audiostar

I think I am going to enlarge the front end board so I can stack it on top of two CFA3LargeT boards and mount them exactly the same way as the split boards are mounted. This leaves me the middle of the case for two stacked GRLVs in the front and a toroid in the back. What was the max output a GRLV can be modified to? I think @sorenb did a special power version of it.

Ready to order BOM here, Mouser ID=43398b8123. Everything included for a 4ch amp, except for 24x 2sc4886 and 20x 2sa1860, which are double the cost of the items in the bom above and are pretty much nowhere to be found except for some 2sc4886 at Digikey.

If you mean the Protector3, yes, it cuts off only R+ and L+ to protect the phones. That's enough.

Hmm, while XLR pin 1 is fine going to chassis as it is basically shield, RCA GND should not go to chassis. This is why the RCA sockets have an insulation ring. It goes to circuit ground and is shorted to - half of the channel when the RCA input is engaged. This is a balanced amp, so I would switch all 4 channels (+ and - halves) between the outputs. And I would handle the speakers like balanced headphones, i.e. wire the +/- to the banana plugs and not circuit ground. Especially important when using a balanced source. For when you use the RCA input, the - half would be shorted to circuit ground anyway.

Yes, ceramic sockets have bit of different pin legs which do not fit the board properly. Use the teflon sockets, you can get them from the diyhifisuppy you linked above or on ebay as well. 8 and 9 pin available, check out this seller https://www.ebay.com/itm/223597938937

Make sure the thermal compound paste you are using is non-conductive as well as not all of them are.

Those large boards on top look interesting.

Exactly because of their physical properties and being so thin, I wouldn‘t even think in using them in HV environments with naked tabs and inox bolts. Heck, I am not using them at all, especially if space permits it. Frst comments were already regarding those silicon insulators! Just no way one can tighten up the sands to specs at around 8-9 Nm with those without some damage .

Before you go deep into the rabbit hole with insulation testing, first you check extremely careful all connections through the umbilicals to the amp boards by continuity. Then you load test the PSU with some resistors, do insulation testing and all the other fancy things.

400mV is around 10x too much for the offset. 8 rotations are normal for the bias pot until you start noticing the voltage increase. The pot has around 30 turns or so. 150 to 200mV would be in range.

I would go with the higher.

I would stick to 10k

Think about keeping it modular and separate the tube pre from the power amp. Same as you separated the PSU already and not stuff everything into a single like 6U 800mm deep chassis

The Amphenol's don't have removable pins, so no crimping possible and also no variable size pins available as well. It only has one 18 AWG pin (and all the others are max 20 AWG wire pins), so not really suited for a high current class A amp. A much better connector is the AMP CPC shell Size 17, p/n 206043-1, 206044-1 (PSU side), 183040-1, 183039-1 (amp side), as used on the BHSE or the Dark Star. Pins are removable and all sorts of pins for crimping (as well as soldering if you wished) and sizes for 16...26 AWG wire are available for the same size 17 connector. Very nice modular and serviceable system. It is HV rated and the 16-18 AWG pins would be perfect for the beefy GRLVs. Really nice.

Oh, right - thanks Kevin

What is a grhv100? The CFA runs on a GRLV...

I am only using aluminium standoffs. If I don't need grounding, I just don't put pads on the PCB around the mounting holes. (If needed) I usually have a single hole only making contact to the case through the standoff for grounding. I also use female standoffs only. If I need a male on one of the sides, I add a male headless screw and some red of blue Loctite. Makes me keep less parts around. The hight of the standoffs really depends on the application. Around 10mm is common. #4-40 or M3 is a good common size for the thread.

Newer GRLVs have a place for a 10R directly on the board. Make sure you understand the AES48-2005 as well https://usermanual.wiki/Document/ShieldWiringOfBalancedInputsAndOutputsAes482005F.2144015621.pdf

Connect amp's chassis to the same bolt where you have connected PE to the PSU case. To this same point you connect both GRLV grounds, say via a 10ohm resistor. That's it, for now, for safety. Measure and make sure there are no shorts between the pass transistors and the chassis. Then power on, play some music and check if you get any hum.

They must be isolated from chassis. Must use proper isolation. Wrong, it must be connected. Now, it has do be done properly, so you do not get any hum. The moment you do something wrong and you get hum. And this applies all the way to XLR pin 1 and case wiring and so on. Not good. Even worse.

Hi Pars, yes, PE is connected to the case in the PSU chassis. But you connect there the amp's case as well - missing. 2nd, you connect there circuit ground as well (best is through a circuit breaker or via thermistor like Pass is doing or via 10ohm resistor like Kevin is doing). Then, the pass transistors are isolated from the case, so you don't get any shorts here. In his case the Amps chassis is not connected anywhere to PE. And in the PSU there is no connection from circuit ground to PE at all.

Nice! Miss the chassis pin on the three pin DC-In connectors, not a separate connector either. Chassis should go from the amp to the PSU case separately from circuit ground and make the connection to PE and circuit ground in the PSU case, close to the IEC inlet. Or how do you handle that? No ground to PE in the PSU case as well. Could be dangerous.

Well, reading the threads always helps. There is a ton of information in there.

Not really going to work as there are caps on the GRLV boards. Maybe, with a 5U case 😎 The pass transistors you better mount directly to the bottom plate, like John has shown above. Oriented to center, straight below the Goldpoint stepper.

Stacking is vertically for proper heat dissipation, bolted directly to the heat sinks (so boards are long and narrow). * vertically in terms the boards are parallel to the sinks.