6e6p-dr Headphone Amp – part 3

I’ve been running with this HP amplifier for a few weeks now and I have to say I’m delighted with it. I matched a pair of 6e6p-dr on my eTracer and after fiddling with the operating point a bit, I settled for Ia=25mA and Va=180V. Anode voltage will depend on the valve as said before, the Russian valve parameters tend to be all over the place. Anyhow, expect anode voltage to be around 170 to 185V. The beauty of the gyrator PCB is that you can adjust the anode voltage with the trimpot.

I’m using the fantastic panel meters from situbes. They are brilliant to monitor the anode current. As described before, I’m reusing a pair of PCBs I designed for fixed bias cathode protection with a fuse and also a measuring point for the anode or cathode current.

The cathode bias is provided with the SiC diode array. I installed a SiC PCB which has capacity for 6 diodes and multiple tapping points. I’ve done this to allow me testing different valves. I have a set of D3a, E282F, 12HL7 and a few other pentodes (triode-strapped) which have same pinnout and am looking to test how they sound in comparison.

I played for a week the cap-coupled output configuration with the huge 100uF Mundorf EVO Oil caps you can see on the back from the picture above. Sound is very detailed, clarity and bass is strong. I used my Sennheiser HD650 as well as my Beyerdynamic DT770 pro headphones.

Last night switched back to the Sowter 8665 output transformers and replaced the 100uF for the 4.7uF Mundorf EVO oil caps. These are much smaller as you can imagine. Smaller cap, happier listener to me.

I have to say and ratify, that I prefer the clarity and overall sound of the output cap. Indeed.

Don’t want to put away any builder who wants to build this without the expense of the Sowter Output Transformers. Believe me, the difference in sound to me is minor and if you want to build the HP amp within budget, you may spend less on the output capacitor by avoiding the output transformer.

I still need to try a standard 100uF Film cap, which are significantly cheeper than the Mundorf EVO Oil. Likely you will get a very good sound, as I’ve listened to Geoff’s 2P29L version recently.

An interesting finding was how sensitive this amp can be due to its gain and wide bandwidth. I put the RCA input sockets as well as the stepped attenuator mounted in a small piece of clad copper PCB. I forgot to ground it. What happened? Playing the HP amp I could hear some very soft hum and also eventual/random HF oscillation could kick in after a period of playing. When I touched the plate with my fingers, everything will stop. Aha! nice antenna. I grounded and ended story. Lesson learned, never forget to ground those metal plates (even in a breadboard) 🙂

I have to say that this 6e6p-dr HP amp has nothing to envy to his brother DHT incarnations. Without the DHT power supply complexity, this is an amazing HP amp worth to be added to your collection.