Class B amplifier with SINAD of 120, how is that possible?

[DanielT]

Regarding the technical details, I just follow, as best I can, what y'all are discussing. Interesting and I'm trying to learn more.

BUT what I'm wondering, which as far as I can see has not been answered or discussed is why Topping B100 chose the design they did? IF it is Topping's intention to be class leading in the SINAD war why choose a class B design? Given that it's class B, which, to be honest, I don't really understand if it is. Or maybe it is, like a little, in a way (that's how I interpret the answers with my limited knowledge).

Like this. If you were to design an amplifier with the power that Topping B100 has with the same low distortion, would you choose a class B design? Is it the easiest, most cost-effective way forward?
Note you cannot choose class A because a criterion, which I now add, would be a physical size and weight similar to that of Topping B100. Maybe that also excludes class AB? So the choice then is between class B and class D, right?

Excuse my word salad, I don't really know what I'm talking about, but I can always ask.

 

[JSmith]

why choose a class B design?

I think it's just because they can... they've done D, AB, so now B. They seem to like covering all bases in the market.


JSmith

 

[wwenze]

We don't know what Topping did, so we don't know why they did what they did.

 

[ryanmh1]

I'm sure it's been mentioned, but just look up what Douglas Self calls "class B" in his handbook. It's just an optimized bias point which actually involves very little bias current. On further reflection, that's probably all they mean and they call it Class B because Douglas Self says they can since he wrote the book on amplifiers.

 

[JZXZMM]

"Class B", there have bias voltage and changes with the temperature of the output stage BJT,the bias voltage is small,so maybe we can call it “Class B”

 

[solderdude]

You can call it class-B but it secretly still is class-AB as it does have a higher quiescent current than a real class B which would have none.

 

[solderdude]

I think it's just because they can... they've done D, AB, so now B. They seem to like covering all bases in the market.


JSmith

Then there is (real) class A, G and H which they still haven't done (I think)

 

[wwenze]

What is real?

 

[EddNog]

What is real?

View attachment 399513

What?!

 

[Cbdb2]

"Class B", there have bias voltage and changes with the temperature of the output stage BJT,the bias voltage is small,so maybe we can call it “Class B”
View attachment 399421

Pr1 adjusts the output stage bias current so that Amp can be class B or class A/B. And TR13 should be on the output stage heat sink to keep the bias constant with temperature of output devices.

 

[Mnyb]

The home market for topping requests small devices with low heat losses ? They seem not to be prepared to build class A space heaters ?
Class B is an old concept for colder running amps , it’s an engineering challenge to also get very good performance at the same time yes because they could ……

 

[JZXZMM]

its realy class B and composite circuit

 

[DonH56]

its realy class B and composite circuit
View attachment 399614

As discussed by others, TR13 and the circuitry around it allow it to be biased in class AB, and unless TR13 is biased completely off (unlikely if you want a functional circuit) then there is the potential for trickle bias current in the output devices though it can still operate in class B as long as the Vbe multiplier (T13) is set appropriately. TR13 will also affect the temperature coefficient, of course, so it unless it exactly matches the output devices in bias ratio and temperature there will be drift with temperature.

 

[JZXZMM]

Negative feedback will solved anything.Only one BJT will "on" anytime.

 

[DonH56]

Negative feedback will solved anything.Only one BJT will "on" anytime.
View attachment 399689

I am not sure the purpose of your posts? There are a number of design engineers here that are very knowledgeable regarding amplifier design (and many other things), including classes of operation, biasing, and feedback (as well as feedforward) compensation. Do you have additional insight about the Topping B100 design in question?

 

[Old_School_Brad]

Yeah, you are right. Anyway, I was curious. The test files, together with delta (difference) file are here:

xoverdist.zip

drive.google.com

"Optimalbias" is with 22mV across 0R22 Re resistor (100mA current), "zerobias" measures 0.0 mV across Re resistor, so there may be some negligible current as the lowest measurable voltage was 0.1mV (0.45mA current). Spectra at 1.5W comparison:

View attachment 392824 View attachment 392825

Though the deltawave delta file sounds ugly (but only after huge unrealistic amplification), the files are indistinguishable to me by listening.

Paul's @pkane excellent Deltawave software says:

View attachment 392826 View attachment 392827

The crossover distortion should have been much higher to be audible. Even in this 55 years topology a moderate feedback factor made the crossover distortion inaudible with music.

7/16
77,2 % p