Topping B100 Amplifier Review

[firestart3r]

THX standard suggests that the gain should at 23db for balanced or 29db for unbalanced.

Wouldn't be better to have the standard gain instead of 20 and 23db?

For example, if your AVR preouts are a bit low in voltage, a bit more gain could be handy.

I feel Topping wants impressive SINAD numbers so they bring the gain down...

 

[dpuopolo]

OK, I found some information on this. Perhaps the best explanation is this one from Keysight support:
_________________________________

A feedforward amplifier is a type of power amplifier that utilizes a feedforward technique to improve linearity.
Here is a step-by-step explanation of how a feedforward amplifier works:

1. The input signal is split into two paths: the main path and the error path.
2. The main path signal is amplified by the power amplifier.
3. The error path signal is delayed to match the propagation delay of the main path signal.
4. The delayed error path signal is then amplified by a separate amplifier called the error amplifier.
5. The amplified error path signal is subtracted from the main path signal.
6. The resulting difference signal, known as the error signal, represents the distortion introduced by the power amplifier.
7. The error signal is then fed back to the input of the power amplifier.
8. By subtracting the error signal from the input signal, the power amplifier is forced to follow the input signal more closely, reducing distortion.
9. The combination of the power amplifier and the error amplifier effectively cancels out the distortion introduced by the power amplifier, resulting in improved linearity.

It is important to note that feedforward amplifiers require precise component manufacturing and knowledge of the signal path to achieve optimal performance. Additionally, the loop in a feedforward amplifier is not self-stabilizing, so careful monitoring is necessary to maintain stability. Feedforward amplifiers are typically used in high-frequency (HF) and lower very high frequency (VHF) applications due to the requirement of small delays for stability.
________________________________

It looks like Topping have used their experience with radio frequency design concepts to apply them to an audio amplifier. That's very interesting stuff. I can see how -- if implemented successfully -- a feed-forward network could be used to remove the crossover notch from a class B output stage. But this is the kicker...

"...feedforward amplifiers require precise component manufacturing and knowledge of the signal path to achieve optimal performance. Additionally, the loop in a feedforward amplifier is not self-stabilizing, so careful monitoring is necessary to maintain stability."

Is this Topping amplifier unconditionally stable, under all conditions of operation? Yes, it appears to be so with sine waves applied to its input, but what about a 10kHz square wave, or other more difficult tests? Is the 'monitoring' constant enough for the desired results at low frequencies such as those in the audio band?

It could be that this amplifier accomplishes all the goals, including stability under all signal conditions. That would make it a true breakthrough product. The smallish power output is probably a product of the complexity of this kind of design compared to the usual class AB or class D designs.

I wonder how this amp sounds in operation, driving today's relatively difficult speakers with very wavy impedance curves dipping down to under 4 ohms with steep phase reversal angles, etc.

This is called PRE DISTORTION where you add in an inverse distortion signal to make the output better. It's been used in Tube TV transmitters for just about FOREVER! I published an article about it six years ago: https://www.radioworld.com/tech-and-gear/put-synergies-to-work-at-your-station

 

[somebodyelse]

THX standard suggests that the gain should at 23db for balanced or 29db for unbalanced.

Wouldn't be better to have the standard gain instead of 20 and 23db?

For example, if your AVR preouts are a bit low in voltage, a bit more gain could be handy.

I feel Topping wants impressive SINAD numbers so they bring the gain down...

It depends a lot on the rest of your system. In home cinema it makes sense, at least if you're sticking to THX approved components throughout. If you've got very sensitive horns, like some who have posted to this thread, 29dB of gain will be WAY too much. Another argument would be that sensitivity should be standardised so that amps reach full output at 2V unbalanced or 4V balanced input, the de facto standard(ish) output for DACs. Pick an amp with more or less the power you need for your preferred maximum volume. But there will be counterarguments to that one too.

 

[Sean_S]

This is called PRE DISTORTION where you add in an inverse distortion signal to make the output better. It's been used in Tube TV transmitters for just about FOREVER! I published an article about it six years ago: https://www.radioworld.com/tech-and-gear/put-synergies-to-work-at-your-station

That's a similar concept to THX/Benchmark feed-forward error correction, except in Benchmark's case, the input signal is not altered, but the inverted error signal amplified by a low-power amplifier is summed with the primary signal amplifier's output.

