bonnie & jason

Millett Minimax headphone amp

This is officially my last project before the arrival of the twins. You may remember I took on a small DIY headphone amp project a couple weeks ago. Although that amp performed pretty well, I still wasn’t really impressed with my new headphones. After doing some research, I thought they might reach their full potential with a higher powered amp. Furthermore, many folks swear by vacuum tube amplification for great sound quality. As is usually the case, I figured I’d try to build my own rather than purchase a retail version of one of these amps.

Lucky for me, a number of enterprising folks have put their heads together and developed the parts list, assembly instructions, and other resources to help you put your own amplifier together. So after some more research and a couple mail order deliveries, I had everything I needed to git ‘er done.

I still need to find a volume knob.

(this image courtesy of www.diyforums.org)

Assembly notes:
As you can see, it’s a fair bit more complex than the little Cmoy amp, but the assembly was actually fairly straight forward. For those of you who are looking to build your own, here are some thoughts (based mostly on my mistakes) that might help supplement that already extensive instructions found on the official website:

1. The standoff kit works great, but pay attention to the instructions to make sure you have the washers in the right place. Otherwise, it won’t fit in the enclosure.

2. Tom (the proprietor of the official site) doesn’t yet have instructions for the final connections for the RCA jacks and such but does have some pictures to show how others have done it. I would probably leave enough slack in those wires to be able to just take the back panel off by no more than 1″. Any more and the slack in the wires gets in the way of bolting the panel to the enclosure.

3. When you first get all the baggies of parts, separate and order them by size (height) so the assembly process simply requires going through the little baggies one at a time.

4. The BOM is confusing in what buffer transistors you really need. At first glance (and second and third for me) it seems like you need eight. This made sense to me since there are eight spots on the PCB for said transistors. As it turns out, you only need four. The extra four spots are used if and only if you use transistors of reversed pinout (in which case you would leave the other four empty.)

5. I followed Tom’s advice of using the 12AE6 vacuum tubes and eliminating the RB14 transistors considering my Sennheiser HD 650′s are 300 Ohm impedance. I also used the “can’t miss boutique” parts listed on the website with 2SC3422/2SA1359 transistors. Although I have nothing to compare against, I’m very happy with the results.

Listening impressions:
1. Wow! Although I’m still relatively new to the high end audio scene, I’m very happy with the results. Whereas before, the headphones seemed a bit tentative and “veiled” as some users have stated, everything opens up with the new amplifier. Soundstage is larger, vocals sound more intimate (both female and male), and bass notes are tight and accurate.

2. The difference in good vs. bad recordings is more evident now. I guess the sound engineers in the booth really do make a contribution behind the scenes!

3. I’m hoping that everything sounds even better as the amp gets broken in. However, even if that doesn’t happen, I’m still very impressed. Unfortunately, I don’t have enough experience to say if it’s the “tube” sound that appeals to me or if it’s just the fact that this amp has more power. Maybe I’ll just have to find a similar power DIY solid state amp to build next!