Introduction

This stage has a pretty large part count..  It consists of four unitary gain op-amps, arranged in pairs, one per stereo line out signal into the board.  The left channel's input resolves to two signals: 0° and 180°. The right channel's input resolves to two signals: 90° and 270°.

These four outputs will be muxed together in the mixer stage to produce the desired exciter output (thus, the term Quadrature Sampling Exciter (QSE)).

Schematic

(Click for full TX Schematic) Transmit OpAmps

Summary Build Notes

  • Install Ceramic Caps C1, C3, C5, C7, C8, C10, C12, and C14
  • Install Electrolytic Caps C2, C4, C6, C9, C11, C13, and C15
  • Install Resistors R1-R14
  • Install U1 and U2
  • Test the Stage

Bill of Materials

CheckDesignationComponent(Color) CodeTypeQtyNotes
[__]C011000 pF 102ceramic1
[__]C0210 uF 16Velectrolytic1E=+
[__]C03100pF101ceramic1
[__]C0410 uF 16Velectrolytic1S=+
[__]C050.022 uF 223ceramic1
[__]C0610 uF 16Velectrolytic1N=+
[__]C070.022 uF 223ceramic1
[__]C081000 pF 102ceramic1
[__]C0910 uF 16Velectrolytic1E=+
[__]C10100pF101ceramic1
[__]C1110 uF 16Velectrolytic1W=+
[__]C120.022 uF 223ceramic1
[__]C1310 uF 16Velectrolytic1N=+
[__]C140.022 uF 223ceramic1
[__]C1510 uF 16Velectrolytic1E=+
[__]R0110 kbrown-black-black-red-brownResistor 1%1N-S
[__]R0210 kbrown-black-black-red-brownResistor 1%1E-W
[__]R0349.9yellow-white-white-gold-brownResistor 1%1S-N
[__]R0410 kbrown-black-black-red-brownResistor 1%1N-S
[__]R0510 kbrown-black-black-red-brownResistor 1%1S-N
[__]R0649.9yellow-white-white-gold-brownResistor 1%1E-W
[__]R0710 kbrown-black-black-red-brownResistor 1%1S-N
[__]R0810 kbrown-black-black-red-brownResistor 1%1E-W
[__]R0949.9yellow-white-white-gold-brownResistor 1%1E-W
[__]R1010 kbrown-black-black-red-brownResistor 1%1N-S
[__]R1110 kbrown-black-black-red-brownResistor 1%1S-N
[__]R1249.9yellow-white-white-gold-brownResistor 1%1S-N
[__]R132.21 kred-red-brown-brown-brownResistor 1%1S-N
[__]R142.21 kred-red-brown-brown-brownResistor 1%1W-E
[__]U1TLV2462IC SOIC-8 dual Op-Amp1(bottom)
[__]U2TLV2462IC SOIC-8 dual Op-Amp1(bottom)

Detailed Build Notes

  • Need to do topside components first, as many holes for these are very close to the IC pads on the bottomside - avoiding solder splashover

Install the 8 Ceramic Capacitors

TX OpAmp Ceramic Caps

Install C1, C3, C5, C7, C8, C10, C12, and C14
CheckDesignationComponent(Color) CodeTypeQtyNotes
[__]C011000 pF 102ceramic1
[__]C03100pF101ceramic1
[__]C050.022 uF 223ceramic1
[__]C070.022 uF 223ceramic1
[__]C081000 pF 102ceramic1
[__]C10100pF101ceramic1
[__]C120.022 uF 223ceramic1
[__]C140.022 uF 223ceramic1

Install the 7 Electrolytic Capacitors

Electrolytics Layout
Install the 7 electrolytic caps: C2, C4, C6, C9, C11, C13, and C15
Note the orientation of the positive lead ("notes" column, below)
CheckDesignationComponent(Color) CodeTypeQtyNotes
[__]C0210 uF 16Velectrolytic1E=+
[__]C0410 uF 16Velectrolytic1S=+
[__]C0610 uF 16Velectrolytic1N=+
[__]C0910 uF 16Velectrolytic1E=+
[__]C1110 uF 16Velectrolytic1W=+
[__]C1310 uF 16Velectrolytic1N=+
[__]C1510 uF 16Velectrolytic1E=+

Install the 14 Resistors

TX OpAmp Resistors

Install Resistors R1-R14
Note: orientation is in "Notes" column below.
CheckDesignationComponent(Color) CodeTypeQtyNotes
[__]R0110 kbrown-black-black-red-brownResistor 1%1N-S
[__]R0210 kbrown-black-black-red-brownResistor 1%1E-W
[__]R0349.9yellow-white-white-gold-brownResistor 1%1S-N
[__]R0410 kbrown-black-black-red-brownResistor 1%1N-S
[__]R0510 kbrown-black-black-red-brownResistor 1%1S-N
[__]R0649.9yellow-white-white-gold-brownResistor 1%1E-W
[__]R0710 kbrown-black-black-red-brownResistor 1%1S-N
[__]R0810 kbrown-black-black-red-brownResistor 1%1E-W
[__]R0949.9yellow-white-white-gold-brownResistor 1%1E-W
[__]R1010 kbrown-black-black-red-brownResistor 1%1N-S
[__]R1110 kbrown-black-black-red-brownResistor 1%1S-N
[__]R1249.9yellow-white-white-gold-brownResistor 1%1S-N
[__]R132.21 kred-red-brown-brown-brownResistor 1%1S-N
[__]R142.21 kred-red-brown-brown-brownResistor 1%1W-E

