Class D vs Class A or A/B

[agedhorse]

To your second point, that IS my point. Kind of supporting Andy's point above.... if you like the way an amp sounds, you shouldn't care if there are two chipmunks cranking on a wheel in there... who cares

Hey Ken, you might want to check to see if Apple has a patent on this first

 

[seamonkey]

T if you like the way an amp sounds, you shouldn't care if there are two chipmunks cranking on a wheel in there... who cares

Edit: AND, if you are lucky enough to find that a 4 pound amp is among the best amps you've ever heard, then you are REALLY in good shape!

+1


Quantum amplifiers are next that will change their insides when you peak in the box.

 

[fdeck]

I am going to say something that might be disturbing to some of the technophiles, but I think that maybe worrying less about topology and more about getting out and just playing bass and enjoying it might have more impact on the overall musical experience.

Thanks, I needed to be reminded of that.

 

[KJung]

+1


Quantum amplifiers are next that will change their insides when you peak in the box.

Schrodinger's Shuttle. It is tube and solid state until you pop the top

 

[Mark Reccord]

Good counterpoints made by all, but still, I think the differences in power amp topology make a difference. If not, when I run the preamp of my B-15 through the power amp of my PF350, it would sound the same as when I use the B-15's own tube power amp. Clearly that's not happening It does sound very good, yes, but not quite the same.

However, Ken, I do think you're right that we should worry about the topology less and about what we're hearing more as different amps don't sound alike even when the topology is the same.

I think the B-15 falls into the category of amp where the power amp definitely does have a sonic signature whether by design or by fluke. That's not necessarily due to its topology. Given fully linear operation, I think it would be difficult to pick up much difference between competently designed power amplifiers that were designed to be as transparent as possible (i.e. all professional power amps). Like I always say in these things, once you introduce any clipping/overload behaviour the differences become apparent. Again, not necessarily due to topology per se.

I am going to say something that might be disturbing to some of the technophiles, but I think that maybe worrying less about topology and more about getting out and just playing bass and enjoying it might have more impact on the overall musical experience.

Anathema!

I'm luckily able to turn the technical side of my head off when I'm playing. The last thing I'm thinking of on stage is power amp topology.

Schrodinger's Shuttle. It is tube and solid state until you pop the top

Sort of related to this, I'd like to do 4 different implementations of an amp. Common preamp, with the following combinations of power supply and power amp:

SMPS, Class D
SMPS, Class AB
Conventional PS, Class D
Conventional PS, Class AB

All designed to be as transparent as possible, with best case overload behaviour; set up to be gain matched; same power output. Then I'd also add weight to the appropriate amps such that they all weighed the same and not put any indication of which was which on the outside, which would totally flatten the playing field for testers. Then see if there was a clear sonic winner.

 

[BbbyBld]

Sort of related to this, I'd like to do 4 different implementations of an amp. Common preamp, with the following combinations of power supply and power amp:

SMPS, Class D
SMPS, Class AB
Conventional PS, Class D
Conventional PS, Class AB

All designed to be as transparent as possible, with best case overload behaviour; set up to be gain matched; same power output. Then I'd also add weight to the appropriate amps such that they all weighed the same and not put any indication of which was which on the outside, which would totally flatten the playing field for testers. Then see if there was a clear sonic winner.

New monkey wrench...I think, because this thread has gotten long...

Which SMPS topology? That makes a difference in my experience.

Regulated or unregulated SMPS? That also makes a difference depending on application of the amp AND topology of supply and amp.

Same thing for the conventional power supply.

Which class D/AB topology with which supply?

These things matter for bass guitar. The amp macro-topology, AB/D, doesn't matter as long as the design doesn't suck.

 

[will33]

Dang......nice read.

I hadn't opened this thread the last few pages, figured it probably just degenerated into some amp pissin' contest or something. Well, that couldn't be further from the truth.

Many thanks to our engineers here for sharing their experiences with this stuff. Very informative....and civil.

 

[teemuk]

On stage I don't consider any specs or schematic designs.

Not many of us do. But if people wouldn't consider those things at least some time you wouldn't have amps to use on stage.

I don't see how such arguments should or could negate the importance of this discussion.

