QUASI Amplifier for Beginners

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djk

djk

R.I.P
Joined 2001
There is a limit to the voltage, so adding more outputs will only give more power into a lower impedance.

At some point the driver transistors will not be up to the task. At that point I would probably go to a triple (pre-driver, driver, outputs). I found six pair of outputs into a low impedance gave a circular 'bite' out of a sine-wave in the second and fourth quadrant (classic sign of not enough drive current). Crown uses the triple in most of their amplifiers.
 
djk

djk

R.I.P
Joined 2001
"Ok...i think the output power it depend to the,input voltage?"

The ± supply voltage.

"Then if you,add,more transistor i think to prevent over heating? Because the output transistor is in parallel,connection so that the power input divided, on how many output transistor have? Am I right? "

Basically, yes.

With good heat sinks you will be able to get roughly 100W per pair of outputs. A Crown DC300A doesn't have real big sinks, so they use four pair of outputs to do 300W/4Ω. They later offered a heat sink up-grade, or you could add fans.

See here for up to 10,000W with the 2N3773.

http://www.diyaudio.com/forums/solid-state/211635-simple-100w-power-amp-3.html
 
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A

AndrewT

R.I.P.
Joined 2004
A single pair for 100W of maximum output power is a bit ambitious, especially if the devices chosen have poor SOAR.
I prefer to use device power rating as a guide to maximum output power.

Pmax ~ {total device power rating} divided by 5 to 6 for BJTs. I use divide by 4 for FETs
A two pair 1943/5200 has a total device rating of 600W. That would indicate a safe and reliable 100W to 120W of maximum power output.
For an 8ohms amplifier that would require a +-50Vdc to +-54Vdc PSU.
For a 4ohms amplifier that would require a +-38Vdc to +-42Vdc PSU.
For a 2ohms amplifier that would require so much output current, that I would not bother entertaining such a nonsensical target.
 
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djk

djk

R.I.P
Joined 2001
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djk

djk

R.I.P
Joined 2001
"When i put 80+- it is ok and add more output transistor? "

Only if you can hand-select the outputs to be sure of a higher voltage than what the part is rated for. For instance, Crown hand-selects all the 160 outputs used in the MA10K to run at 163V (rail-to-rail), plus a safety margin for high line-voltage.
 
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