Saturday, November 20, 2010

DIY - Tube Buffer (***Updated#2***)

I finally gave up trying to get my hands on a used Musical Fidelity X-10D and bought a DIY PCB based upon the infamous unit thru a DIY outlet.

Used my spare NOS Russian 6N23P-EV(s) for this project - as per my Musical Fidelity Tubalog. Other components include the Audiophiler and Wima's (red and yellow "bars") for signal path, EPCOS for non-signal path, Nichicon MUSE (outlet recommendation), and Rubycons.

I began using a regulated "off-the-wall" PSU 12V 500mA to power the PCB. Sounded terrible with much "audio breakage". When I contacted the DIY outlet, they informed the original design was based on a unregulated PSU e.g wavely line vs bar with 3-dots above on the PSU. Sounded much better once fed the proper diet!

Started tweaking since it is now operational. Initially used Nichicon Muse 1000uF 35V capacitors (light metallic Green) as per recommended by the outlet. Later replaced these with equivalent Multi-Comp (aka United Chemicon) on my 2nd iteration as there was no audible difference via my Leak, mod DVD2900 and HoneyComb speakers when I replaced them.
2nd iteration
The highs and mid-range sounds extremely nice. Bass was better than before insertion of the PCB into the circuit but a little "muddle round the edges".

On my 3rd iteration, I replaced the 1st two filter caps with a single Rubycon. The "yellow" Wima was replaced with a larger value Silver Mica.

Wundabar!!! Everything fell into place.

3rd iteration
Another view of 3rd iteration

Forth iteration. Replaced the Rubycon 10uf with Panasonic FC 22uf, as these were on the signal path. Sounds rich and life-like thru the Luxman L410, especially the piano pieces.


I found the following schematic from the web and updated it with the changes made. The shaded area is the section which is in the signal path. Changes are in red text. The shaded area of the schematic clearly shows the audio signal path and I personally believe money should be spent on components in the shaded area. I tried better components in the unshaded area before and there were minimal improvements except for the upgrade of the power filter caps from 1000uF to 2200uF. I used 16V instead of the original 35V as I measured the voltages at these points and were below 16V. Using 2200uF resulted in a quieter background in the output e.g when you are next to speakers and no music was playing. And I did not use the 4007 diodes as per the schematic as I had many IN4004 leftover from my Quad 33/303 upgrades.
Schematic with changes

Update#2 - 27Sep2012

Both channels died and the valves do not glow anymore.

Checking the power section of the PCB reveals the 2.2R 2W resistor to be faulty and when tested shows a value above 400ohm.

Replaced the 2.2R 2W did the job!


  1. friend, can arrange for a date/time to enjoy this?

  2. Hi SK,

    Will SMS to yourself tonight.

    The components are still not fully seasoned yet for the tube buffer.

    Took a while for similar components in the Tubelog to be seasoned aka tubalog just "seasoned" mid-Nov2010. If you like it previously, you will definately love it this time around!!

  3. Hi.

    Do you have schematics of your 4th iteration? Can you send it to me? Please.

  4. Hi Tomislav,

    Sorry do not have a schematic handy. Will need to locate one off the net in the future to illustrate the changes.

    Basically the 10uF electrolytic is the smallest of the EC on the PCB and are located next to the valves / Audiophiler poly caps. These were replaced using 22uF 63V Panasonic FC. I know other sites have suggested using bi-polars. Found the 22uF more than adequate for my ears.

  5. Ok, but if you find it, could you send it to my mail account?

    Please, much appreciated,

  6. Hi Tomislav,

    Please retrieve from the blog as I have updated it for everyone to review.

  7. FYI

    Recently I was helping my friend clear their old Technics hifi set which included a SU-V505.

    When the buyer came to audition the set, he was shocked - eyes open up wide and commented that the amp sounded like his valve units!!!

    He only intended to get the V505 for background music. Hence I explained the impact of the tube buffer on the actual reproduction since I heard the V505 without it before. Was using the Technics Honeycomb speakers. He decided to take the V505 and built himself a tube buffer unit since he was a electronics engineer.

  8. Hi,

    What caps do you use on C102 and C202 (the silver caps)?


  9. Hi Shadow,

    I purchased them from

  10. Hi! Which DAC chip using in Musical Fidelity tubalog DAC? Can you send pictures, where I can read semionductor name or ID. Thanks!

  11. You can right click on the pix and open it in a new tab. You will then be able to magnify it