spritzer

The difference in pads is tiny assuming they are of equal quality i.e. age. My Mk2's just have the ports plugged, nothing else. I messed with the arcs a bit to get the fit just right but it was a minor adjustment.

Does the offset pot adjust at all? I mean if you can get a higher value by turning the pot the other way then you need to change the 2K series resistor. Measure the resistance value of the pot + this resistor. If it is just 2K then you need to go to say a 1.5K resistor. If it is 4K then you need a higher value.

I got a power amp from China and it was naturally ungrounded and it hummed no end. I could actually feel the current flowing when I touched it. One wire later and it was fine. Take one wire from each of the amp boards to the PSU and one from the pot to the PSU. Then one wire to the chassis, nothing else. That should fix the issue.

So the chassis is not earthed? That is very, very bad idea. All the GND pads on the boards are connected together.

No....just no....

No shoulder washer with the SiC but be careful as the gap isn't so big. With the PEEK stuff I hand tighten as when you've done it enough times you know how far to go.

Where did you read such bullshit?

My two failed units would beg to differ. I've stopped using the shoulder washers as they simply don't cut it.

I've had two arc through so I'd advice against it.

When using RCA's you only use two of the four decks on the pot. The output of those is taken to the + input of the respective channel while the - input of the each channel is connected directly to the ground tab next to it. Those diodes have to go and the board is clearly marked for the insulated units. The person who built this board doesn't have a clue what they are doing as the tabs of the transistors is indeed live. Wrong heatsinks for the bias supply and I guess the other current sources as well. Inadequate isolation as well since the tab of these sits at a very high voltage.

Ehhh why are you using a RCA to balanced converter? Bypass that crap and just ground the - input of the amp. Grounding is simple, they all go to the PSU including the chassis.

I bet the hum is coming from the transformer. That is literally the worst place possible to put it. As for the bass issue, what PCB is that hiding underneath the volume pot? Not a chance the RK27 is the culprit and I can't even think what could possibly do that to the circuit. Edit: Also the diodes in the power supply could go boom at any moment... They have to be insulated with this PCB layout.

I'd love to hear some of the speakers some day.

Yup, that's it.

Bunnies and cables is a special kind of hell.

You are probably running higher mains than the original design called for which explains the higher voltages. This happens all the time here as the gear was designed for 220V but we are edging closer to 240V. When using contact cleaner on the pot make sure it has some lubrication. Some are just cleaners and they will kill the pot quickly by washing away all of the lubrication. I would use shielded wire due to the small nature of the box. You could just use a super thin microphone cable with two contacts and a shield. Edit: Side mounding the tubes is actually better in many ways. The chassis acts like a cooling tunnel for the tubes.

Who knows why Stax swapped it out. Might be some part issues as the amps are filled with out of production transistors.

Both of those are very obvious...

Stax never bothered with that...

It has nothing to do with the build, it's built in into the circuit. Any peaks that are double the bias voltage will run a high risk of damaging the drivers. That's why the old transformers were fitted with clamp circuits. Run an active preamp into the KGSSHV and you can have enough gain for this to happen...

If you do something stupid then the KGSSHV has more than enough potential to fry any Pro bias headphones.

It's always fun to see how badly this shit is made so I bought one. As for the pads, the SR-1 was never supposed to have flat pads. See this original instructions booklet: They are a tall ring of neoprene so I've been experimenting with various pads to try and find a modern equivalent.

Maybe in some rare cases that might be the case but I've never run into that even with my super cramped PCB's. Filaments being the most obvious example. That's clearly not the case here as we could do this layout in our sleep with a complete ground plane.

Hmm why on earth are they using jumpers on a double sided board? Seriously!! The feedback is still identical though. Two 150K resistors in series so just remove the bottom one and connect the new resistor between the top pad and the empty socket connection.

I didn't know there was a new version of the amp boards so can you post some pics?