How exactly is the Port connected to the CD player?

I'm running analog cables out of the Port, into the amplifier.

I'm running analog cables out of the CD player, into the Port

I think the Port should only be connected to the CD player, not to the amplifier. Connect from the Port’s Digital Out to the CD player’s digital input using a digital audio coaxial cable.

If I don't connect the Port to the Amplifier, how will sound get to my in wall speakers?  Also, I tried the digital out to digital in and then the Line Out option disappeared from the Music/Browse options.

Ok, I see what you are doing now…

Connect from the Port’s analog audio OUT to the left and right inputs on the amplifier. Then connect the CD player from the left and right audio outputs to the Port’s analog audio IN. If you are still getting distortion, try different audio cables. Also try the different Line Out Levels settings for the Port in the Sonos app.

Can someone from Sonos chime in here?

Is your Port set to Fixed or Variable output? The A150 has quite a low input voltage spec and the Port could potentially overload it. 

Are you able to test the Port into any other device to verify its outputs are working correctly?

Why? Do you think they can offer better advice for this specific problem? 

First time here. Saw it on a few threads done the way. Didn't mean to offend.

Thank you for this perspective. I have it on Variable. There's no volume control on the Acurus so I'm not sure how Fixed would work. Would limit the volume to something low versus 100/full?

Now that you mention it, I do have an Onkyo AV receiver that powers 4 in ceiling speakers that I could test it on.

Additionally, when I stream music from Pandora, SiriusXM, or SoundCloud, there's no distortion. It's still being powered by the Acurus (obviously) which makes me think the issue is with the Line In feature.

Okay, so the Port provides volume control. Fair enough.

If other sources are fine through the power amp then the Line-In does indeed sound like it’s the issue. Source Level 1 is the lowest sensitivity, so ought to be fine with any standard line-level signal. I couldn’t readily find a detailed spec for that ancient CD player. You are using the unbalanced RCA outputs I assume?

You could independently test the Port’s Line-In, e.g. using the headphone output from a phone. 

Have you tried simply inserting some attenuation in between the CDP and the Port? Either a passive volume control or in-line fixed attenuators?  

It's definitely ancient but I've tried other CD players and nothing sounds as good!  Yes, using unbalanced RCA outputs.  I have the tech specs if there's something that would be helpful. I'm not smart enough to know how it would impact the Port so many thanks again for your help!

I have another ancient piece of equipment which is a passive volume control that can act as a pre-amp. When I hook up the Amplifier and CD player to it, the sound is incredible. BUT, even on  "1" it's really loud and obviously no Sonos capability.

Any chance you think it's just a bad unit with a problem in the Line In circuitry?

I was curious as to the nominal output level of the CD player’s RCA outputs, to see whether that could explain the behaviour. 

Have you tried inserting your ‘ancient’ passive volume control between the CD player and the Port? 

First time is a good reason/excuse. You will not get better support than what you are getting on this issue from anyone that I know of in Sonos that posts here. It probably won’t even be as good. 

One reason why you see some high post counts among some users here is because Sonos is often not to be seen - or seen in time - on many threads here.

Or such users were moderators in an earlier incarnation of this community. 

Jumping in because I did not see an answer to the quoted. This is an easy way to test the line in circuitry of the Port. Have you done that?

The tech spec for the RCA out of the CDP has two numbers - 3 volts and 6 volts. I don’t know if this means that the minimum is 3; if so that explains to an extent why it goes so loud, but from the little time I spent looking at reviews I did not see this pointed out as an issue by users as one would expect. And I would expect setting Sonos line level to 1 should fix the problem. Unless something is wrong with the Line In, which a test with any phone should throw up.

It looks like 3V is for unbalanced, 6V for balanced. At 3V it could be in danger of clipping on the Port’s ADC, since the Level 1 Line-In spec is 2.2V.

I invited the OP to insert his existing passive volume control into the line, to attenuate the signal and see if that helped.

Really appreciate the perspective!

I haven't. I'm trying to think how I'd rig that. I'd still need the out to the Amplifier from the Port  How would I wire the CDP and passive volume control?

I have not. So I'd need an RCA(s) to single headphone jack?

Well, I’m assuming the control is either RCA-in/RCA-out, or it’s combined with an input selector so it’s multiple RCA-in with a single stereo RCA-out. You could post some more info if relevant.

Either way, you’d just connect the CD player to an input and run the control's output into the Port’s Line-In. Set the volume to full, then lower it until (hopefully) the distortion goes away.

Yes.

Just went through my old cord box and I think that one got tossed in the last purge. Ugh.