Install the 2 SMT Op-Amps

TX OpAmp Bottomside

Note: one of the pin indicators (below) refers to a molded "U" on the chip. Do not confuse this with the "U1" and "U2" annotations in the above picture of the IC placement on the underside of the board.
Thanks to Ross OK5AZ for catching this.

Install U1, U2,

Watch out for solder splashover on any adjacent, open holes


CheckDesignationComponent(Color) CodeTypeQtyNotes
[__]U1TLV2462IC SOIC-8 dual Op-Amp1(bottom)
[__]U2TLV2462IC SOIC-8 dual Op-Amp1(bottom)

Completed Board

Topside

Bottomside

Testing


Current Limited Power Test

  • Connect a 100 ohm resistor in series with the power line and apply 12 V dc power
  • the current should be less than 120 mA (nominally 100 mA)
  • Measure the voltage WRT ground at the +5 V and at the 3.3 Vdc testpoints.
  • A voltage of around 2 V dc indicates the power rails are not shorted
  • Remove the current-limiting resistor.  Subsequent tests in this stage are with the current-limiting resistor OUT of the circuit.

Current Draw

  • Without Limiting resistor the draw should be < 102 mA
  • Your measurement: ________________________________

Op-Amp Voltage Divider (R13/R14)

  • R13/R14 form a voltage divider to halve the 5 Vdc rail
  • measure the voltage WRT ground at the R14 hairpin.
  • You should see nominaly 2.5 Vdc (actual would range between 2.4 and 2.5 Vdc)
  • Your Measurement: _________________________________

Op-Amp Pin Voltages

  • If the voltage divider tests out OK, measure the voltages at the pins of U1 and U2 using the table below
  • You should measure at the actual pins on the ICs as well as using the convenient resistor hairpin testpoints
U1, U2 Bottom U1, U2 VCC Testpoints
Actual values in the 2.5 nominal measurements will range from 2.4 to 2.5 Vdc
PinNominal ValueAuthor ResultYour Measurement
1 (R4 hairpin)½ 5V rail2.48
2 (R2 hairpin)½ 5V rail2.48
3 (R14 hairpin)½ 5V rail2.48
40 (gnd)0
5 (R13 hairpin)½ 5V rail2.48
6 (R5 hairpin)½ 5V rail2.48
7 ~2.5 Vdc½ 5V rail
8 See testpoint picture above5V rail4.96
U2
PinNominal ValueAuthor ResultAs Measured
1 (R10 hairpin)½ 5V rail2.48
2 (R8 hairpin)½ 5V rail2.48
3 (R14 hairpin)½ 5V rail2.48
4 0 (gnd)0
5 (R13 hairpin)½ 5V rail2.48
6 (R11 hairpin)½ 5V rail2.48
7 ½ 5V rail2.48
8 See testpoint picture above5V rail4.96

Op-Amp Function

This test validates that the OpAmps are actually functioning. Each Opamp IC will have a 0.4 Vdc reduction in the pin 1 voltage and a 0.4 Vdc increase in the voltage at pin 7.
  • Connect a test lead with a spare 10 kOhm resistor in series between R1 hairpin and the 3.3 V test point at JP1 (alternatively you can clip to the R39 or R40 hairpin for a 3.3V source)
  • Power up the board
  • Measure the voltage at R4 hairpin. It should be ½ the 5 V rail - 0.4 Vdc (about 2.1 Vdc)
  • Measure the voltage at pin 7 of U1. It should be ½ the 5 V rail + 0.4 Vdc (about 2.9 Vdc)
  • Disconnect the lead and resistor from R1 and connect it to bridge between R7 hairpin and the 3.3 V test point (JP1, R39, or R40)
  • Measure the voltage at R10 hairpin. It should be ½ the 5 V rail - 0.4 Vdc (about 2.1 Vdc)
  • Measure the voltage at pin 7 of U2. It should be ½ the 5 V rail + 0.4 Vdc (about 2.9 Vdc)
Test PointNominal Your Measurement
R4 hairpin - R1 bridgedaround 2.1 Vdc
U1, Pin 7 - R1 bridgedaround 2.9 Vdc
R4 hairpin - R1 unbridged½ 5V rail
U1, Pin 7 - R1 unbridged½ 5V rail
R10 hairpin - R7 bridgedaround 2.1 Vdc
U2, Pin 7 - R7 bridgedaround 2.9 Vdc
R10 hairpin - R7 unbridged½ 5V rail
U2, Pin 7 - R7 unbridged½ 5V rail