Phat Beat and powered/active speakers...?


#1

Hi folks

Would/should I be able to connect powered speakers to a Phat Beat?

I have a old set of PC speakers (these, basically, although a few years older) - it’s a powered subwoofer which the satellite speakers plug into, with a left/right phono input into the subwoofer.

It works just fine with a 3.5mm jack plugged into a “full size” Raspberry Pi, but I’m trying to use Phat Beat on top of a Pi Zero - I’ve stripped the connectors off one end of a phono cable and I’m pushing the exposed wires into the “R” and “L” connectors on the underside of the Phat Beat. But, no sound.

I’m fairly sure it’s not a software issue - when I try the speaker-test test on the Pimoroni set-up page the LEDs light up, so a signal is getting to the Phat Beat.

I also know that just jamming exposed wires into the connectors isn’t ideal, but before I go down the path of buying a soldering iron to tin them, and/or digging deeper in the software to diagnose that, I want to make sure I’m not on a wild goose chase in the first place.

I’m surprised that I can’t seem to find anything online (Pimoroni forums or elsewhere) where someone appears to have tried this, so I’m thinking that maybe it’s obviously not going to work and I’m crazy to even try, but… any thoughts?


#2

Just a wild guess. You should connect to the terminal marked with +


#3

I did it, kind of sort of. I had an old set of Logitech R20’s. The built in amp had died. I took the subwoofer out of the box and mounted my Pi Zero and pHat Beat in it. The Vu meter is visible through the speaker cloth. I then connected the speakers to the + - on the pHat Beat. One speaker had the amplifier board in it. I striped that out and bypassed it so the speaker wire goes right to the pHat Beat. My build pictures are here.
https://1drv.ms/f/s!AjOYwiwlwDtpgrJY6ORLsK5AVpwNuw

Originally I just tined the original speaker wires and used them. What I do is press down on those release points on the terminals on the pHat Beat with a screw driver. Like what you do to remove the wires. Then slide my wires in and release. Works a lot better than jamming the wires in, IMHO. Just gently press down until your wire easily slides in.
Now I have some RCA jack pig tails hooked up to make speaker disconnect and connect easier. No having to mess with those connectors on the pHat Beat.

Make sure the speaker switch on the under side of the pHat Beat is switched to Stereo and not Mono.


#4

If your trying do drive them via the original line in that plugs into the PC, you may have issues. Number one is its a low level input on the speaker amp. It’s looking for ear bud level audio not amplified audio. You’ll have a signal level miss match and impedance mismatch. Not saying it won’t work, just make sure your volume control on the amplifier is turned way down. Now since its a Tip ring sleeve jack there are only 3 wires. Tip will be one channel, ring the other, and the sleeve will be a common ground for both. Connect tip to one of the + terminals on the pHat beat, Ring to the other + terminal, and ground to one of the - terminals. I wouldn’t short the two - terminals together just yet. I don’t know if that is a bad thing or not. @gadgetoid would likely know if its OK. Even with just the one - hooked up one speaker should work to let you know your on the right track.


#5

Looking at the spec sheet of MAX98357A it seems output terminals are “floating” , so therfore I support the idea NOT to tie the -terminals together. I hope @gadgetoid could reveal the output circuit of phatbeat. As an example stopping the service with “sudo service vlcd stop” can cause totally different DC-levels on L and R terminals.


#6

The ICs aboard pHAT BEAT are definitely not suitable for this- at best you’ll get some approximation of the audio signal, but I suspect it’s more likely going to be subject to loss and distortion due to travelling through two amplification stages.

I’d grab a pHAT DAC and just add that underneath the pHAT BEAT. It’s possible to have two or more (I don’t know the practical limit) DAC products running from the same i2s signal since it’s a write-and-forget output in this case.

The speaker terminals are connected directly to the MAX98357 with nothing between. Shorting the terminals together would - at best - result in terrible audio quality and - at worst - would cause enough voltage drop to brown-out your Pi. Don’t do it :D


#7

Amazing, thanks everyone!

So a couple of speakers like this wired directly into the pHAT BEAT might be a better option…?


#8

They will work. I have two of them wired to an analog amp in one of my Pi Projects. Sound quality was good if I remember correctly. I haven’t used them all that much lately. I was using them with a Software Defined Radio dongle at the time. Mostly voice communications not music.