Class D vs Class A or A/B

[rumblinbass]

Hm, OK, I have to go do some more reading about that then.

I think of IC Op Amps as small power amplifiers. They share the same general topologies - input stage, voltage amplifier stage, and output (or current amplifier) stage. It is typically the output stage the determines whether it is Class A or AB. IC op amps typically have Class AB output stages. I haven't heard of any with a Class A output stages.

 

[teemuk]

At such low currents it doesn't practically matter one bit.

 

[jason weatherby]

Class A amps are typically found in mic pre-amps, high-end stand-alone audio pre-amps, the pre-amp stages of power amps and relatively low-power very high-end audiophile power amps. Nothing wrong with Class D amps. Many/most new very high-power PA amps are Class D including well-known PRO-grade amps from Crown, QSC, etc. Class D amps will likely obsolete Class A/B amps in most/all audio & instrument power amp applications as more new amps are designed. Class D amps have substantial advantages in power output, cost, weight, heat and efficiency.

 

[rumblinbass]

At such low currents it doesn't practically matter one bit.

we will agree to disagree then.

 

[ThisBass]

I think of IC Op Amps as small power amplifiers. They share the same general topologies - input stage, voltage amplifier stage, and output (or current amplifier) stage. It is typically the output stage the determines whether it is Class A or AB. IC op amps typically have Class AB output stages. I haven't heard of any with a Class A output stages.

They can be biased to work as class A.

 

[rumblinbass]

They can be biased to work as class A.

yes, they can. however, the typical current source/sink method tends to make them run hotter.

 

[ThisBass]

yes, they can. however, the typical current source/sink method tends to make them run hotter.

I myself don't need class A for an op amp
Maybe somebody else has an interest to do it ...

 

[ThisBass]

Beyound that A/B discussion even Class A is possible with Push Pull.
Push Pull does not signify it is always A/B.
Some HiFi push pull designs are class A
But I'd point out it's not an audible benefit.
My HiFi amp is class A push pull, never the less the cabs are more important.

 

[seamonkey]

There are Class-D pre-amps
Saves batteries
Even chips for it:
GS3018

 

[ThisBass]

Okay, so sonic differences aside, are there any other factors at play that keep leading me to believe that class D has certain characteristics I can detect? In my experience with the class D amp modules, I find that the notes have a very immediate feel to them. We tried a Hypex module and the punch and attack were so immediate that I kept thinking the notes were flying off the fretboard before I even plucked them. The big transformer based class A/B amps I tried had a more plush, slower response that I seem to prefer.

Another thing I noticed was that the class D amps seemed, to my ears to sound very similar at all volume levels, while the class A/B tended to have a different feel and response as the volume was increased and reached maximum output. Is there a basis for any of this? Maybe some difference in how these different amps control the speakers?

Total agreement.
For me that is the best description because I feel and understand with every word.

sorry, but I found no other words to explain.

 

[seamonkey]

Some of you should just go out and claim your $10,000
Link Removed

 

[12bass]

Part of the explanation for the "slower" sound of the line transformer/Class AB combination might be sag in the supply rails as power demands go up causing some dynamic changes in perceived transient response. Perhaps the Class D amp used for comparison has much stiffer supply rails, and thus stays more consistent (linear) up to the clipping point?

Also, bass amps tend to be called upon to work harder than most hi-fi amps, which may serve to highlight such differences.

 

[ThisBass]

I can understand all the tecs arguments whenever I myself thinking as a tec,
I can understand all the players arguments whenever I myself thinking as a player/musician.

All the long time I’m playing bass guitar and the piano, what means as long as I’m working as a musician and as long as I’m working as an audio technician/engineer, so far as I can remember there was always a difference in understanding and expressions between tecs and musicians.


So do I wonder about this long thread and the many different meanings?
No I don’t.

Do I wonder about the different meanings of different musicians?
No I don’t. Every musician plays different and feels different.

Do I wonder about the different meanings of tecs?
No I don’t. It is probably more the difference how to express.
I’m sure that a lot of differences in forum discussion would lead to a same view whenever discussed face to face.

As a musician I can point out statements that will be hard understood by a tec.
As a tec I can point out statements that will be ignored by musician.

 

[will33]

Part of the explanation for the "slower" sound of the line transformer/Class AB combination might be sag in the supply rails as power demands go up causing some dynamic changes in perceived transient response. Perhaps the Class D amp used for comparison has much stiffer supply rails, and thus stays more consistent (linear) up to the clipping point?

