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Class D or AB

#81
warnergt said:
On the contrary, quantization does occur in class D amps.
It is not quantized to something like 64,000 or 4,000,000,000
levels (probably what you're thinking of); it is quantized to 2 levels.
The output voltage is compared to the input voltage (using
some circuitry for scaling the voltage) to determine which is
greater. The result of this comparison is "true" or "false" -
the discrete results required of a digital system. That result
is used to determine if the output signal should be pumped
more positive or more negative.

This comparison is quantization. Don't believe me?
Check the Wikipedia definition.
"Quantization, in mathematics and digital signal processing,
is the process of mapping a large set of input values to a
smaller set."
I'm not making this stuff up.
Click to expand...

I agree with that. There are steps in the process that are digital. I would have to ask the same question, though:
What digital code is representing the signal at any particular point in time?

Keeping in mind that the output is analog and unquantized, how is this represented as a unique set of logic levels?
 
#82
JimmyM said:
This may be crazy but I have to agree with Seamonkey on this one and guess that it's in the preamp. I think they sound completely different, but my Micro VR and PF350 sound exactly the same to me, even though the Micro VR's class AB and the PF350's class D.
Click to expand...

Do you know if different power levels can alter tone? In other words, all other things being the same, could an 800 watt unit sound different than a 500 watt unit other than how the ear may perceive the increase in volume?
 
#85
Discrete physical states are not what distinguish a digital system. In fact, a digital circuit has voltage levels that vary all over the place. In a 5-Volt logic system, "0" might be represented by voltages from 0 to 1 V, and "1" by voltages from 3 to 5 V. And the voltages swing between these levels during transitions. Even in the time domain, there is variability in the exact timing of transitions. In the words of the famous electronics textbook by Horowitz and Hill, "Digital Meets Analog" at the cutting edge of digital technology. That's why people still use analog scopes to analyze digital circuits.

What makes it digital? It's a factor called noise immunity. A digital system has rules for whether the varying signals in the system represent specific discrete states. Noise immunity is often determined by setting voltage thresholds and time thresholds, e.g., in clocked systems.

Noise immunity allows a digital signal to be copied with no error. If you e-mail an audio file to two people, those copies are utterly identical. Virtually all digital systems operate with a high degree of noise immunity under normal conditions.

In contrast, a typical switchmode amplifier has no noise immunity. The PWM output signal could spend upwards of 10% of the time in between the two rails, even before filtering. The duty cycle is a continuous variable. The error amplifier is a purely analog circuit. Feed the same signal into two switchmode amplifiers, and the output signals will be different from one another.
 
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#87
warnergt said:
Wikipedia recognizes Morse Code as a digital system. Morse Code uses mere "ons" and "offs" modulating the width of the "ons" and controlling the timing between each. I'll be damned if that doesn't sound exactly like the controlling signal in a class D amp.
Click to expand...

Morse code uses ons and offs but they are meaningless individually. It's the combination of ons and offs that digitally represent characters e.g. ...---... , in this case 3 ons and offs to represent each of the characters s, o and s.

There is no digital, i.e. numerical, representation of anything in a class D amp. In PWM, pulse width is analogous to an instantaneous voltage of the input signal so by definition it's an analog process. The amplitude of the pulses doesn't represent any characteristic of the input signal. Amplitude is chosen arbitrarily to deliver the desired output power to a specified load.

By the same token, neither a multivibrator circuit nor a Schmitt trigger is digital. They might be used in binary logic circuits (which may or may not be digital) but they aren't digital in themselves any more than their forerunners with electromechanical relays can be considered digital.

warnergt said:
I'm an electrical engineer. I say class D is digital.
Click to expand...

And I'm an ex-engineer and now English teacher. I say a process involving one quantity as an analog of another is an analog process.
 
#90
duty_calls.png
 
#91
SJan3 said:
OK thanks but it's then possible that LM lll and 800 sound different because of a different power amp design?
Click to expand...

Possible, but unlikely. Most likely they are voiced a bit different in the preamp section, or in other sections of the signal chain (hi passing, power management, etc.).

All amps sound different, even coming from the same company.

Again, totally moot point. All amps have their own voice (both within and across companies), and I have seen absolute no indication or data that one design is 'better or worse' than another.

Of course, you have execution issues (i.e., some of the Ampeg small amps and some of the GK amps), that seem to have many more issues than other amps, but that has little to do with the topology of the power amp or power supply.
 
#92
JimmyM said:
This may be crazy but I have to agree with Seamonkey on this one and guess that it's in the preamp. I think they sound completely different, but my Micro VR and PF350 sound exactly the same to me, even though the Micro VR's class AB and the PF350's class D.
Click to expand...

