Before you start
Please pay attention. This amplifier uses high voltages. There will be 600V from rail to rail. Use every precaution when dealing with this HV as it can KILL YOU. If you are not familiar with or comfortable with HV circuits then don't build this amp or power supply. However, in every instance during the prototype phase where the builder has put the right parts in the right places with the correct orientation the amp has come alive properly.
Common Mistakes to Avoid
- Reversing the rectifier or zener diodes (see picture below).
- Swapping the P and N mosfets in the PS.
- Swapping the PNP and NPN transistors in other parts of the PS.
- Putting the wrong resistor values in the wrong places.
- Reversing the orientation of Z1/Z2 in the PS.
You can print silkscreen images of the boards from these links:
It's a good idea to study the board and components. Also, look at the schematic diagrams to locate each part on the layout. Measure each resistor before you install it to make sure that you're reading the code properly.
Board Assembly Instructions
The boards are fairly compact with just enough spacing to prevent HV arcing problems. Note that some of the resistors are tombstoned. Pay attention to their part labels. Take your time!!!!
PAY ATTENTION: Be very careful with your soldering techniques, especially at the pins of the power transistors. All of these transistors have HV between some of their pins. Do not shorten the distance between pads by dropping excessive solder blobs. Make sure you don't have solder bridges. Anywhere.
Have the components specific to your build in the parts box.
Solder the components to the board from lowest profile to highest, roughly in this sequence:
- Flat placement resistors and diodes (tombstoned later).
- Mount vertical diodes with cathodes up and anodes down, like this:
- Small signal transistors.
- KSA1156 on the amp boards.
- Film capacitors on the PS board.
- Trimots, tombstoned resistors, and connectors.
- Tube sockets on the hybrid board..
- Mount the transistors loosely to the heatsinks. Press the heatsinks to the board inserting the pins of the transistors.
- Hold the heatsinks down while soldering the transistor pins. Then tighten the heatsink mounting screw/nut.
- Some devices are double mounted on a single heatsink. Use the above technique to get both of them on the board at the same time.
- Electrolytics on the PS board.
- DO NOT connect the PS to the amps until it has been setup.
Clean up the solder flux residue from the board with isopropyl alcohol (or electronics flux remover) and a brush.
Inspect all solder connections carefully, using a magnifying glass, to make sure there are no solder bridges or cold solder joints. Use a multimeter in ohms scale to check for short circuits. Correct any mistakes before proceeding.
Triad Transformer Wiring
One low-cost transformer alternative is a pair of Triad Magnetics VPS230-110 transformers. Each of these transformers supplies 240VAC. To get the 240-0-240 that we neeed for the eXStatA the transformers must be wired in series. To do this right we have to get the phasing correct on both the primaries and secondaries. This diagram (for 120VAC line/mains) shows how to do this: