amps, and generally put out less
than 10 watts per channel, so driving huge subs isn't a priority with
these amps.

So, it sounds like if sound quality isn't your top priority, and
you're just using it to efficiently throw a LOT of power to a
subwoofer, a "class D" amplifier might be a good choice. Do you know
of any models that are accurately-rated as to their power output? I'm
still getting over that 2300W PowerAcoustik amp for $300, and I'd like
to find out if that kind of watts-per-dollar ratio is really possible
with a "digital" amp.

Scott Gardner


On Sun, 21 Dec 2003 12:35:06 GMT, "John Spagnolo MMXpress.com"
wrote:

First, I know your calling them "digital" because thats the way they are
marketed. So I am not attacking your choice of words. But there is no
such
thing as a "digital amplifier". Digital means 1s and 0s. You can't
amplify
1s and 0s! You can convert an analog singal to digital, process the
signal,
and convert it back to analog for amplifying. Hence "digital singal
processing".
I have no idea why they are called "digital", but it just bugs me....

To try and answer your question though, they are much more efficient than
a
typical class A/B design. They take less space. Those are the major
advantages. I wont say "all" of them, because I dont know for sure, but
every one I have seen has a fairly poor damping factor, which means less
"control" of the sub, so it could sound sloppy (compared to a good Class
A/B). Overall they are not as good for sound quality as a Class A/B of
equal
quality build. Class D (or Class T, or BD, or whatever) use a different
type
switching which makes them useless for full range. They can't operate
fast
enough for full range. Infinity used to make a Beta series amp (they even
had the words DIGITAL on the amps) that was supposed to be OK for full
range. Not sure how well they did it, but they were supposed to be
capable
of it. I heard them used on subs, never on full range, so I can't say. So
with some exceptions, the basic rule is subwoofer use only.
If I were you, I would NOT get rid of that PPI A1200 for a PowerAcoustik
ANYTHING. Class D or not. But, that's just me.

--
John Spagnolo - teamROCS #016
Multi Media Xpress Car Audio www.mmxpress.com
"It's about the music stupid!" John "Batvette" Lucier 98'
R.A.C. FAQ: http://www.mobileaudio.com/rac-faq/
JL Audio Tech Section: http://www.jlaudio.com/tutorials
MMXpress Tech Section: http://www.mmxpress.com/technical/


"Scott Gardner" wrote in message
...
I don't have any first-hand experience with "class D" digital
amplifiers, but I saw an ad for a PowerAcoustik model that supposedly
puts out 2300W RMS into one ohm, and costs just a little over $300.
Even if they're wildly inflating the power numbers, that still sounds
like a hell of a deal. I paid almost that much for a Linear Power
2202IQ (about 375W RMS mono) in 1991, and $300 is about what I paid
for the used PPI A1200.2 (1200 WRMS mono) that I'm using now.

I know that digital amps are bandwidth-limited, making them
more suitable as subwoofer amps than as full-range amps, but are there
any other drawbacks to this design?

Scott Gardner

Class D amplifiers are quite effective at low frequencies, they have severe
problems with harmonic distortion at higher audio frequencies. It is for this
reason they are popular as subwoofer amplifiers, but little else. Tripath
(class T) amplifiers are fullrange amplifiers that sound just as good if not
better then most class A/B amplifiers, and are just as efficient as class D
amplifiers.



To try and answer your question though, they are much more efficient than a
typical class A/B design. They take less space. Those are the major
advantages. I wont say "all" of them, because I dont know for sure, but
every one I have seen has a fairly poor damping factor, which means less
"control" of the sub, so it could sound sloppy (compared to a good Class
A/B). Overall they are not as good for sound quality as a Class A/B of equal
quality build. Class D (or Class T, or BD, or whatever) use a different type
switching which makes them useless for full range. They can't operate fast
enough for full range. Infinity used to make a Beta series amp (they even
had the words DIGITAL on the amps) that was supposed to be OK for full
range. Not sure how well they did it, but they were supposed to be capable
of it. I heard them used on subs, never on full range, so I can't say. So
with some exceptions, the basic rule is subwoofer use only.
If I were you, I would NOT get rid of that PPI A1200 for a PowerAcoustik
ANYTHING. Class D or not. But, that's just me.

K, so you already knew the "skinny" on the circuitry, you were just amazed
at the price points! :-)
Gotcha.
And I know what you mean about the much-to-high damping factor on some amps
not mattering. PPI is one that comes to mind for having one that is VERY
high. Overkill, but it looks good. The amp you mentioned, low power pure
tube amps, are like you said, low power. Damping doesn't really come into
play much with that kind of wattage. Tube amps also tend to have very high
(relatively) THD ratings. Compared to some amps, very high. Some of them
with 6% and I've seen as high as 10%. But there are other factors that
negate these points. The end, IMHO, is a much warmer sound.
I think most of the class D's that are out now in car audio have fine sound
quality, and I doubt *I* could tell the difference.
I was just trying to give you the simple differences in design, and keep it
simple. Obviously you already knew the differences!

