E282F HP Amp

First and foremost, Merry Christmas! I hope you’re having a great time with your loved ones and good music.

Without a mood for public introspection this time, I have to say that I will celebrate this holiday the best I can. I will be hosting today with a lot of meat, wine and single malt. What else can I do? When I escape from the little ones, will get back to spin some records and hopefully work on the projects.

Headphone Amp Quest Continues

Obviously, I needed to pursue this project further. I’ve been lately listening a lot to HPs as simply is the best choice for me when the young family is in bed. In addition to this, I find the HP setup to force me to connect a bit more to what I’m listening to as I don’t get easily distracted.

Anyhow, the testing of the previous HP amp evolved a bit. From the great 6e6p valves, I moved to the D3a (triode-strapped) which I feared of delivering too much gain into my system and hence noise would be a problem potentially.

The results where more than interesting. As expected, the D3a delivers a superbly clean and detailed sound. I love it but yes, gain is too much. Noise wasn’t a problem though as the system I built is dead quiet. Good job on this one.

The operating point I used for the D3a was Va=170V/Ia=24mA and biased with 2 SiC diodes. This was very easy as just needed to move the wire jumper on the SiC bias PCB to set it for 2V and job done.

I can try several pentodes with minimum readjustment providing bias is 6V or less and have same pinout than the 6e6p/D3a amongst others.

The breadboard morphed into a vertical setup as per below picture. You will see a Cap Multiplier for the HT (Which also helps setting the HT level to desired one) . A pair of SI-Tubes current meters (thanks Pete Millet for these ones), the SiC bias PCBs and a pair of anode/cathode current protection + sensor PCBs which I use to take the anode current for the SI-Tubes. I have also multiple connectors for DHT filament supplies. A pair of LV regulators for the IHT filaments which I also use instead of Rod Coleman regulators for simplicity in this bread board. The gyrator PCBs are mounted vertically and the LEDs are set for always-on operation. As you have probably seen on the previous posts, the parafeed caps are mounted with 2mm connectors to allow me swap between them and use / bypass the Sowter step-down transformers:

The next valve I tried was the E282F. A fantastic pentode I used primarily as a driver. I have a few on my collection, mainly Siemens and Valvo.

After playing a bit with the operating point, I settled for 180-183V / 5 SiC diodes (about 4.8V bias voltage) which delivers a quiescent anode current of about 20mA:

Another fantastic triode-strapped pentode for the HP design. Microphonic noise is minimal and you don’t get any warm up “dings”. Sound again, very similar to D3a, strong bass, detailed and as best as you can get with an IHT.

This is a very simple circuit to build. Tom Brown sent me an HT SMPS module he design and built for the 2P29L HP amp. This is powered with a good-quality 48Vdc SMPS supply. You can use a simple stepdown isolated converter from 48V to 6V to feed the filaments directly. If you want to use a DHT you can add a BJT cap multiplier and with a pair of isolated converters you can build a stereo system powered from a single 48V converter.

Merry Christmas!