EL84 Amp II – Progress post 5 + listening tests

It’s been a little while since I posted an update on this project, and there’s been a lot of progress, as well as one or two hiccups.

Thought I’d put up a few photos today since I’ve been taking plenty.

Following the previous post, the next order of business was to get the top panel of the chassis ready. This involved a lot of measuring and drilling – the mounting holes for the boards and transformers, then the chassis punch for the valve sockets. A lot of swarf ended up on the floor during this process.

After getting the top panel ready, it needed to go to the laser etching workshop before I could do anything with it. This is to get the identifiers for the valves etched on – this design uses four different types, so it’s important to know which type goes where!

Once that was back, it was time to begin assembly. Mounting up the transformers and sockets to the top, and circuit boards underneath. A delightful jigsaw puzzle, but everything fit together nicely and it was not necessary to utter any curses.

Transformers and output valve sockets in place

Next it was time to fit the circuit boards inside, for a photo shoot:

The front panel design concept. Sharpie markers are a valid design tool and don’t let anyone tell you otherwise!

Following this photo it was time to take it all apart again for lasering and drilling on the front and back panels. Once that was done it was time to assemble all the boards together and make up all the various connectors.

From here it was time to take it to the listening room for some tests.

Connected to the KEF C-95 floorstanding speakers (early 90s vintage) the sound quality was subjectively is clean, pleasantly detailed, no trace of any distortion or harshness in the treble, and with plenty of power to the bass. I would be happy having this sound quality as my daily driver.

The tone control behaved exactly as the previous build of this circuit, this is the second time I’ve built this one.

There was a small amount of ground loop hum on the photo stage which necessitated a bit of re-design of the earthing point ofr the power supply and the addition of a 100µF capacitor in the power supply very close to the photo stage.

Once this was done, the amp was deemed electronically fit for use, and a very enjoyable few days burn-in testing was had. A few cosmetic finishing touches were completed, the cover for the remote sensor, and a bit of cable dress inside

Finished unit, awaiting packaging and shipping

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