150hz hum - Increase with volume!

Hi,

I have pl-518 TT with rewired tonearm and it has 150hz hum and its increase with volume.
TT metal chassis and motor grounded at ground post.

Tried different phono preamps with no luck.

Using Empire 2000e/iii cart. If I replace it with grado cart this same hum fq gets louder.

Checked continuity with arm pins to rca, all checks out.

Any idea where to check next?


Thanks

Edit: measured fq with phone app.
 
Last edited:
Typical? Do you have three phase rectification?

No, why? 3rd of 50Hz? 5th at 250Hz, 7th at 350Hz? Surely you have seen that many times?
You can also see it at the primary side due to the 'cut off' top on the primary due to rectifier diodes opening up.
All just as predicted.

But mainly my point was that it is MUCH easier to troubleshoot if you have an idea WHERE the problem is. Try to 'box it in' as it were.

Jan
 

Attachments

  • Mains harmonics.PNG
    Mains harmonics.PNG
    50.2 KB · Views: 75
  • Mains waveform.PNG
    Mains waveform.PNG
    36.4 KB · Views: 76
Last edited:
TT not connected to mains.

Arm tube and arm base is grounded. All cart and headshell connections checked, all ok.

Removed headshell and cart; loud sinewave hum.

Connected headshell and cart; 50hz sawtooth hum (much quiter than 50hz sinewave hum) but it's really annoying at 11 o'clock volume position.

Tried different cart (at95 and grado); at95 hum is same as Empire. Grado has more hum than others(as usual)...

Isolated female rca sockets from tt chassis. No change.

Tried different interconnects. No change.

Tried other phono pre. No change.

Removed everything from mains (including kitchen stuff!), except power amp and pre amp. No change.

Installed emi-rf pcb to preamp main input. No change.

I believe there is a ground loop somewhere but I still couldn't find it.

Will try another amp with integrated phono............