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Class D popping up everywhere. Innovation?

#82
agedhorse said:
There are a lot of class G/H power amps out there, Crest, Crown, Peavey all make them.
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I guess I was referring to the micro head craze more than the PA amp side of things as the question pertained to you.

I'm very glad that people like you, Bob Lee, Bill FitzMaurice, GreenBoy, etc.. are on here. I really enjoy learning from the knowledge that you all freely post on this forum.
 
#83
All power amp output sections are essentially analog - they MUST be to drive speakers. There are linear types (A, AB, etc.) and non-linear (D).

Class D amps are so efficient because the outputs only switch ON or OFF very quickly. It is the in between that creates the heat and distortion of linear amps. They are NOT "digital" which generally refers to to a bit stream created from the analog audio so that it can be stored and manipulated in digital memory and processor chips.

Class D amps can use cruder output transistors that are chosen for high output power handling rather than low distortion. The low heat generation also makes them ideal for small IC amps used in virtually all MP3 players, etc.

With present technology, it is difficult (read expensive) to create high power at wide bandwidth with Class D, which is why Class D amps are more often found in bass amps, where they work very well.

There are 2 problem areas in power amps - the output section and the power supply - that handle a lot of power and create heat. Either or both can be replaced with switching technology that removes the heat by using the transistors only in ON or OFF modes, where little heat is created. However, it is difficult (read expensive again) to have the power supply AND the output section doing switching, so usually it is only one or the other.

Sorry if this is overly technical, but it seems that many of you would like to know this.
 
#84
Gio S said:
Class D amps can use cruder output transistors that are chosen for high output power handling rather than low distortion.
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I'm not sure I would use the term crude... they must be blazingly fast, high output current and low gate capacitance and high (current) gain. They did not exist in the form they do today even 10 years ago.
 
#86
seamonkey said:
http://www.freepatentsonline.com/3011025.pdf
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Very cool, notice that there is little practical description of what's going on within the multivibrator block, which itthe heart of the process. Nowadays they discuss the comparator and gating of signals to create the PWM pulse train. Back then, it was very difficult to do and tricky too. Also notice that the waveform reconstruction is being done with the transformer (matching also) and the electro-mechanical properties of the speaker. It's the low pass function that's important.

Want to bet that amp spewed RF?
 
#87
There have been experiments with digital amps but there are none on the market. They have serious problems that have not been resolved. Class D has pulse width modulation not pulse code... it is properly called a switching amp. This is a power supply thing and it can power an AB or whatever amp. THERE ARE NO DIGITAL PREAMP OR AMPLIFIERS ANYWHERE! A class A amp has pos & neg signal going through one device, tube or transistor, and a class B has pos going to one and neg going to another one. It is the transition from pos to neg where around zero the signal can become nonlinear. This is the advantage of class A. The advantage of class b is efficiency and power output. The class AB will stay at A until at higher power output is required whereby it will switch to B. The sound of these amps will be essentially the same until they hit clipping. A tube amp will distort in even harmonics 2nd mostly and some 4th that are musical and are related to the fundamental like a instrument resonates (warmth). The transistor will distort in 3rd, 5th, 7th harmonics that are very non-musical (dirty). A class D clips like smashing into a brick wall and simply runs out of power without any reserves (nails on a chalkboard). This is the best I can do to explain without getting complex.
 
#88
Bellair Audio said:
A tube amp will distort in even harmonics 2nd mostly and some 4th that are musical and are related to the fundamental like a instrument resonates (warmth). The transistor will distort in 3rd, 5th, 7th harmonics that are very non-musical (dirty).
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A tube amp will typically distort with both even and odd harmonics. However, the actual harmonic content is related to the symmetry or asymmetry of the clipping rather than the type of device used. A waveform that clips symmetrically on both polarities of the signal will distort in a way that produces odd-order harmonics. This is a common characteristic of transistor power stages, but transistor and tube circuits alike can be designed to have any of a very wide range of clipping behaviors (this is the idea behind fuzzboxes).
 
#89
Bellair Audio said:
THERE ARE NO DIGITAL PREAMP OR AMPLIFIERS ANYWHERE!
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Wrong to the bolded part. Been using multieffects pres that are at least partially DSP-driven for a long time, and the Roland V-Bass became my primary preamp in early 2003. A fair number of other examples are to be found as well (POD ring a bell?). Also more people are beginning to explore using laptops with real-time control pedals to play live (Squarepusher being a notable early example worth checking out), as well as for recorded stuff where VST is not snickered at. Among others, the Peavey Revalver seems to be selling decently - both as a software package and running as firmware on dedicated combo "amp" hardware for guitarists.
 
#90
I am speaking in general terms and not about circuits designed to distort. A tube will distort MOSTLY 2nd harmonics and not enough of the others to discuss. And I forgot to mention transformers. A class D does not require a transformer as it is replaced by the switching transistors. Class A & B have transformers and large capacitors for a power supply so the lightweight amps are class D or a variation of D.
 
#93
Bellair Audio said:
Once again THERE ARE NO DIGITAL AMPS!!!!! You are confused! DSP is used in class T amps in the delivery of voltage to the amp - read power supply.
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Poor reading comprehension or memory retention on even your own text from a few minutes back, eh? ; } Look at the word I bolded when I quoted your post: PREAMP. And that was exactly what I addressed: PREAMPS - and not AMPS. You brought PREAMPS up, in case you still are having trouble with this line of thought.
 
#94
Bellair Audio said:
I am speaking in general terms and not about circuits designed to distort. A tube will distort MOSTLY 2nd harmonics and not enough of the others to discuss. And I forgot to mention transformers. A class D does not require a transformer as it is replaced by the switching transistors. Class A & B have transformers and large capacitors for a power supply so the lightweight amps are class D or a variation of D.
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You are confusing the power supply with the output stage. Most class A or class AB transistor power amps have no output transformer, the transformer is for the power supply.

There also exist class D amps with linear(transformer) power supplies, I've got three of them sitting right across the room form me (Crest CD series).

There is also no reason one couldn't put a SMPS in front of a transformer coupled tube output stage. I think the Peavey VB3 is supposed to do this.
 
#96
Bellair Audio said:
I am speaking in general terms and not about circuits designed to distort. A tube will distort MOSTLY 2nd harmonics and not enough of the others to discuss. And I forgot to mention transformers. A class D does not require a transformer as it is replaced by the switching transistors. Class A & B have transformers and large capacitors for a power supply so the lightweight amps are class D or a variation of D.
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The second harmonic will typically be the strongest after the fundamental. The third, fourth, fifth, and others will be progressively weaker. They are present, nonetheless.

You are confused about transformers and amp classes.
 
#99
THERE ARE NO DIGITAL PREAMPS!!!! I dont care if its pre, post or linear! We are talking about amplifying digital signals and this does not exist. The power supply is a different matter and that is what makes class D different in that it does not REQUIRE a transformer.
The advantage is weight of course but you could use a transformer if you wanted. DSP is the difference to make a class T amp from a class D and all this is is power supply variation. If you are talking about class A or B it is assumed there is no output transformer! Of course there are ALWAYS examples that differ. Macintosh has output transformers on their transistor amps and I have seen tube amps with no transformer!
 

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