Purifi Amplifier in Ghent chassis

This shows the chassis parts for the amp, from Ghentaudio.com, highly recommended.

The chassis is very heavy duty aluminum, with lots of ventilation, both essential for good heat dissipation. Also note the silver circles on the bottom where the chassis is not anodized to ensure good ground connections.

I ordered the version with SpeakON speaker connectors, planning to modify the rear panel a bit as shown below.

I drilled out the 11mm binding post holes to fit my 1/2" Superior BP-30 binding posts, show in process here. I also replaced the stock IEC power inlet with a Schurter 3-131-451, which includes a fuse. The IEC/switch opening had to be a bit enlarged as shown here. Note that Bruno Putzeys, the Purifi designer, recommends NO line filter be used with these amps.

This is the EVAL1 setup from Purifi, with two 1ET400A amp channels and an input/output PCB which includes a bypass-able buffer using the OPA 1612 IC. The amp itself provides 12.8 dB of gain, and the buffer board can supply another 14dB for a total of 27 dB gain, which is pretty typical for an audio amplifier.

The I/O PCB includes both balanced XLR inputs and well as banana jack speaker outputs. I'll be removing the on-board banana jacks and replacing them with rear panel mounted binding posts in parallel with SpeakON connectors. The standby switch (lower left) will be redundant in my setup and will also be removed.

This is my input board after removing the banana jacks and standby switch. I've marked the 3 parallel solder pads for the speaker plus and ground connections, along with the sense pads near the edge of the PCB. Each of the latter needs to be connected back to the plus and ground respectively for the amp to work correctly.

This shows the sense connection wires in place for both channels. These are normally connected inside the (now removed) stock banana jacks.

The Purifi input board has now been attached to the rear panel and wired up. Very short wires connect the binding posts to the PCB, and short twisted pairs connect the output pads to the SpeakoON connectors. Since the SpeakONs and binding posts are wired in parallel, either (or both) can be used for speaker connections.

This is a look at the rear (after completion) showing the new 5 way binding posts, the SpeakON connectors and the Schurter IEC. I typically use Superior BP-30 gold binding posts, shown here, as they can be tightened down very securely on spade lugs.

You may also note a 1/8" jack that serves as a 12V trigger for remote startup of the amp.

I designed a small PCB (front and back shown here) for the remote trigger circuit. It uses a low current (30mA) 10amp relay thats wired in parallel with the power switch to turn on the amp when a 12 volt signal is applied to the trigger input jack on the rear panel (typically supplied by the preamp).

This shows the remote trigger board (bottom center) wired up in the amp, behind the IEC Inlet/switch. The yellow & black wires supply the 12 volt trigger signal from the rear panel 1/8" jack.

This is a wider view of the assembled amp with the Purifi boards at the rear and the Hypex SMPS1200A400 power supply at the front. The heavy black wire bundle are the connections from the power supply to the amp, and the 120v AC power is supplied by the red & black twisted pair on the left. Details on the wiring from the amp boards to the power supply are on my first Purifi project page, here.

Ghent includes a small PCB with a power-on indicator LED that connect to the Hypex power supply. It even has switchable intensity via a switch under the chassis.

Completed amp, front view. Pretty utilitarian, but the chassis is very nicely finished.

This photo shows the new Purifi amp on the right compared to another well regarded class D amp: the Hypex NC252 amplifier (also in a Ghent Audio chassis) on the left. The Hypex is rated at 250 watts/channel into 4 ohms, the Purifi 425 watt/channel.

As you can see, the Purifi is almost twice as large, but still relatively compact.

This shows some of the cabinet parts being assembled. The window-box frame on the left is the back to mount the plate amps. Next to it in the middle is a piece of scrap ply that I veneered with bird's eye maple for the top. It will have 1/4" wenge trim added along with a solid cherry frame as well. The balance of the cabinet is solid cherry or cherry veneered ply.

This shows the main cabinet being assembled, face down. The back has openings to mount the two Hypex plate amps, along with holes for both dual binding posts and SpeakON speaker connectors.

The base is what I typically build for speaker cabinets. It will be screwed to the cabinet above so it can be removed and refinished if necessary, and its made of oak to withstand bangs and bumps. The oak frame is beveled in at 15 degrees, and the gunk you at the joints is filler covering any gaps before sanding and painting.

Bottom view of the base showing the corner braces with embedded tee-nuts for mounting the feet.

The base, now painted.

The main cabinet and top completed, ready for sanding and finishing. This is the front of the cabinet.

You can see the unattached top of bird's eye maple, with a band of wenge trim and outside trim of solid cherry.