Jump to content

Class D amps with Vandersteen? Anyone?


Recommended Posts

I have been observing the progress of class D amps from a distance for the past few years.  I am intrigued by some of the newer offerings like the Peachtree aGan 400 for instance.  This amp has received pretty impressive reviews and I have been tempted to try one.  I am currently using a Bryston 4bsst2 with my Quatro CTs.  A solid performer for sure but perhaps not in the rarified air of many of the higher end and more expensive brands.  Lately I have been considering updating my electronics (amp and preamp) without breaking the bank.  I am considering Ayre, PS Audio BHK250, Aesthix Atlas among others. With the exception of the Ayre, most of the amps I have considered are big, heavy, imposing components.  As I am getting older I am less inclined to try to handle big 80 pound amps.  The idea of simplifying and downsizing my equipment seems more and more appealing.  Hence my curiosity about the Peachtree or similar.  Anyone try these amps with their Vandersteens?  ...specifically Quatro CTs?

Link to comment
Share on other sites

Hi @randyhat
I have a couple of the Hypex 502 amps, to try out for HT subs. And they are two channel or can be bridged to one channel. 
The hypex allows one to IIR DSP, for say bi amping.
(But that does not allow any feed forward correction.)

And I have been looking at the Atmasphere and also the March Audio Purifi Class-D. The later is more like a the US Buckeye I think.
The others would require something like a MinidDSP Flex to do 2 channel FIR, for an Active-crossover (Active-XO).

One could also probably just use the 252 corer (dua channel 250W), and use a capacitor on the high freq side to remove the bass.
However a capacitor likely introduces some phase shift.

In reality, I probably just run the tube amp. 😉

Link to comment
Share on other sites

I have heard some of the higher end class D offerings and they left me cold still.  For sub's I can easily see them used for many reasons.  I too love a smaller box to move around and to store.  I LOVED owning a great integrated amp in the AX5/20.  It was amazing and I would have been very very happy with it forever.  They ran the Quatro's incredibly well, but I fell in love with Richards mono's and took that plunge.  They are very special.

Link to comment
Share on other sites

the way to think about negative feedback is: take something  ( waveform aka musical note ) , lower the volume on it, flip it around out of phase and mix it back into a temporally different but somewhat similar input….

We went down that road in the 70’s and into the 80’s. high negative feedback = Vanishingly low THD but it didn’t sound good….. Dr Mati Otala figured out why, discovered TIM = Transient Intermodulation Distortion….

One of the first SS amplifiers to exploit this discovery was the Audionics of Oregon CC-2, a gem of a 70 wpc amp. My lucky exposure to this amp ( and a time and phase correct loudspeaker ) set me on a musical path 😉

Happy Sunday !

Jim

  • Like 1
Link to comment
Share on other sites

That is a wonderful resource.  

Of course, on the same website that hosts that paper there are other papers that refute a lot of what Otala wrote.  Or, at least, claim to tell you why Otala's analysis doesn't matter and there are other solutions that are better.  

There are lots of reasons why loads of feedback could be a bad idea for audio.  For example, since the open loop gain of a high feedback amplifier isn't flat across the audio band, the intermodulation distortion products caused by non-linearity and the application of feedback don't appear the same way as they do in other non-linear systems in nature.  (Air is a non-linear system...)  That might be kind of a big deal to how a human perceives the sound.  Most species today have evolved over millennia to adapt to the naturally occurring non-linear systems.  Not so much for non-linear electronics.

A couple English guys published a paper toward the end of World War II about non-linearities in transmission systems that still holds today.  The math hasn't changed.  Unfortunately, you probably have to pay to get yourself a copy:

https://digital-library.theiet.org/content/journals/10.1049/ji-3-2.1945.0011

They explain why IMD is a big deal, in actual numbers.  

Another pragmatic problem is that very often the designers of audio gear apply feedback as a universal panacea for all that is wrong with an amplifier.  So, they often tend to ignore problems that feedback only partially has a chance of solving, like power supply noise/crap rejection.  Is that actually helpful?

