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SUT Hum

I bought a Hashimoto HM3 SUT.
It has a ground connection, but when the ground cable from the turntable is connected to the SUT, there is an audible hum. However, when the ground cable is connected to the ground connection of the preamp, there is no hum.

Is it a common problem? I'm OK as long as the SUT does not generate hums. But I wonder whether it is due to faults in the SUT.
ihcho
whatthe's avatar
whatthe
87 posts
 
Don't get this thread. Ground connected to preamp, NO hum. No problem.
I'm just say'n ✌️
atmasphere's avatar
atmasphere
12,154 posts
 
I connected the ground cable from the turntable to SUT and a wire from the SUT to the phono preamp.
Then, most of the hums were gone. The level of hum was further reduced compared to the ground cable connected to the phono preamp or the preamp.

Is it normal?

Yes- that is normal.
dover
2,337 posts
 
Yes - this suggests that in your SUT the chassis is not grounded unless you connect a wire to the preamp from the earth post of the SUT. If the SUT chassis is not grounded then all the soldered connections inside are unshielded and prone to RF and this is why the noise reduces further when you connect the SUT ground to the preamp.
ihcho's avatar
ihcho OP
612 posts
 
Good to know that there is nothing wrong with the SUT.
Thanks.
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