The AHB2 - A Radical Approach to Audio Power Amplification

The Benchmark AHB2 is a radically different audio power amplifier. It delivers the lowest distortion and lowest noise of any commercially available power amplifier. The THD+N and SNR specifications are 20 dB better than many high-end hi-fi power amplifiers. The unique high-efficiency design...

benchmarkmedia.com

 

[dpuopolo]

That's a similar concept to THX/Benchmark feed-forward error correction, except in Benchmark's case, the input signal is not altered, but the inverted error signal amplified by a low-power amplifier is summed with the primary signal amplifier's output.

The AHB2 - A Radical Approach to Audio Power Amplification

The Benchmark AHB2 is a radically different audio power amplifier. It delivers the lowest distortion and lowest noise of any commercially available power amplifier. The THD+N and SNR specifications are 20 dB better than many high-end hi-fi power amplifiers. The unique high-efficiency design...

benchmarkmedia.com

Yes, they are summing in a correction signal. This is valid too.

 

[ryanmh1]

It depends a lot on the rest of your system. In home cinema it makes sense, at least if you're sticking to THX approved components throughout. If you've got very sensitive horns, like some who have posted to this thread, 29dB of gain will be WAY too much. Another argument would be that sensitivity should be standardised so that amps reach full output at 2V unbalanced or 4V balanced input, the de facto standard(ish) output for DACs. Pick an amp with more or less the power you need for your preferred maximum volume. But there will be counterarguments to that one too.

tl;dr: The power amp gain does not matter all that much, unless you use it to make the amp smaller and reduce output.

What is most important is to match gains for the typical volume position on the pre-amp. Let's pick a few pre-amps. I'm going to have to link Stereophile reviews for this since older ASR reviews often don't include SINAD vs output voltage chart for line outs, and it was just taking too long to find two good illustrative products. So, we'll go with this. First, Eversolo DMP-A8: https://www.stereophile.com/images/0724-ES-A8fig03-600.jpg. Next, Topping Pre90: https://www.stereophile.com/images/122Top90fig03.jpg. The Eversolo is effectively completely quiet from 1V to a whopping 15V. .0002% or -114dB in the whole range. The Pre90 doesn't appear to approach that until a huge 5V out, where it quiets to -108, or .004%. At 2V, it's .0025, or -92dB. Notably, this is worse than the best AV receivers, which are ~110dB at this point. (Note: I don't know that something didn't go wrong with the Pre90 here, it's MUCH quieter in the ASR measurements, but that's not relevant for this example. I just needed some charts with appropriate curves.) Let's just call those SNR measurements, since they mostly are since the curve is still sloping down.

If I need 100W and my amplifier is -95dB at 100W, and it reaches full output with 2V (which is maybe 25 or 26dB gain), I have hit full quiet (-95dB less a trifle) with the Eversolo and a typical AVR. But here's where it starts to get fun. With the -110dB AVR the overall noise is -9593. With the Eversolo? -94.95, maybe. I didn't get much extra. With the Topping? -90. Now let's say I have a "low gain mode" on the amp, and it requires a 10V input to max it out, and allows the amp to pull another 4dB to get to -99dB. Obviously, I can't use it in this mode with the AVR. It's probably out of the game. But I can with the Topping and the Eversolo. And it does get me something. With Eversolo, I now get -98.8dB. With Topping, I get -98.5. So, I've picked up something, at least, but not all that much. And I had to spend a bunch of extra money to get there, and can no longer use my AVR preouts.

To stay on topic, the B100 will at least hypothetically always allow me to lower overall system SNR by blowing more voltage out of the preamp (as long as the preamp doesn't start distorting). The "problem" though is that it does nothing for me. Even in high gain, I already get -135dB noise at full power. What speaker can take advantage of that even at 6 feet from the speaker? Almost none. By 2V (on ASR measurements) Pre90 has hit -116. Total system noise is -115.95. I need 99dB horns just to take advantage of that from only 6 feet away. At 9 feet, 104dB sensitive horns. Even the receiver is guaranteed inaudible at 2V for 98dB horns at 2 volts!

Once you've got the high gain mode quiet enough, keeping going just doesn't do much for any real-world use case. The limitations are always upstream, and even then they're almost always just fine in high gain too! You'll almost never need the gain control to put more than 2V into the unit. The only place you conceivably might use it is to "size down" the amplifier even more, so that 2V gets you 10W output (with very sensitive speakers), and allows you more range on the volume knob and to maximize pre-amp SNR at 2V. Essentially you're then turning it into a 10W amp and readjusting your gain staging so that the amp continues to put out the desired output with a 2V input.

 

[dsnyder0cnn]

Impressive, but I can't help wondering if the B200 might take the top spot if given a chance.

