Port Line In Levels

  • 28 February 2024
  • 16 replies

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I have an old Quad 33/303 set up that I love and works very nicely with my turntable and Sonos Port as sources. 

It has a line-level output that I connect to the Port’s Line In so that I can listen to the Turntable in other zones. However, I have to turn the volume up on the other zones WAY higher than from other sources. The 33/303 Line Level output is adjustable, and I’ve set it to it’s max (“H” in the table below). The Port’s input settings are set to 1 (low) and it’s still too quiet. Not distorted, but just too low.

What are the actual line-in sensitivity levels of the Port? I can in theory change the component values in the 33/303 to output more than 100mV, but I’d like to know what the Port’s inputs are in order to choose correct values.



Best answer by Ken_Griffiths 28 February 2024, 13:18

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I understand that these are the line-in voltages expected for each source level …

  • 2.2V - Level 1 
  • 2.0V - Level 2 
  • 1.8V - Level 3 
  • 1.6V - Level 4 
  • 1.4V - Level 5 
  • 1.2V - Level 6 
  • 1.1V - Level 7 
  • 1.0V - Level 8 
  • 0.8V - Level 9 
  • 0.6V - Level 10 (500mv)
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Thanks for that Ken, v kind.

For clarity, if I may:

  1. Why have you labelled 0.6V - Level 10 “500mV” when 0.6V is 600mV?
  2. The Sonos App lists Level 10 as “High”, which seems as the opposite to what might be expected. If the input levels are small, you’d want Level 10, which is definitely not a high-level


The values were a mere copy/paste from another online source @Captain Biggles - I just had it stored in my notes here. I can’t recall the source of the info. (sorry). but that’s exactly how it was written/presented originally. I’ve not altered it in any way.

Note @Ken_Griffiths hasn’t labeled anything, he is a user just like the rest of us.  Actual Sonos employees are designated as such in their usernames.  As to the numbering convention, it is an argument as old as the hills.  You may as well ask why a top 5 draft pick in a sport is a “high draft pick” or went “high in the draft” when their number is so low.  Same idea as this. 

@Captain Biggles,
In my own case I choose to just play the source audio (Turntable/Bluetooth RX/CD or MP3 Player etc.) at/near full volume and then I reduce the Sonos line-in source level until I do not hear any distortion. That’s been my own method for setting the level. However there is a formula to calculate the setting which is…

V-output = V-input * 10^(gain / 20)

Maybe see this link on Reddit from Sonos Staff for a TT line-in level selection.

Hope that will assist you further.

I have some notes from when I did my own pre-amp/turntable line-in calculations too (a while ago), so if I can be of any further help, then let me know. I still find it easier though, to select the line-in level as described - until no distortion can be heard at/near full volume level. 

Just as a very quick example, if a TT cartridge voltage output is 3.5mv and the gain seen on the pre-amp is 42dB (that’s normally a default setting for say a Mani pre-amp), then the calculation is this…

3.5mv * 10^(42db/20) - which gives 440mv

So that infers one should use Sonos line-in source level 10, but I’ve seen some mention that they get distortion with some equipment and so they end up reducing the level down anyway.🤷‍♂️ So you may find my chosen method of source-level selection, might ‘perhaps’ prove to be the best option anyway.

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Thank you very much for taking the time to answer Ken, I am very appreciative.

Sadly your method for setting the Line -In Source Level won’t work for me.

You can treat my input source as fixed, at 100mV. So even at the Sonos’ most sensitive end (Level 10), at 600mV I’d still only be using 1/6th of the available input range. Which means (roughly) I’d have to turn my Sonos zone volume up 6 times more for this one source than any others.

Looks like my two options are:

  1. persuade Sonos to add a 100mV level (like a Level 13 or similar) - I accept this isn’t going to happen
  2. Modify the internals of my Quad to output 500mV (say) rather than 100mV. This is possible, but I’d need to study the schematics to choose a suitable resistor value. For those interested,the relevant circuit is below:

For completeness’ sake, Pin 1 is the output I’m interested in. Pin 2 is GND, Pin 4 is the o/p to the rest of the amplifier, pin 3 is the input signal from the source and the wire in the top right corner is +12vDC. The bottom of R212 is also at Ground

You can see that Pin 1 can be switched between the H / M / L pins, where H gives an ouput of 100mV, M of 20mV and L of 3.7mV.

It’s been many years since I did my Electronics Degree, but if I choose different values for R210, R211 and R212 I should be able to scale the 100mV to a 500mV output instead.

@Captain Biggles : Have you actually tried setting the Port line level at 10 and see how things fare? 

If you want a back up opinion on what may be done inside the Quad unit, you may want to check with Rob Flain in Quad UK service; he has been there for decades in charge of service and may give you the assurances you are looking for.

Keep in mind that phono cartridge output is specified using a reference record. In my experience this  level is a bit low. A sudden music peak can easily be 10 to 100 times this level. Depending on how things are adjusted this can result in obvious distortion.

With respect to “line level” source's, traditionally the Europeans have used lower levels, often in the 100mV range, while the US used 0.5 to 1.0V. Many compact disc players output 2.0V or more. Some line level inputs will begin to distort at about two Volts, while others will tolerate ten Volts.

Currently, input adjustments are common. These adjustments make life easier. Early in the CD era, connecting a European CD player to US equipment resulted in low levels. Likewise, connecting a Japanese CD player designed for the US market to an European receiver resulted in very loud levels and sometimes distortion.

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Having got home I can confirm that my line-in level is set to 10 and I have to turn the volume right up when listening to that source compared to all my other sources.


I get that different sources have different levels, and Sonos caters for a range already. I guess the short way of asking for summarising my problem is to say:

“what can be done when Level 10 isn’t enough?” (Also known as the “why can’t I turn it up to 11?” conundrum)

You can search Amazon for “line level booster”. These are external devices that will amplify the level of your turntable. I don’t have experience with any of these units. Note that some of them include a 240V power supply. You may need to replace an included power supply. Be sure to check the power requirements. Many of the units will accept a wide range of power supply Voltage. You may have an appropriate power supply in your junk box.

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I heard back from the excellent Quad customer service today who confirmed that sadly there aren’t any internal modifications that can be made that will increase the 100mV “line level” toward 500mV.

So I guess now the only options are:


  1. Use a Line Level Booster like Buzz suggests (needs a gain of 15dB or more) like this one here although that has the disadvantage of adding additional circuitry that may distort the signal or
  2. Start a campaign for Sonos to accommodate input signals lower than 100mV. Now officially known as the Turn It Up To 11 campaign.

Anyone at Sonos care to comment?


What about using voltage attenuators for the other sources? These may not even need a power source. I cannot see Sonos providing more gain capability in the Port.

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Follow-up question to the above (and thanks for all the answers):

What is the fixed line level of the output of the Port? And why is this not listed anywhere in any of the literature or on the App?

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What about using voltage attenuators for the other sources? These may not even need a power source. I cannot see Sonos providing more gain capability in the Port.

Because the other sources ARE the Sonos. I.e. when playing internet radio or streaming or from my digitised library the outputs are normalised and the volume is the same whichever source is being used. So they cannot be attenuated as they’re internally generated.

The issue arises from the low line-levels coming from my external sources being 5 times (c. -14dB) smaller than the Sonos input can amplify currently.