4P1L DHT Preamp Siberian (Gen3) finished!

No Gravatar

IMG_1568Introduction

Building a new version of the venerable 4P1L “Siberian” was very encouraging. This belated project finally came to life after some recent work on a new set of power supplies. So why 4P1L again? I always found the 4P1L sound to be unique. Great detail, overall tone and fantastic treble. What it makes it well suited for pre-amplifiers is not just its linearity (probably being the most linear valve out there) but the fact that it has a low anode resistance and current capability to ensure any challenging load can be handled effectively without any sound degradation. This can be heard particularly on the treble where the input capacitance of the amplifier is more evident and it is translated into treble loss. Other DHTs like 26, 01A, 30sp can only handle a few milliamperes of anode current and is not enough to charge and discharge the  parasitic capacitance at high frequencies. More importantly, the 4P1L has filaments which aren’t demanding. This is a unique feature amongst DHTs that is rare and very useful. Having low-current filaments that can be either configured at 325mA or 650mA, low grid voltages and high transconductance in a valve is very useful. This mean that filament bias can be easily implemented without burning unnecessary power by swinging many volts to perform the desired level of amplification.

Continue reading

  

4P1L Siberian DHT Preamp (Gen3)

No Gravatar

Recently I finished the filament supply for the latest incarnation of my 4P1L pre-amplifier.  Here is the next instalment of this project. The HT power supply was refined after builiding more than 7 stacked HT supplies for the 814 SE Amplifier.

The supply design is very simple. Perhaps the selection of components and the refinement of some aspects of it is what makes the difference to me: Continue reading

  

Listening to the new RIAA phono stage

No Gravatar

20140417-194534.jpg

It’s been some time since I built my JFET shunt-cascode RIAA MC stage.  I have listened to several well know records for some time with this phono stage in my system and others. I took it to the London Circle Audio meeting recently and it was very well received by most of the circle members. I even had some requests to build units!

IMG_1420

VT-154 SE’s warm sound

Now I can say that it’s completed. Albeit I haven’t built the charger for the lead-acid battery pack, it sounds fantastic and has great autonomy. Long gone days were I was recharging my NiMH pack! Now I can relax and enjoy music without worrying about charging the batteries now and then. I haven’t measured the voltage across the battery cells so far.

More lasting than bronze – John Coltrane

Usually I play my John Coltrane records. Not just because I personally find Coltrane to be one of the best musicians ever existed on earth, I have some specific songs I use for testing. When I was younger, I used to listen for hours the same Coltrane records when learning saxophone. I was keen to listen to every single detail on the phrases, solos and arrangements of the Quartet, Quintet or the Sextet formations. As a sax player, you learn many solo parts, tunes and you know by memory every expression made when blowing the horn. If you don’t have any Trane’s record or even you haven’t heard any of his compositions, I urge you to seek his wide and bast repertoire. From “Love Supreme” to “Giant Steps” and many other gems. Several years ago when I started to rebuild my vinyl collection here in London, I found this excellent compilation of Coltrane: “More lasting than bronze“. It’s a great sample of Coltrane’s music. I use it to test my system. The horn bass notes, the pulsed bass, drums and pianos have a great level of dynamics and detail I constantly listen to. It grabs my mind and takes me to another planet. That is music, more lasting than bronze…

 

 

  

JFET RIAA Preamp – battery supply

No Gravatar

I built a new pack of 12V+6V lead-acid batteries to provide +/- 18V for my JFET RIAA MC phono stage. Despite the bad reputation of these being noisy, Geoff tried them with great success. The Haze brand are the recommended and the low capacity ones (i.e. 1.3Ah) are very quiet.

I decided to build and test it. As the proof is in the pudding!

Here is a simple test on my workbench of the 18V battery set with a 20mA load to simulate the RIAA stage consumption. The LC is formed by a 33mH choke in differential mode + 100uF/20V OSCON capacitor.

No twisted cable pair, just banana alligator clips. The noise level is really low and is obvious that 3.3μV 50Hz hum is picked from the workbench. I also listened to it for a while and can hear the difference. I monitor the FFT with no average and lower FFT size and also couldn’t see any spikes due to chemical reactions. They may happen in future though :)

18V lead-acid battery noise test

The performance of this battery pack is outstanding, so far so good!

 

 

 

 

 

  

4P1L Siberian Gen3: Loctal socket board

No Gravatar

Here is the 4P1L Siberian DHT preamp (Gen3) socket board. I’m using a pair of custom made teflon sockets mounted on a PCB sandwich with a 4mm silicon rubber sheet. The lower board is mounted over 4 silent blocks:

This should be a great improvement to reduce any further microphonic noise in the preamp!

 

  

Siberian DHT Preamp Gen3: filament supply

No Gravatar

Time to upgrade my pre-amplifier (again) and is perfect timing to go back to 4P1L. The Siberian preamp had a fantastic bass response and detail.

Here is the new filament raw supply. It has split bobbin transformers, schottky rectifier bridge and input choke LC filter stage. It also has a CM choke and EPCOS electrolytic capacitors:

Dead quiet at 16V output and 550mA which is the load used by 4P1L starved filaments in parallel with filament bias.

Soon to build the preamp!

 

  

Building your own interconnect cables

No Gravatar

20140405-134559.jpg

I’ve been struggling for some time to find an affordable interconnect cable choice without falling into the trap of the ultra-expensive hi-fi commercial cables. In the end, an interconnect cable has to provide low capacitance, low resistance and proper shielding to protect our desired signal from external noise. We don’t need exotic cables or connectors to achieve this. Ideal dielectric is air, but is not practical build cable using air as dielectric :)

Continue reading