Any performance differences between the B100 and B200 apart from power output are likely to be academic, of course.

 

[EddNog]

Impressive, but I can't help wondering if the B200 might take the top spot if given a chance.

Any performance differences between the B100 and B200 apart from power output are likely to be academic, of course.

Cost difference.

-Ed

 

[dzerig]

What you’ve heard there is audiophile mythology.

Have you tested this for yourself?

 

[Sokel]

Impressive, but I can't help wondering if the B200 might take the top spot if given a chance.

Any performance differences between the B100 and B200 apart from power output are likely to be academic, of course.

No difference at all.
What will be a meaningful addition will only be a specified below 4 Ohm amp.

All the existing ones are specified either by 4 or above Ohm or 4-8 Ohm.
It's of little interest that they maybe can go down to 3-2-1 Ohm if it's not officially specified.

 

[totti1965]

Impressive, but I can't help wondering if the B200 might take the top spot if given a chance.

Any performance differences between the B100 and B200 apart from power output are likely to be academic, of course.

I think performance is absolutely identical for LA90 / B100 / B200. Not only little (academic) differences (because fully transparent), but no measurable differences at all.
First I assumed that the B200 is cleaner than the LA90 (about 3 dB), but then I saw: the topping guys are using a-weighted measurements, so it is 3dB or so better than @amirm ˋs measurements.
It’s only the power (8 Ohm) that differs:
LA90: 40 Watts
B100: 50 Watts
B200: 140 Watts
LA90 bridged: 270 Watts (but on 4 Ohms)

What scares me most, is the LA 90 poll: exactly half of the users have had problems with their devices!
That is not much better than the PA 5.
If all three „Top of the Pops“ Topping amps are practically engineered in the same fashion,
I am afraid the issues will appear in the same fashion.

There is something very very nice with the Benchmark AHB-2: it sounds AND works. Day by day by day in many recording studios. VW Beetle-like.

 

[EddNog]

I think performance is absolutely identical for LA90 / B100 / B200. Not only little (academic) differences (because fully transparent), but no measurable differences at all.
First I assumed that the B200 is cleaner than the LA90 (about 3 dB), but then I saw: the topping guys are using a-weighted measurements, so it is 3dB or so better than @amirm ˋs measurements.
It’s only the power (8 Ohm) that differs:
LA90: 40 Watts
M100: 50 Watts
M200: 140 Watts
LA90 bridged: 270 Watts

What scares me most, is the LA 90 poll: exactly half of the users have had problems with their devices!
That is not much better than the PA 5.
If all three „Top of the Pops“ Topping amps are practically engineered in the same fashion,
I am afraid the issues will appear in the same fashion.

There is something very very nice with the Benchmark AHB-2: it sounds AND works. Day by day by day in many recording studios. VW Beetle-like.

The B100’s Class-B topology is not the same as PA5’s Class-D topology at all. B200, if I’m not mistaken, is also different, as I believe they’ve stated that it is Class-AB. The only other amplifier in Topping’s line-up using the same topology as B100 is the A70 Pro headphone amplifier.

All of this being of what Topping has said is true about all of these amps’ topologies.

-Ed

 

[totti1965]

The B100’s Class-B topology is not the same as PA5’s Class-D topology at all. B200, if I’m not mistaken, is also different, as I believe they’ve stated that it is Class-AB. The only other amplifier in Topping’s line-up using the same topology as B100 is the A70 Pro headphone amplifier.

All of this being of what Topping has said is true about all of these amps’ topologies.

-Ed

B100 Class B - typo of @amirm (at least I think so)
B100 and B200 same layout.
PA5 - Class D but comparable in reliability! There was a LA90D Poll also!

[Poll] What is your experience with the reliability of the Topping LA90D?

Hi! Since some ongoing discussion in this thread I wanted to create a poll where people could vote and then share their experiences. I have two LA90D in monoblock configuration, figuring these would be the last amps I'd ever need in my lifetime if vented well. Because of the above mentioned...

www.audiosciencereview.com

(LA90D is also class AB, like the B100 and the B200)

 

[EddNog]

B100 Class B - typo of @amirm (at least I think so)
B100 and B200 same layout.
PA5 - Class D but comparable in reliability! There was a LA90D Poll also!

[Poll] What is your experience with the reliability of the Topping LA90D?

Hi! Since some ongoing discussion in this thread I wanted to create a poll where people could vote and then share their experiences. I have two LA90D in monoblock configuration, figuring these would be the last amps I'd ever need in my lifetime if vented well. Because of the above mentioned...

www.audiosciencereview.com

(LA90D is also class AB, like the B100 and the B200)

Topping initially told me Class-AB when I first asked, and then they came back after the fact and corrected themselves to say B100 is Class-B.

