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Why did Class H amps never really catch on?

Calleberg

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Que, it's not Class H? It is Thomann who states it is:

You mean it is Class G?(Not that there's anything wrong with that).:)

Yes, they are also saying it is "two stage" which tells me they are actually talking about Class G, with "two stages" refering to two levels of rail voltage, that and the price :)
 

DanielT

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Yes, they are also saying it is "two stage" which tells me they are actually talking about Class G, with "two stages" refering to two levels of rail voltage, that and the price :)
Would you look at that.:)

Which, incidentally, illustrates what I said earlier that buyers do not directly care about different amplifier classes.
the t.amp E-800 has been around for a while. Thomann has probably sold quite a lot of that model and my guess is that no one returned it and said:
I thought I bought a Class H but it is actually a Class G!:oops:
yYou probably do not buy such an amp for "nice" hifi in the higher frequencies. Many people probably have it as a utility machine to, for example, pump subwoofer bass air. As long as it is not driven into clipping, everything is peace and joy.:)
Edit:
Why you would not have one for "nice HiFi" because it has Total harmonic distortion, 50% of maximum power output <0.03% you may wonder , but never mind. :)
 
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killdozzer

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More importantly take a look at it's predecessor's in History labeled part where you will see 1977 class G one's (as that is not that new) as we nead to put an end to the classification nonsense.
In my pic is the 8300 that belonged to me and was in top shape. The very one from '77. I sold it because it is very valued and I bought numerous other gear (it went for 2k $). They decided to describe it as "series E" in the manual and I obviously mistook that for Class. I'm not all that into classification nonsense, but I asked for Class E (believing my Hitachi was one) because it was explained that very fast switching between rails made it effectively operate close to A and solve distortion in high freq that old Class D used to have.

However, E would be a modification of D (hence my question), but G is a modification of AB, so I asked to no avail it would seem.
 

rwortman

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According to their description, the Benchmark AHB2 has a class H main power stage mixed at the output with a low power feed forward error amplifier. They are selling a lot of them so I guess it caught on.
 

Digital_Thor

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I do agree that class D is a nice touch of fresh air, when it comes to size, efficiency and ease of build, especially when Hypex/Purifi pushed them into usable realms, without the problems of older designs.
But through the years, my Groundsound class H amp has served me incredibly well. I only use it for subwoofers because of its grunt and ability to just pull anything I throw at it. But I did try it on B&W 800 Nautilus and Magico Q7 - with no difficulties at all. No issues in the upper frequencies or missing details of some sort, even compared to huge Marantz mono blocks, YBA or Dan Dagostino, just to name a few.
It's a diy kit from groundsound:
http://groundsound.com/hpa2k.php
I "only" run it with +/-52V and +/-104V - because that was the transformers I already had lying around. The modules are build for 60 and 120V.... but I chose to live with that :cool:
Even in my homemade wooden box - there is no issue with noise of any sort. The foam on the top and bottom of the transformers, remove almost all physical noise that could come from any small amount of DC that my plasma screen produce,
The first HPA2K have served me greatly... so when upgrading to a fully individually controlled multi sub system, I build a second one :D

When I look at class D - it should cost almost nothing compared to mine. No big transformers and lots of big expensive capacitors, big cooling fins and the like. I know I got a deal on the kit and build almost everything myself. But hey... if it's fun, I save money, and it still works awesome - I'd do it again :p
H-amp.JPG
 

killdozzer

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It's a nice DIY project and that's a main thing. You're obviously happy. Although, Class D today is not just a touch of fresh air. They are taking the lead in the "big, clean power" domain. This becomes painfully obvious when you try to construct a 470w AB amp, we won't even mention A.

I agree with you that at the moment, Class D is expensive. But it's not the parts, it's performance driven high price. It doesn't matter that they have no large chunk of toroidal. Passive coolers are not an ornament or a bragging feature, they served a purpose which became obsolete and that's also good.

All this could be seen as a good thing since it's easier to expect the price to go down on performance with cheap parts, then it would be on a heap of copper which is in growing demand. When technology spreads, companies will look for their place under the sun with lower prices. This will give Amir some extra work since not all of them can be good. ;)

At the moment, you can still get AB watts cheaper because there are a lot of good working AB around. But I think this will change. I gave 200$ for a 110 AB few years back when Purifi was nowhere near. And even today, I'd still have some trouble getting contemporary Class D 110W where I live that would have all the features of my amp.

