Gyrator PCB


After 7 years of working with the gyrator load circuit in DHT preamps and valve amp driver stages, a friend of mine suggested in building this PCB for the DIY audio community. The result of many years of experience and testing plus some refinement of the PCB design made by Tom Browne from Sonic Illusions, is this flexible PCB.

If you don’t know what I’m talking about, however someone told you about this board, then I suggest you pay a visit to some of the following articles and blog entries on my website:

01a DHT Pre-amplifier (Gen2)

Gyrator boards

PCB Features

  1. Gyrator load (or voltage-controlled CCS) to build a “hybrid” mu-follower stage for either DHT or IHT valve stages:
    1. DHT Preamps (e.g. 4P1L, 01a, 26, 10Y, 3A5, 71a/CX371a, 2P29L, )
    2. IHT Preamps (e.g. 27)
    3. DHT output stage drivers (e.g. 4P1L, 300B, 45, 10Y, 211/845, 813,6J49P-DR, 6SF5,  etc.)
    4. Push-pull drivers in LTP configuration
    5. Phono output stages
    6. Parafeed stages
  2. Flexible PCB design to fit multiple capacitors
    1. From a low cost WIMA MKS 100nF / 630Vto
    2. Any boutique cap up to 2.7cm x 6cm
  3. It can be re-wired to build a CCS load instead
  4. Stable voltage reference source provided by a cascoded pair of LND150 FETs
  5. The top MOSFET is located next to the edge of the PCB so you can use the heatsink (if needed) of your choice
  6. Top MOSFET can be either DN2540 or any other HV depletion MOSFET like IXYS 01N100D, IXTP08N100D or similar
  7. Various options in the PCB to fit low noise and capacitance JFET according to the anode current demands like:
    1.  J309/J310 (TO-92)
    2. 2SK170/LSK170 (TO-92)
    3. BF862  (SMD SOT-23)
    4. MMBJ310  (SMD SOT-23)
    5. BSH111BK (SOT-23)
    6. BSN20BK (SOT-23)
  8. Anode current test point across a 10R resistor
  9. PCB characteristics:
    1. 70x65mm board on a high-quality 1.6mm thick FR4 board
    2. ENIG finish, 2 oz. copper.

SMD pre-soldered boards

You can get your pre-soldered SMD jFET or MOSFET device (BF862 or BSH111BK) if you are not used to do SMD soldering. Here is how I do it:


Each board is tested individually and its wrapped on an individual antistatic bag per board.

Ping me a message for availability. I don’t always have these boards in stock. It takes time to do this neat soldering job!

Rev07 Update

New SMD pads to fit BSH111BK/BSN20BK and most of enhancement MOSFET in SOT-23 package:

How to get the boards?

If you want to send me your requests please use the form below:


If you don’t hear from me in a couple of days, just ping me an email to the following address as generally the contact form doesn’t work in WordPress:

contact address


18 Replies to “Gyrator PCB”

  1. Hi Ale,

    Much thanks for all your hard work in both experimenting, posting detailed construction techniques, as well as offering your gyrator PCBs for sale.

    You inspired me to tackle my own 01A preamp. Thanks to your gyrator boards (which were easy to assemble), along with the great work of Rod Coleman and his regulator boards, I now have a most amazing 01A preamp.

    It truly does sound different: more lifelike, more dynamic, yet smoother. Even older Red-book CD rips seem to have more depth and dynamics. My wife, who knows next to nothing about high end audio, immediately noticed an improvement over the previous, not-too-shabby 6NS7 preamp.

    There are noticeable 01A sample variations in terms of noise and 3mA adjustability (but then who really knows the varied paths these tubes have had over the past 80 to 100 year!).

    The preamp is dead quiet (once I sorted out the grounding of the remote’s PS).

    Thanks again!

    God bless,


  2. Hi Ale,

    Is that possible to set Gyrator load up to 400V-450V voltage?

    If yes, which parts are needed to adjust?


    1. Hi Gary
      I’m afraid you haven’t provided enough information about your plans to answer this question. The gyrator can be biased to provide 400V-450V, yes. However depending on the output swing required, you will need to change the CCS as the LND150 can only do 500V.

  3. Hi Ale,

    I have recently ordered your new Rev07 PCB’s.
    Wich I received very quick and I have to say that these PCB’s are made very nice!


