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Old 21st September 2012, 05:09 AM   #1
treez is offline treez  United Kingdom
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Default Class B guitar amplifier questions

Hello,

1....Generally speaking how efficient is a Class B guitar amplifier going to be? ( i appreciate that 78% is the ideal).
2....How well does a Class B amplifier tolerate rail sag?
3....Are Class B amplifies >100W always driven off of spilt rail power supply outputs.......?
4.....Is the Bridge Tied Load topology possible for Class B and does it mean a single rail output power supply only is needed?
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Old 21st September 2012, 06:47 AM   #2
Mooly is online now Mooly  United Kingdom
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1. Correct In practice real efficiencies are lower due to power losses in real components.
2. Amplifier dependant really. Any sag is reflected in reduced voltage swing being available. Of ore concern is that sag may be accompanied by ripple which can enter the amplifier stages and increase hum and noise. The answer is to ensure the PSU is correctly rated for the design considered.
3. No. Single ended or split rails can be used.
4. A bridge amp can use two Class B output stages. There is no reason a single rail can not be used although both amps would need precise setting of their "mid point" voltage to ensure no DC is present across the speaker. They would need to be stable in holding that setting too, maybe using a servo type set up. Again it all depends on the amp design.
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Old 21st September 2012, 02:59 PM   #3
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In the real world you are doing well if you achieve more than 60% efficiency in your Class B amp.
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Old 21st September 2012, 10:46 PM   #4
Enzo is offline Enzo  United States
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On split rails. You know, I could be totally wrong, but I had assumed that the single rail was popular in the past because back then it was easier and cheaper to use a big speaker output cap than it was to find cheap and reliable PNP power transistors for the negative side of things. The 2N3055 was king if the heap back then, and while there were PNP equivalents, none of them achieved the same status.


Then again I can wipe the speaker cap off the equation because the split supply requires a second big filter cap.
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