Tools required:

  • A regulated temperature soldering station or iron with a large chisel tip. (The board wicks heat away quickly due to double-thick copper and wide PCB traces.)
  • #1 Phillips screwdriver (Mounting screws)
  • #2 Phillips Screwdriver (Bridge rectifier mounting screw)
  • 5.5mm socket or nut driver (Bridge rectifier nut)
  • Small flat-blade screwdriver (For pushing WAGO Cage-Clamp terminal levers.)
  • 1/8″ drill bit
  • Automatic center punch.

Preparation:

Don’t populate the board just yet! We’ll be using it as a template to mark some holes first. We’ll do the chassis work first, and then assemble the board itself.

Don’t build me up just yet.

Remove the back panel from the amplifier and set aside.

Remove the old power supply board and binding posts. Remove the three brass standoffs. Sorry I don’t have a picture of the old board, but basically, we’re starting here, with a blank slate.

Marking and drilling holes:

Position the board precisely over the existing three mounting holes. (The ones where the brass standoffs used to be.) Tape it in place.

Use an automatic center punch to mark holes to be drilled.

  • Two mounting holes for hex standoffs…
  • And two holes for mounting the bridge rectifiers.

Drill with a 1/8″ bit.

Remove the burrs, so that the bridge rectifier has a nice flat surface to bolt to. Also to prevent stray metal shavings in your amp!

Install (5) 12mm hex standoffs. Don’t tighten, attach loosely for now to allow for slight misalignment. We’ll tighten them fully once the board is attached.

Bend the leads of the bridge rectifiers so that they are reaching for the sky. Place two thermal pads.

Install bridges as shown.

Earth-Grounding the Chassis:

This is an optional, but highly recommended step. For safety, as well as better noise performance, install either a 3-wire grounded plug to your amplifier, or install a grounded IEC or Powercon input jack. Connect the earth ground lead DIRECTLY to the chassis, using its own dedicated bolt. Please read more on earthing your Hi-Fi at Rod Elliot’s excellent website.

A different model amp, but you get the idea. Use a ground wire the same gauge or larger than the power wires. Crimp, and optionally solder a ring terminal to the wire. Remove paint around the mounting hole and attach with a sturdy bolt with lock-washers on both sides.

Often people are concerned that a grounded chassis amplifier will cause more noise in the system, due to ground loops. To prevent such an issue, this power supply board features an Earth Loop Breaker circuit, that inserts a buffering impedance of 47 ohms between the amplifier’s ground, and the earthed chassis, so that significant currents do not flow between the two. The parallel capacitor conducts high frequencies that the metal oxide resistor can’t, and the 35A bridge rectifiers in the center of the board, are actually acting as dual-parallel diode clamps.

OK, back to…

Building the circuit board:

There’s no particular order in which to build things, except install the power supply capacitors last, and don’t solder the bridge rectifiers in place yet! (Install the two bridges in the middle now. They are actually diode clamps for the earth loop breaker circuit.)

The WAGO Cage-Clamp terminals snap together like Lego!

  • The 5.6K drain capacitors are labeled “ELEVATE” on the board. This is to allow heat to escape and not scorch the board. Elevate them 5-10mm off the board.
  • Careful not to mix up the 47ohm earth-loop breaker resistors with the 5.6K drain resistors.

Install the power supply capacitors last. Your board should look like this.

Installing the board:

Lower the board down onto the leads of the bridge rectifiers.

Install all five mounting screws, and don’t forget to tighten the screws from the bottom side as well!

Soldering the bridges:

Now that the board is mounted and aligned in its exact position, we can solder the bridge rectifiers in place. It’s a bit tight in there, so try not to melt that capacitor.

Wiring up:

How to use WAGO Cage-Clamp terminals:

  • Strip about 5mm insulation from the end of the wire
  • Push firmly straight down on the lever with a small flat-blade screwdriver. (It’s a really strong spring)
  • Insert the wire and release.
  • Tug the wire firmly to be sure it does not move.

Connections are all labeled the same as OEM. E2 goes to E2 on the amp board, as E3 goes to E3. The right-channel amplifier board will be missing a ground wire labeled E2. (This was done as a factory bodge to “fix” the ground layout issue of the original power supply board. See my original blog post on the topic here.) Install an 18ga or thicker wire and connect to E2 on the power supply board.

Connect the ground wires of the LEDs to the small terminal block. From left to right, Power, Left Distortion and Right distortion.

Note on RCA jacks:

For best noise performance, Do not connect the RCA shield grounds together at the RCA jacks. Everything ultimately connects back at star ground. (The center mounting bolt of the board)

Binding posts:

The kit assumes that you’ll be removing the crappy twist-lock speaker connectors in favor of a single set of nice binding posts. The holes left behind in the chassis are too large to mount normal binding posts. Most people will solve this issue by either attaching a piece of sheet metal over the original holes, or purchasing my binding post kit for the GFA-535.

Installation instructions for the binding post kit are here.

The end.

Please contact me if you have any questions or suggestions to improve this document.

Thanks, enjoy your amp!