SoftRock Lite - Amplifier

Description

The amplifier U5, which could have been built right after the power supply, is a dual opamp. One side amplifies the In phase signal from the "mixer" and the other amplifies the Quadrature signal. These are then output to the left and right channels of a stereo headphone jack.

Components - blue on schematic

• U5 - TLV2462CD
• C11 - 0.047uF
• C12 - 1500pF
• C13 - 0.047uF
• C14 - 1500pF
• C16 - 0.1uF smt, bottom below U5
• C17 - 0.1uF smt, bottom upper right of U5
• C18 - 10uF +
• C19 - 0.1uF smt on top
• R10 - 10 ohms
• R11 - 1k ohms
• R12 - 10 ohms
• R13 - 1k ohms
• R14 - 1k ohms
• R15 - 1k ohm
• 1/8 stereo phone jack

The opamp U5 chip has been added to the bottom of the board. Two more smt caps have been added to the board, C17 just below U5 and C16 above and to the right of U5.

For the top board view you can see the amplifier components in the lower right with the red clip lead attached to R12. The other end of the red clip lead is attached to the tip of a 1/8 stereo plug. The bare clip lead is attached from the RX enable ground point to the sleeve of the plug. The other end of the stereo cable is plugged into the Grundig. Of course head phones are plugged into the SoftRock Lite's stereo phone jack.

Test

To test this stage I used an audio signal from the headphone jack of my Grundig (I had tuned it to 40m CW). I used a stereo cable with 1/8 plugs on either end to transmit the signal from the radio to the SoftRock. I clip leaded the sleeve of the plug to the enable RX ground point and used a clip lead attached to the tip for my test probe. I plugged a headphone into the jack on the SoftRock Lite and applied power. Next I touched the test probe to the exposed lead on R10, which feeds the first amp. And I heard CW in one of the earphones. Then I touched the test probe to the exposed lead on R12, which feeds the second amp. And I heard CW in the other earphone. Note, if you do not plug the battery into the SoftRock Lite you will still be able to hear the test audio signal. When you do plug the battery in there should be a noticable increase in volume.