Thanks for your tips. And I emphasize an apology for my poor communications skills.
My main question is about the L2 bead. Note it's slightly different location in the two diagrams posted by Gertjan. Is one implementation superior to the other?
In my implementation, the input signal path is first through the beads then to the cap, at the connector/chassis wall. The output path is similar in that the first filter component encountered is the bead, followed by the cap also both at the connector/chassis wall but bead and cap are reversed order with respect to RF energy coming into the box from the i/o cable. This is all per Gertjans diagram.
My understanding from reading this thread is that from an RF standpoint, ie RF getting into the box from the outside on the various io port cables, seeing the bead first then the cap is ideal. But in the case of the output driver, it may not like that configuration, ie having a cap before the bead at it's output and so the bead impedance gets inserted between the output and cap. Hopefully I haven't misunderstood...to keep the output driver happy the bead, cap order gets reversed even though this may not be the best RF rejection.
OK that is what I was hoping. Maybe I can run an experiment later to see if I hear anything.
Even better. No caps at all just beads on the input. I'll try it.mediatechnology wrote: ↑Thu Jan 25, 2018 12:31 pmI wouldn't put capacitors to ground and imbalance the instrumentation amp on the phono input.
You'll just make CMR worse.
I wouldn't over-think this.
Are you having an RF problem and if so what is it?
My instincts tell me that we make a huge mistake when we apply the same RFI/EMI solutions that apply to low impedance mic and line outputs to a balanced phono input.
1) The input already has differential termination capacitance because the cart requires termination.
2) Any common mode capacitances you add is in parallel with the cart's differential termination.
3) Any capacitive imbalance to ground is going to wreck CMR because the source impedance is high and inductive.
4) There's series resistors available to form an RC filter to prevent rectification of CM signals.
I can't argue with putting ferrite beads in series with each input but I would avoid putting CM caps on a balanced phono input.
Just don't do it.
Honestly I think I'm just freaking out and being overly analytical about it since this is my first ever solder to audio hardware. I simulate lots but haven't ever listened to anything I've put together. I know I can cause problems in my home audio equipment if I try...key up my RF amplified am signal too close to any of the single ended stuff and it sounds like aliens are coming down. I've also noticed cell phone activity but haven't had that particular type of noise in a while.