eXStatA Setup


Power Supply Setup

Follow this procedure to bring up the power supply.

Connect the power section (transformer, switch, fuse, etc) and the 250-0-250 windings to the terminal block at the left of the board.

DO NOT turn on the power supply without connecting the dummy 10k load resistors.

Rails

  • Connect one 10k/25W load resistors from the positive rail to ground.
  • Connect the other 10k/25W resistor in parallel with 51k/5W resistor from the negative rail to ground.
  • Set P1 and P2 to their halfway positions.
  • Do all of the rest as quickly as possible so as not to overheat the transistors in the regulator.
  • Power up the transformer.
  • Look for smoke. If no smoke, continue.
  • Measure each rail. They will be less than 300V. This is correct.
  • Place the DMM on the 3V scale and attach to T1-T2.
  • Adjust P1 until the meter reads 360mV.
  • Attach the DMM to T3-T4.
  • Adjust P2 until the meter reads 410mV.
  • As you turn on each regulator the associated LED on the board should light.
  • Measure the rails again. They should both be around 300V. As the PS heats up they will drift upward but eventually stabilize.
  • After they do measure T1 and T3 with respect to ground. These should be greater than +320V and -320V respectively.

Power LED

  • If you are using a power LED and have installed R23/R24, power down and wire up the LED to the L+ and L- terminals on the 7 pin block.
  • Power up again. The LED should light. It will be conducting about 5mA.

Bias Supplies

Bias voltages are measured at the testpoints NOT at the terminals on the block.

  • Turn on the PS.
  • Measure from either test point to ground. The instant you touch the DMM to the testpoint is the correct voltage. If the DMM lead stays in contact with the testpoint it will pull the voltage down. Therefore, get the measurement at the moment you touch the testpoint.
  • Adjust the associated trimpot to change the voltage, repeating the process of momentarily touching the testpoint until you have the voltage you want.
  • Do the same for the other bias supply.
  • Power down.
  • You're ready to attach the amplifiers.

 


Solid State Amplifier

Follow this procedure to bring up the solid state amp.

  • Disconnect the dummy load resistors from the power supply.
  • Connect the power supply ground and the two amp SG ground to the star ground point.
  • Connect the +300V and -300V from PS to both amp sections.
  • Be sure not to mix up -300V and SG. They are on the same terminal block.
  • It is not necessary to ground the inputs.
  • Set P1 and P2 to their halfway positions.
  • Check all of the connections. Twice.
  • Turn on the PS.
  • Look for smoke. If no smoke, continue.
  • Measure between the two output termnals on one amp. Adjust P2 until this voltage is close to 0VDC.
  • Measure from either output terminal on this channel to ground. Adjust P1 until this reaches close to 0VDC.
  • Repeat for the other channel.
  • Measure the rails to ground. They should be near 300V. If they are ...
  • Wait at least 1/2 hour with the amp under some supervision.
  • Repeate the balance and offset adjustments.
  • Wait another 1/2 hour.
  • Measure the offset and balance again. If they are less than 1VDC then ...
  • Set your bias supplies for the headphones you are using.
  • Go for it.

 


Hybrid Amplifier

Follow this procedure to bring up the hybrid amp.

  • Disconnect the dummy load resistors from the power supply.
  • Connect the power supply ground and the two amp SG ground to the star ground point.
  • Connect the +300V and -300V from PS to both amp sections.
  • Be sure not to mix up -300V and SG. They are on the same terminal block.
  • Connect the heaters by running wires around the boards. Bring the wires into board from the output edge of the board.
  • RH1 and RH2 provide the heater biasing. You do not have to do anything to get proper heater bias.
  • It is not necessary to ground the inputs.
  • Set P1 and P2 to their halfway positions.
  • Check all of the connections. Twice.
  • Turn on the PS.
  • Look for smoke. If no smoke, continue.
  • Wait for the tubes to warm up.
  • Measure between the two output termnals on one amp. Adjust P2 until this voltage is close to 0VDC.
  • Measure from either output terminal on this channel to ground. Adjust P1 until this reaches close to 0VDC.
  • Repeat for the other channel.
  • Measure the rails to ground. They should be near 300V. If they are ...
  • Wait at least 1/2 hour with the amp under some supervision.
  • Repeate the balance and offset adjustments.
  • Wait another 1/2 hour.
  • Measure the offset and balance again. If they are less than 1VDC then ...
  • Set your bias supplies for the headphones you are using.
  • Go for it.