Shawn

Here is a long post I wrote, but may have a little help to someone who tries to build the T2 mini by JoaMat. Transformer Specifications: There are two transformers in total. Primary: 120V(USA or other countries like 230V) Secondary: 320V 0.25A 365V 0.25A 190V 0.25A 16-0-16V 0.5A 6.3V 4A × 2 6.3V 2A × 2 I highly recommend adding a soft-start circuit because the inrush current generated by the transformers is significant. High inrush current can easily blow the fuse and cause long-term stress on the filter capacitors. If a soft-start circuit is not added, a high-current fuse will be required, but that would compromise the protective function of the fuse. Chassis: I housed the power supply and amplifier in two separate chassis. For the PSU section, I used Kerry-designed GRHV and GRLV. Pay attention to the chassis height clearance to ensure it can accommodate the transformers. The specific drilling hole specifications can be found in the current thread—I recall JoaMat mentioned them somewhere. All panel holes were made using a desktop CNC router. I believe it's a good investment to have a desktop CNC router, as it ensures precise hole dimensions. The text and graphics on the panels were also laser-engraved using the same machine. Watching the CNC mill parts is quite satisfying. Power Supply: Three different high-voltage power sources are required: -460V, +400V, +220V ±15V for the servo For details on Kerry Design’s GRHV/GRLV, refer to this link: GoldenReference Low Voltage Power Supply Two mainboards are required—one for -460V and +400V, and another for +220V, leaving the rest of the board empty. To save space, I designed a new PCB specifically for the +220V rail. Notes: If using Kerry Design’s GRHV/GRLV, I suggest disabling the high-voltage delay function. In my tests, the 220V rail initially outputs only 20V, while the 460V and 400V rails start around 200-300V before reaching their nominal voltages after approximately 37 seconds (time varies based on capacitor size). Although this delay is short, it prevents the servo from functioning correctly. During this period, the balanced voltage remains around 200V, which could be harmful to headphones over time. A better solution is to add a dedicated tube warm-up circuit. Output voltages may have minor deviations. For instance, the actual 220V rail might measure around 217V. Even with 0.1% tolerance resistors, small variations can be amplified. A good approach is to use a trimmer resistor—for example, replacing a 20kΩ resistor with an 18kΩ resistor in series with a 2kΩ trimmer. Amplifier Assembly: SMD components should be installed first, followed by through-hole components and tube sockets. To simplify the process, I used a paste stencil and a heating plate, which significantly saves time. For the other side, I used a syringe and a heat gun. A more efficient method would be using a heating plate for both sides, with two different solder pastes. For example, using 183°C solder paste for one side and 138°C solder paste for the other. Notes: Don’t forget to connect the +15V jumper and the servo jumper. Otherwise, the balanced voltage may stay at 400V, potentially damaging the servo. This damage may not be immediately obvious, but you might notice the servo stabilizing more slowly, tiny background noise, or excessive sensitivity of the EL34 filament power supply to external interference, leading to noticeable microphonic effects. The T2 Mini’s heat dissipation is moderate, somewhere between the Grounded Grid and KGSSHV. If your enclosure is large enough (not wooden), power transistors like KSA1156 can be directly mounted to the chassis. However, a better approach is to use an L-bracket mounted to a heatsink. My enclosure measures 300mm × 297mm × 62mm, resulting in an internal temperature of around 45°C. Do not use this approach for KGSSHV, as SiCFETs generate a significant amount of heat. 01N100D must be properly insulated. Use single-point grounding as much as possible to avoid ground loops. If using aviation connectors, ensure they are rated for at least 500V. HN4C51J and HN4A51J look very similar—don’t mix them up. Ensure correct polarity for LEDs and 1N914 diodes. Test all components before powering on to verify continuity and check for shorts. For EL34 filament wiring, use at least 18AWG wire. One Last thing: Enjoy the build🙃

The STN9360 has no problem in megatron build. Make sure to check the pin out as I remember that the adapter board needed to be rotated back.

The picture is from your earlier post. I will go through other files to check for any errors this weekend. Congrats for your new driving toy. I remember the Z06 comes with a flat-crank engine which sounds insane. Does it have bucket seats?😍

Based on the megatronxl layout, the second 100k resistor on the top left is float, any reasons for that? And what is the purpose of those 10K trimmers? I assume they are for grid bias.

Another KGGG alive. I separated the GR power supply and the GG amp into two chassis, making it easy to reuse the GR power supply for the next project. The four holes with the rubber blocker on top of the amp are for balance and offset adjustment. I made a side mount board for the 10M90S instead of using the L bracket. The side mount board is attached if someone is interested in it. It is a 450V version, The tail resistor near the offset pot is 200ohms to track the offset voltages down to 0. To make the servo work, offset voltages must be higher than 15v. The power supply comes with a soft starter of about 50s. I don`t want to talk more about the sound since many comments were mentioned. Pretty decent with my Omega and 009. Thank Kevin Gilmore for bringing the project to the table. SideMountV3.zip

Another option for the desktop CNC machine that I purchased from Snapmaker works as well. The working space makes it easy to fit the whole chassis unit with the enclosed cover. It has two different laser modules that work perfectly for engraving. I have some pics shown while I was working on the GG upper and front panels. Milling the holes for tubes, Stax jack, and screws. I settled the speed to 100mm/min and 0.1mm step which gave me the balance of speed and a nice outcome. The bit is from Datron, 3mm Single Flute End Mill. I have another 2mm ball end bit from Snapmaker which I also used for milling the M2-size screw holes. The only complaint about it is the limited 200W CNC power which does not allow the drilling process. The 8nm laser module is the most satisfying. Easy to manage and nice outcome for the front and back panels engraving.

Updated for 571-1-770873-0.

Another idea of mounting those heat generators using the JST jumpers.

I just completed it last week by setting it to ZF and 100ma bias ( +-20V rail). Still waiting the chassis and soft starter. Sounds better than my dynalo\hi with my HD800 and K1000.

Thx for the suggestion. Seems like I real need a softstart borad to built.

haha it seeems like a little bit overkill... i agreed but the price between 200VA/100VA is almost the same. same price more weight🤣

Thx Pars. Actually, i did`t ask the question clearly😑 My apologize. It`s the one in CFA Board near the VCC+- terminals.

Another CFA3 here to be built: The transformer i used is from Antek with 200VA 25V for each channel. Still waiting for the rectifier bridge.d which probably will arrived tmr. Hope i can power it up tmr ASAP, can`t wait to enjoy it. BTW, any help about the trimmer resistor near the VCC+- terminals. What`s it used for?