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Old 19th September 2012, 05:29 AM   #21
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by a.wayne View Post
What was the Quiescent value in the AB mode on that marantz and what impedance/sensitivity were the speakers. There's a lot more to consider than just throwing a switch and one would suspect that amplifier might have been a compromised class-a design...
As far as I can tell from the service manual:
class AB: +/- 56 V power rails, 50 mA quiescent current;
class A: +/- 20.5 V; 500 mA.

The switch activates a relay that selects different windings on the transformer and activates an optocoupler to put some extra resistors parallel to the ones for class AB quiescent current.
Other than that there don't seem to be any differences.

The speakers were 4 Ohm and not particularly inefficient.
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Last edited by jitter; 19th September 2012 at 05:32 AM.
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Old 19th September 2012, 06:57 AM   #22
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Default Jean Hiraga Superclass A 30Watts why does one need 1.2F caps?

Maybe because it has poor PSRR?
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Old 19th September 2012, 07:15 AM   #23
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I believe Jean Higara's amp is supposed to be driven from batteries.

All audio that is run from mains is a compromise and includes counter measures for every possible scenario and in so doing affect the outcome adversely.

There is zero induced rubbish not even if you wound the voice coil around you eardrum will you hear any mains induced artifacts.
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Last edited by Nico Ras; 19th September 2012 at 07:18 AM.
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Old 19th September 2012, 07:28 AM   #24
AndrewT is offline AndrewT  Scotland
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Originally Posted by jitter View Post
.............The switch activates a relay that selects different windings on the transformer and activates an optocoupler to put some extra resistors parallel to the ones for class AB quiescent current.
Other than that there don't seem to be any differences................
A bit like D.Self's Trimodal and the first of the KSA100 Klones. The second Klone version did not adopt the extra pads for the extra resistor.

By the way 500mA of bias current in the output devices gives a 1Apk ClassA current when driven that hard.
1Apk into 8r0 is 4W of ClassA output, not 25W !
If that was a 2pair output stage, then we are talking 2Apk of ClassA output and this is equivalent to 16W of ClassA power.
3pair would be equivalent to 36W of ClassA but the output would voltage clip before that. 3Apk *8r0>>Vcc/Vee
3pair would result in ~60W of dissipation for the 25W of ClassA power. Sounds about right for a beefy heatsink and robust output stage.
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Old 19th September 2012, 08:59 AM   #25
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Because the JLH rail voltages are not high it's not too expensive nor too large size wise to use a large amount of capacitance and even better to pie filter it with a choke or small resistor splitting the capacitance in 2. A Class A amplifier fed from a large amount of capacitance has an effortless quality of reproduction. Reducing the capacitance by half each time in multple steps is heard as reduced bass dynamics, loss of overall clarity, and the effortless quality becomes noticeably less evident - how does one statisically measure those listening observations? What measurement describes the difference between an art student portrait and a great master, though some may differ on which they prefer or value enough to pay for.
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Old 19th September 2012, 09:19 AM   #26
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If you listen to "head-banger" music fed via an iPod into low definition speakers then it probably won't matter what sort of amp you use, class A, AB, D, t, Z or whatever.
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Old 19th September 2012, 05:57 PM   #27
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by AndrewT View Post
A bit like D.Self's Trimodal and the first of the KSA100 Klones. The second Klone version did not adopt the extra pads for the extra resistor.

By the way 500mA of bias current in the output devices gives a 1Apk ClassA current when driven that hard.
1Apk into 8r0 is 4W of ClassA output, not 25W !
If that was a 2pair output stage, then we are talking 2Apk of ClassA output and this is equivalent to 16W of ClassA power.
3pair would be equivalent to 36W of ClassA but the output would voltage clip before that. 3Apk *8r0>>Vcc/Vee
3pair would result in ~60W of dissipation for the 25W of ClassA power. Sounds about right for a beefy heatsink and robust output stage.
The PM-80SE has two pairs of 2SA1265/2SC3182 per channel. I quoted the power output from the service manual which specifies it as:
FTC 8 Ohms (20 Hz - 20 kHz) 110/25 W (Class A)
DIN 8 Ohms/4 Ohms 120/180 W.
Not sure about how trustworthy these specs are...

Last edited by jitter; 19th September 2012 at 06:02 PM.
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Old 19th September 2012, 06:13 PM   #28
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with 2 pairs and 500mA pr fet. there is 2A peak.
so 2A x 2A x 8ohm /2 = 16W class A at 8ohm load.
25W demands 650mA pr fet
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