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01-13-2021, 11:33 AM
Hi Guys
The predecessor of the LP-PRE with a PCB was GPK Guitar Preamp Kit with an eyelet board layout. is that what you built, Strelok? If so, the decoupling could be improved and that effects the overall layout.
Ghosting is often attributed to bad filter caps and that might be the case here. It is also related to layout with respect to supply+ground feeds and whether gain stages share a filter cap. Ghosting can also be via induction or electrostatic coupling via proximity of signal paths - so another layout related problem.
Where a DPDT switch or relay can be used for channel switching, this brings in-phase signal points close to each other with the risk of oscillation. It can also allow signal bleed-through, a common problem with high-value value controls wired with 2-conductor shielded cable. The fix for these kind of problems is to use separated muting elements placed where the signal already is so the signal does not have to be moved elsewhere. Another fix is "double muting", particularly effective when jfets are the mute elements.
So,the ghosting cure will likely come down to layout and decoupling.
The predecessor of the LP-PRE with a PCB was GPK Guitar Preamp Kit with an eyelet board layout. is that what you built, Strelok? If so, the decoupling could be improved and that effects the overall layout.
Ghosting is often attributed to bad filter caps and that might be the case here. It is also related to layout with respect to supply+ground feeds and whether gain stages share a filter cap. Ghosting can also be via induction or electrostatic coupling via proximity of signal paths - so another layout related problem.
Where a DPDT switch or relay can be used for channel switching, this brings in-phase signal points close to each other with the risk of oscillation. It can also allow signal bleed-through, a common problem with high-value value controls wired with 2-conductor shielded cable. The fix for these kind of problems is to use separated muting elements placed where the signal already is so the signal does not have to be moved elsewhere. Another fix is "double muting", particularly effective when jfets are the mute elements.
So,the ghosting cure will likely come down to layout and decoupling.
