Headphone Amps - A Review

Over the course of my audiophile life, or around five years, I have amassed (like most others) a stash of components, schematics, ideas and projects (mostly half built...). To date, I can happily say that I have 4 working headphone amps, and 2 headphones. Learning my lessons from previous hobbies, I shelled out the Sennheiser HD650 from the start. I didn't want to buy cheap and upgrade later. For me, that has always cost me more time, pain and money. The second set of cans are my travel set of Shure SE210 in-ear monitors. Whilst I love the size and compactness of the SE210, I do not really like the way they sit in my ear. Though they are a good fit and comfortable to an extent, having these things in your ears for long periods is not the best feeling.

With the headphone amps, my first build was a PCB (original version) of Peter Millett's Hybrid 12AE6A amp. This was a great project. Easy to build, fun to use and good sound. It was my default amp for a few years. Using pretty much the standard parts, it has proved to be a reliable and enjoyable amp.

The second venture was with a full point to point kit, in Maple Tree Audio's Ear+. This was the version with the line stage. The build was done with the Blackgate, Tantalum and Noble pot upgrades. This was really a step up for me in terms of building and testing. Being a full point to point kit, it proved to me that good solid experience is required to ensure a smooth build. Overall, I thought the kit was well designed, laid out and provided good to very good sound. My main issues with this amp are:

1. There was hum. (Bad soldering and wiring??)
2. Left channel was always buzzy and intermittent. (Bad tube socket??)
3. Sound could be considered a little flat or laid back.

Whilst items 1 and 2 can most likely be attributed to bad construction on my side, I could not find a way forward with item 3. Hence, my quest continued in search of a better headphone amp. With this design, I have always mooted about doing a full re-build, with the courtesy of a few years of experience. This would include taking out the line stage, full rewire and layout, replacing the cathode coupling capacitors and general parts tweak and upgrade. Also would try to get rid of the 12AX7 as the input tube and replace with something more interesting. This I will leave for later, as there are more exciting projects in my mind.

After a few years, I decided that the next upgrade would be in the MiniMax Millett. I chose the PCB version and it basically replace the OPAMP buffer on the original with a discrete diamond buffer, and it replaces the current sources in the original with more robust IC versions. This time around, I also tried to build an enclosure of timber sides and metal top panel. The net result was a great sounding amp, that has been really fun to use. The build was fairly straight-forward, with the only parts tweaking being the coupling capacitors. I added a Russian K40 and Vishay MKP in parallel with the Nichicon Muse electrolytic.

During this period, life caught up, and babies were now in the picture. Headphone hifi seemed to be the most logical method, as speakers would inevitably get damaged or disturb the family. Though loud singing when listening to headphones could still be a source of nuisance. By this time, I had built a transformer coupled (cathode) amp, two hybrids, and wanted to try an OTL. At the same time, Bottlehead released their Crack. $200 and a few months later, the kit was delivered.

First, I can say that the value for money, from the Bottlehead kit is far above the Maple Tree Audio. Though the latter did have better components, it was not worth THAT much more. The kit was built with the Speedball upgrade at the same time, to avoid having to build and test twice. The end result was a great amp. The sonics seem to combine the best the amps to date. From this point, I can see that there are a few items that can be upgrade and improved.

1. Volume control, replace with nice GoldPT or DACT attenuator.
2. PUS Caps, replace with Oils (means a new enclosure).
3. Input and output jacks replace with quality Neutrik ones.
4. Potentially adding a choke to the PSU.
5. New Tube sockets.

A lot to upgrade, but I believe that they will bring it amp from a 90/100 to a 98/100. But right now, I am just enjoying the amp for all its worth.

Where to from here? Well, there are two upgrade/rebuild paths for my existing amp. But I have always wanted to build a standard SE Transformer coupled headphone amp. And to that extent, I have taken a few designs from the net, and made a few changes, and made my own. For me, I have coined it my final headphone amp, the one amp to rule them all! Perhaps not. But, the basic design premise is similar to the designs by Andrea Ciuffoli, Lynn Olson, epc.cc and a few others out there. Nothing unique.

The design is a D3a feeding into a Amorphous core Lundahl transformer. The PSU is glow tube VR150 regulated and the PSU itself is a choke loaded in common mode, followed by one shared LC stage and one channel specific LC stage. More details and schematics to follow. But this should be an interesting build.

Having looked back on all of this, I think after completing the D3a headphone, I will go back and rebuild the EAR+ and the Crack and then have on hand 5 quality tube based headphone amps. This will I think give me a good overall impression of tube headphone amps, and probably serve as a foundation for any future headphone amps. Finally, considering an upgrade to my HD650, and the two choices so far are the Beyers T1 and the HD800. But that, will have to wait for some time.

Anyway, will be posting more info and build notes on the D3a amp, and I will hope to write sensible and proper reviews on the other amps later this year.