Hi... Me again... Does Class D (digital) & Class A/B make a differnce in the sound.


Bronze Member
Username: Baba


Post Number: 20
Registered: Mar-05
Am looking to buy a good 4 channel amp.
Suddenly came across the alpines which said class 'D', first thought it was a sub woofer amp but it was a 4 channel, little more research and turns out to be a digital amp..

Are the Digitals any good.
I have a choice between...

Alpine PDX-4.100
Alpine PDX-4.150

Amps i am considering ( in order of prefernce....)

Hifonics 4-Channel XXV Gemini 4 x 125-Watts.....RMS @ 4-Ohms
JL AUDIO 450/4 Amplifier
Rockford Fosgate Power T8004


If you not fed up with the mail till now... please read on...

(Others ( are they worth considering)
MTX Audio TE1004 ELITE 4 CHANNEL 1000W
HIFONICS XX-JUPITER 4 CHANNEL 4 x 75-Watts.....RMS @ 4-Ohms

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11923
Registered: Dec-03
I prefer a class AB for full range. when you see a full range "digital" amp its actually most likely a class T amp, not an actual D, as D topology doesn't filter the high frequency signal well enough to produce full range audio.

a bit on amp classes:

What are Amplifier Classes?

The Class of an amplifier refers to the design of the circuitry within the amp. There are many classes used for audio amps. The following is brief description of some of the more common amplifier classes you may have heard of:

Class A: Class A amplifiers have very low distortion (lowest distortion occurs when the volume is low) however they are very inefficient and are rarely used for high power designs. The distortion is low because the transistors in the amp are biased such that they are half "on" when the amp is idling. As a result, a lot of power is dissipated even when the amp has no music playing! Class A amps are often used for "signal" level circuits (where power is small) because they maintain low distortion. Distortion for class A amps increases as the signal approaches clipping, as the signal is reaching the limits of voltage swing for the circuit. Also, some class A amps have speakers connected via capacitive coupling.

Class B: Class B amplifiers are used in low cost, low quality designs. Class B amplifiers are a lot more efficient than class A amps, however they suffer from bad distortion when the signal level is low (the distortion is called "crossover distortion"). Class B is used most often where economy of design is needed. Before the advent of IC amplifiers, class B amplifiers were common in clock radio circuits, pocket transistor radios, or other applications where quality of sound is not that critical.

Class AB: Class AB is probably the most common amplifier class for home and mobile audio and similar amplifiers. Class AB amps combine the good points of class A and B amps. They have the good efficiency of class B amps and distortion that is a lot closer to a class A amp. With such amplifiers, distortion is worst when the signal is low, and lowest when the signal is just reaching the point of clipping. Class AB amps (like class B) use pairs of transistors, both of them being biased slightly ON so that the crossover distortion (associated with Class B amps) is largely eliminated.

Class C: Class C amps are never used for audio circuits. They are commonly used in RF circuits. Class C amplifiers operate the output transistor in a state that results in tremendous distortion (it would be totally unsuitable for audio reproduction). However, the RF circuits where Class C amps are used employ filtering so that the final signal is completely acceptable. Class C amps are quite efficient.

Class D: The concept of a Class D amp has been around for a long time, however only fairly recently have they become commonly used. Due to improvements in the speed, power capacity and efficiency of modern semiconductor devices, applications using Class D amps have become affordable for the common person. Class D amplifiers use a very high frequency signal to modulate the incoming audio signal. Such amps are commonly used in car audio subwoofer amplifiers. Class D amplifiers have very good efficiency. Due to the high frequencies that are present in the audio signal, Class D amps used for car stereo applications are often limited to subwoofer frequencies, however designs are improving all the time. It will not be too long before a full band class D amp becomes commonplace.

Other classes: There are many other classes of amplifiers, such as G, H, S, etc. Most of these are variations of the class AB design, however they result in higher efficiency for designs that require very high output levels (500W and up for example).
At this time I will not go into the details of all of these other classes.

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11924
Registered: Dec-03
a bit more from another article I did on amp specs

Amplifier Classes

There are five main amplifier designs: Class A, A/B, B, D, and Tube amplifiers. All of these but tube amplifiers are considered "solid-state."

Class A amplifiers are the most sonically accurate. On the other hand, they have some drawbacks that make them not be the most common choice. Class A amplifiers use only one output transistor that is turned "on" all the time, giving out tremendous amounts of heat. Class A amplifiers are very inefficient (~25%). More heat means more heatsink area, so even though most class A amps have built-in cooling fans, they are big. Pure class A amplifiers are usually expensive.

Class B amplifiers are the most common and use two output transistors. One for the positive part of the cycle and one for the negative part of the cycle. Both signals are then "combined". The problem with this design is that at the point when one transistor stops amplifying and the other one kicks in (zero volt line), there is always a small distortion on the signal, called "crossover distortion". Good amplifier designs make this crossover distortion very minimal. Since each transistor is "on" only half of the time, then the amplifier does not get as hot as a class A, yielding to a smaller size and better efficiency (~50%).

Class A/B amplifiers are a combination of the two types described above. At lower volumes, the amplifier works in class A mode. At higher volumes, the amplifier switches to class B operation.