The question we always ask at my day job is: "What problem are we trying to solve here?"  Here is an example of an engineer doing that in the audio world:

https://benchmarkmedia.com/blogs/application_notes/tagged/crossover-distortion

I don't really subscribe to his overall solution, but at least he's trying to look at the actual challenges rather than just polishing the turd harder and faster.  Credit where credit is due.

Anyway, the problems that switching amplifiers generally are trying to solve are power consumption, size, and weight.  They actually do a pretty good job with that...

  • Like 2
Link to comment
Share on other sites

1 hour ago, BKDad said:

That is a wonderful resource.  

Of course, on the same website that hosts that paper there are other papers that refute a lot of what Otala wrote.  Or, at least, claim to tell you why Otala's analysis doesn't matter and there are other solutions that are better.  

There are lots of reasons why loads of feedback could be a bad idea for audio.  For example, since the open loop gain of a high feedback amplifier isn't flat across the audio band, the intermodulation distortion products caused by non-linearity and the application of feedback don't appear the same way as they do in other non-linear systems in nature.  (Air is a non-linear system...)  That might be kind of a big deal to how a human perceives the sound.  Most species today have evolved over millennia to adapt to the naturally occurring non-linear systems.  Not so much for non-linear electronics.

A couple English guys published a paper toward the end of World War II about non-linearities in transmission systems that still holds today.  The math hasn't changed.  Unfortunately, you probably have to pay to get yourself a copy:

https://digital-library.theiet.org/content/journals/10.1049/ji-3-2.1945.0011

They explain why IMD is a big deal, in actual numbers.  

Another pragmatic problem is that very often the designers of audio gear apply feedback as a universal panacea for all that is wrong with an amplifier.  So, they often tend to ignore problems that feedback only partially has a chance of solving, like power supply noise/crap rejection.  Is that actually helpful?

The question we always ask at my day job is: "What problem are we trying to solve here?"  Here is an example of an engineer doing that in the audio world:

https://benchmarkmedia.com/blogs/application_notes/tagged/crossover-distortion

I don't really subscribe to his overall solution, but at least he's trying to look at the actual challenges rather than just polishing the turd harder and faster.  Credit where credit is due.

Anyway, the problems that switching amplifiers generally are trying to solve are power consumption, size, and weight.  They actually do a pretty good job with that...

 

1 hour ago, BKDad said:

That is a wonderful resource.  

Of course, on the same website that hosts that paper there are other papers that refute a lot of what Otala wrote.  Or, at least, claim to tell you why Otala's analysis doesn't matter and there are other solutions that are better.  

There are lots of reasons why loads of feedback could be a bad idea for audio.  For example, since the open loop gain of a high feedback amplifier isn't flat across the audio band, the intermodulation distortion products caused by non-linearity and the application of feedback don't appear the same way as they do in other non-linear systems in nature.  (Air is a non-linear system...)  That might be kind of a big deal to how a human perceives the sound.  Most species today have evolved over millennia to adapt to the naturally occurring non-linear systems.  Not so much for non-linear electronics.

A couple English guys published a paper toward the end of World War II about non-linearities in transmission systems that still holds today.  The math hasn't changed.  Unfortunately, you probably have to pay to get yourself a copy:

https://digital-library.theiet.org/content/journals/10.1049/ji-3-2.1945.0011

They explain why IMD is a big deal, in actual numbers.  

Another pragmatic problem is that very often the designers of audio gear apply feedback as a universal panacea for all that is wrong with an amplifier.  So, they often tend to ignore problems that feedback only partially has a chance of solving, like power supply noise/crap rejection.  Is that actually helpful?

The question we always ask at my day job is: "What problem are we trying to solve here?"  Here is an example of an engineer doing that in the audio world:

https://benchmarkmedia.com/blogs/application_notes/tagged/crossover-distortion

I don't really subscribe to his overall solution, but at least he's trying to look at the actual challenges rather than just polishing the turd harder and faster.  Credit where credit is due.

anyway, the problems that switching amplifiers generally are trying to solve are power consumption, size, and weight.  They actually do a pretty good job with that...

BKDad, a great synopsis of amplifier operation over the years.  Power consumption is not a problem as it is not significant for the few hours we listen to music, compactness is easy to overcome because our homes are relatively large, and weight is only a factor when moving the equipment (hopefully seldom unless you're an insecure audiophile).  Our music and its positive effect on our health is the real issue.  For 45 years I have believed timing is the most important parameter in our long-term listening experience, but I work in an industry that thinks, measures and believes amplitude is the only important parameter therefore feedback.  All parameters are of some importance, but they are not as important as timing as we are timing devices first!  Medicine is beginning to address this especially the forensic field and I believe research will show sources with timing errors will cause more brain activity therefore fatigue.  It is the timing errors unavoidable in feedback, digital and non "Time and Phase Correct" speakers that hinder long term pleasure, IMO.  These facts are often challenged but if you are using a digital source that has its timing already decimated, Class "D" amplifier may sound great, DSP may sound totally transparent, or one may not hear the difference between amps with or without feedback.  In the long run one's emotional connection to the music is what matters most and is the easiest to compromise.  In some ways this is the "itch" we all scratch.

RV

  • Like 1
Link to comment
Share on other sites

I'll probably never understand the sound reproduction equipment business.

For example...

I don't understand loudspeakers real well, so I'll just look at the amplifier part.

Imagine that I am trying to accurately reproduce a recording of a small jazz group.  

I just looked at the audio spectrum of a recording like that.  It's kind of generous to say that there's ten equal amplitude tones being played at one time.  But, ten makes the math easier, so ten it will be.  Of course, there's all sorts of harmonics being produced by each instrument, but their levels relative to the fundamentals are relatively low power wise, so allowing for ten equal amplitude tones is probably a decent baseline.

Let's assume that the sound level I'm listening to is in the mid to high 90's.  That's maybe on the loud side, but since I'm making up the experiment, that's what we'll call it.

Since I listen using Vandersteen loudspeakers, that suggests that the total power to each loudspeaker is about 10 Watts, based on the published and measured efficiency.  Again, since it's my experiment I'm declaring that the tones are not phase locked and they are not harmonically related.  So, therefore, each of those tones is about one Watt each.  

OK, now let's assume that I build an amplifier that has distortion products that are each 80 dB below the desired musical tones.  That distortion ends up being pretty low relative to the ambient noise level, so their audibility is probably relatively low.  One could argue about that detail, but that's not where I'm going here.

A lot of people associated with the audio industry - either as manufacturers, customers, or pundits -  would think that this amp is perfectly fine, at least with regard to distortion performance.  Others would scoff and throw cow excrement in my general direction.

But, once I let slip that this amplifier didn't use overall loop feedback, that cow excrement current would go up by at least 20 dB.  

Why is that?

My point would be, and is, that the distortion performance they value so highly is the distortion performance no matter how you get there.  If I used rotted cranberries spread over the active devices, so what?  Either the distortion matters or it doesn't.  (I'm not saying that this distortion performance is all that matters - hold that thought)  So, why the crap?  

That's the hole in their argument.  To them, the amplitude of the distortion on static test signals is all that matters.  Yet, if I attained it in an unconventional manner, it would have to be bad.

That make any sense?  I guess if you want to limit your thinking and make life simpler than it really is, that might work.

Anyway, that's a pretty simplistic view of the amplifier performance.  There's clearly way, way more to it than that.  The complex audio waveform almost always has a really high crest factor, so the required peak power may really be 100 Watts to avoid distorting that same musical signal.  The amplifier is part of a system and interacts with the other components of that system.  And, so on.