I'm glad to hear your amp stands ground when it comes to Marantz. Not so much YBA and D'Agostino, I think those are boutiquy overprioced BS. But, more importantly, what sort of problems did you have with vibrations? Why would it affect your amp and what is the physical noise of plasma screens? I've never seen any sponges on toroidals in conventional amps.
 

restorer-john

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It's a gem (a MOSFET one) but same can be said (even more in relevance to this thread) for HMA-8300 from 1977 (200W class G).

I've got an HMA-8300 in the storeroom. Insane headroom over and above the 200W rating. But nowhere near enough SOA for continuous rating. A beast.
 

Digital_Thor

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It's a nice DIY project and that's a main thing. You're obviously happy. Although, Class D today is not just a touch of fresh air. They are taking the lead in the "big, clean power" domain. This becomes painfully obvious when you try to construct a 470w AB amp, we won't even mention A.

I agree with you that at the moment, Class D is expensive. But it's not the parts, it's performance driven high price. It doesn't matter that they have no large chunk of toroidal. Passive coolers are not an ornament or a bragging feature, they served a purpose which became obsolete and that's also good.

I'm glad to hear your amp stands ground when it comes to Marantz. Not so much YBA and D'Agostino, I think those are boutiquy overprioced BS. But, more importantly, what sort of problems did you have with vibrations? Why would it affect your amp and what is the physical noise of plasma screens? I've never seen any sponges on toroidals in conventional amps.
Thank you. I know it could have been done prettier. But I'm all about sound quality at the moment - as long as it's also electrically safe :D
I had the Vincent SAV P200:
https://www.hifiengine.com/manual_library/vincent/sav-p200.shtml
But it simply "cried" when trying to produce lower frequencies. I could literally see how the subwoofer swung and showed off how the amplifier lost grip. When borrowing the HPA2K, I saw how the cone of the subwoofer settled and made the driver play deeper and louder. Such an experience to actually see the big difference in "grip" or control between two amplifiers with the same driver unit - is something I clearly remember - and the reason I bought Groundsound amplifiers to begin with :)

I look forward to maybe transition to a sleek but powerful cabinet in the future, that pulls and plays like the 10 channels of amplifiers( 2 x 3x200W and 2 x 2 x 1000W) I have in my current system. But I had to start somewhere. And back when I began building fully active speakers... class D was more trouble than good and AB amplifiers were cheap and fitted well with freedom to play and experiment.

To get the furthest with less money. I found 4 identical transformers at a former job, for almost nothing. They are good quality, but a little old, and therefore they seem to hum a bit more. It's a droning noise, that seem to follow in the steps of the power usage from my plasma tv. So even though I changed a few caps in the power supply in my tv - and the noise did drop a little. I'm simply thinking of getting an extra outlet for the tv and computer, than the one for my amplifiers, to see if I can reduce DC interference.
It produces no problems in the sound - only my 6 transformers hum physically. So my trick/experiment was to suspend them in a foam cushion, to simply remove the physical contact between the amplifier casing and the transformer. Apparently the baseplate of the amplifier cabinet, acts as a sound transducer, and the foam simply dampens this to a very low level. A long bolt and locking not with pig shim, ensure that the transformers still stays put on it's soft "pillow".
My old Panasonic P50VT20E(bought used for 250$ 5 years ago) is known for it's noisy fans and buzzing power supply that change in pitch and magnitude, according to the amount of light scenes on the screen - but damn - always a great picture from this oldish technology.
Former owner got the fans fixed.... almost inaudible now. But I think the many little power supplies around the tv, simply start to show their age, which is just a natural thing I guess. now that I think of it... I actually think that the panel itself... is the one buzzing. Maybe I'll jump on a used OLED.... and then maybe I can hear new weird buzzing or humming from somewhere... as the disturbance goes away - haha :p
For now. I simply turn the tv off... when listening seriously.... the calmness that spread in the room, when only the music is present... is still a special experience.
 

killdozzer

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I've got an HMA-8300 in the storeroom. Insane headroom over and above the 200W rating. But nowhere near enough SOA for continuous rating. A beast.
I liked the preamp - HCA-8300. For the time it had many nice features.
1642768066669.png

Two phono inputs, one with variable voltage. Back then it made sense. All sorts of filters. Mine was so well kept that my buyer didn't believe it was genuine. He thought it was some knock-off from China. He checked it for serial number, but... What can I say, I'm no cheater, of course it was genuine.

