Sunday, August 21, 2016

op amp radio update

My first post was an op amp radio. It used a LM741 which is a 1Mhz amp. I built it with a NE5532 which is rated at 5Mhz. It was designed to drive a small speaker and it will. I'm using it with an earbud  and have to be careful to keep the volume down. The NE5532 is a dual amp chip so why not add a RF amp? The only circuit modification for the NE5532 was the pin out. Here is the modified circuit.

 The original to compare.

The NE5532 output is pin 1 . The NE5532 power is pin 8. Changing those two pins is all that's needed.  Pin 5, 6 and 7 are the second stage. They could be used for an AF preamp, IF or Rf stage. This circuit gain is controlled by the ratio of R3 to R6. 1,000,000 / 10,000 = 100. the circuit gain could be adjusted by varying R6. If we change R6 to 1,000 ohms then 1,000,000 / 1,000 = 1000. The gain would be 1000. If we leave R6 at 1,000 ohm and add a 10,000 ohm pot with the wiper tied to one end between R6 and the tie point between R6 and R3 we would have a gain or volume control. It would adjust between R6 + 0 = gain of 1000 as just calculated to R6 + 10,000 = 11,000 ohm. which gives 1,000,000 /11,000 = 90.9.  Adding a 100KOhm pot would allow you to adjust the gain down to around 10. Because the op amp is so flexible I'm abandoning the hearing aid amp for the time being. If you only want a low frequency amp you could also use a LMx58. The LM358s are about a dime apiece and are rated 1 MHz.

No comments:

Post a Comment