-Ed

 

[totti1965]

Topping initially told me Class-AB when I first asked, and then they came back after the fact and corrected themselves

-Ed

Most important thing is, that you will inform this community if issues occur.
Btw: I tested my need of power
I heared yesterday the complete jazz at the pawnshop with my Fosi v3
Low was 38.2 dB Peak was 93.2 dB - 55.0 dB Dynamik range!

Peak SPL Calculator

6.5 food away from my 85 dB /Watt speakers.
It was very very loud.
So I need 13.5 Watt Peak at 8 Ohm.
Adding 6 dB extra reserve:
54 Watt need.
So the B100 will fit also for me perfectly.
Best amp on the planet. At least on paper. Hopefully it’s reliable!

 

[EddNog]

Most important thing is, that you will inform this community if issues occur.
Btw: I tested my need of power
I heared yesterday the complete jazz at the pawnshop with my Fosi v3
Low was 38.2 dB Peak was 93.2 dB - 55.0 dB Dynamik range!

Peak SPL Calculator

6.5 food away from my 85 dB /Watt speakers.
It was very very loud.
So I need 13.5 Watt Peak at 8 Ohm.
Adding 6 dB extra reserve:
54 Watt need.
So the B100 will fit also for me perfectly.
Best amp on the planet. At least on paper. Hopefully it’s reliable!

So far mostly well. I have them set to Medium Gain. Not sure if it’s an impedance incompatibility or too high input voltage, but High Gain is not an option because it is audibly distorted if I try to use High Gain. If I use Low Gain, it is a little short on volume for quieter tracks (like All-Star Percussion Ensemble). Using the Topping L70 for preamp helps as it has +6dB Gain for balanced input on Low Gain. I need not bother with High Gain from my preamp.

I have had my right channel B100 safety kick in twice now, both times while playing Medium Gain with my preamp maxed out (volume -0.0dB). It had to have been cranked because I measured almost 90dB peak from my listening position 3 meters away before it cut out, and for me it was playing uncomfortably loud, but I wanted to push the limits to see where it would give up. Having pegged it enough for safety to cut in twice, I know how loud it needs to be pushed before safety kicks in and at least for me personally both times it was playing louder than I like, so at least for me, it provides more than enough power with the KEF LS50 Metas.

The safety is ultra-conservative. There was zero clipping or distortion both times safety kicked off.

-Ed

 

[pjug]

So far mostly well. I have them set to Medium Gain. Not sure if it’s an impedance incompatibility or too high input voltage, but High Gain is not an option because it is audibly distorted if I try to use High Gain. If I use Low Gain, it is a little short on volume for quieter tracks (like All-Star Percussion Ensemble). Using the Topping L70 for preamp helps as it has +6dB Gain for balanced input on Low Gain. I need not bother with High Gain from my preamp.

I have had my right channel B100 safety kick in twice now, both times while playing Medium Gain with my preamp maxed out (volume -0.0dB). It had to have been cranked because I measured over 85dB peak from my listening position 3 meters away before it cut out, and for me it was playing uncomfortably loud, but I wanted to push the limits to see where it would give up. Having pegged it enough for safety to cut in twice, I know how loud it needs to be pushed before safety kicks in and at least for me personally both times it was playing louder than I like, so at least for me, it provides more than enough power with the KEF LS50 Metas.

The safety is ultra-conservative. There was zero clipping or distortion both times safety kicked off.

-Ed

You are OK with those problems?

 

[EddNog]

You are OK with those problems?

I don’t plan to use High Gain (was just testing it) and I don’t listen nearly that loudly to set off the safety (again, just testing), so it’s fine. In normal use I’ve had zero problems.

I’m not going to pass up on a car because it can’t do 135mph when I don’t normally even go 100, right?

-Ed

 

[pjug]

I don’t plan to use High Gain (was just testing it) and I don’t listen nearly that loudly to set off the safety (again, just testing), so it’s fine. In normal use I’ve had zero problems.

I’m not going to pass up on a car because it can’t do 135mph when I don’t normally even go 100, right?

-Ed

OK. Thanks for reporting the experience for others looking at this.

 

[EddNog]

OK. Thanks for reporting the experience for others looking at this.

Absolutely. One has to be realistic. I wouldn’t, for example, tell my dad to get these. His Magnepan speakers would choke these amps. The V3 Monos that I gave him definitely make more sense.

-Ed