  4. I want to test this board with a 4p1l as DAC-output. The DAC has a differential output and I want to use both signal, + and -.

    Can you give some guidance how to apply your board for

    a.) balanced –> SE: I saw Allan Kimmel suggested to connect the cathode of a second triode, give her half of b+ and that is it ? Really that simpel ?

    b.) balanced in, balanced out: Would this be four SE-amps or do you make them differential with connected cathodes / CCS in the tail ?

    All the best

    1. Hi Frank.
      If you want to use a gyrator load, you probably want to study a bit the LTP circuit. I’d recommend Morgan Jones’ book highly.
      You can use an LTP with gyrator loads in both anodes. You then take the differential signal out from each mu-follower output.
      With a DHT like 4P1L, you can use filament bias. See circuit 5 in the following link:

      You will have to build and experiment…

      1. Hi Ale,

        I studied my Morgan Jones again and found:”A differential pair can be made using the basic common cathode triode amplifier or with cascodes. (The μ-follower is not suitable because differential pairs attempt to exploit the normally large ratio between RL and Rk.)”…are your boards not making up a u-follower basically…so not good for a diff. pair ?

        I found some examples in his book where he used active loads in a diff. pair though…

        I have looked at this here originally: …would this be suitable to be used with your boards (balanced to se) ?

        Best Regards


        1. Hi Frank,
          See chapter 2 and figure 2.54 of Valve Amplifier 4th Edition.

          You will need one gyrator board per 4P1L valve in each LTP. Tail could be either a resistor, filament bias or CCS. Up to your taste. You will need to design the stage though.

          1. Thanks for taking the time…yes, I saw that one, but as this was only an example how you can combine two ccs on the anode which are dominated by one in the tail and not a mu-follower, I did figured that you meant this one…

            I would prefer a ccs in the tail, but the question is which one would dominate your boards I guess like in Morgan’s example…

            I will try it for sure…any advise highly appreciated…

            Thx a lot !

  5. Hi Ale,
    Amazing works!!!
    However as I understand (I’m just a novice in solid state), BSN20BK and the like are Enhancement mode MOSFETs while 2SK170/J310 are JFETs and they are a bit different in how they work. Do we need to make any change in circuit to make them work in the same position in your gyrator baord?

    1. Hi Hoang. The CCS arrangement caters for both VGS bias requirements (positive or negative). No changes needed in the board. Only different pads are used depending on the FET and package type (SMD or TO-92)

  6. Hi Ale, the boards look great and I can’t wait to start building!
    For my new amp I plan to integrate a high-pass filter as per my current amp arrangement, which has a first order HP filter around 150Hz.
    Can R6/C1 be varied sufficiently to perform this function (i.e. 100K/10nF) or would these values interfere with its native operation?

    1. Hi Bez
      I haven’t tried it myself, but other builder have implemented a bi-amp with a 10Meg/510pF. The 510pF can be a nice mica capacitor. Try to keep R6 between 4M7 to 10M

  7. Hi Bez and Ale.. the builder which Ale references would be myself. 150kHz, you will be very happy.. again, keep R6 as high as possible, 10M and reduce C1 to suit. First order crossover is perfect for this.. 6dB per octave and my situation as well. Use an RC calculator on line and choose appropriate value for C1, it will be small, really small – which opens the door to silvered mica and or one of the better (Rel-Cap) polystyrene caps rated appropriately WRT VDC. You have the unique possibility here with Ale’s cct to HP at your desired point without increasing output impedance. A very very neat function.

  8. Hi Ale, Shane – MANY thanks for the replies and details. This is a super neat way to achieve what I need! Yes ill be using the 2SK170 – I didn’t realise it was in parallel – so many thanks!

    I have two other questions;
    – if I wish to test gyrator without additional stage following should I add additonal load other than R8? (perhaps making 100k total?)
    – Is there an upper limit for +HV with the default components? For simplicity I would consider sharing with following stage however that may around 500v. I plan to use IXTP08N100D2 for M2 which I assume would be fine, but the LND150 has BV(d-s)of 500V.


    1. To test the gyrator I would recommend an output capacitor (220nF) and then a RL of 100kR. R8 can then go in the real circuit if you’re using a preamp stage.

      The HV limit is indeed 500V due to the limitation of the LND150 and the PCB. I’d not run it above 450V.

      Why do you need a higher HV?

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