 

[Calaverasgrande]

To be honest I think 90% of what we think of as "tube tone" is not the power amp specifically. It is more in the much different EQ section you find in most tube based preamps and in the power output transformer.
If you made a bass amp using transistors for a class a preamp, followed by an inductor passive EQ with various emphasis circuits that can be switched in. Then a class AB push pull output feeding an output transformer for the speaker out.
That would be hard for most of us to distinguish from a tube amp.
AFAIK only GK and Warwick have done anything like this. GK had some guitar combos with a transformer coupled output. The Warwick Jonas Hellborg "expensive as a new kidney" line of amps appear to have this type of design in mind. Of course I would rather upgrade my right kidney before I could afford the Warwick stuff.

BTW I've gigged vintage Traynor, Ampeg and Mesa all tube gear. All sounded completely different. With the Traynor sounding the most "tubey" and the Mesa the least.

 

[Calaverasgrande]

except, I guess, those head bangers that really get their tone from power tubes being pushed.... I get that. Also, I get that you like the tone of an SVT run clean, and that makes it worth carrying around a 100 pound head.

Hey my Mesa only weighs 45 lbs!
Which I do have to admit I once broke my thumb trying to catch when my rig got knocked over.

 

[Duke21]

I know the Sansamps are not really amps, but they are preamps. I do not own any other amp then my Ibanez 20W combo.
Just out of curiosity, do anybody knows what kind of class is the preamp in the BDDI?

 

[Duke21]

To be honest I think 90% of what we think of as "tube tone" is not the power amp specifically. It is more in the much different EQ section you find in most tube based preamps and in the power output transformer.
If you made a bass amp using transistors for a class a preamp, followed by an inductor passive EQ with various emphasis circuits that can be switched in. Then a class AB push pull output feeding an output transformer for the speaker out.
That would be hard for most of us to distinguish from a tube amp.
AFAIK only GK and Warwick have done anything like this. GK had some guitar combos with a transformer coupled output. The Warwick Jonas Hellborg "expensive as a new kidney" line of amps appear to have this type of design in mind. Of course I would rather upgrade my right kidney before I could afford the Warwick stuff.

Interesting!

 

[bongomania]

I know the Sansamps are not really amps, but they are preamps. I do not own any other amp then my Ibanez 20W combo.
Just out of curiosity, do anybody knows what kind of class is the preamp in the BDDI?

That word "class" doesn't apply to preamps, only to power sections (in this context).

The BDDI is solid state, it uses transistors for distortion.

 

[Duke21]

That word "class" doesn't apply to preamps, only to power sections (in this context).

The BDDI is solid state, it uses transistors for distortion.

Yes, I guess, you are right. But what about headphone amps, are these amps or preamps? As you see earlier in this thread I placed a picture of my SS class A headphone amp.

 

[seamonkey]

Sort of related to this, I'd like to do 4 different implementations of an amp. Common preamp, with the following combinations of power supply and power amp:

SMPS, Class D
SMPS, Class AB
Conventional PS, Class D
Conventional PS, Class AB

All designed to be as transparent as possible, with best case overload behaviour; set up to be gain matched; same power output. Then I'd also add weight to the appropriate amps such that they all weighed the same and not put any indication of which was which on the outside, which would totally flatten the playing field for testers. Then see if there was a clear sonic winner.

It doesn't need to be so stringent, Richard Clark was offering a $10k prize anybody who could hear a difference in just off the shelf amplifiers.

Link Removed

I'm not sure that this is still on, he started it in 1990, but I read hundreds participated and nobody has ever scored over 65%

"
Richard Clark is an audio professional. Like many audiophiles, he originally believed the magazines and marketing materials that different amplifier topologies and components colored the sound in unique, clearly audible ways. He later did experiments to quantify and qualify these effects, and was surprised to find them inaudible when volume and other factors were matched.
His challenge is an offer of $10,000 of his own money to anyone who could identify which of two amplifiers was which, by listening only, under a set of rules that he conceived to make sure they both measure “good enough” and are set up the same. Reports are that thousands of people have taken the test, and none has passed the test. Nobody has been able to show an audible difference between two amps under the test rules."


