Introduction
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:
PCB Features
- Gyrator load (or voltage-controlled CCS) to build a “hybrid” mu-follower stage for either DHT or IHT valve stages:
- Flexible PCB design to fit multiple capacitors
- From a low cost WIMA MKS 100nF / 630Vto
- Any boutique cap up to 2.7cm x 6cm
- It can be re-wired to build a CCS load instead
- Stable voltage reference source provided by a cascoded pair of LND150 FETs
- The top MOSFET is located next to the edge of the PCB so you can use the heatsink (if needed) of your choice
- Top MOSFET can be either DN2540 or any other HV depletion MOSFET like IXYS 01N100D, IXTP08N100D or similar
- Various options in the PCB to fit low noise and capacitance JFET according to the anode current demands like:
- Anode current test point across a 10R resistor
- PCB characteristics:
- 70x65mm board on a high-quality 1.6mm thick FR4 board
- 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:
Rev08 Update
Read this blog entry to see what’s new on the latest PCB version
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:
I’ll appreciate if anyone using the gyrator with the gyrator PCB shares feedback on this page.
Many thanks
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,
Robert
Hi Ale,
Is that possible to set Gyrator load up to 400V-450V voltage?
If yes, which parts are needed to adjust?
Thanks
Gary
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.
Cheers
Ale
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!
Thanks,
Kees.
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
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:
http://www.bartola.co.uk/valves/dht-push-pull/
You will have to build and experiment…
Cheers
Ale
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: http://audio.fam-gelder.nl/images/kimmel/figure-6.jpg …would this be suitable to be used with your boards (balanced to se) ?
Best Regards
Frank
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.
Thanks
Ale
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 !
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?
Thanks,
Duong
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)
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?
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
thanks
Ale
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.
FWIW Cgs of 2sk170 is ~25pF (if you are using that device, and will be in parallel to C1).
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.
Thanks
Bez
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?
I ordered the Gyrator PCB awhile back and the SMD pre-soldred parts were so small I didn’t even notice them resulting in an e-mail to Ale. He kindly asked for a pic at which time I realized the error of my ways. After populating the rest of Gyrator board and before “officially” starting the 01a Gen2 amp project on this website, I also ordered the Source Follower boards (I say “officially” because I had yet to commit to the the most ominous part of amp building, for me anyway, drilling the chassis! I have enough experience to safely work with these circuits and associated voltages but I’m clearly a relative novice in amp building. Ale really went the extra mile with me answering numerous e-mails when things weren’t going as planned or I induced oscillation into the project with my long “temporary” alligator clip leads among other challenges. He patiently guided me through to success! I really appreciate all his help! . . . in addition, an e-mail to Rod Coleman was quickly answered regarding his filament regulators for the 01a tubes. A fabulous pair of resources for the DIY community!! Thank you again!
The 01A is a nice tube, as is 112A. Especially CX-301A and UX-201A. However, what I find really shines is triode connected E280F (Siemens SQ 10,000 tube, frame grid) into 4:1 transformer. Voltage gain of 12, output impedance at ~120 ohms, no solid state parts, nothing to fail.
I could live with either, but I know after living with all three which is better (for me) and that is the trans coupled E280F.
I think D3a is also very well, but at the inflated prices not any more.
Look Aries Cerat. Uses E280F in 70k Eu DAC output.
Hanze
Hi Hanze,
What design did you implement on the CX-301a? I really love the E280F and D3a amongst other IHT. However, getting the most out of the DHT isn’t the same challenge.
Over the years of experimenting with these stages, I found out the big difference introduced by the filament regulators instead of AC, filament bias and the gyrator load over the normal step down transformer.
All the DHT complexities make a stage like this to be not the most attractive solution for a commercial product, hence you won’t see it in the audio gear out there very often.
I have to say that if I compare the CX-301a with step down transformer with my latest implementation, there is a gap in terms of sound.
The additional challenge with the old DHT is that you also need to source some pair of valves in good shape which is a daunting task in itself as these are very old devices!
Of course at the end of the day, your personal opinion and taste is what it matters in the end.
Thanks for sharing your views
Ale
Hi Hanze
The high anode resistance is what makes very unsuitable the transformer for the job. Hence my quest on the gyrator. However, I have found that low anode resistance valves like 4P1L, 71a and others sounds actually better with the gyrator compared to a good TX doing the same job.
I used the E280F successfully with SiC diodes for bias and a gyrator load to drive the 300B. Excellent valve indeed
I’ve got a lot of inspiration (and respect) for Gary’s work. These days there has been a lot of advance on the available depletion MOSFET for HV.
I’m also currently working on a variation of the Swenson regulator which Gary also revisited. Hope to get a decent PCB available to support varied designs, phono stages in particular.
I’d be interested in hearing your tricks around avoiding the bypass cap.
One thing also that I used a lot when I don’t have the gyrator load (or a CCS) is the CCS+VR combination. Gary explains it very well on his presentation by showing the current path and isolation of the power supply. That is why I developed a flexible CCS PCB which accommodates the varied offer of FETs available today for different currents to make a simple VR+CCS arrangement.
