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I’m trying to find the optimal settings for gain staging for my turntable, but when I use what I calculate should be the optimal setting, I get a lot of distortion.

TLDR: math says I should set Sonos Line In Level to 10, but in reality it’s so distorted I have to set it down to 1 or 2

My setup is:

  • AT-LP120XUSB (with preamp switch disabled)

  • AT-VM95ML cartridge / stylus

  • Schiit Mani 2

  • Sonos Connect (non-amp version)

  • Sonos Beam (speakers I output from Connect)

From this thread, I’m using the formula V-output = V-input * 10^(gain / 20)

https://www.reddit.com/r/sonos/comments/g6q6ua/calculating_linein_level_for_turntable/

Here’s my current calculations and setup:

  • the preamp is disabled on the LP120xusb

  • VM95ML has output of 3.5mv and recommended loading of 100-200pf at 47k ohms

  • short RCA and ground wire cables are used between turntable and Mani

  • Mani filter settings are off as factory default

  • Mani default setting is 47k/47pf, so I have enabled the switch to add an additional 47pf to get closer to the 100pf recommendation for the VM95ML

  • Gain on the Mani is set to factory default of 42db

  • Sonos system is set to Uncompressed audio quality and the Connect is set to set to max delay (2000ms)

With this data, the formula should be

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

From the Sonos Line-In guide, there are 10 Levels that correspond to voltages between 2.2v and 0.6v, with the highest voltage at Level 1.

https://en.community.sonos.com/components-and-architectural-228996/using-a-turntable-with-sonos-6769426

With the Mani supplying 0.44v, there should be plenty of headroom at Level 10 set for 0.6v, but at this setting, I get plenty of distortion. I have to drop it down below Level 5 to clean up the signal. If the formula above and my variables are correct, in theory I should be able to boost the gain on the Mani to 48db to give nearly 900mv, allowing me to set the Sonos Line In to Level 8 for 1.0v, but that introduces extreme distortion.

Anyone have any ideas, or at the very least, settings recommendations for my system?

I didn’t read your whole post, but the pre-amp needs to be on, not turned off, if I understand your setup properly. Sonos always expects line level inputs, and your phono level input is too low, even with the Sonos settings set to 10. 

The Schiit Mani is the preamp, the turntable has one but it’s not great so it has a switch to disable it and it becomes a normal phono output, and the Mani is the preamp that sits between the table and the Connect. 

What happens if you skip the external phono preamp and just use the one in the turntable to get things started?

You could try playing something, submit a diagnostic and contact Sonos support to see if they can see anything.

scottfrans,

Your calculations ignore one point. The cartridge output voltage is measured at a fairly low modulation level. A high level passage is overloading CONNECT. Also, I didn’t check your preamp specs. Make sure it is a MM, not a MC preamp. If the system sounds OK with CONNECT at a lower setting, declare victory. 

There’s surely a danger of overthinking things. The Mani looks like to be eminently configurable, and it sounds like it’s in the default MM mode. After setting the recommended loading I’d simply be tinkering with the 4 different gain levels if necessary and the Sonos Line-In level until it felt right. If it sounds good now at Sonos level 2 -- a nominal 2V -- I’d leave it there since you’d probably have the best overall SNR. 

Well I get all the calculations as being correct - 3.5 x 10^2.1 (or 3.5 x 125.89254) = 440mv

So my initial thoughts are to double check this …

  • VM95ML has output of 3.5mv and recommended loading of 100-200pf at 47k ohms

In the Mani 2 instruction it does mention if it’s an MM cartridge to not even bother turning over the Mani 2 and messing with the switches 😀ha ha. This document made me chuckle…

https://www.schiit.com/public/upload/PDF/mani%202%20manual%201_1.pdf

I think I would - just leave the pre-amp at its current settings and just adjust the level in the Sonos App until you get no distortion and leave it at that - (as Schiit says "don’t flip it over”).

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