The return of the Siberian
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.
How does it perform?
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.
How does it sounds?
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!
I wonder how you could have made the microphonic noise lower.
Three things that help:
1) Use a solid top plate – 4mm or thicker. In my Mule preamp breadboard I use a 1cm thick hard wood plate instead
2) Valves with +200 hours use decrease significantly their microphonic noise. True, but not practical unless you want to burn them in!
3) rubber dampers are very effective as well as mounting the loctal sockets in a sub-chassis
How would you describe the sonic differences between 10Y and 4p1L when used in the (nearly) same preamp ?
No transformers here? In v3 You used LL1660.
Nope, if you read the blog you will find out why. The gyrator outperforms any transformer-couple version or preamp I’ve built or heard before.
Hi Ale,
Please tell me the output impedance of this circuit. I want to try it like driver to a Push-Pull Lateral Mosfets Amp so I need to see if I need a buffer or not before this Pre and the output Fets.
Thanks!
Hi Horia, output impedance is low, it all depends on the load and current requirements.
You have a few posts in the blog with calculations and also search for the ETF presentation I posted as well. It has all the info you are after. Just need some reading 🙂
When using the pcb with BSH111BK…which diodes need to be implemented really on the boards as I understand it comes already with its own protection diodes ?
Only D3. D1 and D2 are built-in on the BSH111BK
Hi Ale,
Nearly, you didn’t use SSHV2 board in your project? maybe Gyrator board worked very well.
in 4p1l, usually, 2-3-4 are combined together according to the classical scheme of 4p1l. Recently, on the recommendation of a friend with reference to your circuit, I put one resistor 150ohm, 2 – 150 Ohm – 3 – 4 in my DAC tube buffer. It was very impressive. The scene became much airier with increased images. in the current version above v4, you changed the circuit again in comparison with the previous generations and put two 300 ohm resistors for 3 and 4 (R9 R10). Can you please explain the principle of operation of these resistors and why you set exactly 300 ohms!
This preamplifier sounds lovely, it really does! Just mind that this tube is rather microphonic. Also, for posterity I had a chat (email) with Rod Coleman regarding biasing as I was not sure what was the correct procedure for this preamplifier using his Filament modules. His advice is as follows (hope sharing this helps someone):
Go round a circle of three measurements, to get the optimal settings.
1. Choose a nominal Anode current and bias voltage. The value of bias resistor follows as Vbias = (Is + If)*Rfb. Data sheet bias voltages need ca. 0.5xVf adding, to account for the assumption that the filament centre is the effective bias point.
2. Start up with Va at around halfway through the adjustment range. adjust the filament regulator till you get Vf a little lower than nominal…. This is the voltage across the filament, not the regulator output voltage.
3. All the time checking the anode current. Adjust the anode voltage and see if the desired anode current can be achieved, on each side.
Hello Ale
First of all, congratulations for your work that I have been discovering for several weeks without ever getting tired of it! After tens of years of work on the tubes by original ways, I discover that there are still other ways to explore.
In practice you use wound resistors for the polarization of cathodes of Russian military origin, can we ask you where you get your supplies? My supplier of Russian tubes and capacitors in Ukraine has difficulty in making proposals to me ….
Thank you in advance
Bonjour Alain,
Thanks for the feedback. I purchased them years ago from Russia directly, something isn’t possible these days. You should check on eBay as there are several sellers
Good luck
Ale