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I have an old Vivanco MX300 mixer which runs of a 9v battery. I have it in the same place and it's an inconvenience having it run by batteries. Could I use an old AC/DC adapter that would supply 9v at 1A or will it blow my desk.

Funkyguy
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Alexander Harris
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2 Answers2

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If the current rating of the supply meets or exceeds the current demand of the mixer it should be fine. For your example as long as the mixer needs 1A or less, it will work.

ACD
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  • what are the current ratings of a standar 9v batery – Alexander Harris Jul 24 '14 at 18:54
  • You want to be looking at the mixer's specifications, not the battery's. There is no standard current rating for a random 9V battery. You'd have to look at that particular manufacturer's spec sheet. – ACD Jul 24 '14 at 18:56
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    9v batteries are rated generally in Amp-hours, rather than Amps. Shorted out, a 9v battery can deliver a pretty good amount of current for a little while (as in a few seconds) before it explodes. Look at what the mixer needs, don't worry about the battery. – whatsisname Jul 24 '14 at 18:57
  • @AlexanderHarris, a more helpful question would be: How long does the device last before you have to replace the battery? Unless you grab a datasheet for the device you want to power then it'll be guess work. You can draw high current for short amounts of time or low current for much longer - both situations have different power characteristics. – sherrellbc Jul 24 '14 at 18:57
  • if you use 1 amp and it needs less will it not damage the mixer – Alexander Harris Jul 24 '14 at 18:57
  • @ACD i cant find a data/spec sheet because its like thirty years old – Alexander Harris Jul 24 '14 at 18:59
  • @AlexanderHarris, find whatever part numbers you can on the device and search those. Chances are if you look hard enough you will find something. – sherrellbc Jul 24 '14 at 19:42
  • "if you use 1 amp and it needs less will it not damage the mixer" - No, the mixer will just draw the current it requires. – Rev Jul 24 '14 at 20:39
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Batteries have a very "quiet" supply voltage; there is no mains hum or switching spikes as you would find in a lot of DC converters so be prepared to be disappointed should you use one. Also, a lot of DC converters are a bit flaky on low loads and can rise significantly above their "so-called" output voltage.

My yamaha dc converter for my piano is rated at 12 volts but produces about 16 volts on light load. The problem with noise on power lines in mixers should be fairly obvious - you'll get noise/hum on every channel unless internally the device has linear voltage regulators.

My suggestion is pick one that you are sure about but still the question arises of how much current capability a converter would need to be rated at so I suggest you measure the current taken from a fully charged 9 volt battery with audio signals on all channels lighting all the LEDs up.

Once you have this info you are better armed to decide whether 1 amp is sufficient or not.

Andy aka
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  • What does the linear votlage regulator do to attenuate any mains-induced noise? – sherrellbc Jul 24 '14 at 19:44
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    @sherrellbc Linear regs will tend to largely ignore a lot of noise and spikes on their inputs and still produce a clean output. This is why power supplies in a lot of "better" audio stuff use a switcher followed by a linear reg. – Andy aka Jul 24 '14 at 19:51
  • Would that be consequence of the required input capacitance? – sherrellbc Jul 24 '14 at 19:54
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    No, the input capacitance is needed to stabilize the linear reg - the reg has a linear pass transistor that continuously is tweaked by internal circuitry to keep the output voltage constant irrespective of input fluctuations. Obviously beyond a certain point it can't keep up. Take a look at the spec for the 7805 - input signal rejection (or similar) is what you should read up on. – Andy aka Jul 24 '14 at 19:58
  • Fun simulation excercise: Draw a 7805 circuit using datasheet values, with a 1k load resistor. Feed it 12V, with a 2Vpp 60Hz sine wave superimposed on it. Using the simulated values, verify the Spice model's ripple rejection ratio. – Matt Young Jul 24 '14 at 20:01
  • @MattYoung does it work as expected Matt? – Andy aka Jul 24 '14 at 20:04
  • It worked in Multisim a few versions ago. I would imagine it works very well in LTSpice with a Linear Tech part or TI-Tina with a TI part. – Matt Young Jul 24 '14 at 20:16
  • but probably rather poorly in LTSpice with a TI part, and vice-versa! –  Jul 26 '14 at 12:08