I don't regret selling it, but I hoped I found someone who wants exactly that and will have it till it dies. But I found my amp resurfaced in the ads for 2,5k, I sold it for 2k. It was very soon removed, I'm guessing someone gave that money.
 
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mocenigo

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So we have a repetition again.
Classification goes up to Class G, the H inherits class G characteristics with what ever they added (hybrid). They are DC and less efficient than traditional class D. Class D did conquered the world long time ago (all the small amplifiers in numerous things) for the price and whose never meant to be great. Simplicity of class AB will continue to keep it live probably for ever (ever more so in critical applications).

Not all small things, however. The CS43131 (an example already made in this thread) shows it is a Class G (the description makes it clear, even though they call it Class H)
 

mocenigo

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Back to Class H...

The reason I reckon that this amp that I bought would be great for a pair of subs is that when I bought it I remember, after a bit of research, reading online that something to do with the Class H topology means that there can be issues with distortion at the higher frequencies. Can't remember the reason but perhaps someone more knowledgeable can chime in?...

Anyhoo, perhaps this is the reason why Class H never really caught on for hifi use.

Maybe in the past voltage tracking was not very precise, and therefore in the presence of large and fast swings the rail change would not follow quick;y enough. But this does not seem to be the case in current Class G designs from Arcam or Benchmark's Class H.
 

mocenigo

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@mocenigo I don't think you're even started reading my posts.

Ah, it was you that wrote “Clas G-H got it's usage secured in but not for power amplifier (where it likely will stay in the exotic category) but in small integrated power amplifiers for hedaphones/preamplifiers and such (and not for a high gain but lo gain with high SNR)” and also mentioned the power savings coming from ARM (Fujitsu with v8.2+SVE2). About the latter, I feel very honoured you mention the power savings thanks to the ARM architecture, being myself a member of the Arm Architecture team, having been consulted internally about SVE/SME (and being a designer / codesigner or internal analyst of most recent security features; such as being a codesigner of PAC and designer of the QARMA cipher).
 
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ZolaIII

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@mocenigo that whose more for illustration. Whose thinking more about one's where I prise the CS43131 design (and not just for it's 139 dB rated integrated amp but it's efficiency and rated EMI rejection rate). If you have to read papers let them be white one's.;):)
 
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DeItaBravo

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Yamaha had Class H designs in their amps through the 80's. Many reviews lauded the performance. In fact, there are some very high dollar designs that mimics the design even down to the same bipolar output Sanken MT200 devices.
 

Digital_Thor

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It's a nice DIY project and that's a main thing. You're obviously happy. Although, Class D today is not just a touch of fresh air. They are taking the lead in the "big, clean power" domain. This becomes painfully obvious when you try to construct a 470w AB amp, we won't even mention A.
I am :)
True ... but maybe the combo of class AB and class D, like in LabGruppen, where they "simply" expand the rails around a small clean class B with class D power.
https://www.labgruppen.com/technologies/class-tc-output-stage.html

fonctionnement-de-l-ampli-classe-td-lab-gruppen.jpg
 

pma

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As per the manufacturer, Benchmark AHB2 is a class H amplifier.


The AHB2 is a linear class-H amplifier with bipolar output transistors and a unique feedforward error-correction system.

And yes, it has high side and low side power supplies.

  • Class-H Tracking Rails - Tracking power supply rails (class-H), can significantly improve the efficiency of a class-AB amplifier. But,the improved efficiency provided by this topology usually comes at the cost of increased distortion. For this reason, there are very few amplifiers that use multiple supply rails. In a traditional feedback design, every rail switch point adds another layer of crossover distortion. In contrast, the feed-forward error correction used in the AHB2 is so effective that multiple rails can be added without incurring a distortion penalty.

 
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