Author Topic: A Chip Amp I Could Live With  (Read 17054 times)

Offline richidoo

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Re: A Chip Amp I Could Live With
« Reply #15 on: June 14, 2011, 11:08:29 AM »
Thanks Scotty! Great info there as usual. I knew about dead band, but not that Tripath was selectable. You mentioned that all class D amps must have deadband between the positive swinging output device and the negative (and I agree,) but Mark Levinson #53 is a class D amp which claims no dead band, even slight overlap of output devices. Ironically it is by far the worst sounding class D amp I have ever heard, even for my tin ear it is unbearable, even on easy listening classic rock. On the plus side (I think) the transient response is so violent it is physically painful to listen to action movie soundtracks or synth dance music. I'm sure it's measured specs are quite amazing, since that is Levinson's thing. Their new linear 532 costs almost as much and is one of the best sounding amps I've ever heard.

Scotty, what do you think about the idea that switching frequency jitter adds nonlinear noise to high freqs via intermod distortion? Possible or am I missing something fundamental? Some class D designs have even have variable switching freq. which seems to me to make any potential jitter issue even worse. I never believed much in the importance of low intermod distortion until my friend/amp designer Sol showed me how damping an oscillation at 60kHz cured problems at 4kHz.

Offline _Scotty_

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Re: A Chip Amp I Could Live With
« Reply #16 on: June 14, 2011, 12:01:39 PM »
Intermodulation distortion is a measurable parameter. It should be possible to minimize its contribution to the problem.  The Tripath designs I am familiar with all have a dead-band between 20 and 60 nano-sec. I think this part of the problem was solved by both B&O and Hypex.
  Downward intermodulation distortion may not be that big a problem with a switching frequency at 1/2 mHz or higher. These frequencies are a long way from the audio band.
  As far as the ML 53 goes there are a lot of things that could be going wrong that would contribute to your negative impression of the amp.
 Ringing on the power supply rails could be occurring. The storage-caps and the inductance in the wiring from the the caps to the output transistors form a resonant circuit that can be excited by the high currents and switching frequency the amp operates at.It may be a work in progress and not quite ready for prime time.
  I wouldn't use the term jitter in regards to switching amplifiers. It implies a timing error which is not the source of problems in these amps.
The interesting thing is how the ML53 and the ML532 sound so different from each other. They both can't be right. You would think there would some convergence in sound as each approach to amplifier design improves and moves closer to a theoretical ideal.
Scotty

Offline richidoo

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Re: A Chip Amp I Could Live With
« Reply #17 on: June 14, 2011, 12:41:03 PM »
Thanks for responding to all of my points, Scotty!

Offline richidoo

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Re: A Chip Amp I Could Live With
« Reply #18 on: June 14, 2011, 03:46:57 PM »
There is a new class D design from Hypex called N-Core. It looks very interesting. The white paper touches on some of the points made above, and their solutions.

White Paper

Offline rollo

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Re: A Chip Amp I Could Live With
« Reply #19 on: June 16, 2011, 08:17:42 AM »
      We did not detect any of the traits described. The Arion Hybrid design seems to have overcome the nasties associated with Class "D" amps. When I get one to demo in my system I'll really know.
    So far the first demo with Analysis speakers was well breathtaking. How will they sound with the Pipedreams ? Time will tell.



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Offline rollo

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Re: A Chip Amp I Could Live With
« Reply #20 on: June 16, 2011, 08:25:28 AM »
 Scotty the Arion has adressed the phase shift dilema according to its designer. That was one of his goals, besides other issues. Sounds like he has accomplised that goal to my ears. Then again it just may have a super synergy with the Analysis speakers.  :roll:
   If you or anyone wants to try a pair, let me know.



charles
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Offline rollo

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Re: A Chip Amp I Could Live With
« Reply #21 on: January 20, 2012, 08:52:39 AM »
  Well its been awhile. Ordered a pair for evaluation finally. Just too many other things going on.   Parts are coming in. Hopefully within two weeks it will be ready for prime time.  The only change to the original [ option] will be Deuland Cast output coupling  caps. 
   After hearing Joe's modded Spectron it moved me to act. As good as the Arion sounded when first heard it was not through my speakers. The Spectron did not sound like SS or tubes. Since I was unfamiliar with Joe's system it was hard to tell if it was any particular component. Synergy was very good. Nervosa edging in. Since my experience with both amps was positive , make the move.
   It would be interesting to compare a hybrid design to the Spectron.
   Being an SET type of guy this is new territory for me. As good as the Cyber 211s sound with the Pipes I oftened wondered about how having more juice would sound. 500W per channel just may handle all those drivers better. At 94db one would think not, however there is a lot of mass with [ 9] mid/bass drivers and[ 24] tweeters.
  When shown originally the Pipes were driven by Melos amps. I believe 200W per ch. The designer Lee Porzilli did state they perform better with more juice. What does he know.  :-P
   When we used the AR 250 with 240W per side the Pipes sounded fuller and more dynamic . However tube rush city.  The cost of new tubes [ 32] killed the decision. I mean [ 20 ]6550s alone oh my. Some day when flush new tubes will be had.  8)
   With the Qol inserted now the RCA 211s in the amp just may be too colored towards the lush side. Just exposes every darn thing. Changed the output tubes to GE 211s and it made a difference for the good.  Not as lush however still rich in character. With more dynamic impact. The jury is still out with the treble region.
    The tube change as well as Joe's Spectron got the Nervosa up again. Yeah I'm done HA !! *&^)$# you know what I said.  :lol:
   Time will tell.


