WiiM Ultra direct to Purifi amp (Audiophonics LPA-S450ET): audible hiss – anyone else experienced this?

[Valentino]

^ @harkpabst It is common to put a serial resistor (say 100 Ohm) in line with the output to avoid trouble with marginally stable input circuits. WiiM has not done so.

 

[TonyE]

What are the input impedances for your NCore and the NAD's aux input?

Also what are the output impedances for the NAD's preamp out and the Ultra?

Are you using the same cable between the Ultra and Purify amp as you're using between the NAD and Purify amp?

 

[slartibartfast]

^ @harkpabst It is common to put a serial resistor (say 100 Ohm) in line with the output to avoid trouble with marginally stable input circuits. WiiM has not done so.

Which amplifiers are unstable with a low output impedance source?

 

[Valentino]

I do not know. What I do know from this thread is that the input boards in these Audiophonics amps have had issues with their integrated circuits and that the op has had no hiss problems when using his NAD to feed the power amp.

 

[Corchea]

@etc, sorry — I missed your earlier message.
Thanks for the suggestions. I’ll run the tests you recommended and report back with the results.

 

[Corchea]

Hi everyone,
I’ve been away for a few days and couldn’t reply earlier.
I’ve done some additional tests:
• WiiM Ultra → NAD C320 used as power amplifier → speakers: completely silent, no noise.
• RCA cable with 120-ohm resistor: noise still present, no change, and it does not vary with volume.
• RCA → XLR connection to the Audiophonics amplifier: noise still present.
At this point I think I have to assume that direct connection between the WiiM Ultra and the Audiophonics power amplifier is not workable in my setup.
Using a preamp between them (NAD or Aiyima T20) solves the problem, so that will probably be my practical solution.
Thanks again to everyone for the suggestions and help.

 

[Aquaman]

Hi everyone,
I’ve been away for a few days and couldn’t reply earlier.
I’ve done some additional tests:
• WiiM Ultra → NAD C320 used as power amplifier → speakers: completely silent, no noise.
• RCA cable with 120-ohm resistor: noise still present, no change, and it does not vary with volume.
• RCA → XLR connection to the Audiophonics amplifier: noise still present.
At this point I think I have to assume that direct connection between the WiiM Ultra and the Audiophonics power amplifier is not workable in my setup.
Using a preamp between them (NAD or Aiyima T20) solves the problem, so that will probably be my practical solution.
Thanks again to everyone for the suggestions and help.

Like I said, if I was in your shoes I‘d contact Audiophonics and hear what they have to say. Even if the result is that the Ultra is defective.
I would not settle for a preamp in between.

 

[TonyE]

Have you put a voltmeter across the outputs of your Ultra to see if there's any DC coming out of it?

The NAD might be AC coupled so it removes that...