I decided to design an AM radio with an Op-amp; it works with a 9V battery.
Ok here it is, Please put your comments if you think I can improve this circuit (I am learning Op-Amps yet).
I have a question too, I have used a coil and a variable capacitor out of a one channel Am radio for this circuit, But it just receives our local station (the signal becomes weaker when I turn the variable capacitor but I am not able to get another stations). What's the reason?
Does it comeback to the nature of my design or…??
Thanks.
P.s. does everybody know how many volts (I do not know if I am allowed to ask how many currents though) I should expect out of the coil part?
Why are they called 'crystal' sets?
How can Improve it so that you do not call it a crude set?
I thought maybe the first stage op-amp will help to increase the very weak signal coming from the coil.
More selectivity, more sensitivity - a single transistor reflex circuit would out perform this one easily. A crystal set, even with an opamp audio amplifier, is about the crudest (and poorest performing) you can make.
I thought maybe the first stage op-amp will help to increase the very weak signal coming from the coil.
The TL072 will stop working when the battery voltage drops below 7V, to get the maximum battery life, it's better to use an op-amp that will work down to 6V.
Because pre-semiconductors (and pre-valve) you made crystal sets, using a gelena crystal and a 'cats whisker' to make a rectifier.
QUOTE]More selectivity, more sensitivity - a single transistor reflex circuit would out perform this one easily. A crystal set, even with an opamp audio amplifier, is about the crudest (and poorest performing) you can make.
Yea I am agreed with you but just want to improve the selectivity performance. I will read the link and will reflex circuit (why it is called reflex circuit?)
Please tell me If I am wrong, in several op-amp designs with virtual resistors ground I have seen a zero gain op-amp stage which its input is connected to the resistor divider and its output acts as virtual ground. So I thought maybe this stage acts like a Buffer ( gives more current at its output with the voltage value the same to its input I.e voltage gain of 1), Am I wrong?
The diode can only charge the capacitor, i.e. it can push but it can't pull.
Connect a high value resistor from where C1 and D1 meet to 0V.
See the site pointed to by the link in my previous post for an example.
The TL072 will stop working when the battery voltage drops below 7V, to get the maximum battery life, it's better to use an op-amp that will work down to 6V.
I've never heard of it either, but any silicon transistor should be fine, either general purpose or RF. Personally I'd use a BC107.
In case you're not aware, the transistor is been used TWICE - first as an RF amplifer, then as an audio amplifier as well - this is what gives it good performance.
In case you're not aware, the transistor is been used TWICE - first as an RF amplifer, then as an audio amplifier as well - this is what gives it good performance.[/QUOT]
In case you're not aware, the transistor is been used TWICE - first as an RF amplifer, then as an audio amplifier as well - this is what gives it good performance.[/QUOT]
So suppose if I need more curent for a circuit and have to use 2 resistor dividers, Can I use the Op-amp Buffer to do so? If no Why we use Op-am buffers? I have heard the answer to this question is 'impeance matching' But do not know if it has anything to do with giving more current (while making the volatge to be equal to the input)??
besides in accordance to my Op-amp radio, Can I use several turns of wires connected to the main ferrite somehow to improve the signal somehow (I do not want so much of quality).
So suppose if I need more curent for a circuit and have to use 2 resistor dividers, Can I use the Op-amp Buffer to do so? If no Why we use Op-am buffers? I have heard the answer to this question is 'impeance matching' But do not know if it has anything to do with giving more current (while making the volatge to be equal to the input)??
Your second opamp is already giving exactly the same input impedance as the first one, which is why the first one is doing absolutely nothing.
besides in accordance to my Op-amp radio, Can I use several turns of wires connected to the main ferrite somehow to improve the signal somehow (I do not want so much of quality).