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Re: AT3032 and instability in Sound Devices MixPre and 302, 442, MM-

Subject: Re: AT3032 and instability in Sound Devices MixPre and 302, 442, MM-
From: "Rob Danielson" danielson_rob
Date: Mon Dec 10, 2007 8:09 am ((PST))
At 9:42 AM +1100 11/29/07, Paul Jacobson wrote:
>On 28/11/2007, at 11:16 PM, artsonics wrote:
>>  4.Power the mixer from an external DC power supply....just great when
>>  yer miles from now where.
>external dc power supply = battery pack _or_ ac adapter.
>I'd personally prefer to carry extra weight in the form of a battery
>pack, which would allow the mixer to perform as designed and give
>extended run time, than to add a dedicated phantom supply.

I agree. It would be prudent to try a higher voltage battery first. 
Test this with a car battery? That said, I have encountered the 
modulation with Rode and AKG mics when running an MP2 and MixPre on a 
12 volt battery pack. The problem seems to be a specific mic<->pre 
relation.  If the motor-boating persists when the gain is 3/4 or 
less, I suspect the external power solution might resolve it. Taking 
the phantom power load off 302/MixPre with a Rolls PB224 has always 
worked for me. The Rolls can be powered from the same 12 volt battery 
sled as the 302/Mix Pre. One need not worry about the Rolls PB224 
adding audible noise. Rob D.

>From the tech note it sounds like the source of the problem lies
>with limitations using internal 2or3xAA cells to power the SD mixers.
>Using an external 12VDC power supply should result in less
>sensitivity to current fluctuations. The easy way to test this would
>be to check how the mixer performs with the AT3032's while powering
>the SD mixer from wall power adapter. Running off an external battery
>pack should give similar performance to the wall adapter as it should
>remove at least one stage of voltage boost from the power supply and
>reduce sensitivity to current fluctuations. According to the SD web
>site their mixers can run from 5-18VDC external so there is a wide
>range of battery packs that would work.
>I'd suggest looking at a 7.2V tamiya type pack as a minimum or
>alternatively a12V Li-Ion pack. You'd also need an adapter cable to
>run either of these packs into the hirose plug on the SD mixers.


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