Long Weekend Summary

It was a good audio weekend for me. I got over five hours of good listening sessions over the three days. During this time, I spend listening to both the AD700 and the DT880 with the Ear+. The sessions were both enjoyable and allowed me to take stock of the projects that I have going, and focus my efforts on those which can be fulfilled as quickly as possible. The Ear+ performed well over the weekend, with no playing up. I did notice that this amp gets very hot, even the chassis and the wood side panels. This is probably due to there bring no ventilation at all in the chassis. There are no air vents, holes, slots, etc, where air can cool the transformers and diodes. The two transformers are completely enclosed in the steel box above, and thus rely purely on the black case being cooled. This is something that should be addressed if, and when, I rebuild the amp.

The Headphones

Being able to compare both sets, with similar amount of burning in, on the same system was enlightening. The method I used to test was not very scientific, nor very systematic. Very simply, I listen to various music on each one for about and hour and then swapped. No scientific A-B testing, but a lot of the music was common between each session. Both headphones have had at least five hours of burning in, and both have experienced the full works of Handel’s Messiah and the four Coldplay albums during the burn-in. Some initial findings.

• Bass is firmer and better controlled on the DT880.
• Generally more detailed on the DT880.
• Sound is more open, possibly a larger sound stage on the AD700.
• More depth to the music in terms of extension of frequencies and layering on the DT880.
• More engaging, vocals more addictive on the DT880.
• A little flat or boring on the AD700.
• Overall musical presentation on the AD700 seems to be more ‘dynamic’, and more balanced with the DT880.
• Comfort was better with the DT880. It had even pressure between the headband and each headphone. A light, constant pressure, which was quite comfortable.
• Comfort on the AD700 was a little different. No pressure on the head via the 3D wings. The headphone itself had pressure at the lower end, and very little on the top of the headphone. Overall, comfortable, but a little strange to get used to.

Comparing the two headphones, whose price difference is double, is probably not a fair comparison. However, when I listen to the AD700 it was enjoyable and musical. It was only when it was replaced with the DT880 that the AD700’s limitations were made apparent. However, I could not complain about have either headphones in my inventory. They do present the music in a different manner, and perhaps in a complementary manner.

In the future, I plan to write reviews based on each amp used with different headphones and each headphone used with different amps. This can begin once the HD650 have been repaired and returned. To this, I plan to add a pair of Grado’s and maybe a few more from AKG, Denon or Audio Technica.

When using the Ear+ amp with the AD700, the volume control was around 50% to 70% range depending on the program material, and with the DT880 it was between the 70% and 100% range. Obviously, not a great match with the DT880. With the 600 ohm version, I’d suggest that there just isn’t enough voltage at the headphone terminals. The Hammond 119DA used in the amp has a ratio of 600:8, which may be a little too high to provide enough voltage. They seem to work well with the HD650 (from distant memory), but it struggles to get enough volume with the 600 ohm DT880.

Projects

Having the time to review the stock piles of components, PCB and project ideas has led me to the following conclusion. There are three projects that have are fully funded with all components on hand, that require assembly and chassis work. They are, in no particular order:

1. D3a Headphone
2. K and K ST70 Upgrade
3. Aikido 5687 PCB Headphone 

The Aikido build is something that I had time to dig up and check over, ensuring that I had all the necessary components. The only items missing for the above three projects are the chassis work and the large output coupling capacitor for the Aikido 5687. I do have a pair of Solen 47uF MKP on hand, which would work well with 300R plus headphones, but given I have the AD700, and plan on a pair of Grados, it may make sense to budget in a large pair (say 200uF plus) to allow them to be used. To expedite the construction, I have ordered a number of custom aluminium panels from Front Panel Express. They are basically a small panel with cut-out for the tube sockets. This then allows me to cut the timber chassis without exact precision (i.e., oversized hole). Preserving the convenience of metal panel, on which most of the circuit can be assembled with stand-offs and tag boards, and keep my aesthetically desired timber external.

During this time, I also took the opportunity to order the replacement active components for the Crack. To piggy back on the order, I also topped up on the Neutrik headphone TRS plugs, some additional heat sinks and enough active components to make another Speedball.

The goal is to complete all three projects by Easter this year, which is in late April. All the chassis timber work will be done at once as well as the assembly. I am estimating that it’d take the better part of a week or evenings and a few day sessions to complete all three projects. The ST70 mod and Aikido will probably be the quickest, given it has a PCB based construction, making all the wiring and soldering much faster.

Future Projects

Having the opportunity to take stock of the current headphone amps and planning on the next stage. What I would envisage is having one amp of each of the major topologies to be able to evaluate and compare how they perform. To that effect, I have come up with the list of the final assemblage of headphone amps. With each of the project, I eventually plan to have a page dedicated to each of them, providing information, schematics, photos and possible upgrades.

1. Transformer coupled. D3a project. All parts collated, awaiting chassis assembly and build.
2. Parafeed transformer anode coupled. To be determined, most likely a clone build of the Espressivo or L’espressivo and another link here.
3. Parafeed transformer cathode coupled. Maple Tree Audio Ear+, completed.
4. OTL. Bottlehead Crack and Speedball, completed. Awaiting repair of RHS Driver CCS.
5. Aikido OTL. All parts collated (except output coupling capacitor), awaiting chassis assembly and build.
6. Tube/Mosfet Hybrid. Mini Max Millet, completed.
7. Transformer coupled with negative feedback. Elekit TU-882R kit ordered, awaiting delivery and assembly.
8. Ultimate Headphone Amp. After the completion and analysis of the above amps, an uber-no expenses spared amp based on the design and headphone that best meets my needs and suits my taste. I am hoping that the D3a would be that amp, but until it is built and compared, this project is still the ultimate goal.

With regards to stereo amp projects, as mentioned before, they are taking a back seat to headphones for the time being. This is primarily due to the lack of appropriate space in the current house and young kids. But for the moment the project on the cards are:

1. K and K ST70 Build 8W. All parts collated, awaiting chassis assembly and build. I should start referring to this as the Class A, fully differential push-pull triode amp.
2. Ultrapath DRD45 1W. All parts collated (some have been scavenged for the projects above), awaiting replacement parts, chassis assembly and build.
3. F2a amp 6W. 4 tubes on hand and sockets, everything else not yet sourced. Yet undecided on whether it’d be a SE or Class A PP design.
4. Future 32W Tube. Unknown design, topology and tubes complement at this stage, but planned.