Then, there's the details of what happens in the amplifier.  Otala touched on some of it.  What he neglected to say in bold font at the bottom of the first page is that the techniques you need to employ in an amplifier circuit in order to get all that extra gain - the gain that gets thrown away as part of the feedback correction - can be pretty limiting and usually creates more distortion unto itself.  This counts, too.   As does the measures you need to take to make a system with feedback stable.

Even the example from Benchmark Media regarding crossover distortion is pretty telling.  The listeners could hear crossover distortion at .01 Watts.  Because of the feedback constraints, feedback doesn't correct for that.  Does that matter?

  • Like 1
Link to comment
Share on other sites

Class D amps with Vandersteen? Anyone?

Not quite class D, but I'm using a Linn Majik 2100 Chakra power amp with my Vandersteen 1Cs. They use a switch mode power supply but that's where the similarity to Class D ends.

According to Linn's CHAKRA white paper: CHAKRA is a linear (continuous time) amplifier technology with a switch mode (discrete time) power supply.

A Class D amplifier uses very high speed switches to send the entire voltage of the power supply, with minimal power loss, as a sequence of pulses to the output, where a filter averages the pulses before the loudspeaker terminals. The frequency, density and duty cycle of these pulses determine the average output voltage. This is exactly how a switch mode power supply works, except that instead of generating the system power supply, the Class D amplifier circuit is generating the final audio output. Class D amplifiers have been around for 30 years, but have failed to penetrate the specialist high fidelity sound equipment market, primarily because they lack the subtlety of well executed linear amplifier technology. (So that's their story.)

The Linns would sound different from your Bryston amp. You would have to listen to powering your speakers before committing to buying. The Akurate runs 4,140.00 pounds. The Klimax starts at 8,780.00 pounds.  My Vandersteen dealer also carries Linn. They would likely setup a home loaner for demo.

Link to comment
Share on other sites

  • 2 months later...

Yesterday I hooked up a pair of Topping PA3s amps, bi-amped to each of the twin posts on the 2C.
They measure pretty bad from SINAD on the RCAs… (69 dB. But ~84 dB on the XLRs)
(~$150 via Amazon.)

I had to put a piece of tape on the knobs to have a mark and they were hissing like snakes by 12 o’clock.

I had to run the preamp at ~ -8dB to get a moderate level of sound. The hiss was more like an old TV fly back transformer.

I am returning them.

 

Today I hooked up an AIYAMA ($70) Class-D A07 amp as stereo, and hence reterminated the lamp cords to a single banana at the amp end.
I railed the volume knob full clockwise and no hiss at all.
The preamps is back at -30dB and it sounds pretty good.
The SINAD with RCA is measured around 84dB, so not 100dB, but much better than 69dB.

I also got a big linear power supply, but today I was running it of the supplied switcher, so 55W at 8 ohms with 24V rail input.
With more voltage they go to something like 180W, using a 48V rail.
(It might be more like 200W if the VCC-5 dips down towards 6 ohms??) 

https://www.aiyima.com/products/amplifier-aiyima-a07-tpa3255-2-0-channel-300wx2-hifi?variant=32922293272651

Sonically it is pretty good, and really great for $70.

There are a bunch of Class-D amps in the 100dB (+/- 5dB) SINAD that are multi $1000.
I will be using this for the center channel with the VCC-5, and therefore the bigger power supply.

For the other surround channels I’ll just run it with the 24V supply which ends up as 55W/8-ohms stereo.

It absolutely rocks it for a surround amp, and for a budget amp, it is really pretty decent.
(So I’ll order 2 more to replace the Topping pair that is being returned.)

 

I would be tempted to use some inline RCA hi/Lo pass filters to bi amp a pair of stereo amps to each set of binding posts of the 2C, but I have no idea what values to use… like where the woofer crosses over, and how much phase they introduce… so the HP would need to be much lower at 12dB/octave to not interfere.

if that worked, then I would use some of the Purifi based class-D amps which are more like $1500/ea for the stereo. And bi-amp vertically using the 250W or 400W version, which gets halved going form 4 ohms to 8 ohms. 

Edited by Holmz
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...