All about electronic valves and hi-fi
It’s been a while since I experimented with preamps again. I settled as a permanent setup with my 01a/ER801a which I love. However, I wanted to continue with my experiments so I built a new Mule, let’s call it “Mule 2” for now. It’s based out of multiple PCBs which simplifies the construction process and reduces build time:
A friend from Canada ordered a pair of boards and I used the opportunity to test the newly arrived hybrid mu-follower (aka as gyrator) Rev08 PCBs. He will be using these boards in the 300B design posted here.
A belated test of this simple, yet effective PCB. I made it as small as possible, however in order to provide flexible connections, it’s actually double the size. Still at 4 x 4 cm is small enough.
The 45 DHT is probably one of the best sounding valves out there. In fact, I have struggled to get a similar level of detail and timbre in a 300B or 4P1L output stage. Even my 814 SE Amplifier (which was class A2 and had thoriated-tungsten filaments) couldn’t replicate that sound. I posted time ago my incarnation of the 45 single-ended amplifier here. The main challenge with this valve is that it can only put out there nearly 2W, not more. With its 10W anode dissipation, you will struggle to get more juice from it in class A at a low distortion level.
However, if we look at a push-pull amplifier with the 45, we can hopefully retain the timbre characteristic of the valve, despite it won’t be a single-ended one. Well, I love good PP amps, so why not?
ETF.18 has been an emotional journey. I moved house literarily when I got back from ETF so my life has been more than hectic over the past few weeks.
I promise I will do a write-up of this amazing experience. There’s a lot of people out there who would love to attend so is my duty to reflect and share as much as I can.
In the meantime, I wanted to share the lecture I gave at ETF on DHT preamps. It was a challenge on its own but went really well. This was my first ETF and without knowing the audience I had to guess the level of detail, entertainment and expectations of an unknown audience. I knew a fair bit of the ETF folks, but audience was big and wide.
I struggled to find the time to prepare this lecture I have to confess. Between moving house, house building works, my second daughter’s arrival , weekly work travel and everything else, I seemed not to find the time to get this done. Thank you Morgan Jones and Rod Coleman for proof-reading and making this an easier task.
I hope you enjoy it. There are some notes on the slides I put together for the people who didn’t attend ETF. Otherwise the slides aren’t of much use on their own.
I’m writing this blog entry whilst enjoying the lovely Bourbon that Pete Millett gave me on the way back. Thanks Pete!
ETF Lecture on DHT Preamps (with notes):
DHT-Preamps-ETF2018-final-notes
ETF Lecture on DHT Preamps (slides):
Just in the last days before the arrival of our second child, I had a spot of luck and managed to get some free time to work on my DHT preamp experiments.
Originally I was put off by the hum pickup susceptibility of the Ba German DHT. However, I decided it was time to listen to the design I worked and experimented in my workshop time ago. I remember listening to this valve and was very pleased with its sound.
Continue reading “Ba DHT Preamp Build”After doing all the soldering part (which I enjoy much), the preamp is now finished. It sounds as good as the original breadboard:
For the curious ones, here you have a picture of the inside:
The teflon sockets are bolted straight into the 4mm top aluminium plate. No microphonic noise this way. Rod Coleman V7 regulators set to 200mA. A pair of Russian Military NOS wire-wound resistors in parallel provides the filament bias. The gyrator PCB is set as per original circuit and each valve at 3mA. These are DC coupled to the MOSFET follower PCB set at 10mA each. The output is then taken out from a pair of FT-3 teflon caps.
Now to enjoy this beauty!
Travelling around Europe on business is paying its toll. I’m away from home every week and pretty exhausted now. I don’t have much time free and whatever is available I spend with my family. Hence, the lack of posts recently. I hope this will change in the future.
Anyway, what’s up in the DHT world? I listened the Aa/Ba valves long time ago but never played with them. Mainly due to their higher anode resistance. With the gyrator load and the source follower output, things take a different dimension.
I have a nice stash of Aa from Valvo (globe) and Ba from Siemens. Interesting to see that curves are not easy to find, so I submit them both to the mercy of the uTracer. Nice to see the linear curves with high mu about 14 on the Ba to 30 in the Aa.
Here is an example of the Ba loadline:
After trying out so many DHTs and pre-amplifiers, I decided to wire up my 4P1L preamplifier Gen3 and fit the gyrator board to drive my 4P1L PSE Amplifier.
I have a pair of 4P1L/4П1Л dated 1968 which are properly burnt in. I’ve used them lately in my previous preamp incarnation with great results.
The circuit doesn’t need explanation, I think I’ve covered this repeatedly for a long time. I will only point out the differences:
The main change was fitting a pair of Russian wirewound 27Ω resistors in parallel to get closer to the 15Ω used in this position. I found these Russian wirewound resistors to sound extremely well as filament bias resistors. I tend to be skeptical about the “sound” of some components in circuits, however, they do make a big impact in the cathode of a filament bias arrangement.
The gyrator has my preferred combination: IXTP08N100D and BSH111BK. I have now an upgraded PCB Rev07 which fits the BSH111BK and similar FET and I will offer them shortly.
The latter benefits from the 30mA idle current. The result is lower output impedance whilst providing a great frequency response overall.
M3 needs a proper heatsink, it does get hot with about 2W of dissipation.
Well, this valve has the reputation of amazing performance and low distortion. The gyrator setup provides the best out of this valve in my view. You can get a flat response as well as great bandwidht from 10Hz up to 3MHz loaded with 100kΩ:
The distortion is very low and is lower than 0.05% below 10Vrms. Dominant H2 with a lovely harmonic profile characteristic of this valve.
i’ve been listening and using this valve extensively since 2011. I have to say that it sounds amazing. I never get tired of its sounds. Before I listened to a 4P1L-4P1L system and found a slight edge on the sound (probably due to its H3 component) which I don’t hear on my system. The drive, clarity and tone is amazing. It can drive the 4P1L PSE perfectly well and you get a strong and clear bass. Very powerful. My +600 hours 4P1L are very quiet in this setup, no microphonic noise. I don’t have even dampers in the 4P1L sockets!
Anyway, if you need 19dB (x9) gain in your system or you need a driver for your SE amp, then this is the valve to go. I Still can be found cheaply and is a great contender to the thoriated tungsten filament DHTs like 01a and VT-25.
Build this one and enjoy!