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Another Amplifier Question

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New Member
I got this book at Radio Shack that has an amplifier project in it .It uses a 741 and a 386 op-amp. When I finished it I noticed it wasn't very sensitive compared to a transistor amp I built before .I'm not sure why the transistor amp was so sensitive( by sensitive I mean it picked up softer sounds etc.).
You have to almost yell in the op-amp version to get any output.Did I do something wrong , is this normal or would using different components (capacitors etc.) make a difference.

Also could someone give schematics for amps of both types.
I'll look around the site for some too.



New Member
One of the benefits of Op-Amps is their gain is set easily with resistors. If you look at your circuit there should be some resistors connected between the - terminal and the output terminal. These resistors set the gain of the circuit. In a feedback configuration the Op-Amp will output whatever voltage is nessesary to make the - terminal the same as the + terminal. So if you think of the resistors going from the output to the input as a simple voltage devider you should be able to come up with which resistor values you need to change.

Hope this helps.



New Member
op amp741 & low voltage power amp 386

:D hi,

are you using the 741 as mike pre-amp and the 386 as your power amp?

here's the pin assignment of those ic
741 1. offset null 386 1. gain
2. inv. input 2. inv. input
3. non-inv. input 3. non-inv. input
4. Vss 4, gnd
5. offset null 5. output
6. output 6. V+
7. Vcc 7. Bypass
8. open 8. gain

pls. take note that the 741 is a dual supply ic and the 386 as a single supply. are you operating the 741 on a single supply manner?

since you have not posted the schem of your project its quite hard to give you solutions to your problem although the circuitry used for this kind of devices are quite simple. the problem could probably lie in the construction of your project.
the 386 is internally set to have a gain of 20, if you want to increase the gain say 200 you can place an electrolytic cap of 10uf/16v across pin 1 and 8 with the positive (+) terminal of the cap at pin 1.

as to the 741 theres a feedback network in your circuit. heres a formula use can use to check the gain set of your project.
for an input at pin 2 (inv. in) Gain = Feedback Resistor/ Input resistor
for an input at pin 3 (non-inv. in.) Gain = 1 + (Rf/Rin)

if you want to increase the gain say 200 you can retain the input resistor (Rin) and mutiply if by 200 and that product is your feedback resistor (Rf)

hope this can solve your problem. :wink:
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