So far I have found that running the MixPre with the AT3032's using the 15 volt
phantom power setting seems to cure the problem and there is no motorboating
and I do not need to engage the 80Hz filter either leaving me to record full
Someone was concerned that running the AT3032's on 15 volts might cause a
problem with headroom, this does not seem to be the case. As the AT3032's vari
the current drawn depending on the level they are producing rather than voltage
then 15 volts should not be a problem. If the microphone varied the voltage
depending on level then yes running at 15 volts might well prove a problem.
----- Original Message ----
From: Rob Danielson <>
Sent: Thursday, 29 November, 2007 3:11:53 AM
Subject: Re: [Nature Recordists] AT3032 and instability in Sound Devices MixPre
and 302, 442, MM-1, M
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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