Wiring Pages:

Wiring the Rev A/D/F with a Hairball Case


Let's just make it clear now that the original schematics for the 1176 are the definitive documents for wiring your build. Schematics contain agreed-upon, unambiguous symbols that show how electronic components are interconnected. This is quite different from an ordinary drawing or photographs such as the ones contained on these pages. Drawings or photographs of builds can be incorrect or could be mis-interpreted.

If you have any doubts, refer to the original schematics that correspond to your build. They are confirmed as correct!

Hookup Wire

Hookup Wire Comparison

Before getting started a quick word about hook-up wire that we'll use in this and subsequent steps.

Have a look at the image to the right. These are two examples of hook-up wire - one purchased off-the-shelf at Jaycar Electronics in Australia for around five dollars Australian for a 25 meter roll (82.02 feet). It is described in their 2010 catalog as "Quality...tinned hook-up wire..." and the guage is indicated as 26AWG but also as 25AWG in the same listing.

The other was purchased off-the-shelf at Fry's Electronics in the US for around five dollars US for a 22 guage 100 foot roll (30.48 meters). The currencies are near parity at the time of this writing.

Note the thickness of the insulation in comparison to the conductors. Look at the thickness of the wire strands themselves. Notice that one wire has tinned copper strands while the other does not (even though it is claimed to be tinned - see the description above).

If the wire you are using looks like the crap sold at Jaycar at the bottom right, you should look elsewhere for better material. One possibility is to use the individual conductors from stranded alarm wire or other multi-conductor cabling. Some of the wire shown on these pages was mined from old computer cables.

Look for the marking AWM on the wire which stands for Appliance Wiring Material. This wire is made to a standard and should provide adequate strength and durability for the purpose of wiring this and other projects.

The AC Power Circuit

The AC power section of any DIY project is not something that can be taken lightly. Lethal current is involved and if you have no experience wiring circuits that use high voltage you should find someone who does to help you or leave this work to someone experienced in wiring high voltage circuits.

Laws and standards vary from country to country; familiarize yourself with local regulations concerning electrical wiring involving mains/wall power. If you have any doubts at all, seek out the assistance of a technician, electrician or repair person who can help you. This does not mean simply posting to a forum asking for help! Get some hands-on assistance from a knowledgeable person who can physically help you with the wiring.

You could be held liable if a piece of equipment you miswired causes injury or death. Don't fuck around; this isn't the time to pretend you know what you're doing if you really don't.

You should at least know how to read a schematic if you are going to complete this section safely. You might be able to convince some people that you're a great musician even if you can't read music but no one ordinarily gets killed for hitting a few wrong notes. Mess up here and you may have a hard time convincing anyone of anything after you've electrocuted yourself.

Use an RCD or GFCI equipped circuit to power your unit when you are building/testing it. This may protect you in case of accidental contact with a live wire.

Case Continuity

Testing Continuity

Before starting any wiring, check that the case itself is electrically connected between all panels. The screw holes make a convenient place to insert your probes as they are free of any powder coat. If you find a panel is not making electrical contact with its neighbor, tighten the screws until it does. Failing that, scrape a bit of paint off between the surfaces that contact each other when the panels are tightened against each other.

Don't forget that the top and bottom must also make electrical contact with the sides. The Hairball case has the countersunk screw holes masked during power coating to help conductivity between the top and bottom panels and the case sides, front and back.

Chassis Ground

Let's begin with the single most important connection you will make.

IEC Ground Pin to Chassis

Look at this picture closely. It shows the ground pin of the AC connector wired to the chassis. Note that the chassis connection does not share its function with any other device or element of the unit. If the IEC connector itself is unscrewed from the chassis it will not affect the function of this connection - the ground pin will remain connected to the chassis.

This connection is crucial to ensuring your safety and the safety of others who come in contact with your project. Do not skip this step or think that you can consider it optional. If you believe that "ground loops" are causing problems with your interconnected equipment this is not the ground you want to break!

Hole in Chassis Near IEC

Start by drilling a hole nearby to the IEC connector itself. I'm using a flat head machine screw (pictured below) so I've used a countersink bit to cut the angle to the hole. This helps expose the metal beneath the power coating of the cabinet ensuring that there is good contact between the screw and the chassis.

Chassis Ground Screw

Chassis Ground Screw, Lock Washer and Nut

Use a star lock washer and nut to secure the screw to the chassis. Tighten the screw and nut securely.

Chassis Ground Screw, Solder Lug

Add a solder lug, another star washer and a nut to complete the chassis ground assembly.

IEC Ground Pin to Chassis

Mechanically secure a thick, insulated wire to the chassis ground solder lug and the IEC ground pin. Solder the wire in place.

As this wire is bonded to the chassis and grounded there is no need to insulate it with heatshrink.

Testing Ground Pin Continuity

Test continuity between the ground pin and chassis. If there is a reading any greater than 1 Ohm figure out why and correct the problem before proceeding.

Power Transformer Types

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.

240VAC Single Primary Power Transformer 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.

120VAC Dual Primary Power Transformer 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

IEC Neutral Quick Connect

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.

IEC Neutral Heatshrink

IEC Live Quick Connect

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.

AC Live Switch Connection

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.

AC Neutral Switch Connection

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.

AC Power Parallel Primary Transformer Wiring 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.

AC Power Single or Series Primary Transformer Wiring 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.

Power Transformer Primary Parallel Connection

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.

Power Transformer Primary Parallel Connection Heatshrink

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".

Power Transformer Secondary Terminal Strip

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.

Terminal Strip Output to Main Board

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.

AC Power Wiring at Main Board

Connect the other end of the wires coming from the terminal strip to the main board as shown.

AC Power Wiring Overview

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.

IEC Fuse Holder Removed

Remove the fuse holder from the IEC power connector.

IEC Fuse Holder with Fuse

Insert the appropriate 5 x 20 mm fuse in the fuse holder. See this post for the way to select the correct fuse.

Inserting IEC Fuse Holder with 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.

Next: Input Circuit