QUASI Amplifier for Beginners

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#842
hi
can anyone upload pdf file for this pcb?is it tested? thanks.
296296d1345055690-quasi-amplifier-beginners-prototype_small_001.jpg
 
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#847
I also agree with bepowell and JC. There are several basic errors that beginners would not be advised to make:
(1) no emitter degen = slew induced distortion
(2) no emitter ballasting resistors in the lower NPN output transistors =recipe for disaster (current hogging in one transistor)
(3) 2N3773 was never a good transistor (ft=200kHz when RCA made it. Devices today won't be built the same but fT spec. has not changed.
 
#848
john_ellis said:
I also agree with bepowell and JC. There are several basic errors that beginners would not be advised to make:.
Click to expand...

I made an error with my first quasi.
I put the electrolytic feedback capacitor in wrong way around.
Due to different driver stages for upper and lower output transistors the feedback DC voltage is negative so cap has to be in the right way around for that.
 
#850
A severe reactance speaker can demand peak currents of around 3times what the equivalent resistor would draw on fast changing signals.
That peak current has to come through your output devices.
The driver must be capable of driving the gate/base of those outputs.
I allow for 15Apk in a 100W into 8ohms speaker instead of the usual 5Apk into an 8r0 dummy load.
The output BJT will have a lowish hFE at 15Apk output, so the drivers may have to pass around 1Apk for a millisecond or so.

Supplies of ±80V into 4ohms is in a different field.
Are you really aiming for 500W into 4ohms and yet don't know how to assess current requirements?

BTW,
500W into 4r0 dummy load is already up above 15Apk and that is without applying a fast signal into a reactive speaker load.
 
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#852
AndrewT said:
A severe reactance speaker can demand peak currents of around 3times what the equivalent resistor would draw on fast changing signals.
That peak current has to come through your output devices.
The driver must be capable of driving the gate/base of those outputs.
I allow for 15Apk in a 100W into 8ohms speaker instead of the usual 5Apk into an 8r0 dummy load.
The output BJT will have a lowish hFE at 15Apk output, so the drivers may have to pass around 1Apk for a millisecond or so.

Supplies of ±80V into 4ohms is in a different field.
Are you really aiming for 500W into 4ohms and yet don't know how to assess current requirements?

BTW,
500W into 4r0 dummy load is already up above 15Apk and that is without applying a fast signal into a reactive speaker load.
Click to expand...

MAX current via driver transistor is 0.66 * 3 times about 2 A .

Now we look for driver 150-200 V , 3-4-5 A .....

I'm worried because the last amplifier which I did with Supply + -80 volts driver was the same as the final transistors ....
 
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