Hi:

I found a schematic for a 1 watt amplifier. I did a Spice simulation
and it looks like it only produces 490 mW into a 16 ohm speaker.
Is that correct? How could I modify the circuit to produce 1 watt
into an 8 ohm speaker?

Thanks,

M

 

If the selected Components of the Amplifier can withstand the additional Current,
then changing the Speaker to ~8-Ohms will result in almost ~1-Watt of Power
with no other Circuitry-changes.

It would be much more efficient to simply use 2- 16-Ohm Speakers instead of 1- 8-Ohm Speaker.
.
.
.

 

If the selected Components of the Amplifier can withstand the additional Current,
then changing the Speaker to ~8-Ohms will result in almost ~1-Watt of Power
with no other Circuitry-changes.

It would be much more efficient to simply use 2- 16-Ohm Speakers instead of 1- 8-Ohm Speaker.
.
.
.

Thanks LowQCab

 

The formula for power is

P = V x V / R

For example,
if V = 4 V rms and R = 16 Ω, P = 1 W rms
if V = 4 V rms and R = 8 Ω, P = 2 W rms

Multiply 4 V rms by 1.4 to arrive at peak voltage, i.e peak voltage = 5.6 V
Peak-to-peak voltage = 5.6V x 2 = 11.2 V
Hence you need at minimum, 12 V power source into the amplifier.

 

The formula for power is

P = V x V / R

For example,
if V = 4 V rms and R = 16 Ω, P = 1 W rms
if V = 4 V rms and R = 8 Ω, P = 2 W rms

Multiply 4 V rms by 1.4 to arrive at peak voltage, i.e peak voltage = 5.6 V
Peak-to-peak voltage = 5.6V x 2 = 11.2 V
Hence you need at minimum, 12 V power source into the amplifier.

Hi MrChips! Thanks.

M

 

Hence you need at minimum, 12 V power source into the amplifier.

I allow 2V extra. It is hard to get mote than that out.

 

12 V peak-to-peak into 8 Ω load is 6 x 6 / 2 / 8 = 2.25 W rms.
You are not going to get this from the class AB amplifier. It would be more like 1.5 W.

 

it only produces 490 mW into a 16 ohm speaker.

Where did you get a 16 ohm speaker?
They are not common anymore.

 

See

 

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

 

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

But the first stage is covered by local negative feedback.

 

The formula for power is

P = V x V / R

For example,
if V = 4 V rms and R = 16 Ω, P = 1 W rms
if V = 4 V rms and R = 8 Ω, P = 2 W rms

Multiply 4 V rms by 1.4 to arrive at peak voltage, i.e peak voltage = 5.6 V
Peak-to-peak voltage = 5.6V x 2 = 11.2 V
Hence you need at minimum, 12 V power source into the amplifier.

Is this correct? The peak output from the circuit in post #1 is 2.82 which is 2.82 * 0.7071 = 1.99 vrms.
Prms = (1.99)^2 / 16 ohms = 247.5 mW rms?

M

 

I don't read .asc files. Is 2.82 peak or peak-to-peak?
If it is peak voltage, then yes, Power is 1/4 W rms.

 

I don't read .asc files. Is 2.82 peak or peak-to-peak?
If it is peak voltage, then yes, Power is 1/4 W rms.

Yes, 2.82 is the peak.

I find that a lot of posts show a circuit and claim that the output is a certain value
and when you simulate the circuit the output power is not even close. I am trying
to find a simple class ab that will produce 1 watt rms into an 8 ohm speaker.

M

 

I redesigned your circuit and got more than 1 W of power! Didn't you look at the results I got? The distortion was 3%.

 

But the first stage is covered by local negative feedback.

The distortion of the 1st stage is reduced by its R4 emitter negative feedback. But the distortion caused by the output stage has no negative feedback then its distortion is high.

 

See
View attachment 328677

If you simulate this circuit it does not work. There is dc on the speaker!

And this is not the appropriate forum for analog design. Because a person simulates
such a circuit doesn't make it a simulation issue.

 

The DC on the speaker is only about 16mA which is close to nothing.
It is a simple way to add bootstrapping to the driver transistor.

 

The DC on the speaker is only about 16mA which is close to nothing.
It is a simple way to add bootstrapping to the driver transistor.

My point is that if you run a sim on the circuit as shown, it does not work.

 

I am trying to find a simple class ab that will produce 1 watt rms into an 8 ohm speaker.

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