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Old 17th August 2006, 11:26 AM   #31
AndrewT is offline AndrewT  Scotland
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Hi Anatech,
I built a pair of low bias ClassAB amp modules (BJT quasi) into stereo power amp.
It had a single pair of 150W output devices running, almost cold, on +-50.5Vdc.
It put out 110W +110W into 8r and 200W into 4r. The supply rails only fell about 2.5V from the quiescent condition. It sounded so good I built two more. This was all about 30years ago before I knew much, if anything, about analogue electronics.
Now, looking back, I suspect the peak voltage on short term signals might be just 2V higher than the sustained peak voltage. This implies an approximate headroom of 0.4db (44Vpk into 8r vs 42Vpk into 8r). Even a 3V gain in Vpk will still result in a dynamic headroom of 0.6db. Dynamic headroom figures of 2db to 3db are terrible.

I could skimp on the smoothing caps and get a lower continuous power. I could skimp on the transformer and get a further lowering of continuous power. Doing both will definitely achieve a greater headroom but the result will be an amplifier that would sound less good.
I would call the high headroom ampilfier flawed but significantly cheaper than the "balanced" design.
I would certainly NOT call it "efficient".
"Cheap and nasty" seems a more appropriate term.
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Old 17th August 2006, 12:04 PM   #32
anatech is offline anatech  Canada
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Hi Andrew,
I haven't measured this, but the design of the 300DC is anything but cheap. Each power section has it's own winding, rectifiers and filtering caps. Each voltage amp section has it's own winding, rectifiers, filtering and regulators.

It could be Marantz's way of understating the normal RMS power output compared to the real peak. The output rails are around 70 VDC I think. The main filter caps are 10,000 uF things for each channel.

I guess I'm tring to point out the specs are not always arrived at the way you might assume. Marantz has always had a reputation of understating the capacity of their products.

-Chris
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Old 17th August 2006, 04:16 PM   #33
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by mikeks
SOA Protection by Relay
This is possible if the electromechanical relay in series with the output is dispensed with, and replaced by solid-state alternatives, as discussed here and here.

Power solid-state switches in the supply rail can be persuaded to disconnect the ouput stage virtually instantaneously.
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Old 17th August 2006, 04:23 PM   #34
anatech is offline anatech  Canada
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Hi Mike,
Yes, I was thinking of the previous discussions when I first replied. The second link where it refers to SS devices between the amp and speaker are out.

Power supply shut down is fine as long as it works properly. You would need some capacitance after the parts to bypass them. I doubt they would sound any good without.

However, for SOA protection, wouldn't it be less disruptive to limit the current in a multislope fashion. You could kick the power off if SOA limiting occurs for a time period. Just simply shutting everything down right off is drastic, don't you think?

-Chris
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Old 17th August 2006, 04:32 PM   #35
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by anatech
However, for SOA protection, wouldn't it be less disruptive to limit the current in a multislope fashion. You could kick the power off if SOA limiting occurs for a time period. Just simply shutting everything down right off is drastic, don't you think?

-Chris

Yes........i think you're right.

http://www.diyaudio.com/forums/showt...604#post629604
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Old 18th August 2006, 12:51 AM   #36
mikeks is offline mikeks  United Kingdom
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Default Re: Examples:

Quote:
Originally posted by mikeks
Sony's 'best':

http://www.audio-circuit.dk/Schematics/Sony_TA-NR1.pdf

http://www.audio-circuit.dk/Schemati...y_TA-N80ES.pdf

http://www.audio-circuit.dk/Schemati...y_TA-E90ES.pdf


These are excellent designs in many respects, but, alas, are ruined by this relay SOA 'protection' arrangement.

Moreover, these designs compound the problem by detecting SOA conditions from only one polarity, which is a false economy at best as speech, for instance, is frequently offset to one polarity.
Sony TAN-R1:

http://www.thevintageknob.org/SONY/s...NR1/TANR1.html
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Old 18th August 2006, 01:53 AM   #37
anatech is offline anatech  Canada
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Hi Mike,
I'll bet that Sony is class "D" under those fake heatsinks!

Sure is pretty though, I'd make the meter larger.

-Chris
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Old 18th August 2006, 02:52 PM   #38
mikeks is offline mikeks  United Kingdom
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http://www.audio-circuit.dk/Schematics/Sony_TA-NR1.pdf
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Old 18th August 2006, 02:59 PM   #39
anatech is offline anatech  Canada
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Hi Mike,
I can't believe R125 and R126 are fusible!! R208 as well! Looks like they've declared war on their customers and non-intelligent technicians.

I was only kidding. Many of the top end products in 2004 were PWM type designs.

-Chris
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Old 18th August 2006, 03:16 PM   #40
mikeks is offline mikeks  United Kingdom
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Thumbs down Fuseable...

Sony folk always have hard-ons for these excreble fuseable thingy-bobs....What are they on?
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