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John Williamson wrote:
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He claims that with an open circuit, he gets the normal white noise we
all expect, but when he connects the speaker input to the output on the
converter, he gets an audible hum. There is a pair of domestic standard
(And quality) RCA phono connections on the converter, so the only thing
I can suggest is that the shields on the two phono leads are making an
earth loop connecting the two speaker inputs and the two phono sockets,
which share an earth on the adaptor circuit board. The speakers will be
sharing the safety earth of the whole system with each other. Going from
a single ended output to a balanced input with no isolating transformer
won't be helping.

** That is the likely scenario.

I did not expect balanced input, JBL self powered monitors with SMPSs to be other than class 2.

https://jblpro.com/en-US/site_elements/lsr305-back

**** poor design if this is true - cos it wont matter how you connect them.


...... Phil