Most audio amplifiers have negative feedback from the output to reduce distortion. The original circuit does not.

It looks to me like R1 from the output to the base of Q1 is providing some negative feedback.

 

This circuit I designed will do that and has been verified on the breadboard.
View attachment 328785

Thanks. I will look at this!

 

Thanks. I will look at this!

Certainly a better design. Thanks.

 

Thanks. I will look at this!

Hi:

Here is a sim of your circuit. Not sure about setting the idle current to 10mA (probably due to newbness).
Thanks,
M

 

Here is a sim of your circuit.

Can you convert that file to some other format?

 

Can you convert that file to some other format?

It just the LTSpice .asc file for that nice amplifier circuit that you posted earlier.
At this point I have only simulated the circuit but I intend to breadboard it soon.
It looks like the current through R6 is only 961 uA.

M

 

It looks to me like R1 from the output to the base of Q1 is providing some negative feedback.

I mentioned the original circuit that has R1 connected to VCC.

The idle current (with no input signal) of the entire amplifier circuit is mostly from the output transistors. Then at low signal levels the output transistors operate at class-A producing no crossover distortion.

 

It looks like the current through R6 is only 961 uA.

Probably. The 10ma refers to the total current with no input signal which is mostly the output transistors as mentioned previously.
Have you tried using different values for R5 up to 1K in the simulator?

 

Probably. The 10ma refers to the total current with no input signal which is mostly the output transistors as mentioned previously.
Have you tried using different values for R5 up to 1K in the simulator?

The total current drain on the sup

Probably. The 10ma refers to the total current with no input signal which is mostly the output transistors as mentioned previously.
Have you tried using different values for R5 up to 1K in the simulator?

The current drain on the supply is only 1.5 mA (per simulation) with R5 at 500 ohms. The value of R5
doesn't seem to affect the cuurent drain at all.
M

 

If you build the circuit as designed R5 will definitely affect the current drain.
I found that 10ma was sufficient to remove any crossover distortion.

 

If you build the circuit as designed R5 will definitely affect the current drain.
I found that 10ma was sufficient to remove any crossover distortion.

Hi.
I am going to breadboard this circuit in the next while. I will let you know how it goes.

M

 

For your interest, below is the sim of a perhaps more elegant circuit, that uses a differential input stage (Q1 and Q2) with both AC and DC negative feedback from the output to bias the output at 1/2 the supply voltage largely independent of transistor or diode variations, establish the gain and reduce distortion (around 0.2% in the sim).
I think it's one of the better simple AB audio amp designs, due to the negative feedback that stabilizes the DC output operating point at 1/2 the supply voltage and gives low output distortion.

 

For your interest, below is the sim of a perhaps more elegant circuit, that uses a differential input stage (Q1 and Q2) with both AC and DC negative feedback from the output to bias the output at 1/2 the supply voltage largely independent of transistor or diode variations, establish the gain and reduce distortion (around 0.2% in the sim).

View attachment 328895

View attachment 328898

Thanks. I will delve into this circuit also.

 

Thanks. I will delve into this circuit also.

Since the 2N2222 is obsolete, what would be a good substitute?

M

 

Since the 2N2222 is obsolete, what would be a good substitute?
M

2N2222A or 2N2222A-B

 

2N2222A or 2N2222A-B

Can't get them.

 

PN2222A

 

Or P2N2222A or PN2222
Those are plastic package versions of the 2N2222(A).

In that circuit you could also substitute most small NPN's such as the 2N3904.

 

PN2222A

Thanks.

 

Or P2N2222A or PN2222
Those are plastic package versions of the 2N2222(A).

In that circuit you could also substitute most small NPN's such as the 2N3904.

Thanks.