The class D amplifier (known as digital amplifier) is the last of the solid-state types. These amplifiers are not really digital (there is no such thing), but operate similarly in manner to a digital-to-analog converter (DAC). The signal that comes in is sampled a high rates, and then reconstructed at higher power. This type of amplifier produces almost no heat and is very small in size. Efficiency is much higher in class D amplifiers (~80%).
The sound quality of a Class-D amplifier is much lower than that of other solid-state amplifiers, which is why Class-D amplifiers are only used for subwoofers in car audio. This is because the switching speed of the transistors, and lower sound quality are masked by the lower frequencies being reproduced by the subs, since distortion is harder to discern at low frequency.

other variations on a theme:

Class T: Class T (Tripath) is similar to class D with these exceptions: This class does not use analog feed back like its class D cousin. The feedback is digital and is taken ahead of the output filter, avoiding the phase shift of this filter. Because class D or T amplifier distortion arises from timing errors, the class T amplifier feeds back timing information. The other distinction is that this amplifier uses a digital signal processor to convert the analog input to a PWM signal and process the feedback information. The processor looks at the feedback information and makes timing adjustments. Because the feedback loop does not include the output filter, the class T amplifier is inherently more stable and can operate over the full audio band. Most listeners can not hear the difference between class T and good class AB designs. Both class D and T designs share one problem: they consume extra power at idle. Because the high frequency waveform is present at all times, even when there is no audio present, the amplifiers generate some residual heat. Some of these amplifiers actually turn off in the absence of music, and can be annoying if there is too much delay turning back on.

Class G: Class G improves efficiency in another way: an ordinary class AB amplifier is driven by a multi-rail power supply. A 500 watt amplifier might have three positive rails and three negative rails. The rail voltages might be 70 volts, 50 volts, and 25 volts. As the output of the amplifier moves close to 25 volts, the supply is switched the 50 volt rail. As the output moves close to the 50 volt rail, the supply is switched to the 70 volt rail. These designs are sometimes called "Rail Switchers". This design improves efficiency by reducing the "wasted" voltage on the output transistors. This voltage is the difference between the positive (red) supply and the audio output (blue). Class G can be as efficient as class D or T. While a class G design is more complex, it is based on a class AB amplifier and can have the same clean characteristics as well.

Class H: Class H is similar to class G, except the rail voltage is modulated by the input signal. The power supply rail is always just a bit higher than the output signal, keeping the voltage across the transistors small and the output transistors cool. The modulating power supply rail voltage is created by similar circuitry that you would find in a class D amplifier. In terms of complexity, this type of amplifier could be thought of as a class D amplifier driving a class AB amplifier and is therefore fairly complex.

Lastly we have tube amplifiers, which aren't often used in car audio. Tube amplifiers have about 50 to 60% efficiency.
Tube amplifiers are said to sound more musical. The reason is that tube amplifiers produce even ordered harmonics. Musical instruments give off harmonics in even orders. Transistor amplifiers tend to give off harmonics that are odd ordered. These harmonics are not pleasing to the ear as second order harmonics are. Modern solid state amplifiers have very low distortions but their distortions are less tolerated by the ear than even ordered harmonics. This means that when you hear someone say a Tube amp is "warm" sounding, they are actually talking about the second order distortion produced by that tube amplifier, which they find pleasing to the ear. A good example of this is in guitar amplifiers, which often pride themselves on their second order harmonics.
One should note that while most solid state amplifiers have very low distortions (Total Harmonic Distortion) for the left and right channel, other channels are often much higher as these specifications are rarely noted. Subwoofer amplifiers are particularly bad at creating odd ordered harmonics.
I believe that the best tube and solid state amplifiers sound amazingly alike. Bad tube amplifiers sound tubby and slow. Bad transistor amplifiers sound harsh, bright and strident.

Bronze Member
Username: Baba


Post Number: 22
Registered: Mar-05
thanks for the amazing replys glasswolf....
am so confuse now though..
I was buying the audison 2 channel amp, then thought go for more power so i thought of the
Jl audio 450/4..
Came across the new alpine PDX 150.4 , an amp that boasts both analogue and digital prowness.

Finally was offered a Japanese amp called Flying Mole DAD M100.. amazing reviews, can drive anything, they r small and digital..
So how would one choose..

Cause here we have all types..
I have a simple set of speakers the focal polyglass 165 V3E... ( 3 way comps, 75w @ 4 ohms)

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11939
Registered: Dec-03
those should do fine with 50-75 watts per channel.
if space or current (charging system) are concerns, go with the class D or T amps throughout. they are small, run cool, and draw less current.
If you're after the utmost in sound quality, I'd lean more toward the AB amps for full range at least.. class D do fine for subs.
Just remember class AB draw more current, and take more space. This can lead to a need for charging system upgrades.

Bronze Member
Username: Baba


Post Number: 25
Registered: Mar-05
nope, space is not a problem, budget is , have a budget of 400-500$s.
could you please suggest me a good ab amp, to run my focals..
I know very few people give out right suggestions but i am unable to try and kind of rely on reviews..
Thanks once agin glass house...
Please do suggest me an amp though... hehehe

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11958
Registered: Dec-03
look at PPI (precision power)
they make very nice amps, and a 75x4 @ 4 ohm amp shouldn't cost you nearly $500
« Previous Thread Next Thread »

Main Forums

Today's Posts

Forum Help

Follow Us