Thanks for chipping in, always keen of learning from experienced people out there 🙂
Cheers
Ale
Dear Ale,
I think transformer is difficult for 10k Rp tube DHT. My experience is like most who want to have the best from the tube. Coleman regulator, filament bias and CCS load (Gary Pimm latest rev before it was pulled from the interweb). PS as is usual for me damper diode and choke input to oil cap, and selection of teflon/foil or PIO output caps (my amplifiers are 470k Zin) so less than 0.1uF is more than enough for zero phase issues down to 20Hz.
I regret that I have not tried your gyrator load.
However, with the same power supply and a decent 4:1 step down, .. 150Vp no volt drop across the load (appreciable volt drop).. maybe its something to do with E280F and inductive load, I really cannot say.. but I did and still do find a preference for choke input and constant current heater supply. I have a few tricks to avoid a bypass cap (not that difficult, just out of the box thinking a little).
And yes, you are very correct.. easy to find tube, I have 20 all from the same production run at some cost, but.. when you weigh it all up, as with all.. its a compromise.
Anyway, I think your site is wonderful, as are your cartoons.
All the best.
Hanze.
Dear Ale,
I can see the timing of replies and I refer to your second post here.
Agreed about the difficulty of winding a truly good transformer for high Rp tubes, it is a battle between inductance and capacitance… hard to get decent LF and HF at the same time, and of course when you gap the core for more current, we know what happens to permeability.
With lower Rp triodes, I guess it becomes a matter of taste. What I do note, though, is that the choke/transformer primary does store energy, and so the B supply requirements are significantly reduced and full gain can be had with as little as Vp + (Ip x winding DCR), and of course not all transformers are created equal, and there is flexibility with step down if and when required.
With regard to cathode bias cap omission, a highish current source fed bias resistor will achieve the same as filament bias, except the extra current does not come from the tubes filament supply. That said, ever tried it with say a 600mA IDHT supply with cathode tied to heater?.. hey just an idea, I’d go the other way first!!.. Split rail supplies.. so many ways…. I think CCS fed transformer loads decoupled by a capacitor are also a good idea 😉 but we all have our own take.
What I do note about your gyrator, is that it will set a constant plate voltage, and so if fed from a (the gyrator this is) stable voltage, DC coupling becomes very convenient, practical and easy as variation is moved to the plate of the second tube, very nice!.
Most of all, you make your work available to the DIY’er, which I think is the most important thing.
Keep sharing. Thank you and more please (saw that in a movie recently, resonated with me, unlike my transformers :-))
Kind regards,
Hanze
Hi, Ale. Your new gyrator boards are very nice! Thanks for your efforts.
I notice in your comments that the board can be configured as either a gyrator or CCS. Out of curiosity, do you have any comments regarding the sonic or performance differences between this gyrator and a CCS implementation?
Hi John.
To be precise, we call them “gyrator” but actually is a hybrid mu-follower or a totem-pole series push-pull circuit. The CCS can also be connected as “mu-follower” but has a restriction on the value of the mu resistor and therefore the FET may end up unbalanced with the triode. Not a big deal if you’re using the stage for “gentle” loads.
The hybrid mu-follower allows fixing the voltage at the anode, the CCS doesn’t as it fixes the current instead. When the valve ages, this point will drift (as if the valve is changed) with a CCS. The gyrator will will keep the operating voltage. This is important when being used as a driver as it’s critical to keep the anode voltage at quiescent point to ensure sufficient headroom is provided to swing lots of volts when needed.
From a sound perspective, I prefer the sound of the gyrator. However, I have to admit that still haven’t made an A-B comparison between the 2 with similar circuits. Still on my list. The difference though is minor when the CCS is implemented correctly and components are chosen carefully.
Hope this helps.
Ale
Hi, Ale. Yes, this does help. I have been doing some simulations to compare the 2 with some interesting findings. Basically, the distortion is pretty much the same in either case. However, the CCS has less bandwidth (only 1.5Mhz!!) and exhibits several dB of peaking. I don’t know why at the moment. OTOH, the gyrator has much wider [theoretical] bandwidth (>5MHz) and no peaking. I don’t know how any of this will play out in practice.
FWIW, this would be for a linestage application. I’m running sims up to 30Vpk output (!) with very impressive performance in either case.
Hi Ale,
would like to thank you for making the gyrotor boards for me.
I used them in my amplifier in the driver stage and it works and sounds very good.
In combination with the Sic diode boards, the driver tube is also very easy to adjust.
Thanks and keep up the good work!
Best regards,
Martijn
Been using these Boards for some time now & find them extremely flexible, they have been used on 01a (with & without source follower boards), 4P1L & 2P29L Preamp Projects, I know some of the purists out there only believe in Iron output & loading, I’ve been down that route & trust me the boards are superior to my ear. If you follow Ale’s guidelines properly, you can’t really go wrong. my preference for 01a is BF862 & BSH111BK for the others, with top fet being IXTP08N100D, very pleased with all results achieved. I’ve had 5 pairs so far of varying incarnations.