Sonos ZP-100 Custom Robinette Box for Headphones

[ikrananka]

I'm trying to put together a custom Robinette Box that will allow me to use headphones with my Sonos ZP-100 units. Sonos made the bizarre design decision to not put headphone jacks onto these units. I'm buying my wife a decent set of headphones for Christmas but now need to build an adapter box that will allow her to use them with our ZP-100 units.

I'm basing my design on a basic Robinette Box design but with a 4PDT switch that allows the speaker output from the amplifier to be either routed to our main speakers OR the headphones. I have put together a diagram of my proposed setup below. I'm certainly no expert in these matters and so would greatly appreciate ANY constructive comments on what I'm proposing. Any pitfalls I should be aware of?

 

[GPG]

Looks like L- and R- get connected. Not a good idea

 

[Martaine2005]

Why don't you buy decent wireless headphones and use the analog audio out of the ZP100?
The speakers can be turned down with the volume and the headphones have their own amp and volume.
Example.

Martin

 

[GPG]

There are a few stereo FM transmitter kits available.

 

[ikrananka]

Looks like L- and R- get connected. Not a good idea

Indeed. I forgot to test the ZP-100 and have confirmed that the speaker outputs are balanced and not single-ended. My diagram above would only work if the amp was single-ended. So, I have now added a couple of resistors to the negative outputs as suggested by Rob Robinette on his website. New diagram below.

Why don't you buy decent wireless headphones and use the analog audio out of the ZP100?
The speakers can be turned down with the volume and the headphones have their own amp and volume.
Example.

Martin

I'm going to be buying V-Moda Crossfade Wireless headphones. These also have the option of working wired and so the Robinette box that I want to build is to allow my wife to do that when she wants to use the Sonos amp and bypass the on-board headphone amp.

 

[GPG]

There are plenty of headphone amp kits available, using the RCA outputs. The problem with a bridged amp is the return. Connecting 2 resistors as shown results in the phones getting mono on the common, reducing the stereo width. You could use amplifier ground.

 

[ikrananka]

There are plenty of headphone amp kits available, using the RCA outputs. The problem with a bridged amp is the return. Connecting 2 resistors as shown results in the phones getting mono on the common, reducing the stereo width. You could use amplifier ground.

My wife wants to be able to use the volume control on the Sonos system to control the volume of the headphones. I could possible still do this using a headphone amp on the RCA outputs, but then the speakers are also still connected. Even Sonos has advised me that a speaker switch would be required in this configuration - so 2 additional boxes and one of them needs power. With what I am proposing this keeps it down to one small unpowered box - just seems a simpler setup (apart from the complexity of getting the box design right).

How do you know that the ZP-100 is a bridged amp? I can find no information to verify this. If it is bridged, then where would I connect to for the "amplifier ground" that you propose.

 

[GPG]

I dont. The RCA outer should be ground and presumably the chassis. You could check for continuity with R- L-

 

[ikrananka]

I dont. The RCA outer should be ground and presumably the chassis. You could check for continuity with R- L-

No continuity between the speaker ouputs L- and R-

Continuity between the the L & R RCA outers.

 

[GPG]

No continuity between the speaker ouputs L- and R-

So probably bridge
You could use isolation transformers to be safe. Or the transmitter.