Help with simple op amp circuit

[FvM]

LM386 is very inefficient with 4 ohm load respective 8 ohm load in bridge configuration, particularly at supply voltages above 6 V as a brief look to the datasheet clarifies. See output swing versus load diagram

I really don't understand what this thread is up to

 

[danadakk]

LM386 is very inefficient with 4 ohm load respective 8 ohm load in bridge configuration, particularly at supply voltages above 6 V as a brief look to the datasheet clarifies. See output swing versus load diagram

View attachment 167898

I really don't understand what this thread is up to

Thread looking into why the bridge config failed, and sims seem to show
too much power for a 8 pin dip with no heatsink probable cause.

And to answer a distortion question.

Regards, Dana.

 

[Audioguru]

I have never tried a low power M386 but I have two amplifiers using the LM390 which is similar but it uses boostrapping and produces 1.1W at low distortion into 4 ohms when the supply is its max at 9V. Into 8 ohms the power with low distortion is 0.67W.

The LM386 produces only 0.3W into 4 ohms and only 0.45W into 8 ohms with low distortion when the supply is 9V.

Years ago I used a bridged and bootstrapped LM2896 dual amplifier IC to produce 4.0W at low distortion into 8 ohms with a 9V supply.

 

[Audioguru]

I analyzed the original amplifier produced by an older "student" at ElecCircuit.com:
The two channels produce hardly any stereo separation and mono in both channels have them out-of-phase.

 

[FvM]

I analyzed the original amplifier produced by an older "student" at ElecCircuit.com:
The two channels produce hardly any stereo separation and mono in both channels have them out-of-phase.

In other words, it's a useless circuit implemented with an unsuitable amplifier.

 

[Audioguru]

In other words, it's a useless circuit implemented with an unsuitable amplifier.

Like most circuits from students "over there".

 

[danadakk]

@Audioguru

I can confirm bridge with 9V supply and slightly lower drive yields a good
distortion number (see lower right result)....

Regards, Dana.

 

[Audioguru]

Ho Dana.
With the 9V supply, the bridged LM386 circuit is still overloaded producing too much heating instead of output power.

Your output level is higher than shown in a graph on the datasheet because the bridge causes the output current to be doubled then the losses in each IC are also doubled.
Your waveform shows a single amplifier (not a bridged amplifier) causing substantial even-harmonics distortion but actually the even harmonics are cancelled in a bridged amplifier causing the top and bottom of the waveform to be squashed which is odd-harmonics distortion.

 

[danadakk]

Here is bridge with 100 mV of drive -

This shows low distortion. Power levels at chips still show too much chip power.

Note sims not complete design recommendations, they are to show, for configuration, what is going
onl. Nowhere yet has thermal design really been addressed. Sims do seem to help in establishing
max drive level to limit distortion. But the model is not considered real precise by the author.



Regards, Dana.

 

[Alistair Ballantyne]

I have never tried a low power M386 but I have two amplifiers using the LM390 which is similar but it uses boostrapping and produces 1.1W at low distortion into 4 ohms when the supply is its max at 9V. Into 8 ohms the power with low distortion is 0.67W.

The LM386 produces only 0.3W into 4 ohms and only 0.45W into 8 ohms with low distortion when the supply is 9V.

Years ago I used a bridged and bootstrapped LM2896 dual amplifier IC to produce 4.0W at low distortion into 8 ohms with a 9V supply.

Thanks for that.
Any chance you could let me have the circuit details for your LM390 amp?
Regards,
Alistair

 

[Audioguru]

Google has trouble finding the latest datasheet so I looked at Digikey to see that they have thousands of LM390 ICs in stock and a price of $.75US for one. They also have the latest datasheet.
I used the circuit in the datasheet but I doubled the output capacitor value to 1000uF and doubled the bootstrap capacitor to 47uF for a better low frequency output.