charles
   
   
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Offline Barry (NJ)

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Re: A Chip Amp I Could Live With
« Reply #22 on: January 20, 2012, 11:49:24 AM »
Interested in your impressions Charles. Have you heard any of the DAC amps that Tommy makes?
Happiness is when your system overcomes your nervosa ;) 
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Offline bhobba

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Re: A Chip Amp I Could Live With
« Reply #23 on: June 18, 2012, 04:35:37 PM »
Hi Guys

The second of my Arion 500's has finally been released from Customs - Yippie - and I finally got yo listen to them.

I know we are not supposed to do any serious listening for at least 300 hours but I have to tell you right out of the box they are pretty impressive - and in exactly the way Charles said - namely they are real sounding.  They changed a bit during initial listening in exactly that way - becoming a bit more real sounding.  They were within a bulls roar of MAC 501's and I am hopeful once fully burnt in they will give them a real run for their money.  Already I can say they are above any amp I currently own but I do have access to some much pricier stuff and it will be interesting to see how they go against that as time goes by.

Thanks
Bill

Offline ampdesigner333

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Re: A Chip Amp I Could Live With
« Reply #24 on: December 16, 2012, 03:29:30 PM »
The output filter used in a Class D amp will exhibit phase shift clear down into the mid-range if the filter pole is too close to the audio band. When I used a Tripath amp it had a modified output filter that was only a 12 db/oct filter. The filter was at about 75kHz which is almost twice the frequency of most of the filters used in Class D amps.
  Between the hysteresis distortion from the inductors in the output filter and the phase shift from the filter pole being too close to the audio band ClassD amps have a hard row to hoe. The reason the Tripath amps have a lean sound comes from the dead-band time chosen by the amp manufacturer.
Both positive and negative output devices cannot be in the on state at the same time. There has to be a certain amount of time between the switching on of one device and the switching off the other device.
  Into this gap between the on state of the two output devices is where the information goes missing.
The dead band time can be set at 20,40 or 60 nano-seconds. The safest dead-band time giving the greatest protection to the output devices is 60 nano-seconds. This is also the leanest sounding choice. The best compromise for sound versus protection is 40 nano-seconds and this is how my amp was setup. It still sounded lean in the midrange compared with analogue amps but I could live with it.
  There maybe a ClassD amp in my future but it will half to equal or beat my analogue amp in the mid-range and highs before it will be allowed in the house.
Scotty
 
Scotty,
Although the phase shift issue is present in 99% of the Class-D amps out there, it is not catagorically true of Class-D.  In fact, at Digital Amplifier Company, we have made conquering this one of our highest priorities.  Our newest design, Maraschino Cherry (TM), in development for several years, has a unique advantage when it comes to phase flatness.  Another interesting point is that flat(er) phase can come at a terrible cost if not done properly (distortion, latency, etc.).
-Tommy O
       
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      ---- www.CherryAmp.com ----

Offline bhobba

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Re: A Chip Amp I Could Live With
« Reply #25 on: December 19, 2012, 05:02:43 PM »
Hi Guys

Heard the 250W non monoblock version the other day in comparison to the 500W version with Duelunds and my new divine KT120 valve amp.

Very good - especially for the money and not as dry as I thought it would be in comparison to the 500W version.  When we switched to the HS-500 sorry - game over - it was clearly and obviously better - but hey - its over twice the price with the Duelunds.

The comparison to the valve amp was mixed - some preferred it while others didn't - which is an extremely good showing considering its price.  It had better bass grip and dynamics were more startling but sorry - the vocal presence of that valve amp gets to me every time - its just so real and alive I am wowed every time I hear it.  Its probably impractical in the sense the valve monoblocks are as heavy as hell and changing them in and out is murder but I will be keeping both amps.  Why oh why does it have to be this hard - ah well.

Thanks
Bill