Power Amplifier Project

[Epicdemise]

I believe I would choose the cap value from fc = 1/(2piRC) where C is the 10k resistor?

 

[ronsimpson]

It acts like the pot is set to max gain which is fine for 100mV.
For 500mV the pot needs to be set to 20%. Do you have a way to set the pot position?

 

[ronsimpson]

I believe I would choose the cap value from fc = 1/(2piRC) where C is the 10k resistor?

Yes where R=10k. Don't set to 20hz. You need to be better than 20hz so set to 15 or 10hz.

 

[audioguru]

Your amplifier is clipping because the simulator sees an input of 500mV instead of 100mV. The simulator did not learn about a volume control that is turned down, instead it just sees the number 500mV.

The opamp has a max output swing of about 16V peak and the speaker output max is about 13V peak. That is full power from this circuit and the opamp is operating at its maximum allowed supply voltage.

For higher output power, select an opamp that works with a supply that is plus and minus 22V like a TLE2141 or MC34071.

 

[Epicdemise]

Yes I do and at the 20% with the 500mV input it acts like the 100mV. Is this what I want? In my thought process I want it to work at full power but I guess I don't know if that is possible or how complicated that is.

 

[Epicdemise]

Your amplifier is clipping because the simulator sees an input of 500mV instead of 100mV. The simulator did not learn about a volume control that is turned down, instead it just sees the number 500mV.

The opamp has a max output swing of about 16V peak and the speaker output max is about 13V peak. That is full power from this circuit and the opamp is operating at its maximum allowed supply voltage.

For higher output power, select an opamp that works with a supply that is plus and minus 22V like a TLE2141 or MC34071.

I do have the option of using the MC34071.

 

[ronsimpson]

Yes I do and at the 20% with the 500mV input it acts like the 100mV. Is this what I want? In my thought process I want it to work at full power but I guess I don't know if that is possible or how complicated that is.

This is what a volume control is for. Taking a loud signal and turning down the volume so the amplifier will not clip. Go play with your radio.

 

[Epicdemise]

This is what a volume control is for. Taking a loud signal and turning down the volume so the amplifier will not clip. Go play with your radio.

Fair enough.

 

[audioguru]

I don't like acid rock "music" so I never play my stereo with the volume control turned up to maximum. My tweeters will probably be destroyed by all the high frequency high level distortion.

 

[ronsimpson]

When will this 'home work' be done?
When it is over I think some of us could post our idea of a 10W amplifier. (not before)

 

[rumpfy]

Been watching yr progress and looks OK.
There seems to be a failure on the part of the design team to establish the;
1. Input voltage to drive the amplifier to full power.
2. the preamp maximum output.
I aint yet seen a clean sine wave output yet, and I haven't seen a biasing system to set the working bias for the output stages.
I note your 4 diode arrangement, which is essentially a non adjustable bias, but this could be done by using a single transistor. If you replaced the 4 diodes with a few resistors in series, an NPN emitter connects to the lower side of the existing diode D4, and the collector connects to the anode point of D1. Using a potentiometer in the chain of resistance, you connect the transistor base to the moving arm of the pot. There needs to be an AC short circuit across the bias network, so shunt the emitter and collector with a capacitor.
To set the bias, you need enough of it to get the output transistors JUST into conduction. A typical value is around 20 to 50 mA. This is described as Class AB. Without some forward bias, there is the danger that the amp will produce crossover distortion and this is very objectionable to a listener.
There seems to be lots of comment about the ability to overdrive the power amp. When the team agrees on the input voltage requirement for full output, then go to work on the feedback network and keep on increasing the feed back until the amp gives full output at the required (agreed) input. Typical commercial amps use between 100 and 400 mV for full output.
Looking at your circuit, my view is that there is nowhere near enough negative feedback. These things usually have heaps of it to stabilise the DC conditions against drift due to temperature, and changes in the working point due to 'rectification' effects. Looking again at your circuit, you have a tapped power supply. Connecting a loudspeaker to such an arrangement is asking for trouble if, for some reason, the speaker gets connected to the DC supply (eg, an output transistor goes short circuit). I suggest you use a output capacitor in series with the speaker to prevent a disaster. This capacitor can function as a low pass filter if you use a small value.
Of course, testing the amp needs a means of adjusting the input signal level and I note you are incorporating a volume control. When the design is complete, just leave it there set to maximum.
Hope this helps and it looks like yr all going well. So congratulations so far.