[AnalogEuphoria]

I have one, it runs up to 20W in class A, 120W in class A/B. Coupled with 92db/W speakers, it exhibits both finesse and muscularity. I have auditioned and listened to a fair few amps over the years and this one is natural sounding, very detailed, but no hint of graininess, brightness or harshness, unless the music calls for it. Imaging / soundstage is good and it doesn't heat up my listening room!

SA30?

 

[Rob Watts]

What sort of increase in cost are we talking about for Class H, I am talking ballpark figures (eg 5% or 500%) and not any hard numbers that anyone would hold you too.
Also but I suspect that you may not be authorised to talk about, have chord explored Class H for any of their amplifiers?

So I mentioned the increase in cost, but this heavily depends upon the PSU design. So the usual audiophile unregulated PSU would need to be changed by adding a SMPS DC/DC regulator. Then providing a method to modulate the control loop to set the OP voltage. So that would add to cost - but if it already has a DC/DC switching regulator, then the cost increase is small.

Yeah, it's a different kind of device altogether.

I've always been quite sensitive to amplifiers that seem to add "false" detail to the sound. I've always called it "grain" as it's an artificial texture around sounds that you wouldn't hear on the original instruments. It's almost like certain sounds become etched away from their background. It's all very impressive unless you know how the instruments are supposed to sound. It kind of mirrors the visual effect where film grain gives an image extra contrast and pop. Some very big names have this quality to my ears.

Reading this thread and in particular, Rob's assessment of the effects of how noise floor modulation affects the sound, I'm wondering if this is present in amplifiers that I perceive to be grainy?

Absolutely - all analogue electronics suffer from noise floor modulation. And in the case of linear supplied power amps, a huge amount of LF hum modulation too.

going back to my original post, and how we arrived here, another question if I may:
- OK we have established that class D is not good for our use. But I suggested it for its n
1 - efficiency 2- small size 3- low cost , in order to get a possible affordable TT3 that could drive real speakers.
- I understand that you prefer class H or G. I take it class G is cheaper to implement (right?), but I doubt it would be small and light.
- Class H , would cost the most, and will be smaller and lighter.
If I am correct, then Class G implementation would turn our hypothetical TT3 rather large and heavy, and class H would make it expensive and not so affordable!
Is there no way of having our cake and afford to eat it too.
Perhaps a redesigned RW version of a cost effective class D that wouldn't butcher the sound?
Just thinking (& dreaming) out loud . . .

It depends upon the design - class G can be easier (when you are switching in higher rails) but with a modulated regulated PSU it effectively makes little difference. Class H is something I am working on - indeed the Mojo 2 battery charger uses a simple Class H type design and that worked very well.

 

[ChrisGB]

SA30?

A39. It was my preferred sound quality in amps up to around £2500 when I bought it, just before the SA30 came out.

 

[Kentajalli]

It depends upon the design - class G can be easier (when you are switching in higher rails) but with a modulated regulated PSU it effectively makes little difference. Class H is something I am working on - indeed the Mojo 2 battery charger uses a simple Class H type design and that worked very well.

Aha!
So a one box solution, using an external SMPS, with a class H driven output stage may be on the horizon.
Just add a Hugo2 and networking in the box, don't price it out of (my) reach, and I bet it would sell like hot cakes (ghosts of Mojo?).
Or ask Chord not to price it out . . . .

 

[miketlse]

So I mentioned the increase in cost, but this heavily depends upon the PSU design. So the usual audiophile unregulated PSU would need to be changed by adding a SMPS DC/DC regulator. Then providing a method to modulate the control loop to set the OP voltage. So that would add to cost - but if it already has a DC/DC switching regulator, then the cost increase is small.

It depends upon the design - class G can be easier (when you are switching in higher rails) but with a modulated regulated PSU it effectively makes little difference. Class H is something I am working on - indeed the Mojo 2 battery charger uses a simple Class H type design and that worked very well.

Thanks for replying Rob.

After I posted curiosity got the better of me, and I googled Diy Class H amps, and was surprised at how few links there were that discussed the topic for people interested in hifi or audiophile listening.
There were links related to Class H 2kW amps and Class H amps for mobile devices like phones, but very little else in between.
The most informative link explained about the confusion caused by the definitions of Class G and Class H being reversed in different parts of the world, and then explored the concept of a Class H amp before admitting that it was Class G instead.
I was surprised that the Class G power supply only seemed to have an extra two components, but that seems to be back up your comment that the cost increase for a Class H amp need not be excessively high.

All interesting reading but I can now understand why there are so many simple Class A designs for small audiophile amps, in preference for the more complex Class G and Class H amps (especially for tube designs, where using a solid state power supply, would be regarded as equivalent to selling ones soul to the devil).

Anyway hopefully we will start to get reviews of the Bertii later in the year.

 

[Jawed]

Class H is something I am working on

I suppose since there's a lot of latency inherent in your DAC designs, it's possible to predict the supply voltage required at the time the DAC produces the final output.

So this would help with large scale crescendos or sudden big dynamic swings in music.

 

[ecwl]

I suppose since there's a lot of latency inherent in your DAC designs, it's possible to predict the supply voltage required at the time the DAC produces the final output.

So this would help with large scale crescendos or sudden big dynamic swings in music.

I have to admit I’m a bit confused by this comment. Sure, long tap length adds latency. But you want the FPGA to have a separate line of computation to measure the music signal to determine the music volume ahead of time? But even with that, Rob Watts can’t predict what volume level people will set their DAC to. I don’t think most people would appreciate if the DAC/digital preamp has a 1-second delay every time we change the music volume. So it just sounds like a complex engineering solution looking for a problem.

