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.

6e6p-dr HP amp – part 3: measurements

As I promised, I took the HP amp back to the workshop for a bit of abuse on the bench. Here are some interesting measurements which correlate with some of my listening impressions so far.

I added a set of 300Ω dummy loads at the output to simulate the HPs. Firstly I tested the optimal circuit which has the Sowter 8665 output transformer in Parafeed mode (4:1) to drive the load. You can get a very clean and flat response across the audio band from 3Hz up to +90kHz. There is a minor hump to be tuned due to the RLC circuit formed by the parafeed circuit. I used a 4.7μF Mundorf EVO oil cap. It’s pretty flat to me, so will leave it there.

The performance of the circuit is amazing. Distortion is very low, up to 0.07% at 100mW (which is VL=5.47Vrms):

6e6p-dr Headphone Amp performance @ 100mW output level

6e6p-dr HP amp – part 2

My adventure with the HT SMPS modules continued. Did further testing with higher power modules which worked ok.

Testing the HP amp

The headphone stage (HP) has a 1MHz bandwidth, impressive. Here is the circuit breadboarded after the modification of the 2P29L HP amp:

HP experiments – part 1

Experimenting on headphone amplifiers, not always turn out the way you expected. Well, that’s the nature of experimentation and some smoke may come along the way.

Here is my new take on the headphone amp. Modified the 2P29L to fit the 6e6p-dr valve. I love this IHT one, so wanted to experiment more.

Instead of the classic HT, I used some Chinese 300-450V SMPS modules. I used the 70W version with success before, not these tiny ones.

Individually tested all parts and worked fine. Fired up the SMPS with the hot filaments and the 6e6p-dr running at 20mA each and the SMPS oscillated. They went to 450V instead of the 250V dialled and one of my cap multiplier PCB boards got damaged. Damn!

Back to the drawing board. I will probably stick to the simple HT supply 🙂

Headphone Amp Shootout

A few weeks back we managed to meet at Jon’s with a few of the London Audio Circle members. I haven’t seen the bunch for a long time due to family and work travel commitments, however it was a great opportunity I didn’t want to miss this time round.

One of the intended purpose of the meeting , which for obvious reasons these meetings never goes as planned due to the random nature of DIY, was to shootout two headphone (HP) amplifiers over modded HD800 headphones.

Jon’s HP amplifier was a simple stage formed by a C3g (triode-strapped) valve loaded with a nice amorphous-core Valab choke. Output cap-coupled to a TVC to his main system when he uses it as preamp. Otherwise cap couple to HD800s headphones.

Continue reading “Headphone Amp Shootout”

6e5p triode-strapped

The 6e5p is high-frequency indirectly-heated tetrode from our friends in Russia. The specifications can be found here. Anode can easily dissipate 8W and screen can take up to 2W and has a high transconductance of around 30 mA/V

Wired as triode this chap becomes very attractive. The anode resistance drops to around 900Ω – 1KΩ and effective mu is about 30-35. This turns this valve into a low anode, medium mu and high transconductance fellow which is highly regarded as a driver in SE amplifiers. Check out there in the jungle and you will find many good examples of how this valve is being used effectively.

When testing this valve on my curve tracer I found that it probes to be a challenging device. You need to leave this guy running on its own for a while (Lars recommended 30 min to 1 hour). I found that indeed after 20-30 min it stabilise.

Dmitry came up with a very good model. When I created a model based on my curves found a mismatch between my notes and simulation. Checking my notes I think I set up the tester to start plotting curves at 0V with a step of -0.5V, however looking at the model produced by Dmitry’s tool, I got this:

6e5p-triode model — SPICE model to fit 6e5p in triode mode

It looks like the curves starts at -2V. Need to re-check and probably trace this valve again. Either way it does match very well and not far off from Dmitry’s model from above.

Here is my model.

I’m planning to use this valve in my OTL (cap-less) headphone amp. Stay tuned…