Different systems react differently in terms of grounding and hum pickup. It's possible for a preamp like this to be quiet in one environment, but not in another. It might be necessary to detach the inlet's green wire from the power supply and instead attach it to one of the chassis screws. That preserves its use as a safety ground, but will isolates it from the audio circuitry and power supply ground. Of course, this will only work if the circuit boards don't extend any of their ground traces under any screws or metal standoffs holding the boards to the chassis.
Microphonics from the tubes? I pulled the tubes and deoxited the pins and also the tube socket pins. Moved the two gain tubes to buffer position and buffer tubes to gain. With just the shorting plugs installed it was noticeably quieter. Then connected my better TT a Technics SL1210 MK5. It is quiet while connected, but gets a little louder when the stylus hits the record. There has been an improvement. I don't have any replacement tubes, yet. I am ordering some because I need a backup set and who knows may be the noise issue will get better, or worse
The question is whether the electrical ground of the boards - such as the shields of the input jacks - is connected to those screws. Are the input jacks and output jacks all insulated from the chassis?
I had purchased from Roy his Phono Preamp PH16-X and V22 SP14 Pre-Amp installed, and these are dead quiet. I would ask Roy if you can send the Phono Amp to him for a checkup?So, I have been setting here listening to this Phonopre ever since I shortened and rerouted the wires. I have to say this thing sounds really good. I have been given lots of good advice by folks in this thread. It is greatly appreciated and I have learned some more. But I think I'm just going to enjoy it and live with the small hum. If I could have gotten it quiet that would have been great. But I can live with it right now and have no regrets. I got to build my second kit, and it worked. Happy as a pig-in-****. I've decided to listen to records instead of fretting over a little hum. Thanks for the help guys. Hey, noticed I went over 2000 posts. Only took me 15 years
The question is whether the connection at the PCB is signal ground or chassis ground (and whether the two are tied together through the board). I don't think the OP knows, or maybe he doesn't understand the question.
Right. It looked like the earth ground goes to the PCB only. Also its hard to tell if there is any ground from the PCB's going to the chassis or not. Roy's instructions aren't as precise as Bob's were. Roy expects the builder to understand grounding schemes. I know there was some mention of the power transformer being too close, but I've used several toroidal transformers and have had zero problems with them causing any hum.
Yes, earth ground connects from the IEC filter earth to the CT ground on the power board. The ground is then jumpered from the Power board to the preamp board ground.
Could be I don't fully understand. This is what I know, the earth ground at the IEC filter connects to the power board PCB at the CT grnd. The transformer shield wire also connects to IEC ground, the chassis ground comes from the case of the IEC filter itself. I think this is how it works. Take a look at the picture of the IEC filter wiring in post 21.
