A Pi-based whole house system

[chill]

I've been making up a system to go into a house where the previous owner has fitted ceiling speakers into most rooms and has conveniently routed all the speaker wires into a single location. I thought this setup lent itself to a system based on multiple Raspberry Pi players with attached amplifiers.

A Pi Zero W with a JustBoom Amp Zero pHat, fitted inside the JustBoom case and running piCorePlayer, makes a nice compact amplified player. The speaker terminals on the Amp Zero are a touch small for comfort, so I added some chocolate block connectors. Using just the official USB power supply, the JustBoom Amp will make 1.5W into 8 Ohm speakers. I don't yet know the specs of the ceiling speakers so I'm going to see how they perform with that amount of power. If more is needed the JustBoom amp can take an external supply which also then back-powers the RPi.



For the server I've gone with a 3B+, again running piCorePlayer. I had previously made a button board that fits inside the standard RPi case, so this will give some physical buttons for ON/OFF, PLAY/PAUSE, NEXT/PREV, VOL+/- etc. I made two versions, one that fits entirely within the case and one that has an expansion tab on the side that allows additional devices to be daisy-chained onto the GPIO connector. I had designed it such that the button board can use configurable GPIO pins, so this gave me a chance to try that out, since the JustBoom Amp uses a number of GPIO pins that I had to avoid. My button board allows for an easy choice of 2 GPIO pins for each button via jumpers, and I was able to find a set of GPIO pins that did not clash with the JustBoom.



The expansion tab on the button board was intended to take a box header for a ribbon cable, but in fact, since it flips the connector over, I was able to mount the JustBoom amp directly onto this connector by soldering in a set of header pins rather than a box header, and it still fits the case.





I made a case to go around the amp to support it and protect it.







I added some chocolate block connector for the speaker wires, and that's the first two 'zones' sorted. Further zones will just use the Pi Zero W+Amp Zero. I'm including a Joggler as a remote display/controller.

[Apesbrain]

Nice job. I'd be surprised if 1.5W cuts it, but 40W with the bigger power supply should be fine.

[chill]

Nice job. I'd be surprised if 1.5W cuts it, but 40W with the bigger power supply should be fine.

I suspect it'll need something between those two extremes - I don't think they are big speakers. That figure of 1.5W is the rms figure - 3W is the peak figure. The Amp Zero can do a maximum of 15W rms (into 8 Ohms) with a 15V 3A supply.

I noticed that the Amp Zero can only back-feed 0.5A to the RPi - enough for the Zero W I think, but not enough for the 3B+, so the server/player might need two supplies.

[mherger]

> Nice job. I'd be surprised if 1.5W cuts it, but 40W with the bigger
> power supply should be fine.

TBH I'm very much surprised how much I get out of that little power
using the same amp...


--

Michael

[chill]

TBH I'm very much surprised how much I get out of that little power
using the same amp...

That's good to know. Did you configure the Alsamixer Volume to -8dB (92%) as advised in JustBoom's technical guide? I assume that's to limit the output power to what the USB power supply can keep up with, and therefore avoid distortion. There's also a couple of other options:

* Toggle a 6dB increase on analog output level
* Toggle a 0.80dB increase on analog output level

I've disabled both of those for now. Not sure what those are all about, especially that 0.8dB increase, which seems like it could be achieved with a combination of the +6dB option and a bit of attenuation on the Alsamixer volume.

[chill]

There's also a couple of other options:

* Toggle a 6dB increase on analog output level
* Toggle a 0.80dB increase on analog output level

I've found a FAQ on the JustBoom website (here) that explains those two settings a little. It seems like those options mimic the ALSA sliders referred to in that FAQ. One goes from -6dB to 0dB, and one goes from 0dB to +0.8dB, and they make it possible to "to set the gain to -6dB, -5.2dB, 0dB or 0.8dB". So I think the wording of those two options in the pCP driver seems misleading. I think the 6dB option ought to be labelled a *de*crease (and the toggle should perhaps be inverted?).

So to limit the output to exactly -8dB I would want to disable the 6dB decrease (is that the same as enabling the 6dB increase?) and disable the 0.8dB increase, then set the mixer slider to 92%. I guess a quick test with some connected speakers will confirm how that 6dB option works.

[Greg Erskine]

Great work!

What are you doing with the IR?

I have taken note of your comments about the dB settings.

[chill]

So to limit the output to exactly -8dB I would want to disable the 6dB decrease (is that the same as enabling the 6dB increase?) and disable the 0.8dB increase, then set the mixer slider to 92%. I guess a quick test with some connected speakers will confirm how that 6dB option works.

The 6dB option does toggle the way it's described, i.e. with a tick next to the 'increase' option, the sound is louder. But I do suspect it should actually be described as a 'decrease' and the toggle should be inverted, since that FAQ suggests 0dB is obtained with both output options disabled.

Anyway, with the existing 6dB option enabled, the 0.8dB option disabled, and the ALSA volume set to 92%, the sound is surprisingly loud through a 6 Ohm, 91dB Tannoy 611. I'll wait to find out how they sound through the ceiling speakers before rushing to get external supplies.

[chill]

What are you doing with the IR?

I've enabled LIRC on GPIO17, and my original SB3 remote seems to work perfectly. The IR signal seems unaffected by the PLA of the panel around the buttons. But this system is going into a house where there are no native Slim Devices or Logitech products, hence no compatible remotes, so I think the IR feature will not be used.

[Paul Webster]

The IR support is not limited to working with native remotes.
Getting it to work with others usually just requires working out the mapping for the preferred remote.
Sometimes easier to hit pause on a remote that is sitting on the desk than finding a touchscreen or asking Alexa to stop it.