Analyzing my amplifier project

[shaiqbashir]

Hi Guys!

well! i have made the amplifier whose picture i have attached in this post. It is just a voltage amplifier, no sound, no speakers. All the voltages will be provided thru the COnsoles available in our labs. I want to ask u somethings here:


First of all! have a close look at this amplifier, do u think that it can be easily implemented, i mean! should i now make it on a breadboard or veroboard. which one will be suitable.

Secondly, this amplifier, has the speciality in my eyes, that if u just adjust the value of the 100uF trimmer (C4) present, u can vary ur input signal from 30mV to 0.3V, which will give u a contant output of nearly 2.7V. Is it good to see or not.

Thirdly, i want to know the main functions of the feedbacks that i have provided in this circuit. To be more simple, i want to know what is the function of R3, R5, C4. and how it happens that changing the value of trimmer can give u a constant voltage at the output.

Remember the resistor of 10K is my load. and there is nothing such like sound.

If u think that this circuit has some drawbacks, plz point them out clearly so that i can improve it further.

Thanks in advance.

View attachment 37325

 

[audioguru2]

Hi Shaiq,
You can't use a power Mosfet as a low-level preamp. You need a few small ordinary transistors or an opamp.

1) You are using a power Mosfet in your low-power circuit. The IRF510 is rated for 4A, but your circuit's max is only about 2.6mA. The datasheets for power transistors don't show data for such low currents.
2) The 12uF for C1 has an un-necessary value so high that it will take about 2.5 minutes to fully charge after the power supply is connected.
3) The value of R3 is so low that it does nothing, like a piece of wire.
4) Trimmer capacitors are made with pF values, certainly not even as high as 1nF. I have never seen one with a value higher than only 365pF.

You could use a switch to select different capacitors to do the same as the trimmer capacitor C4. The result would be a bass-cut tone control since the high frequencies will always have max gain and the low frequencies will be attenuated when the capacitance is reduced.
5) You need to amplify 30mV to 2.7V, which is a gain of 90. The datasheet for the IRF510 shows a max gain of only 10 at 1A. At the few mA of your circuit maybe it doesn't have any gain, it might even have a loss. Try it and see.
6) Your circuit's 8k output impedance is too low for a 10k load, or the 10k load is too low for the 8k output impedance of your amplifier.

 

[shaiqbashir]

Hi Audio Guru!

Trimmer capacitors are made with pF values, certainly not even as high as 1nF. I have never seen one with a value higher than only 365pF.

my dear friend! i know this thing already, but when i went to an electronics shop, he gave me a trimmer of 100uf. so that is why im using it here. dont u think it is possible?

You need to amplify 30mV to 2.7V, which is a gain of 90. The datasheet for the IRF510 shows a max gain of only 10 at 1A. At the few mA of your circuit maybe it doesn't have any gain, it might even have a loss. Try it and see.

sorry but i really didnt understand what u r trying to say here. My circuit gives an amplification at even 1mV. so why are u saying that it might even have a loss. Plz further clearify it. when im getting a gain at such a high value so what can i do abt it.

You can't use a power Mosfet as a low-level preamp. You need a few small ordinary transistors or an opamp.

1) You are using a power Mosfet in your low-power circuit. The IRF510 is rated for 4A, but your circuit's max is only about 2.6mA. The datasheets for power transistors don't show data for such low currents.

my question is WHY i cannot use, what is the rule of not using it.and if im deliberately using it, what is the harm in it? Plz clearify this as well, secondly give any MOSFET model recommendation which u think can be easily available in the market.

Thanks in advance again

 

[audioguru2]

when i went to an electronics shop, he gave me a trimmer of 100uf.

You were given a 100pF trimmer cap, one million times smaller than 100uF.

My circuit gives an amplification at even 1mV. so why are u saying that it might even have a loss. Plz further clearify it. when im getting a gain at such a high value so what can i do abt it.

With the 100pF trimmer cap, it can't have any gain at audio frequencies. Use a real 100uF capacitor for C4 and measure the gain.

my question is WHY i cannot use, what is the rule of not using it.and if im deliberately using it, what is the harm in it?

The datasheets for power transistors don't show data for such low currents.

give any MOSFET model recommendation which u think can be easily available in the market.

The little 2N7000 is the lowest current Mosfet that I know. Even it doesn't show spec's on its datasheet below about 200mA. Mosfets are used for high current circuits.