I've just bought 3 more RaspberryPi's, two of them model A to be used
has an Airplay speakers.
I'd like to have your input about the best cost/quality speakers to be
user with RaspberryPi.
I was particular interested in amplified speakers (auto on/off, like pc
speakers), specially if they already have a power adaptor capable of 5v
(>2A) that could be used to power both the RPi and the speakers.
All ideas are more then welcome. ;)
Putting regulators in parallel is in general a Bad Thing. They all
have a very slightly different output voltage, i.e. point at which
they try to regulate, because of inevitable production tolerances.
The consequence is that the regulator with the highest output
voltage tries to supply all the current, which it does until it goes
into current limit, and then the on with the next lowest output
voltage will start contributing, etc.
The current is not shared equally between the regulators, in other
words. Some will be more highly stressed than others.
Although paralleling 'same voltage output' smpsus to boost current
rating is generally a bad idea. This arrangement can be used with
smpsus designed to safely operate indefinitely in current limited mode
(designs with well defined maximum output ratings that don't
overstress any of its components) and also designed to tolerate being
hooked up to a power bus that can vary above their set voltage by a
reasonable margin beyond the normal range of preset voltages used by
A system comprised of a bank of such smpsus can be arranged so that
as the load demand increases, successive smpsus will cut in to
stabilise the voltage at a slightly lower level (usually a few
millivolts drop for each successive smpsu).
Assuming a bank of 5 10amp rated 12v smpsus numbered 1 to 5 are
provided to service a load that varies from less than ten amps to a
max of 50 amps with smpsu 1 set for 12.04v, smpsu 2 set for 12.03 and
so on with smpsu 5 set to 12.00v we can wire each of them up to the
mains with a suitably calibrated ammeter to display full deflection at
max output and emulate the metering scheme shown in the movie
This may have been a practice with mainframe computers for a form of
redundency and modularisation (but without the "Forbidden Planet"
metering effect and, therefore without any need to calibrate output
voltage to achieve a predetermined cut in effect). However, I might
just be making this bit up... Time to google.
The only reference I could find to paralleling DC supplies was near
the bottom of this page:
Not exactly what I was looking for. Perhaps someone else with a
knowledge of mainframe power systems might be able to offer a clue.
You're probably best looking the other way around - find USB
_powered_ speakers and then power both from the same self-powered
hub. Note that clarification - strictly USB speakers essentially
have a soundcard built into them, you want the simpler kind with
an analog audio connection, e.g.
Yes, that's my current set up with a Airpot Express that outputs audio
and current to a set of those speakers, but the audio is really low quality.
So I was looking to build something my self for a bit better quality,
eventually with a box big enough to insert the RPi in, or simply paste
it at the side with some dual-faced tape. :)
I will continue to search and let you all know if I find something
average that could be used for this.
Anything that lives of 5 V is never going to be all that good. There
just isn't the energy available 5^2/4 = 6.25 W at the very best. Why
bother spending money on decent drivers, cabinets, etc ...
That would be the way to go, presumably the 5 V @ 2 A requirement is
to power the RPi? Or get some decent self (mains) powered speakers
and either fit a suitable DC-DC convertor on the the DC rail for the
amp or a USB power supply across the mains for the RPi. You may be
able to find powered speakers with both amps in one box and the other
box just has a speaker connection.
Yes I start to think the way to go is having a DC-DC converter (ex.:
12->5v) to avoid having two power adaptors, and paste the RPi inside or
on the side.
I have a pair of PC speakers from JBL (14W "Media 3") with an active
subwoofer, and maybe I'll dig a bit into them to see if they suit my
immediate needs. :)
There is no way to tell about the noise unless you buy one and hook it
up. But you realize that this uses 12 volt power as the source and
produces 5 volts? I thought you were looking for something to up the 5
volt supply to 12 volts for an amplifier?
The problem Dave is describing is the fact that to drive speakers to
significant power levels, you need a higher voltage than 5 volts. But
you also need the power. 5 volts at 2 amps is 10 watts. It won't
matter if you up the voltage to 12 or 24, the 5 volt, 2 amp power source
will always be limited to 10 watts. However, 10 Watts is not a low
volume. If you actually get 10 Watts into your speaker, that is a
significant power level.
What is your power source for this project? How loud do you need this
to be? I can't imagine there aren't products out there to do exactly
what you want without cobbling together a jury rig. If there's not, let
me know and I'll design something and sell it :)
Of course, there are plenty of H-bridge speaker amps, which could provide
about 25w to a 4-ohm speaker. A transformer (unlikely in small speakers)
would also allow significant power to be delivered.
I assume, since the OP asked about PC speakers, that a few watts was
plenty. (That and the 6v, 1A presumed speaker power supply--with 1A for the
-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon
10v peak to peak is about 3.8v rms or 3.7W rms into 4 ohms: From 5V in
Roughly speaking you can 5W from a 12v car supply or in bridge 25W at
'full charge' 13.8v by bending the numbers a little
how LOUD is far more about the speaker itself than the power. there can
be 20:1 ratios in loudness between different loudspeakers at similar power
(in-ep-toc?-ra-cy) ? a system of government where the least capable to
Sim I'm not a electronics guy, I'll try to keep it simple and low-cost.
The idea is to use the same power-supply from the speakers to power the
RPi, and since these JBL I have here are 13.5v I was looking to extract
from it 5v for the RPi.
But thank you for the help. I might come back with some electronic
(dummy) questions. ;)
a fairly simple linear or switching regulator will do that for you.
The ones made for radio control models are useful - they take a typical
flight battery in the range of 8-40V or so and down convert to a
respectable 5V with serious current capability to drive servos etc.
Normally built into the speed controller forte electric motors, but they
are available standalone.
They are very low noise - have to be to work with sensitive SW and UHF
is a very neat device designed to be pin compatible with a typical
linear 5v regulator.
I have used the company before - top quality design engineers.
(in-ep-toc?-ra-cy) ? a system of government where the least capable to
First you would need to check that the JBL power supply has the
capacity to handle an additional load.
The simplest form of regulator would be a linear. Assuming about 300mA
for the pi (i.e. nothing plugged into its USB ports), that would mean
4 watts split between the pi and the regulator. Of that about 2.5
watts goes into the rergulator, so you would need a pretty highly
rated one and equip it with a heatsink. (The 1 amp 7805 type won't
cope with the heat - it will keep shutting down as it overheats.)
You would be better using a switch-mode converter. I don't know of
specific models, but as the requirement is identical to powering USB
devices from a car, they should be fairly easy to find.
Alan Adams, from Northamptonshire
None of the mainframes I used (ICL 1900 and 2900/3900 systems) had
redundant power supplies: it was just that each box in a system (DFC,
disk drive, OCP, bank of tape decks, etc) had its own power supply and
the computer room might, if you were lucky, have a UPS capable of running
everything in the room.
However, the fault tolerant kit I've used (Tandem NonStop [now HP NonStop]
and Stratus [also badged as the IBM System/88]) all came with dual power
supplies. Normally both would be running, but either could fail and leave
the system running on the remaining PSU.
martin@ | Martin Gregorie
gregorie. | Essex, UK