Pete Millett's "Menace" revisited
Feb 17, 2019 at 2:04 PM Thread Starter Post #1 of 4


New Head-Fier
Feb 13, 2019
I’m a long-time fan of Pete Millett’s circuits—particularly his Wheatfield HA-2, which was my introduction to tube audio when I bought one from Headroom nearly 20 years ago. Although I’ve owned (and sold) lots of equipment since then, I still think of the HA-2 as the single best audio purchase I ever made. And I’ve made plenty.

A few years ago, I gave my HA-2 to a young, budding audiophile who still uses it, and I set out to build my own version of the circuit using a bigger enclosure and some upgraded parts (beefier PT, stepped attenuator, some oil motor run caps, better output caps). It didn’t sound dramatically better than the original, but it was an upgrade. I was pleased.

Until, that is, a few months ago when I happened upon a Head-Fi thread from 2008 started by n_maher:

Maher is also a HA-2 fan, and he worked with Pete Millett to re-imagine the OTL HA-2 circuit so it could drive low-impedance headphones. The result, the Millett “Menace,” was a 2 chassis tribute to glorious excess: it featured a 50 lb. power supply with two tube rectifiers, dual output tubes, and oil motor run caps used throughout, including a pair of paralleled 100uF caps used in the output.

I immediately wanted to build my own Menace, but I don’t have room for a 2 chassis headphone amp, and my favorite headphones are Sennheiser HD800s, so I didn’t need all of the steroidal enhancements of the Menace. A single rectifier and output tube were enough, and I didn't need parallel 100uF output caps
I had a couple of Hammond chasses sitting around from projects that never got started, and their sizes suggested that I could bolt them together as a kind of “pseudo”- 2 chassis build. So I built a scaled down Menace, a kind of "Minor Menace."

OK, some caveats: I’m a hobbyist with modest building skills, and I only know enough about electricity to build relatively simple circuits. My goals were to make a quieter, better sounding HA-2 using the “Menace” as a guide. To cut down hum, I used a Hammond PT with an electrostatic shield and I put the PS in one chassis and the signal circuit in the other. I bolted the two together using non-ferrous hardware, some damping material, and a sheet of copper. Wiring between the two chasses go though holes I drilled that ended up too thick for normal grommets, so I used rubber tubing instead.

Some pictures:


HA22_chassis front close-up_v3.jpg

I had no idea what to expect when I first plugged my HD800s into it, but the sound exceeded my hopes. There is the barest hint of hum, ever so slightly above (my) hearing threshold. Sonically, the lushness and musicality of the original HA-2 is retained, but the sound is bigger, richer, more relaxed and assured.

In short, I'm a proud papa. I now have 4 headphone amps but, geez, I'm thinking that HD800s through this amp is my audio nirvana.

I don't know what interest there is in such a project, but I'm happy to answer any questions anyone has.

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Feb 19, 2019 at 4:39 PM Post #2 of 4
This amp continues to sound great. As I wrote in my first post, the combination of the Sennhesier's speed and detail with this amp's tubey richness strikes me as perfect. By contrast, listening through my Burson Soloist, the Sennheisers sound lean and too clinical (instruments' timbres seem washed out, as though a "color saturation knob" has been turned down). For me, this amp tames the HD800's tendency to sound too lean and brittle without getting in the way of its remarkable airiness and imaging.

So here's the schematic as I've modified it from n_maher's Menace (viewable in the thread I linked in my first post). I'll repeat n_maher's original warning:
"WARNING: The following schematics depicts a project that involves working with high voltages. Use of this schematic is permitted with the understanding that if you're not careful, this thing can kill you. Not only are you working with line voltages but the HV (B+) supply has a lot more current capacity than your typical tube project and should be treated with a great deal of respect. Getting hit by ~300V is no fun, assuming you live to tell the tale. That said with proper respect and care there's nothing exceptionally complex about this amp or power supply."

Wasn't sure what to call this modification of the "Menace" but settled on "HA2 Squared."

Voltages here are n_maher's. Mine were within a few volts of each one except for the 6SN7 cathode, which on my amp is 2.1v (n_maher's schematics list 8v[!]) and the 4.7k-15uF RC node: my amp reads 240v (20v low), but I still get the specified 130 volts on the 6SN7 plates, so I'm not concerned.
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Mar 22, 2022 at 2:44 PM Post #3 of 4
Awesome looking amp! Have you compared it to other high end off the shelf amps like from DNA, EC etc ?

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