audiostar

I would not stack anything, at least not horizontally. In addition to what John already said, the upper board will always run hotter and also its transistor will be on the upper part of the heatsink already heated up by the lower row of transistors. Stacking boards vertically on the heatsinks is much better, thus the reason for the CFA split boards. Make sure you mount transistors to the lower on the sinks as heat moves from bottom to top.

You might want to consider having only balanced inputs and *if* you need to connect a single ended cable to it, then use external Neutrik NA2 MPMF to convert a chinch cable. Will make things simpler. The mount-from-inside version for the 3-pin XLR connectors for the inputs on the back would be the Neutrik NC3FBH2-B or the NC3FBV2-B with vertical pins. For the speaker terminals, personally I would use the Neutrik SpeakOn. Would keep your back plate clean and can be mounted from inside as well into a round hole and are the best speaker wire connectors anyway. NL2MP or NL4MP-ST depending on what kind of connection from the inside you want and bi-wiring (4-pole) or not. This will clean up your back panel with only 2 holes on the left and 2 on the right side. In the middle you can have the IEC inlet. Just a thought...

Here an idea for further builds: I am using the Neutrik NC4FAH-0 connector and mount it behind the front panel using blind taped holes, same as with the teflon Stax sockets. The hole is 22mm in diameter and for any panel thicker than 2.7mm a beveled edge on the front is a nice addition. Here the panel cut out and dimensions for the NC4FAH-0. If you do not PCB mount the connector, the NC4FAV-0 would be the vertical pin version where the contacts might be easier to solder wires to. Front design and dimensions are the same. These connectors don't have a locking tab, which is nice as well.

So, you will be running single ended wiring from the back panel's RCA connectors alongside the transformers all the way to the bal/unbal board located at the front panel?

With this 19" 3U case the amp will look like a 100w class-A power amp. A better idea would be to separate the PSU from the amp. Also, 100VA toroids aren't giant, I wouldn't be concerned about mounting them with 4 or more bolts. Depends on how thick the plate is. Dissipante panels are only 1.5mm I think, so this makes sense. Wouldn't be concerned though mounting the 100VA to 3-4mm thick panels. But don't use countersink bolts, only buttheads so you do not weaken the hole. Will be on the underside anyway.

273 series 1/2 watt Xicon resistors seem to be end of life (not recommended for new designs) and disappearing at Mouser. More and more of the 100 packs are gone and replaced by 1000 or 5000 packs.

You must not use the protection board, it is recommended though.

No, I don't like the heatsinks mid inside the chassis 🙂

I have a CFA3 for my HE-6 and like it a lot. But no Dynahi to compare. For me CFA3 was the next evolution step after the Dynahi, but maybe Kevin may chime in.

Nice! Suggestion for a mod, or more like a necessity 🙂 with dynamic headphone you should consider putting the KG headphone protector on the output, before the headphone connector. Why not a CF2/CFA3, just curious?

I see. I tie pin1 to to the case immediately via the XLR connector (and not to ground) and use the metal case as shield. I use twisted wires for the signal inside the case. Circuit ground connects on a single place via a circuit breaker (at least 10ohm resistor) to the chassis. Gives me no hum whatsoever.

How did you ground the pot and did you use twisted only cables or screened?

I have my amp with split boards finished but undecided between a 4CP-2511 and the digital attenuator, so it still sits on a shelf without a pot. While bench testing the boards prior casing it up, I didn't notice anything weird though. I am using the Toshiba 2SK389-BL & 2SJ109-BL JFETs on DIP adapters. I'll order a 4CP-2511 and give it a final bump.

@Kerry Would it be possible to substitute the OPA134UA/2K5 that's used in the PSU with something else that's easier available? Mouser keeps pushing it out, now scheduled for 2024!

Also not to forget that everything got much, much more expensive today, huge inflation, supply shortages, etc. So, to be honest, today's prices aren't comparable to what we had few years ago.

Kerry? 3* 6995 = 20k, no? And I can sell you mine as well 🙂

A "high-end" amp with a build in power supply... You can buy a T2 for that kind of money.

I think I have some .45 boards left.

If you want to use the trimpots, you need to recalculate the 1M resistors depending on selected output voltage. Like for 15V, one of them per side would need to be 473k, so 1M is too hight for 20V output.

I see Is there a final version for the boards?

Kevin, did you switch to M2's? No Wilsons anymore?

The resolution of these measurements look mind blowing precise down to 5 digits. Being able to tell the difference between lid open and lid closed is no joke. Have you ever compared your setup measurements with any other pro gear? Just wondering how really accurate and repeatable those are.

Just stumbled upon this "best class-A amplifier" called "T2", ever heard of? Looks like it was officially renamed to something else...

Phew... couple of days already finishing up the final wiring, setup and calibration of my CNC router. Ended up with a 2.2kW 400Hz water cooled spindle on a 4 axis machine that is connected to a Mach3 system with two LPT cards fully automating spindle start/stop, water pump start/stop for cooling, air cooling for the cutter, etc. Very happy for now how everything goes together. Need to fabricate a heavy duty cabinet for it holding all the electrical stuff and computer below the machine with some drawers as well for the cutting tools, fixtures, vacuum pump and water tank as well. Going to keep me busy for some time.

Ok, right-click and then "save as" works, but then the file needs to be renamed to .pdf in order to be able to open it. Chrome saves it on macos as undefined. Must be something with the formatting thats wrong.