Mark Johnson Noir Class A Amp (aka T2)

I built this 2 watt Class A smp several months ago and thought I would share it with you all, its a really great first time into DIY building and works very well with low to high impedance headphones. Details of mine and several others build is locatated at : https://www.diyaudio.com/forums/headphone-systems/343616-noir-transistor-headphone-amp-class-single-150ma-bias.html

Basically here are the design criteria:

  • Solid state, all discrete: no ICs, no vacuum tubes
  • Single ended, Class A circuit operating at 150 mA bias current (exceptionally high for a headphone amp)
  • No mains voltage inside the DIY chassis. Power is supplied by a commercial, safety rated, wall wart @ 24V DC
  • All thru-hole parts, mounted on a single PCB with generous spacing between components
  • Very easy to stuff and solder; suitable for first time DIYers. Component IDs and component values printed on PCB silkscreen.
  • Headphone output on front panel, linestage preamp output (RCA jacks) on rear panel
  • Pre-made front and rear panels, drilled and silkscreened, for DIYers who prefer not to do metalwork themselves. These are black PCBs, 2.0mm thick, cut to match the diyAudio Store “1U Galaxy” chassis front & rear panels.
  • Detailed, 37 page .pdf file named “Noir Build Instructions” walks you through the assembly process with plenty of photos. It’s 4.7 megabytes long, over the size limit for attachments here on the Forum, but is available for download on the sales page of the Store.

Here are some of my pix:




!

Pix after the T2 name was changed to NOIR to avoid conflict with existing gear:

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A common mode choke! On the power input!
RNHP take note!

The only oddity is the bridge rectifier. Why would you need that when you feed DC to begin with?

Can we also please take a moment to applaud that every screw hole is attached to the ground plane?
image image image image

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POWER SUPPLY

Fig 3 is the supply schematic. The DC wall wart output is filtered by a common mode choke and applied to a bridge rectifier. This means Noir can accept both (positive center, negative sleeve) wall warts and also (negative center, positive sleeve) wall warts. An LC output filter is then applied for additional smoothing. Potentiometer R2 and resistor R7 let builders adjust the current flowing through the LED “pilot light” and thus, its brightness.

You can also ask Mark at diyaudio he often pops in…he is a learning type of guy and often will answer your question with a question to get you to think!!

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Huh for 69 bucks including the PCB and Chassis with all the necessary openings and labels, it’d be a fun quickie, too bad it seems to be out of stock atm on the DIY Audio Store.

Also :

Yeah Drilling holes is a pain, especially when you get that one hole 1 mm off center compared to the other one, making one pot look slightly further away than the other from the center ;-; . . . well we all have to live with our sins I guess.

Still nice job on the amp, hope it sounds well, looks good to boot, and is pretty compact as well.

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