+1 (I guess, this is crazy, but I actually finally agree with something you are posting also:)).

There is so much involved in the voicing of an amp, that attributing performance to one single thing, like amp topology, is a bit silly. Another good example of this is the Genz Shuttle Max 9.2 and the Streamliner 900. From what I understand, they use exactly the same power module, and I don't think there are two more different sounding amps on the market.

Also, many of the class d/SMPS amps on the market use EXACTLY the same B&O ICE power module/power supply, and they ALL sound very different, and even have very different performance leves. Think of the Aguilar TH500 and the Genz Streamliner.... same exact ICE B&O model, but huge difference in output due to the power management and limiting designs employed by the designers, manufacturers.

On the other side, again, from what I understand, the Big Bang (Markbass's new 500 watt class D offering) has been voiced to sound much more like the wonderful LMIII than the F1/F500 that it is replacing.
 
#93
warnergt said:
Wikipedia is an impartial source. Except for politics and
religion, it's pretty darn good. And I'd say it completely agrees
with me.
If you disagree with Wikipedia, you can take your case there.
Click to expand...

Quick jog off topic. In the presence of one of Wiki's founders an interviewer said they were going to add an incorrect definition for Elephant. He shouted, "don't do that!" it would take them weeks to find the error.
It can be a good source. However don't stop thinking for yourself. For more info on how Dictionaries, encyclopedia etc. are assembled read "The Professor and the Mad Man".
 
#94
not to hijack, but I took a shuttle 6.0 to Iraq for 12 months. I pushed it to the limit in 120°F ambient temperature. I had it cranked in duststorms. I even had it cranked on dirty power and this little shuttle 6.0 never quit on me. The only way we lost one of our 2 shuttles was due to user error and turning it on set to 110V with 220V juice; and even then GB fixed the sucker for free! that was 2009. I moved to Japan and I was able to move with my shuttle where she produces the same great sound that she made on day 1.

My Class D is battle effin tested durable!

P.S. The same wikipedia that warnergt cites also states specifically that Class D Amplifiers are not digital.
 
#95
RedLeg said:
not to hijack, but I took a shuttle 6.0 to Iraq for 12 months. I pushed it to the limit in 120°F ambient temperature. I had it cranked in duststorms. I even had it cranked on dirty power and this little shuttle 6.0 never quit on me. The only way we lost one of our 2 shuttles was due to user error and turning it on set to 110V with 220V juice; and even then GB fixed the sucker for free! that was 2009. I moved to Japan and I was able to move with my shuttle where she produced the same great sound that she made on day 1.

My Class D is battle effin tested durable!
Click to expand...

+1 Per James' comment above (by the way, one of the greatest of all Detroit bassists... nice to see him on the site), his experience with 'small amps' is most likely based on very limited data, like a buddy not liking it, or for example, someone having an early version of the GK MB500 that crapped out (I think this might actually be the case, since I was in Detroit when those GK's were regularly going up in smoke).

However, to his point, some micro amps have stricter limiting designs than older models. That makes them a bit more reliable actually, but can cause some executions, like for example, the Markbass LMII/III (as Burningskies mentioned) to feel 'compressed and a bit clamped' when you hit its absolute levels. Of course, most would never hit those levels, but if you have an aggressive technique and use slap style quite a bit, or are using a low efficiency cab, it can drive you nuts. That is execution/model specific though.

IMO and a bit of IME there.
 
#98
I've owned a Walter Woods amp since 1980. My first a MI-100-8 and my second a MI-400-8, which I still own, are analog, solid state amplifiers, with a SMPS. They have a unique sound due to a stellar pre-amp voicing, combined with the power amp and digital power supply.

My third Woods, a Woods Electroacoustic Ultra, has a very different pre-amp voicing, and a digital power amp, with a SMPS. It sounds great as well, but nothing like the older MI series. The series that came between these two models, just didn't have the same "kick" from the power amp section. So there are differences in design, even in hand built amps, by the same builder.

Over the years, being one to experiment with things, I once tried using the Woods pre-amp section into a GK powered extension cabinet that I owned. The combination yielded a totally different sound than the Woods, not as warm and much brighter with less character. Recently, I purchased a Headway EDB-1 Pre Amp. If I use it into the effects loop of either of my Walter Woods amps it sounds very different, the character, warmth, and presence of the amp isn't there.

What I gather from this, is that amps are designed as integrated, complementary systems. You can take the amp out of the country, but you cant take the country out of the amp. :) :)
 

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