Class D Amps - Anyone else having second thoughts?

[Bob Lee (QSC)]

Julian Hirsch was one of the first audio magazine contributors to actually seek to correlate what we can hear with what we can measure. A lot of people still don't understand what he was doing.

 

[R Baer]

Different strokes. If I noticed a difference, I'd be all over it with my test gear, and would probably not stop until I understood the root cause.

Hey fdeck. Now you make a pre amp, correct? Are you saying that you could go out and listen to 4 or five different power amps of different topologies hooked up to your preamp and you wouldn't expect to hear any differences in your final amplified bass signal between them?

Our engineers had a very good grasp of the differences between the amp topologies. All I'm saying is that when it came down to making a final decision as to which power section to put in our amp, I used my ears.

 

[Bob Lee (QSC)]

Unless they weren't very good power amps, I'd expect them to sound alike or at least extemely close.

 

[12bass]

Hirsch-Houck Laboratories tested some of my audio gear, IIRC. IMO, there is much to study in the field of psychoacoustics, as well how that field relates to audio engineering. Although it is reasonable to be skeptical about the claims of many audiophiles, too often engineering types seem to think that which has been quantified trumps what can reliably be perceived by trained listeners. In the early days of digital audio, while extremely low distortion numbers were touted by the industry, there was little focus on linearity and distortion products at low levels. Sometimes what's heard by the listener is not the same as the variable which has been measured.

 

[fretno]

Do you think there will be a reason to go smaller and higher powered than where the current tech is now ? You still need / want speaker cabs which are pretty much at their smallest , lightest & most efficient . I kinda think we are in the high point of bass amp tech and it feels good to be a bassist

 

[fdeck]

Hey fdeck. Now you make a pre amp, correct? Are you saying that you could go out and listen to 4 or five different power amps of different topologies hooked up to your preamp and you wouldn't expect to hear any differences in your final amplified bass signal between them?

I would expect the power amps to sound the same when operating below clipping. That's why I would want to dig deeper if they sounded different.

Our engineers had a very good grasp of the differences between the amp topologies. All I'm saying is that when it came down to making a final decision as to which power section to put in our amp, I used my ears.

That's cool. "Nail down a few good alternatives and then let the boss make the final decision" is a time honored engineering practice. And I would always use my ears in final test, just because it's one more way to cross-check the results obtained by the engineers. Also, it's vital to review aspects such as ergonomics and aesthetics.

By day, I work with "instruments" of a different nature: Scientific instruments. When two instruments that purport to measure the same thing give different results, my instinct is to find out why. But I am also an engineering manager, so I understand that I shouldn't micro-manage. Thus a good compromise would be to ask the engineers for an assurance that they understand and have documented the root cause for the differences in sound between the different amplifiers, in case anything ever goes wrong or the design needs to be updated. Not knowing why something works is OK until it stops working.

 

[pgk]

Julian Hirsch was one of the first audio magazine contributors to actually seek to correlate what we can hear with what we can measure. A lot of people still don't understand what he was doing.

oh i know he Did do a lot of good, holding manufacturer's feet to the fire regarding claimed specs and such. but i think he left a lot of important measurements out of the equation too, or maybe they were'nt known at the time, i just don't know. science advances like everything else, and we have far more precise measuring equipment and a better understanding about distortions and non-linearities than we did back then. "perfect sound forever" anyone? i am a dilletante with this stuff, neither engineer or tech, but have been fascinated by it for well over 40 years now. someone like Vladimir Shushurin of Lamm Industries, now his approach fascinates me. he has a set a mathematical equations and formulas he developed on his own and applies them to his designs. he never listens for his decision making, he makes his judgements based solely on the graphical representations of his own formulas, which are proprietary. and others using more empirical approaches interest me just as much. yeah bob as your sign off sig says, as Duke so aptly put it, "if it sounds good it Is good". it's really all that matters.

here's more on Lamm for anyone interested:

http://www.soundstage.com/revequip/rise39.htm

http://www.soundstage.com/rise16.htm

 

[R Baer]

..That's cool. "Nail down a few good alternatives and then let the boss make the final decision" is a time honored engineering practice...

Well, it does work well with the right combination of people. I'm am not an engineer myself, just a bass player, so a lot of the time I simply have to trust my ears and let those with the engineering know how worry about the how and why.

 

[JimmyM]

Well, it does work well with the right combination of people. I'm am not an engineer myself, just a bass player, so a lot of time I simply have to trust my ears and let those with the engineering know how worry about the how and why.

so how did you get your nam...

oh yeah, i forgot...how silly of me

 

[xray]

Well, it does work well with the right combination of people. I'm am not an engineer myself, just a bass player, so a lot of time I simply have to trust my ears and let those with the engineering know how worry about the how and why.

