Looking for mixer with 12V supply...

[bruce]

A group I’m involved with has set me an interesting challenge. I’m putting together a kit which will have a number of audio items in it, with DC power requirements between 5V and 18V. It will normally be mains powered, but we also want the option of running it from a car battery.

 

Not a huge power requirement - no amplifiers or anything like that.

Running it from mains is easy. I’d rather not use an inverter when we’re running from battery.

 

The kit list so far is:

 

1. a small audio mixer. Something very basic - just needs 2, maybe 4 mic channels, and a couple of stereo line inputs. Doesn’t need phantom, but balanced line inputs would be good. Haven’t identified precisely which mixer it will be yet, but it would be great if it had an external PSU which delivered 12V DC.

 

2. A laptop. It needs an 18V supply; there are plenty of “car laptop PSUs” that should do the job to supply it from 12V.

 

3. a couple of units that need a 5V dc supply

 

4. A unit which needs a USB-type power supply.

 

Running all this from mains is easy - a 4-way extension and 4 plug-in PSUs. Could even power unit4 from the laptop. But what’s the best way to generate the 5V supply from a 12V feed?

 

And any suggestions for a suitable (budget!) mixer?

[ImagineerTom]

Off the shelf in car lighter socket usb plugs for your 5v supply?

[musht]

power everything from 12V and use one mains PSU, either fag lighter plugs or USB sockets for panel mounting, provide a spare for phone charging...

[david.elsbury]

http://www.blue-room.org.uk/index.php?showtopic=66269

 

http://www.blue-room.org.uk/index.php?showtopic=68896

 

Any good?

[Jivemaster]

Do check that your chosen 12v to laptop PSU really likes 12v! I have some that only function when fed 13.4v. They work off a car when the engine is running but not for long off just a battery. Does your intended laptop have a fat battery option? (mine has a 6 cell standard battery and a 9 cell fat battery).

[sandall]

As it's all low-power stuff how about using a cheap 12v inverter from CPC (or your local Maplin before it closes) with a SLA battery, & keeping your 4-way mains strip? There are lots of 2 or 4-mic toy mixers around for under £100), all looking pretty similar.

[Jivemaster]

I think that the DC powered mixer will be the issue. Everything I've seen recently has been 15 - 18vAC from it's own wall wart, it's likely that the quality of that AC will affect or afflict the mixer. Use an in-car multiway lighter socket splitter to get holes for several USB charger adaptors from 12v, be prepared for some to be noisy putting interference out down wires or wirelessly There are some seriously expensive multi USB (5v) outlets available for aircraft use that are supposed to be interference free.

 

Be very careful that going 12v doesn't introduce a (usually now) battery negative rail doing duty as a common ground giving the opportunity for lots of signal grounds being looped by the neg rail.

[richardash1981]

Be very careful that going 12v doesn't introduce a (usually now) battery negative rail doing duty as a common ground giving the opportunity for lots of signal grounds being looped by the neg rail.

That. All the budget/consumer in-car adaptors I have seen have been non-isolated, where as the majority of wall warts etc. are double insulated and so have a floating output. Most of them also put a fair amount of noise between input -ve and output -ve (or maybe the equipment itself does. but you never have problems with an isolated PSU), and that gets into your signal. You either need extra audio isolation transformers, or to go up to isolated DC-DC converters. The latter are easy enough to find as modules (but read the data sheet for the EMC components needed to filter them!) but I haven't seen many ready-boxed examples offered.

 

If it were me I'd be looking at similar modules for driving the mixer - maybe find one that would be happy on +/- 15V DC and then use a pair of isolated 15V output converters.