That said, I believe many class H amps have ways to quickly adjust their power rail based on the music volume. So I don’t think they need to use the long tap length filter latency to make the adjustments.

 

[Kentajalli]

I have to admit I’m a bit confused by this comment. Sure, long tap length adds latency. But you want the FPGA to have a separate line of computation to measure the music signal to determine the music volume ahead of time? But even with that, Rob Watts can’t predict what volume level people will set their DAC to. I don’t think most people would appreciate if the DAC/digital preamp has a 1-second delay every time we change the music volume. So it just sounds like a complex engineering solution looking for a problem.

That said, I believe many class H amps have ways to quickly adjust their power rail based on the music volume. So I don’t think they need to use the long tap length filter latency to make the adjustments.

@Jawed has a point, I think.
Since the latency is constant, by knowing the volume control setting, one can have a heads-up as to when a surge of power is needed and by how much.
By employing a fine step class G amp, it should be possible to achieve a good amount efficiency.
I am no expert, but that sounds do-able to me.

 

[Reactcore]

Hm all this 'dynamic PSU on amp' stuff makes it unneccessary complicated and prone to distortion.

I rather stick with an as rock solid close to the OP stage buffered voltage as possible.

Even with a volume at a high setting doesnt mean youre listening loud as some musics are recorded well below 0dB peak. And theres the impedance and sensitivity in case of direct headphone drive determining the volume too.

 

[Jawed]

I have to admit I’m a bit confused by this comment. Sure, long tap length adds latency. But you want the FPGA to have a separate line of computation to measure the music signal to determine the music volume ahead of time? But even with that, Rob Watts can’t predict what volume level people will set their DAC to. I don’t think most people would appreciate if the DAC/digital preamp has a 1-second delay every time we change the music volume. So it just sounds like a complex engineering solution looking for a problem.

That said, I believe many class H amps have ways to quickly adjust their power rail based on the music volume. So I don’t think they need to use the long tap length filter latency to make the adjustments.

To be fair, if we assume there's only WTA2 latency (because the DAC might be connected to an M Scaler), then the latency is going to be very short, let's say 0.1 millisecond. I should have thought about that a bit more!

Still the point is, the DAC can adjust its rails to suit the loudness of the music just before the "transient" demands a high voltage from the supply rails. This would mean the amplifier doesn't need to apply a safety margin of an extra voltage level, say 10V.

The question of the volume level chosen by the user is not a concern as in this scenario the user cannot change the volume so quickly that the 0.1ms latency would be too short.

I share Reactcore's concerns though. Making a voltage rail track the music level sounds to me like a perfect opportunity to introduce noise floor modulation.

The TT2 is a "mini DX amp" capable of moderate power. I don't understand the detail that allows it to be much more powerful than DAVE. I suppose it's not just that it has supercapacitors for its power supply, there's something different about the way the pulse array and output stage are designed.

 

[Reactcore]

The TT2 is a "mini DX amp" capable of moderate power. I don't understand the detail that allows it to be much more powerful than DAVE. I suppose it's not just that it has supercapacitors for its power supply, there's something different about the way the pulse array and output stage are designed.

The TT2 sports multiple parallelled transistors in its OP stage allowing for higher currents on the same voltage. Backed up by the supercaps.

Other than this the amp circuit is not much different from Dave's single transistor AB stage.

 

[Jawed]

The TT2 sports multiple parallelled transistors in its OP stage allowing for higher currents on the same voltage. Backed up by the supercaps.

How is it able to deliver twice the power into XLR?

Is it a bridged configuration?

 

[Kentajalli]

To be fair, if we assume there's only WTA2 latency (because the DAC might be connected to an M Scaler), then the latency is going to be very short, let's say 0.1 millisecond. I should have thought about that a bit more!

For Hugo2 I believe it 34ms. Dave is 100ms and mScaler is 630ms (max).
Even 34ms should be enough to switch a class G. the switching can be controlled by monitoring the digital data and knowing the volume setting.
Just thinking out loud!

Still the point is, the DAC can adjust its rails to suit the loudness of the music just before the "transient" demands a high voltage from the supply rails. This would mean the amplifier doesn't need to apply a safety margin of an extra voltage level, say 10V.
The question of the volume level chosen by the user is not a concern as in this scenario the user cannot change the volume so quickly that the 0.1ms latency would be too short.

Knowing the volume setting is very useful. If you are listening at -20dB, no adjustments would be necessary. I believe the aim of all this was to improve efficiency of the output section, as to keep the unit cool and small. Varying the SMPS output, in steps (as needed) can achieve this.

 

[GuiltyRocker]

All this talk about Amps, how about you take the Chord gear and pair it with different amps you demo at home and choose what your ears prefer, I did this and settled on Parasound. Try it.

 

[Jawed]

For Hugo2 I believe it 34ms. Dave is 100ms and mScaler is 630ms (max).
Even 34ms should be enough to switch a class G. the switching can be controlled by monitoring the digital data and knowing the volume setting.
Just thinking out loud!

I was referring to WTA2, not WTA1.

It's a guess on my part as to the actual latency, though.

All this talk about Amps, how about you take the Chord gear and pair it with different amps you demo at home and choose what your ears prefer, I did this and settled on Parasound. Try it.

This is about a potential DX amp that has, say, 500W per channel capability. No need for a DAC followed by a power amp in that case, instead plug the DX amp into your speakers.