MixPre Discovery

[Peter C.]

I solved an issue I'd been having for a long time with my MixPre. I'd been getting a hum with lavalier mics. I thought it was the fault of the mics turned out to be a grounding issue with the mixer. I can't explain the science behind it but its related to a ground loop.

When I bought my MixPre 6, years ago, laughably the only way to power it is batteries that last only 10 minutes or usb-c port that only certain cables and power supplies will work. The third option which I picked was to buy $100+ 3rd party adapter that replaces the battery cover to convert it a Hirose power plug allowing you to use a standard Sound Device power supply.

Of course the Sound Devices power supply must be purchased from them for around $140. Instead I opted to purchase a 3rd party power supply with Hirose connction.
It turns out that these supplies which are described as for Sound Devices lack one important thing, they only have a two prong a/c plug. Without a third grounding prong, static electricty from any source (including yourself) coming in contact with the metal body of the mic, xlr plug, or phantom power adapter can travel back into the mixer causing a hum if the devices isn't using a power supply that's grounded.

 

[IronFilm]

What batteries are you using now?

eSmart batteries are what people usually use. Some old school people would still be using NP1.
Or maybe because you're from the camera dept (I guess), then you're using V Mount?? (or even Gold Mount??)

When I bought my MixPre 6, years ago, laughably the only way to power it is batteries that last only 10 minutes or usb-c port that only certain cables and power supplies will work.

If you use quality rechargeables rather than single use alkaline batteries (what I'm guessing you were doing) then you'll get significantly more run time. (still certainly not appropriate for a full day's shoot! But that's normal, nobody should ever be running their field recorder only on internal AA batteries, using external batteries, usually with a BDS, is the normal way everyone does it)

The third option which I picked was to buy $100+ 3rd party adapter that replaces the battery cover to convert it a Hirose power plug allowing you to use a standard Sound Device power supply.

There are a few other options, such as an adapter for NP-F batteries.

It turns out that these supplies which are described as for Sound Devices lack one important thing, they only have a two prong a/c plug.

AC? Surely you meant DC?

 

[Peter C.]

I'm talking about a standard power supply that plugs into a wall outlet. They come in 3 or 2 "prongs". I use the mixer almost exclusively to record depositions that often go all day. In my application I want AC power that I don't need to maintain batteries and the subjects are sitting at a table so there is no need for mobility.

 

[IronFilm]

At the power end, yes it is AC. But the accessory you have on the MixPre is not AC, that's a DC connector.

Sounds like maybe you just have dirty power feeding it, probably due to some old buildings that the courts are in.

Get a cleaner power supply? Or honestly, just running purely on battery power is easier and simpler than you think, a single big 230Wh will run your bag for the whole day! (honestly probably a battery half that size will be enough for your little bag, as it doesn't need that much)

What receivers are you using, how are you powering them?

 

[Throwback]

...nobody should ever be running their field recorder only on internal AA batteries...

Goodness David! I have had a MixPre-3 since they first came out in 2017, bought a few external power options then, but invariably - over the last 7 years of heavy use - have run it on Eneloop Pro AA rechargeables. Comfortably, gives me 2.5 hrs on a set of 4 batteries, with 2-3 P48 mics, and I can swap out the AAs in seconds. Have not been caught out once in all those years. Keeps the miniscule form of the recorder intact (one of its attractions). Others may well have good reason to use external power even with such a small field recorder, and I, for one, wouldn't tell them what they 'should' do!
Cheers,
Roland

 

[Peter C.]

Goodness David! I have had a MixPre-3 since they first came out in 2017, bought a few external power options then, but invariably - over the last 7 years of heavy use - have run it on Eneloop Pro AA rechargeables. Comfortably, gives me 2.5 hrs on a set of 4 batteries, with 2-3 P48 mics, and I can swap out the AAs in seconds. Have not been caught out once in all those years. Keeps the miniscule form of the recorder intact (one of its attractions). Others may well have good reason to use external power even with such a small field recorder, and I, for one, wouldn't tell them what they 'should' do!
Cheers,
Roland

I was off with the runtime because when I tested it with AAs, I didn't realize they were near the end of their life cycle. The voltage would drop off a cliff under a load with in 10-15 minutes. This why only use batteries when I have too because you can be unware of their health as they slowly degrade.

I also rigged up a nice USB battery bank option that's the same width and thickness of the mixer velcro to the battery compartment door. But I use this for depositions that can go over 7 hrs and I'm phantom powering and iso recording 4 tracks. For my application I don't need the chore of maintaining any batteries for a stationary job.

Btw, I tested my mixer today with the power supply that was at issue and there was no hum. With the summer humidity there's no static electricity being generated. That's why it was so hard to track down this hum because it took a specific condition for it to occur.

 

[Jim Feeley]

I'm still powering my bag with NP1 batteries, but will probably move to Smart Lithium batteries soon. I have an Anker power bank with a USB-C connector that I've used with my Fujifilm X-T3 camera, but I'm wary of relying on (and not damaging) USB-C in a sound bag. Maybe for depositions where I'll guess you're not moving once you're rolling, that's not a problem.

But for Smart Lithium... IIRC, Inspired Energy created (and builds most of) these batteries. But they're sold (and integrated into cups and related bits) by several sound-focused companies... A good location-sound dealer probably carries and/or can get any of these.

Inspired Energy: https://www.inspired-energy.com/

Audioroot eSmart line: https://www.audioroot.fr/

Remote Audio HiQ line: https://remoteaudio.com/products/power/hi-q-batteries/

Deity Smart Battery: https://deitymic.com/products/#power-solutions

I think getting rolling with battery, charger, cup+cable will run $250 and up (ie- do you want a distribution system to power mixer & receivers, IFB TX, etc).

 

[Peter C.]

I stayed away from powering it with the USB-C for many reasons. The connection doesn't lock, while I'm stationary it would be easy to kick the cable. I also didn't want to test the longevity of the connection. Once you use Hirose it's hard to go back. Both the cable and adapter must support the high power demand of the mixPre. Finally the USB-C connection is in a cramped location.

I would spend the money for a high end battery solution you listed if I need to be mobile.