"

By Richard Clark
There is no question that all amps are not the same. It is very easy to measure large differences in the performance of amplifiers. This is true in nearly every known specification, including power, noise, distortion, etc. My experience has led me to believe that even though these differences can be easily measured, hearing those differences may not be so easy. Given the relatively small magnitude of performance differences, there is a giant step between amplifier performance and our ability to hear performance differences.
It is claimed by designers, manufacturers and especially salespersons that differences in amplifiers are clearly audible. Reasons include "obvious" advantages of one type of circuit topology over another. For example, it is claimed that certain designs have a smoother midrange response whereas other amplifiers exhibit tighter bass. Tube fanatics claim that tube amplifiers have that "warm" sound we all need in our systems.
Such descriptive terms are certainly subject to personal interpretation. It is not my intention to determine if one particular amplifier is better than another amplifier. Differences in the quality of the discrete components and constructions are more appropriate for settling the issue of "good - better - best." The sole purpose of my amplifier challenge is to determine if the differences in amplifiers are audible."

 

[teemuk]

AFAIK only GK and Warwick have done anything like this.

Trace Elliot did it too. I have also seen a Fender patent for a transformer coupled design (dating to late 1970's) but I have never seen any reference whether they applied that patent to some product or not. I don't know about Hellborg amps but Trace Elliots and GK amps implemented some tube-like soft clipping to the mix too.

I have a hunch that in Hellborg amps the transformer is only a generic impedance matching element, and as such, such impedance matching transformers could be purchased by several vendors and installed to just about any amp. PA amps of the old days used to have such and no one discussed about particular transformer characteristics. They are basically very transparent in that kind of application.

Personally, I feel the transformer coupling may or may not have an effect. In bass amps the demands for the transformer are higher, which introduces greater chance for things such as saturation but all in all I think the greatest difference is actually introduced by the typical circuit architecture a generic "tube like" transformer-coupled design calls for.

Usually you end up with a moderately low open loop gain amp with very little feedback and a highish output impedance. Add the typical use of very non-linear amplifying elements (these could be tubes or they could be MOSFETs, transistors or sometimes diodes, OTAs or even CMOS logic gates) and its pretty easy to design in some sort of "soft saturation", which in the particular design arhitecture is not hindered by negative feedback in great amount. All this will definitely have its effect on tone, particularly in the areas of response to reactive loads and overall characteristics of overdrive.

Then we may have amps with aforementioned soft saturation combined to effects such as DC bias shifts causing crossover distortion when the amp gets overdriven. These can also be mimicked to a great degree as is proven, for example, by H&K "Quantum" series hybrid amps with a very clever and "tubish" power amp design. I'm not sure whether it was class-D or class-AB -based but the core was some pretty neat analog signal processing mimicking the architecture of a typical push-pull tube amp. This processing circuit was basically just coupled to a generic linear power amp but global feedback loops made the stages interact like they do in a real tube system the amp aimed to mimic.

So, not all power amps are deliberately made to be super linear.

 

[tombowlus]

New monkey wrench...I think, because this thread has gotten long...

Which SMPS topology? That makes a difference in my experience.

Regulated or unregulated SMPS? That also makes a difference depending on application of the amp AND topology of supply and amp.

Same thing for the conventional power supply.

Which class D/AB topology with which supply?

These things matter for bass guitar. The amp macro-topology, AB/D, doesn't matter as long as the design doesn't suck.

Good points. In our testing of class-D output sections, our results would indicate that even when manufacturers use the same off the shelf output module, factors such as the power supply, the line filtering, and the approach to limiting have a very measurable difference observed output.

 

[Calaverasgrande]

That word "class" doesn't apply to preamps, only to power sections (in this context).

The BDDI is solid state, it uses transistors for distortion.

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.

 

[bongomania]

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

 

[rumblinbass]

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.

+1.
I haven't come across any (not to say that there aren't any) Class A Op Amp IC's. The only IC's I am aware of are Class AB. Most of the Solid State preamps out there use Op Amps - which again, are Class AB.

I am sure there are a lot of Solid State discrete preamps out there but that does not necessarily mean that they are Class A or AB.