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Old 30th September 2012, 09:32 PM   #1
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Default 32 output devices ffor 60W in Luxman M800A

hi
Just got this On a Higher Note :: M-800A Pure A Stereo Amplifier and i am surprised that each channel has 16 output devices per channel for 60W into 8 ohm. each device is 2SC5200 with its complimentary capable of 100w
Now for each channnel the ouput capacity is 6x100 W class A/B =600 Watt but the amplifier is rated at 60W per channel .

this leads to the question for diy that if i need to maintain a very strict linearity regime then why not parallel as many devices as possible ???? Improved damping factor, greater power handling ? Any warmth in sound ????
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Old 30th September 2012, 09:39 PM   #2
JPM14 is offline JPM14  United Kingdom
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Blimey, 16 of those type devices in a class AB PA amp would output watts in the thousands! Be prepared for a winter time electric bill all year round with that thing lol!
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Old 30th September 2012, 10:13 PM   #3
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it goes to 1 ohm that is a vere nice amp and very well made for sure.
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Old 30th September 2012, 10:19 PM   #4
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my bad. Its not class A/B but clASS a.
Still that makes 60W/8 only 5.5Wx4=22W dissipation for a 100W transistor????? is it a simple way to improve SQ, i mean i intend to do this diy if 8 devices are asked to do the job of 2 and would simply improve SQ keeping every thing else the same,
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Old 30th September 2012, 11:27 PM   #5
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Lanchile has given the reply that the amplifier can drive 1R loads. Think about how much more power it delivers at 1R than 8R and how much more dissipation will be necessary to allow that in class A. Then you may realise why you really need that many devices with high-end speaker drivers like ribbon tweeters.

Lower in the description we read "480W to spare". I think that's what it's all about. Funny, that's 8 x 60 = 480!
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Last edited by Ian Finch; 30th September 2012 at 11:35 PM.
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Old 1st October 2012, 12:30 AM   #6
AJT is offline AJT  Philippines
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Quote:
Originally Posted by muddasirwaheedmalik View Post
my bad. Its not class A/B but clASS a.
Still that makes 60W/8 only 5.5Wx4=22W dissipation for a 100W transistor????? is it a simple way to improve SQ, i mean i intend to do this diy if 8 devices are asked to do the job of 2 and would simply improve SQ keeping every thing else the same,
60 watts at 8 ohms means that the amp is idling at 240 watts(one channel), assuming an efficiency of 25% so that 16 power tranies are each dissipating 15 watts each...no wonder the big big heatsinks....

i suspect that the classA rating goes for the 8ohm load only, other loads the amp goes into class AB...
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Old 1st October 2012, 03:16 AM   #7
jcx is offline jcx  United States
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anyone know the patent number for their "ODNF" - most amp circuit's aren't "smart" enough to recognize the "only distortion" part

I doubt they've really found a way around negative feedback realities - any system which uses one power amplification path to the output, controlled by some function of the input and the measured output is equivalent in principle to other negative feedback structures

the various local loop, nested loop, error correcting loop topologies that have been imagined, reinvented, given cute names all obey basic negative feedback theory with the attendent limitations and tradeoffs


Quote:
Originally Posted by jcx View Post
my mistake, shouldn't have added the comma

http://www.control.lth.se/~kja/modeluncertainty.pdf

From K J Astrom “Model Uncertainty and Robust Control”

“fair use” excerpt:
Click the image to open in full size.

Be sure to read that last para!

and here's the source for that last paragraph


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Originally Posted by jcx View Post
The counterargument:

Hawksford/Cordell error correction is a 2 degree of freedom linear feedback control system,

All expressions of 2 degree of freedom control systems are equivalent.

Therefore Hawksford/Cordell error correction is equivalent to conventional error feedback with a command prefilter

Therefore the output linearizing disturbance rejection effect is exactly equivalent to error feedback and has the same gain-bandwidth/stability limits of ordinary 1 degree of freedom error feedback

A little reading: (slow to load, ~ 500K )

Click the image to open in full size.

Click the image to open in full size.

[I've referenced this a few time before in this thread I.M. Horowitz, "Synthesis of Feedback Systems" 1963 - that makes this a 40+ year old "controversy"]

I like Bob's circuit, I do think understanding it as a local feedback loop and tailoring its loop gain and frequency response is likely to be a good way forward
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Old 1st October 2012, 05:04 AM   #8
Bonsai is offline Bonsai  Taiwan
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32 output devices - tharts class A for you! My sx-Amp is rated at 15W per channel class A and dissipates 62W per channel and runs hot. It does sound good though so I think its worth it.
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Old 1st October 2012, 09:44 AM   #9
a.wayne is offline a.wayne  United States
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That amplifier is designed to drive a 1 ohm load , not 8 , hence the number of output devices. Also isnt class-a efficiency higher with large amount of outputs , closer to 30-33% vs the typical 25 %..

Last edited by a.wayne; 1st October 2012 at 09:47 AM.
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Old 1st October 2012, 10:05 AM   #10
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Jcx I can email some info for you as well as a paper done by an independent source on the subject. Drop me a pm.
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