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Old 14th January 2013, 06:59 PM   #1
basite is offline basite  Belgium
diyAudio Member
Join Date: Nov 2011
Location: Antwerp, Belgium
Default portable set field mixer/ mic pre

Hi all,

somewhat my first post/thread here, longtime lurker

I am planning a pretty ambitious project (for me, anyhow):

I am a film school student, studying sound engineer. I do alot of student films, where there was no real budget for sound equipment, or the sound equipment provided was not ideal for on the spot mixing. Things like a zoom H4n or tascam equivalent are very common. And as a recorder function, they are good for what they are (except the mic preamps, noisy as hell on those zooms). But for on set modulation, the are not handy at all. For quality reasons, and when I am not alone on a set, I also use my focusrite interface to record straight to my laptop. Again, modulation is hard. Pretty much setting at a safe volume, and letting it stand there, and make adjustments between takes.

therefore I was thinking of this:

a portable field mixer. 4 microphone preamps (switchable between mic & line inputs), led VU or PPM meters, for each input. A headphone "amplifier" for listening to the inputs, if possible with various listening modes ("stereo" mix, mono (mix), or listening to one input individually (i think this might be the hardest part, and if possible can be limited to fewer options), and a "return" channel, to listen to the recorder return (this is easy).

the mic preamps should include a -20db pad, phase inverter and a low cut filter per preamp, each channel should be able to receiver phantom power.

Also, a gain trimmer should also be useful. (with professional set mixers, there is a gain pot, and a extra gain/trim control after the gain control to make the actual mix. Giving more gain and reducing volume (like the fader on a mixing desk)

I told myself that I should be able to route the independent channels to a Left or Right "bus", but most of the times I will be able to record 4 channels seperately. But a more simplified version where I would be able to sum channels 2,3, and 4 together to one output (or a combination of those) could be an option too. every output should be balanced/floating...

Extra difficulty: It has to be able to be battery powered! AND be portable, the smaller the better I guess.
for saving battery usage, when I am recording on a set with my laptop, or with a recorder on a steady location (with net power supplied), I would like to build it so that the "mixette", can also receive power from a regulated DC supply (external) (this, I don't see such a difficulty, but I think it's important nonetheless)

I was thinking using 4 9V batteries to create a +-18V supply, and 2 more 9V batteries (in parallell), for the phantom power circuit (seperately). I found a schematic somewhere, creating +48V from a single 9V battery. Anyone have similar ideas here? I could also use 5 9V batteries, but I'd rather not have to carry around 20+ 9V batteries all time in case they have to be changed...

I am now in the phase of wild ideas and lots and lots of reading here and on the internet in general, books etc, and deciding what route I would like to take.

For now, I think that, due to cost and space constraints, I would like to try a THAT 1510 based preamp. But I am looking for opinions and advice.

Also for the meters, anyone has made a DIY version of a PPM led meter small enough for my situation? would it be possible?

Anyone else made a similar project already?

I have designed and built various turntables, and small electronical devices and tools (in the audio genre), so most case design and building will also be done "in house". I really like the challenge of building everything myself, so cases and knobs are no exception.

I am open for all suggestions and improvements. in the meanwhile, I am starting on mock ups of the circuit design

Thanks for any help, in advance
I hope this will be an interesting project.

Keep them spinning,

Last edited by basite; 16th January 2013 at 09:02 PM.
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Old 29th July 2013, 07:54 AM   #2
diyAudio Member
Join Date: Jul 2013
Hi there,
Any update on this project?
I'm designing something similar at the moment and would be interested to hear what you've got so far.
As far as batteries are concerned, I think you'd be better off going with Lithium Ion NP-1 batteries that connect via a 4-pin hirose connector. These are expensive, but they are what all of the professional grade mixers (Sound Devices, SQN, etc.) accept and well worth the investment, especially if you're going to be using phantom on a 10 hour shoot.
They give out around 15V.

Did you set a budget and case size for your build?
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