After a long time, decided to update the PCB of the LL1943 SUT to provide extra flexibility on the grounding connection. This is in essence to ensure no ground loops and noise when either using balanced or un-balanced cabling from the cartridge into the PCB:
The additional jumpers are in line with the recommendations from the Datasheet. Here is the diagram:
For a fixed connection (like in most of the cases once preamp has been tuned/optimised) you can replace the jumpers by solid core wire jumpers soldered to the pad for best connection and performance.
This PCB is also for the LL1933. Basically is the same SUT but with 1+1:8+8 instead of 1+1:16+16 windings.
I made a small batch (I won’t need more than 2 or 4! myself) so the remaining will go on first-come-first-serve basis.
Just updated this post entry. A few asked me about the compatibility of this PCB with the LL1933 instead of the LL1943. The answer is yes, basically is the same SUT but with 1+1:8+8 instead of 1+1:16+16 windings.
ale, the board works just fine. i traced the multiple options with a LL1933 and collected them in a PDF (for download on my server). i never had any issues with both, primaries and secondaries floating, but i assume if cartridge and wiring to the SUT are reasonably well balanced, you could just as well ground the primaries CT. i’m a bit hesitant to ground the CT of the secondaries because that will connect directly to the phono stage (provided the phono stage is balanced. with a SE phono stage, GND is GND is GND sez magritte).
the only thing i would like to see if you made a rev. 3 is a jumper in the secondaries, too. that way one could experiment with the secondaries in series or parallel; if it works, the LL1933 would offer 1:4/8/16 and the LL1943 1:8/16/32. (pls note that i wrote if it works because i’m not sure if the inductance with paralleled secondaries is enough for decent BW).
oh, and one more thing: if no primaries are connected to GND, one can experiment connecting pin 8 to chassis(PE) GND instead of signal GND. even though it shouldn’t, i’ve witnessed situations where PE was actually quieter than signal GND. don’t ask me why.
hth, ©
PS as always: if you find a flaw in my traces, you may either keep it or let me know about it. pick your poison.
Thank you Christian for this. Very useful for sure. Not clear if I’d do another revision of this PCB in future, but will definitely take on your suggestions if I do.