what specs can I expect from this circuit?

Thread Starter

chunkmartinez

Joined Jan 6, 2007
180
Okay so from what I've gathered, the tl082 cannot supply much current, (5ma)? Can I drive some small to-92 bjts in a darlington config and then drive the TIP pair with arounf 110ma? Is 110ma input for the TIP transistors their limit? I probly wouldn't need the op amp huh? Also, the slew rate may not be high enough on cheap to-92 bjts?

Why would i need a high voltage drive for higher power output when the power out depends on the rail supply to the output transistors(the tip out transistors)
 

Audioguru

Joined Dec 20, 2007
11,248
The opamp is needed for its extremely high open-loop voltage gain. Adding negative feedback reduces the gain and reduces the distortion. It is difficult to design a high gain linear amplifier (like an opamp) with separate transistors.

The power transistors can be driven with little ordinary transistors used as driver transistors. Then the combination is a darlington.

Cheap little transistors have an extremely high slew rate. It is the opamp that will have the lowest slew rate.

The driver and output transistors are emitter-followers that have no voltage gain. So their drive voltage from the opamp must be a few volts higher than the supply voltage.
Most opamps have a supply voltage that is 36V absolute maximum.
 

Thread Starter

chunkmartinez

Joined Jan 6, 2007
180
Schematic of a Power Amplifier without an op amp

The outputs are Sziklai Pair (NPN - PNP) rather than darlington pairs (NPN-NPN/PNP-PNP)

The input stages are what the op amp "replaces", saving complexity for a quick medium power hobbyist circuit. The amp in the link uses a dual rail power supply (+V, -V and GND), while the one in the OP is a Single Supply amp.
Thanks for the project suggestion...btw if you were reffering to the original circuit I posted, it is a dual voltage supply, it uses +, -, GND +/-12v with a center tap.
 

Thread Starter

chunkmartinez

Joined Jan 6, 2007
180
Okay, so what I really want to do is design a driver to go betweent he OP amp of this circuit and the output stage so I need a simple driver using bc547 npn transistors(it's what I already have) to supply 100mA to the output transistors input.I am needing to amplify the current of the op amp from 5mA to 100mA. Do I use a common collector circuit? Any ideas on design and values?
 

thatoneguy

Joined Feb 19, 2009
6,359
Which amp are you referring to?

What is your input source, level, and impedance of source?

What is your desired output level/impedance?

I hope somebody good with audio amps stops by to help. :D
 

Thread Starter

chunkmartinez

Joined Jan 6, 2007
180
I will get all that, thanks for the pm response thatoneguy..oh and the amp is oin the OT in a link...the class "B" amp..
 
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