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Old 30th January 2013, 07:26 AM   #21
kf_tam is offline kf_tam  Hong Kong
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Quote:
Originally Posted by cotdt View Post
This is just trying to be overly technical. In practical terms, the average current draw in Class A is constant and you will not see voltage sag.
It may be irrelevant to you but could be not to others. If two channels share the same power supply this is a very revelant consideration.
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Old 30th January 2013, 07:28 AM   #22
cotdt is offline cotdt  United States
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Quote:
Originally Posted by kf_tam View Post
It may be irrelevant to you but could be not to others. If two channels share the same power supply this is a very revelant consideration.
I'm just not seeing how it's relevant. Can you explain?
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Old 30th January 2013, 08:23 AM   #23
kf_tam is offline kf_tam  Hong Kong
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Quote:
Originally Posted by cotdt View Post
I'm just not seeing how it's relevant. Can you explain?
Do you care about channel separation?

A true balanced Class A has ideally constant current draw, so it won't modulate the voltage output of the power supply. With adequate decoupling and grounding you can have two channels from the same supply with very little interactions between the channels.

A two channel ordinary Class A amplifier from the same power supply is difference. The instantaneous power supply output voltage is modulated by the instantaneous current draw so there could be interactions between channels. This, of course, depends on the load, the output level, the circuit PSRR and the stiffness of the power supply.

It would be the best to have separate power supply. But if life wouldn't permit the luxury, then one must work carefully to minimize the pitfall.
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Old 30th January 2013, 11:09 AM   #24
ilimzn is offline ilimzn  Croatia
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Quote:
Originally Posted by cotdt View Post
This is just trying to be overly technical. In practical terms, the average current draw in Class A is constant and you will not see voltage sag.
Actually you will indeed on low frequencies, and in fact often you can see intermodulation products from it. This is one reason why some prefer huge filter caps, however this attention to the value of the cap i sseldomly extended to picking the right transformer for the situation!
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Old 30th January 2013, 12:06 PM   #25
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by KMossman View Post
............................the reasoning: class A draws steady current,.............
He gets it wrong.

Quote:
Originally Posted by kf_tam View Post
Only Balanced Class A draws steady current! Ordinary Class A current changes according to the output waveform. ..............
He gets told he has it wrong.
Quote:
Originally Posted by cotdt View Post
This is just trying to be overly technical. In practical terms, the average current draw in Class A is constant and you will not see voltage sag.
Then you come in with this nonsense.
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Old 30th January 2013, 12:16 PM   #26
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As has been mentioned many times in various threads:
For a typical class A topology the average current over a cycle is constant.
The current will vary with signal (above and below) the large idle value.


Thanks
-Antonio
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Old 30th January 2013, 02:48 PM   #27
alibear is online now alibear  United Kingdom
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Thanks everyone for your comments, but I think my original question may have been ambiguous or misunderstood. Regardless if class A draws constant current or not ( take heed of Andrew T, he's the man ) what I really want to know is which sounds best, regulated, cap mult, or CLC or CRC. Can anyone speak from experiance. It's the sound I am concerned about.
Thanks
Alan
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Old 30th January 2013, 03:08 PM   #28
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by ilimzn View Post
In theory, with a high PSRR design, a regulator is superfluous. Adding one for the input stages is a far less involved affair aind simply put, it keeps a lot of unwanted stuff off the power rails before PSRR even comes in as a consideration. However - there are relatively simple topologies that never the less work well but have relatively low PSRR and a regulated power supply, or, keeping it simpler - a capacitance multiplier - is of great help.
Keep in mind that you can only use the available power supply voltage up to the bottom of the ripple waveform, so if your cap multiplier or regulator regulates to a voltage just a bit below, the losses are minimal but the amp is not subjected to ripple + harmonics from the power supply, and it clips cleanly. Also, it's easier to add a protection mechanism in the power supply, especially for a simple amp, where it will be further from any interaction with the actual audio signal.
QFT.
Lot of good advice
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Old 30th January 2013, 03:13 PM   #29
Telstar is offline Telstar  Italy
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Originally Posted by Fusion916 View Post
Is there any issues of using a linear regular for the input stage and predriver and a capacitor multiple circuit for only the output stage? I suppose as long as the output stage collector voltage is higher than the predriver there won't be any issues of over driving the output stage.
Not at all.
You would get 90% of the performance of a regulated PSU for the output stage as well.
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Old 30th January 2013, 03:15 PM   #30
qusp is offline qusp  Australia
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Originally Posted by cotdt View Post
This is just trying to be overly technical. In practical terms, the average current draw in Class A is constant and you will not see voltage sag.
is that right?....
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