I still hate the words "digital amp". :-)

--
John Spagnolo - teamROCS #016
Multi Media Xpress Car Audio www.mmxpress.com
"It's about the music stupid!" John "Batvette" Lucier 98'
R.A.C. FAQ: http://www.mobileaudio.com/rac-faq/
JL Audio Tech Section: http://www.jlaudio.com/tutorials
MMXpress Tech Section: http://www.mmxpress.com/technical/


"Scott Gardner" wrote in message
...
Oh, I'm not getting rid of my PPI amps for anything. I just came
across the PowerAcoustik model when I was researching some other stuff
for a friend. I don't know anything about that brand, I was just
using it as an example.

As for why they're called "digital", I believe it's in reference to
the power supply switching method. I know it's a marketing term,
that's why I put "class D" in quotes.

I wouldn't be too concerned about the low damping factor. The only
reason that class AB amps have such astronomical damping factors is
because damping factor is related to the amount of global negative
feedback in the amplifier design, and AB amps use a LOT of global
negative feedback. If you look at class A tube amplifiers for home
use, some of them have damping factors of 20 or even lower, and they
have no problems controlling subwoofer movement. Damping factor
turned into a marketing selling point for car amplifiers, but it's
really just a by-product of the feedback circuitry. I think you'd
probably be hard-pressed to tell the difference between a damping
factor of 50 or 500, all else being equal. Some of the best-sounding
pure class A tube amps have damping factors of less than 10. However,
these tend to be single-ended triode amps, and generally put out less
than 10 watts per channel, so driving huge subs isn't a priority with
these amps.

So, it sounds like if sound quality isn't your top priority, and
you're just using it to efficiently throw a LOT of power to a
subwoofer, a "class D" amplifier might be a good choice. Do you know
of any models that are accurately-rated as to their power output? I'm
still getting over that 2300W PowerAcoustik amp for $300, and I'd like
to find out if that kind of watts-per-dollar ratio is really possible
with a "digital" amp.

Scott Gardner


On Sun, 21 Dec 2003 12:35:06 GMT, "John Spagnolo MMXpress.com"
wrote:

First, I know your calling them "digital" because thats the way they are
marketed. So I am not attacking your choice of words. But there is no
such
thing as a "digital amplifier". Digital means 1s and 0s. You can't
amplify
1s and 0s! You can convert an analog singal to digital, process the
signal,
and convert it back to analog for amplifying. Hence "digital singal
processing".
I have no idea why they are called "digital", but it just bugs me....

To try and answer your question though, they are much more efficient than
a
typical class A/B design. They take less space. Those are the major
advantages. I wont say "all" of them, because I dont know for sure, but
every one I have seen has a fairly poor damping factor, which means less
"control" of the sub, so it could sound sloppy (compared to a good Class
A/B). Overall they are not as good for sound quality as a Class A/B of
equal
quality build. Class D (or Class T, or BD, or whatever) use a different
type
switching which makes them useless for full range. They can't operate
fast
enough for full range. Infinity used to make a Beta series amp (they even
had the words DIGITAL on the amps) that was supposed to be OK for full
range. Not sure how well they did it, but they were supposed to be
capable
of it. I heard them used on subs, never on full range, so I can't say. So
with some exceptions, the basic rule is subwoofer use only.
If I were you, I would NOT get rid of that PPI A1200 for a PowerAcoustik
ANYTHING. Class D or not. But, that's just me.

--
John Spagnolo - teamROCS #016
Multi Media Xpress Car Audio www.mmxpress.com
"It's about the music stupid!" John "Batvette" Lucier 98'
R.A.C. FAQ: http://www.mobileaudio.com/rac-faq/
JL Audio Tech Section: http://www.jlaudio.com/tutorials
MMXpress Tech Section: http://www.mmxpress.com/technical/


"Scott Gardner" wrote in message
...
I don't have any first-hand experience with "class D" digital
amplifiers, but I saw an ad for a PowerAcoustik model that supposedly
puts out 2300W RMS into one ohm, and costs just a little over $300.
Even if they're wildly inflating the power numbers, that still sounds
like a hell of a deal. I paid almost that much for a Linear Power
2202IQ (about 375W RMS mono) in 1991, and $300 is about what I paid
for the used PPI A1200.2 (1200 WRMS mono) that I'm using now.

I know that digital amps are bandwidth-limited, making them
more suitable as subwoofer amps than as full-range amps, but are there
any other drawbacks to this design?

Scott Gardner