jensenmann

Re: [BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD
« Reply #400 on: December 20, 2018, 12:17:50 PM »
Next one: there are ground loops if you wire your Sta Level according to the wiring diagram on the first page of the thread.

Filament supply/ground is fine if you follow the wiring diagram. Just make sure your switch for bias adjustment is opening the contact if momentarily pushed.

V+ supply and it´s ground is fine, too. Since it supplies the light bulb and the relays only it has no connection to audio anyway, so it´s not relevant. But be aware of the relay board ground wiring. There are several possible ways to ground that thingy. The best way is to tie pin 1 of both XLR in and outs directly to the starground. That´s the shortest path to ground. But you should use shielded wire inside the box to connect both XLRs to the relay board as well as the main PCB to the relay board. The shield of those four wires should be tied to ground at one side only! E.g. connect all four shields to the relay board but not to the XLRs and the main board. Then tie the relay board to the starground. This way you have no groundloop which is what we want.

Bias and HT supply:
The bias supply gets its voltage from the output of the HT (B+) supply via two wires: B+ and B-. B- is the wrong name since it´s actually ground. But it´s necessary to understand that both supplies have a common ground, just look at the schematic. Now if you wire the B+ output to the main PCB with two wires and the Bias supply with another two wires then you already have a groundloop because on the main PCB both ground connections are tied together via the ground plane. So leave one of those ground wires unconnected.
The main PCB and the PSU needs to be connected to starground. There are two provisions to do so: the ground connector on the main PCB next to the bias voltage input as well as the ground connection on the HT PSU board next to the HT Trim resistor. Connect only one of these two grounds to the starground. Otherwise you get a loop from starground to the main PCB, then via the bias or B+ ground to the PSU PCB and then from it´s ground connection to starground again.

Jens
Quote from: PRR
The tubes of course don't care what frequency they distort


zayance

Re: [BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD
« Reply #401 on: December 21, 2018, 10:36:04 AM »
Quote
C9 in the B+ PSU is rated at 400V. That´s too low. I measure 422V DC here. Theory says 300V AC x 1,4 = 420V DC after the bridge rectifier. So make sure that you use 450V rated caps for C9.

Good catch.  ::)
Well the BOM gives hints if what can be used, and people can fit whatever they like, Bernd and i don't go into the "kits" thingy so...
Dunno if all went 400V Caps way here, depends on the provider, some might have no other choice than 450VDC etc...

But thanks for shimming in and giving hints and infos, always welcome.
BOM Will have update on today.


T