ac ground loop

[maxpou]

Hi Guys
I have a possible ac ground loop with my simplistic riaa phono stage. In another thread i had a AC ground loop with my mono power amps and my preamp. I resolved my problem when I read the groung loop document of Bonsai. I put a hum breaking resistor in my power amp. Now i has a new ground loop problem when i connect my phono stage, i tried a ground lifter in my preamp without success. If I connect my phono stage with my turntable on my old Onkyo receiver and this one has no earth ground I don't have hum noise. Somebody can help me?

thank you! Maxpou

p.s.: my turntable is a thorens td125 modified without ground wire.

 

[maxpou]

Hey Guys,
nobody can't help me!

maxpou

 

[Hans Polak]

Hey Guys,
nobody can't help me!

maxpou

A schematic diagram would help a lot.

 

[U230421]

PF's prism: that's ok.
The TD125 is well known, what is modified?
Can you sketch a block diagram how things are connected?
Which Onkyo receiver?
Bonsai is a very small tree.

 

[rayma]

my turntable is a thorens td125 modified without ground wire.

Does your tone arm have a ground wire?

 

[brig001]

You don't need a ground loop to get hum - parasitic capacitance in class 2 (double insulated) power supplies can also cause hum:
https://www.jensen-transformers.com/wp-content/uploads/2014/08/an004.pdf

Measure the chassis current as described to see if that could be the cause

Brian

 

[maxpou]

hi guys,
sorry for delay and thank you for reply guys. I have worked on my problem last week and I resolved it when I put a ground loop breaker in my amp with a 25A bridge and 0.1 uf cap between the gnds like in the page 56 in this doc. http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf. Now for my preamp and phono preamp I putted the safety ground on my chassis only and my audio ground is floating, should i put a ground loop breaker in all my device or not? thank you! Maxpou