Also, bass amps tend to be called upon to work harder than most hi-fi amps, which may serve to highlight such differences.

Was going to mention possibly power supply drop, that's going to have a bigger effect in a dynamic, plucked string instrument signal than any recorded music, but this probably all comes back around to design intent again. As Roger mentioned, his engineer could probably get the class D module to act like what they were shooting for, but why bother, when the A/B module got them there without all the extra R&D.

When it comes to bass amps, in the end what matters is how it sounds and feels with the bass in your hands on stage, on the gig, in front of people. Measurements and listening tests and blind a/b comparisons and stuff help you reach the goal, they are not the goal in and of themselves but tools used in the process.

 

[ThisBass]

Part of the explanation for the "slower" sound of the line transformer/Class AB combination might be sag in the supply rails as power demands go up causing some dynamic changes in perceived transient response.

I don't think so.
A sag would sound different.
*edit: tecs canceled*

Perhaps the Class D amp used for comparison has much stiffer supply rails, and thus stays more consistent (linear) up to the clipping point?

I try to do a description.
The situation is similar like you have a less dynamic home theater cab system and then put for compare the Klipsch Horns or La Scala down to your walls.

Some cabs sound ever great.

Like the EV B1150M I noticed in a members profile ...
I wish I'd have one.

 

[agedhorse]

Uh there are both class AB and class A preamps. AFAIK there are no other classes of preamps in use.
Which bass amps have class A or AB preamps?
Some classic audio gear is class AB, or a mix of A and AB at different stages (like some famous compressors and limiters).
But then we would quickly start getting into opamp vs discrete etc.
I think that is a whole other thread topic though.

If you get off the beaten track a little bit, there are some fairly intersting IC op amp topologies that may have some impact on sound. I am aware of class A, AB, G/H and D topologies available in preamp IC's, the G/H are usually seen in higher voltage line drivers (very common in ADSL circuits) and class D in lower voltage headphone circuits.

Discrete op amps are usually A, AB and a few G/H, these can be seen in instrumentation products as well as audio.

 

[agedhorse]

I think of IC Op Amps as small power amplifiers. They share the same general topologies - input stage, voltage amplifier stage, and output (or current amplifier) stage. It is typically the output stage the determines whether it is Class A or AB. IC op amps typically have Class AB output stages. I haven't heard of any with a Class A output stages.

They do share the basic topologies but the implimentation (and resulting non-linear operational performance) is often VERY different. Current sources are easier/less expensive to impliment on an IC than a resistor, even if it takes 10 transistors/diodes to do so. A resistor may function identically to a current source for linear operation but as soon as the device is driven non-linearly serious differences may present themselves...

There are IC op amps with both AB as well as A output stages. It's also possible to bias some AB outputs into class A mode (this may or may not improve performance but it does make for interesting marketing ).

 

[Calaverasgrande]

If you get off the beaten track a little bit, there are some fairly intersting IC op amp topologies that may have some impact on sound. I am aware of class A, AB, G/H and D topologies available in preamp IC's, the G/H are usually seen in higher voltage line drivers (very common in ADSL circuits) and class D in lower voltage headphone circuits.

Discrete op amps are usually A, AB and a few G/H, these can be seen in instrumentation products as well as audio.

well yeah, but ADSL circuits have completely different specs than bass guitar. Much higher frequency range, and its not worried about noise floor or THD (at least not the part that exists in human hearing range. Thats why it can co-exist on a POTS line with just some low pass filtering on the phone side.

I didnt know there were class G headphone amps. Makes sense I suppose. I know they use something like that in cellphones too.

 

[agedhorse]

Agreed, I was just showing that it is possible to have an op amp as class H like ADSL. (would like to experiment with something like that but alas, no spare time to play )I also believe Maxim has a class H op amp targeted at head phone applications too.

 

[rumblinbass]

They do share the basic topologies but the implimentation (and resulting non-linear operational performance) is often VERY different. Current sources are easier/less expensive to impliment on an IC than a resistor, even if it takes 10 transistors/diodes to do so. A resistor may function identically to a current source for linear operation but as soon as the device is driven non-linearly serious differences may present themselves...

I have done some experimenting with this myself with discrete amplifiers. very interesting in terms of measurable performance and listening.

There are IC op amps with both AB as well as A output stages. It's also possible to bias some AB outputs into class A mode (this may or may not improve performance but it does make for interesting marketing ).

a couple of the guys I work with swear by the method of biasing op amp output stages into class a.