Class D vs Class A or A/B

[Bob Lee (QSC)]

It would be useful to determine the nature of what you call "fast" or "slow" response. Regardless of the power supply and class of amplification, the signal's going to run through the amp in at most a microsecond or so, unless it has a DSP (with A to D and D to A conversion) or some type of delay effect built in. But even with DSP, the latency is likely to be only a few milliseconds.

All amps are "fast" unless there's something intentionally put into the circuitry to slow the signal down.

In my experience, an amp with insufficient gain might seem "slow" because it makes me have to dig in too much when I play. I don't know if that's similar to the phenomenon you report.

 

[agedhorse]

Note that in my comments, I have qualified them as to well designed products. It's possible to create power amp sound differences and feel differences if you add these into the design... either intentionally or with a poor design. In most cases, the negative differences can be attributed to errors or poor design choices.

It's not the nature of the topology, as much as it's the choices in the design... specifically negative choices that subtract from performance. I suspect that some of these may not be true design choices either, but mistakes made in the design and/or layout.

 

[Duke21]

Bob and Agedhorse. I must say this thread is so far very educating thanks your technical input.
I have one question. Talking about the different classes of poweramps versus the tone created by the preamp, you guys are saying that with the right design any class of poweramp will achieve the desired tone and performance.
What is the point then by making the old type of amps such as all tube heads? If in understand correctly there is no real need for this type of amps regarding tone and performance. So what is left is plain nostalgia and the fact that it is possible to sell these amps for (maybe) higher profit. Or am I wrong?

 

[JimmyM]

Bob and Agedhorse. I must say this thread is so far very educating thanks your technical input.
I have one question. Talking about the different classes of poweramps versus the tone created by the preamp, you guys are saying that with the right design any class of poweramp will achieve the desired tone and performance.
What is the point then by making the old type of amps such as all tube heads? If in understand correctly there is no real need for this type of amps regarding tone and performance. So what is left is plain nostalgia and the fact that it is possible to sell these amps for (maybe) higher profit. Or am I wrong?

I have nowhere near the talent for amp design that guys like Bob and Andy have, but every time I plug into my B-15 or SVT, that tells me you're wrong

But seriously, there are certain characteristics that I've found are common in bass amps of a certain topology. Maybe it's different for power amps, but tube amps, iron powered SS amps, and micros have their own sets of characteristics as far as I'm concerned.

 

[Duke21]

I have nowhere near the talent for amp design that guys like Bob and Andy have, but every time I plug into my B-15 or SVT, that tells me you're wrong

But seriously, there are certain characteristics that I've found are common in bass amps of a certain topology. Maybe it's different for power amps, but tube amps, iron powered SS amps, and micros have their own sets of characteristics as far as I'm concerned.

Well, I'm not sure if I'm right or wrong... as I've no personal long lasting experience of living with an SVT or a B15, you are damn lucky there Jimmy!
Neither I have the technical knowledge of Andy and Bob, so I'm dependent of reading what they or you are saying.

Andy mentioned earlier (regarding this "SS distortion fo the Ampeg SVT VR) that the tone of an amp is the sum of ALL components, which is logical. But both Andy and Bob or maybe mostly Bob said that the type of the amp (A/AB/H or D) are not the deciding factor regarding tone and performance as all type of amps can achieve the same goal when the design is right.

So, I can't really claim anything, I just try to understand what is "right" or "wrong".

Anyway, I find the discussion very interesting from the technical point of view. I'm a product designer myself, but my engineering background is mechanics.

 

[JimmyM]

Well I'll refrain from getting in over my head here, but I definitely hear a difference in bass amps of different power amp topologies. Why I hear them, I don't know, but I really don't think it's all in the preamp.

 

[Duke21]

I'll think that all parts of a product must have an effect over the overall performance.
For instance if a car have one or an other type of suspension system. Both can be tweaked to achieve the same goals and might perform in almost the same manner but I bet somebody will feel some differences.
In bike racing a good rider will be able to tell apart his nr. 1 bike and nr. 2 bikes even if both of them are setup in the same way. So, I bet the rider will be able to tell the different if somebody swap the engine with an other engine which gives exactly the same performance but lets say have an other configuration. For instance going from inline 4 to V4.

 

[arai]

Well, I'm not sure if I'm right or wrong... as I've no personal long lasting experience of living with an SVT or a B15, you are damn lucky there Jimmy!
Neither I have the technical knowledge of Andy and Bob, so I'm dependent of reading what they or you are saying.

Andy mentioned earlier (regarding this "SS distortion fo the Ampeg SVT VR) that the tone of an amp is the sum of ALL components, which is logical. But both Andy and Bob or maybe mostly Bob said that the type of the amp (A/AB/H or D) are not the deciding factor regarding tone and performance as all type of amps can achieve the same goal when the design is right.

So, I can't really clain anything, I just try to understand what is "right" or "wrong".

Anyway, I find the discussion very interesting from the technical point of view. I'm a product designer myself, but my engineering background is mechanics.

It is really interesting. Very informative.

Re the SS distortion of the Ampeg SVT VR and the tone stack etc. I wonder if that is why some people get confused and mistake the pro 7 for having a tube tone, when really they are just used to the "Ampeg" preamp tone and mistake that for tubetone.

 

[KJung]

Well I'll refrain from getting in over my head here, but I definitely hear a difference in bass amps of different power amp topologies. Why I hear them, I don't know, but I really don't think it's all in the preamp.

You definitely hear differences across EVERY amp, like most of us. However, it isn't really a good idea to think about that due to power amp design (unless you really push an amp into distortion, where tube power sections do obviously behave differently).

Just think about it this way.... compare a Thunderfunk to a DB750 to a Glock Heartrock to an SWR900 to an Eden WT800, etc. TOTALLY different tonality to all of them, even though they are all 'class A/B amps' with traditional, heavy power supplies. Totally different, due to a zillion reasons (power management, limiters, THD, hi passing, preamp voicing, etc.).

Compare a Glock Blue Soul to a Markbass F500 to an Aguilar TH500 to a Genz Streamliner to a Genz Shuttle to a GK MB800 to a Walter Woods to a Puma900 etc. All sound VERY different.

Some heads in each group sound much more similar (and feel much more similar) to heads in the other group than to heads within their 'power amp class'.

Also, there are still the 'unusual' combination hybrids (the AG500, which is class D with a power transformer), the LMII/III which is class A/B with SMPS, etc.

All heads sound different, and as Andy and other engineers have posted, it is all about execution and design that gives all these heads (regardless of topology) their unique tone.

Kind of a moot point, since all should use the amp they prefer, regardless of topology, but that is the point of the original question. NO amp shopper should limit themselves to a particular topology (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).

Limit your choices based on brand reputation/reliability, size, weight or features, but I would highly recommend not really bothering with 'what is under the hood' at this point in the bass amplification life cycle.

 

[chadds]

You definitely hear differences across EVERY amp, like most of us. However, it isn't really a good idea to think about that due to power amp design (unless you really push an amp into distortion, where tube power sections do obviously behave differently).

Just think about it this way.... compare a Thunderfunk to a DB750 to a Glock Heartrock to an SWR900 to an Eden WT800, etc. TOTALLY different tonality to all of them, even though they are all 'class A/B amps' with traditional, heavy power supplies. Totally different, due to a zillion reasons (power management, limiters, THD, hi passing, preamp voicing, etc.).

Compare a Glock Blue Soul to a Markbass F500 to an Aguilar TH500 to a Genz Streamliner to a Genz Shuttle to a GK MB800 to a Walter Woods to a Puma900 etc. All sound VERY different.

Some heads in each group sound much more similar (and feel much more similar) to heads in the other group than to heads within there 'power amp class'.

Also, there are still the 'unusual' combination hybrids (the AG500, which is class D with a power transformer), the LMII/III which is class A/B with SMPS, etc.

All heads sound different, and as Andy and other engineers have posted, it is all about execution and design that gives all these heads (regardless of topology) their unique tone.

Kind of a mute point, since all should use the amp they prefer, regardless of topology, but that is the point of the original question. NO amp shopper should limit themselves to a particular topology (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).

Limit your choices based on brand reputation/reliability, size, weight or features, but I would highly recommend not really bothering with 'what is under the hood' at this point in the bass amplification life cycle.

Well said!!!

 

[KJung]

Well said!!!

Your 'class D/SMPS' Bergantino IP310 is the best example of this I know... probably the most hammering low end I've experienced, and it shows how a designer can take a relatively off the shelf ICE module and make it totally sing and hang with 'the big boys' (in this case, through the use of DSP circuitry).

 

[agedhorse]

It is really interesting. Very informative.

Re the SS distortion of the Ampeg SVT VR and the tone stack etc. I wonder if that is why some people get confused and mistake the pro 7 for having a tube tone, when really they are just used to the "Ampeg" preamp tone and mistake that for tubetone.

I think this could be a large part of it.

Regarding a tube power amp, there are things that can be done to take say a class AB or D amp and get very close (probably not identical) performance to a tube power amp but so much of the feel and tone is in the preamp execution that it's more productive to spend much of the (tonal goal) design time there.

It's not that it can't be done, it's sometimes more of liking a particular tube power amp's performance except for "this or that" (like size, weight, tightness, heat, cost, reliability) and finding that it's better achieved in a different approach.

I don't think that designers are attempting to "nail" the SVT tone because at that point why not just "copy it"? It's more likely because they are trying to put their own spin on something that is desireable but to make it in a way that may be more useful to those who find something about the SVT not to their liking. Otherwise, we would all own SVT's. Even Ampeg has different models with different features and performance.

 

[Mykk]

I picked up a Behringer Nu6000 class D poweramp, I use it to amplify an Ampeg SVT-IIP preamp & BBE382i and to power a Mesa 215EV and Fender PRO 810.

During last weekends shows I only used the Mesa 215, at 1/4 volume not only was I delivering enough power and clean tone to fill the big stage and auditorium sized room. I actually had the sound guy ask me to turn down.

It delivered a nice, big, full bodied tone with some serious sub harmonic overtones. It performed beautifully and never really got hot.

I am sold on class D as a nice, lightweight, powerful alternative to otherwise bulky and heavy amps. I say that as I just recently picked up a Mesa M-2000 and intend to retire the Ampeg Pre & poweramp. IMO it's worth lugging around the weight for the Mesa tone

 

[JimmyM]

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.

 

[agedhorse]

I should also mention that some particular architectures within a topology might be preferred to a designer for performance reasons other than sound, feel, tone, etc. These might include non-user related aspects such as thermal stability, EMC radiation or conducted emissions, relaibility, compatability with existing production processes, availability of parts, and even the designer's long term history and comfort level with a particular architecture.

 

[agedhorse]

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 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.

 

[KJung]

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.

To your first point... not necessarily. Probably different gain structures between the signal the preamp is sending to the internal amp versus the external, hi passing and other voicing, etc. that might or might not impact the direct out, etc. Also, most agree that a tube power section seems a bit of a different thing in general.

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

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!

 

[Bob Lee (QSC)]

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.

+googol

 

[JimmyM]

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.

Word.

 

[ThisBass]

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