Need help for an audio amplifier (must use lm386 op-amp ) project

Thread Starter

Shimul07

Joined Oct 24, 2023
13
I have simulated a design for an audio amplifier,in which i have to use op amp lm386 as it is a must requirement.I can't use other op amps.In my schematic R1 will be considered as a voltage controller(potentiometer of 10K ohm value).As i will assemble the project components on a veroboard i have chosen a 3W 8 ohm speaker as a load (in schematic R3).My project requirements are such that-
1)Minimal current should flow through the load(speaker here) and still achieve the needed output
2)supply voltage should be less.I know in the schematic i used a 9V supply voltage,I have read the datasheet and it says lm386 can be operated between 4-12V range ,so i am thinking of using a 5V battery for that.Can anyone tell me should i keep the 9V and try some way to minimize current or go for a 5V battery?Screenshot (195).png
 

MrChips

Joined Oct 2, 2009
30,488
Thread moved from Analog & Mixed-Signal Design to Homework Help.
The rules governing Homework Help are different. You have to show your best effort at solving the problem before you can receive any guidance from members.
 

Thread Starter

Shimul07

Joined Oct 24, 2023
13
well i did specify my problem and looking for answers!!!I am already stuck here as to what changes can i do to achieve my requirement
 

Alec_t

Joined Sep 17, 2013
14,220
R1 is not wired correctly as a potentiometer.
By "5V battery" do you mean some sort of power bank? It has to be able to provide enough current to give the output power you want in your loudspeaker.
 

BobTPH

Joined Jun 5, 2013
8,664
The output of the speaker depends on the current which depends on the voltage. There is no way to reduce the current while keeping the same output. (Not true if there is DC going through the speaker, but the coupling capacitor ensures that there is not.)

So your requirement does not makes sense.

Second requirement: Voltage should be less. Less than what?

The way you have stated the requirements are of no use. Is that the way the assignment is written, or is that your interpretation? If the latter, show us the actual assignment.
 

Thread Starter

Shimul07

Joined Oct 24, 2023
13
yeah i will replace R1 with a potentiometer of value 10K ohm max.By 5V battery i mean that if i choose this 5V as supply source instead of the 9V source...its just a hypothetical what if question i asked!!My main concern is that how to minimize load current with proper output in speaker
 

Thread Starter

Shimul07

Joined Oct 24, 2023
13
The output of the speaker depends on the current which depends on the voltage. There is no way to reduce the current while keeping the same output. (Not true if there is DC going through the speaker, but the coupling capacitor ensures that there is not.)

So your requirement does not makes sense.

Second requirement: Voltage should be less. Less than what?

The way you have stated the requirements are of no use. Is that the way the assignment is written, or is that your interpretation? If the latter, show us the actual assignment.



its a requirement that one should use less supply voltage in the given schematic network.I have clearly (emphasis on this) stated that i used a 9V supply voltage source(DC).I fail to understand what you haven't understood here!?One more note:You basically answered my 1st requirement as to if there is a way to minimize load current in some manner ?Your answer is simply No ,you can't!!!!What i am keen to hear is other's thoughts regarding this, as if by adding/removing any components(connection to series/parallel) or such can the load current be minimized???I will wait for other peoples opinions....Thank you
 

atferrari

Joined Jan 6, 2004
4,748
I would have started by reading first the datasheet. That would have informed the reader that the LM386 is an audio amplifier, not an op camp.
 

Thread Starter

Shimul07

Joined Oct 24, 2023
13
The current is mainly determined by the speaker volume level, not the supply voltage.
A lower supply voltage just means the maximum speaker volume will be less.

So if i want to minimize current(through load) the should i just use less supply voltage here?
 

BobTPH

Joined Jun 5, 2013
8,664
You cannot lower the current without lowering the output! For any output level you pick, the current is determined. What you are trying to do does not make any sense.

If you don’t understand what I am saying, please ask a question to clarify it.

If 5V is capable of producing the desired output level, it will use less power than 9V. But not less current.
 

ci139

Joined Jul 11, 2016
1,898
<circuit diagram>
about "INPUT BIASING" https://web.ece.ucsb.edu/Faculty/rodwell/Classes/ece2c/labs/lm386.pdf#page=3

the full power operation for loudspeaker might not be the best choice https://www.researchgate.net/public...Nonlinearities_in_Electrodynamic_Loudspeakers

(! I am not an "audio" guy, but) as far as i get you won't be exceeding your 3W range with the 9V supply as \[ {\Large \frac{{\left({\frac{±\left({\frac{+9V}2}\right)}{\sqrt{2}}}\right)}^2}{8\Omega}\approx1.3W_{RMS}} \]
 
Last edited:

Audioguru again

Joined Oct 21, 2019
6,610
Don't turn down the supply voltage, instead turn down the volume control.

The input signal is shown as only 4mV peak and the LM386 is connected with a voltage gain of 200 times.
Then the output signal is only 0.8V peak.
0.8V peak into 8 ohms is an output power of only 0.08W peak, or 0.057W average.
The datasheet shows that the idle current of the LM386 with a 5V supply is only 3.7mA.

The datasheet shows that the LM386 is 50% efficient then it heats by its output power with 0.029W (5.8mA for heating plus 5.8mA for the output power).

Then the totals of the currents is 3.7mA+5.8mA+5.8mA= 15.3mA with the volume control at maximum.
But in post#12 you said you want to minimize the load current then simply turn down the volume control.
 
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