From what i "see" (with my eyes, not a piece of test equipment calibrated to the National Calibration Standards) the exterior of your new amp: Valkyrie - looks pretty sexy!!

 

[xray]

Seriously, all this talk about A/B ing two different amps to prove they can sound the "same" -what's the frick'n point? You dial an amp to produce a specific sound - not so it sounds like someone else's amp.

Good grief, engineers and their test equipment! I know an oscilloscopes can display a eletronic trace of current and voltage - but can they hear? NO.

Amp topology makes a difference. Just like the difference between acrylics, watercolors and oils make on a canvas.

 

[agedhorse]

Good amp designs operating in their linear reigons tend to sound similar, I agree.

Where differences can be audible is where amp designs are not good, and specific topologies tend to have particular "defects" or significant artifacts whe driven outside their linear regions (clipping) and especially into reactive loads.

There are some interesting topologies that perform very well under controlled conditions (like CFB output stages) but throw clipping, and throw a slightly capacitive load at them and they can chatter, oscillate, stick to the rails and blow up like the Hindenburg. There are ways to mitigate this but more often than not the cure is almost as bad as the disease.

So, I think the answer to this question is... (yeah you guessed it) it depends.

 

[agedhorse]

Good grief, engineers and their test equipment! I know an oscilloscopes can display a eletronic trace of current and voltage - but can they hear? NO.

Perhaps this is an oversimplified or questionable generalization? I am an electrical engineer, amp and speaker designer, and I can hear quite well. I also mix FOH for fairly well known acts maybe 3 or 4 times a month to keep my listening chops keen. Been doing this for obver 30 years.

 

[agedhorse]

Do you think there will be a reason to go smaller and higher powered than where the current tech is now ? You still need / want speaker cabs which are pretty much at their smallest , lightest & most efficient . I kinda think we are in the high point of bass amp tech and it feels good to be a bassist

Sir, this is one of the most interesting and thoughtful questions I have seen on TB recently.

Where do we go from here? I suspects some of us here are all ears.

 

[bassphase]

Julian Hirsch was one of the first audio magazine contributors to actually seek to correlate what we can hear with what we can measure. A lot of people still don't understand what he was doing.

True enough but after awhile his reviews of audio equipment for Stereo Review became essentially useless. The standard joke regarding Mr Hirsch's reviews went something like--"Of all the amplifiers I've tested this is certainly one of them"...

I'll take J.Gordon Holt's subjective reviews anyday.


bob

 

[KJung]

Do you think there will be a reason to go smaller and higher powered than where the current tech is now ? You still need / want speaker cabs which are pretty much at their smallest , lightest & most efficient . I kinda think we are in the high point of bass amp tech and it feels good to be a bassist

+1 The 'next thing' IMO is what TC Electronics is doing with their amps..... true 'digital' preamps with software that can be used to 'tweak' the parameters of the amp to suite the user (lo and hi pass filters, frequency center/shelving start points and Q, built in boost and cut, tube emulation, compressor levels and attack, release, etc., etc., etc.).

Quite amazing... do a search for the 'TC RH450 Tweaker' test that I was lucky enough to be involved with.

This isn't that lame (IMO) 'modeling' stuff that is out there that tries to sound like other amps, etc., but rather a very powerful, user defined voicing approach.

 

[KJung]

Regarding the OP's original post, there is just as much variability within class D and/or SMPS amp voicing and performance as their is within and across more traditional class A/B amps.... meaningless question IMO. There are class D/SMPS executions that are fat, warm, creamy and smooth, and their are class D/SMPS executions that are bright, tight, and grindy, etc., etc., etc., etc., etc.

 

[Petebass]

Where do we go from here? I suspects some of us here are all ears.

The amps certainly don't need to get any lighter. I think there's room for improvement in the cabs though..... how about speaker cabs which use materials which are as stiff/strong as wood, but lighter! There's a few DIY composite cabs already floating around out there in gigland, nothing mass-produced though.......

 

[aborgman]

T

Where you would likely hear a huge difference is in an application where the op-amp's output is saturating into the power rails. Different op-amp families can behave very differently when clipping, which isn't very surprising.

Yep... if you use an op-amp in a manner it specifically wasn't intended (and most of the ones that clip in really "interesting" ways are definitely in that group) you can get very different behavior among op amps.

Of course - it's all measurable.

 

[aborgman]

Different strokes. If I noticed a difference, I'd be all over it with my test gear, and would probably not stop until I understood the root cause.

Exactly.

How else are you supposed to mitigate/leverage/avoid the effect?

By day, I work with "instruments" of a different nature: Scientific instruments. If two designs for a particular type of instrument give different results, I sure as heck want to know why.

...and I'd like to know which is more accurate also.