There are many types of power transformers available some of which may be specific to your region. You must carefully identify which kind of transformer you have by studying the data provided with or on the transformer itself.
The color of the wires attached to a toroidal power transformer is not standardized! This is why the images of the high voltage wires contained in this section are in black and white! Do not attempt to use one transformer's color code with another transformer.
To begin, have a look at Mark Burnley's illustration of typical power transformer configurations (hosted by DIY Factory). Note that not all transformer schematic symbols include the dots like Mark's diagrams do. The dots show the polarity of the windings. When they are missing, it is assumed that the dots are at the "top" of each winding as shown in each of the symbols shown in Mr. Burnley's diagram.
But here is an image of the schematic provided on the side of one toriodal power transformer - this one is not shown in the document linked above! This power transformer has only a single primary winding as shown on the left hand side of the schematic marked "Primary 240VAC". As there is only a single 240 Volt AC primary winding, this transformer cannot be used in 120 Volt countries as in North America. Most power transformers sold in Australia have only a single 240 Volt AC primary winding. This makes it difficult, but not impossible, to wire incorrectly for a 240 Volt country whereas transformers with two 120 Volt AC windings can be wired in such a way as to cause damage to the transformer and/or the connected equipment.
Next we have the markings on the side of a dual primary toroidal power transformer. While there is no schematic printed on the side of this model, we know from the description - "Prim 2x120V" - that there are two primary windings each capable of handling 120 Volts. This transformer can be used in either 240 Volt or 120 Volt countries - depending on how these two primary windings are connected together.
The Avel Lindberg power transformer sold by Hairball is a dual primary and dual secondary type that, other than its secondary voltages, resembles Mr. Burnley's "Typical Mains (Power) Transformer". You can find the "standard" color codes for Avel Lindberg's transformers here. How many times can I say that you need to use the color codes for your particular transformer as there is no standard color code between manufacturers?
You must know the following things before attempting to wire your power transformer into your unit:
- What is my line (mains) voltage?
- Is my transformer a dual or single primary?
- What is/are the primary voltag(es) of my transformer?
- What colors are used to identify the primary/primaries and secondary windings on my transformer?
- Does my tranformer have a dual or center tapped secondary?
- I can read and understand an electronic schematic.
- I do not suffer from color blindness.
- Is the voltage and current of the secondaries sufficient for my project?
- Is it legal in my country for me to work on high voltage circuits?
If you can answer the first five questions definitively and can answer the last four in the affirmative you may proceed with the AC power wiring.
AC Wiring Step by Step
Use a quick connect or solder a wire directly to the neutral lug of the IEC connector. Make sure that any exposed metal gets insulated. You may use some heat shrink or fully insulated quick connects.
Next connect the live in the same manner with a different color wire. I'm using the IEC color codes for these pictures.
Note that the IEC connector pictured here comes pre-wired between the live leg and the fuse. Your connector may not have the fuse pre-wired and may require you to wire it yourself. Be sure to insulate this connection.
Rather than wire the wall voltage to the common center terminal of the power switch, we'll wire them to the normally closed terminal. This way, when the power is turned "off" (button pushed in) there is no voltage running to any of the other switch terminals other than the ones that the AC line is connected directly to.
We'll wire both the live and neutral to the switch for greater safety. If your wall outlet has the live and neutral reversed it does no good to switch just the supposed "live" wire. A safety hazard might still exist when the unit is switched "off" as the live connection would still be connected if we are only switching one side.
Slip a piece of heat shrink over and wire the other end of the live from the IEC to the terminal closest to the front panel of the switch as shown. Push the wire through the hole on the switch terminal to ensure it is mechanically secure before soldering it in place.
Add a piece of heat shrink to the neutral wire and solder it to the other front terminal of the power switch.
If you are absolutely 100% certain you are using the Avel-Lindberg power transformer sold by Hairball Audio then you may use the Avel-Lindberg Power Transformer Wiring Page to complete the AC power wiring. If you are using ANY OTHER POWER TRANSFORMER you MUST NOT use the instructions for the Avel-Lindberg transformer as the color codes are almost certainly different. You MUST be able to identify each lead using the transformer's schematic printed on the side of the power transformer itself or provided with your transformer's data sheet.
Now refer back to Mark Burnley's transformer connections. If you have a dual primary winding you must identify what your local line voltage is and wire according to the "Typical Primary Connections" shown in the drawing.
For a dual 120 Volt primary and a 120 Volt line voltage from the wall, identify the two wires represented with the 'dots' marked "L" in the Parallel Connection illustration. Run a piece of heat shrink over them and connect both of them to the terminal closest to the brown wire (hidden behind the blue wire - refer to the previous image) as shown in the photograph. Take the remaining pair of primary wires marked "N" and solder them to the terminal closest to the blue wire as shown.
If you have a single secondary which has the same voltage rating as your line voltage or you have a dual 120 V primary and your local power is 240 Volts then take the uppermost 'dot' wire of the primary marked "L", slip a piece of heat shrink over it and solder it to the terminal closest to the brown wire in the picture (just behind the blue wire). Now take the bottom wire without the dot in the drawing marked "N", slip a piece of heat shrink over it and solder it to the terminal closest to the blue wire.
For a dual primary series connection, identify the remaining two primary wires, slip a piece of heatshrink over them then secure and solder them together.
Slide the piece of heatshrink and shrink it over the connection you just made. Make sure it is absolutely secure and that no bare wire whatsoever is exposed.
AC Power Transformer Secondary Wiring
Refer again to Mark Burnley's transformer connections. Under the "Typical Output Configurations" we'll be using the "Split Secondary for +/- Power Supply".
I've used a terminal strip here. A terminal strip makes it simple to connect two or more wires together securely and to extend the reach of the transformer secondary beyond the usually too short length of the wires attached to the transformer.
Identify the two wires coming from the power transformer secondary that are closest to each other on the schematic. These are tied together to form the center tap. Twist them lightly together and secure them in the middle terminal of the terminal strip. Now take the two remaining secondary wires and attach them to either end of the terminal strip. The order of the top and bottom wires is unimportant. Just make absolutely sure you have tied the two secondary side wires together that are closest to each other on the schematic as indicated in Mr. Burnley's OUTPUT CONFIGURATIONS/SPLIT SECONDARY FOR +/- POWER SUPPLY illustration. This will form the center tap.
Attach three hookup wires to the other side of the terminal strip as shown. Use two colors as pictured - the black is the center tap while the red are the two AC wires.
Later, we'll be adding wires to this side of the connector for the VU meter lamp but for now you can secure the screws after inserting the wires.
Connect the other end of the wires coming from the terminal strip to the main board as shown.
Check your wiring carefully step-by-step with the instructions above. Make absolutely certain you have wired the AC power correctly. Any error could cause irreparable damage to the power transformer or other components or even yourself!
When you are certain everything is correct, bundle the wires neatly and add a couple of nylon wire ties.
Remove the fuse holder from the IEC power connector.
Insert the appropriate 5 x 20 mm fuse in the fuse holder. See this post for the way to select the correct fuse.
This completes the AC wiring of your unit. From here, the power supply built into the main PCB will convert the alternating current into direct current and regulate the voltages to the +30 and -10 Volts required for the rest of the circuit.
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