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[Kits avaliable] 4sum - standalone portable audio DIY mixer
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author [Kits avaliable] 4sum - standalone portable audio DIY mixer
syntherjack
After bunch of drum circuits, I finally decided to make something useful - a simple, monophonic  portable audio mixer with 4 inputs and 1 output with separated level controls for each channel. I designed this one for one reason: I did not have any mixer for my Monotrons and other "toys"! It took me over a year to make it as I imagined (although the design is not very complex).

A short story of development

I wanted to make a device without other small mixers problems, so I read tons of reviews and noted other people complains. Among others, the most often repeated:
- poor battery life or no battery option,
- low quality potentiometers,
- output 180° phase shifted (which in some setups caused signal to cancel),
- mono output for mono mixers (only one speaker plays after you connect mixer to amplifier).

Then I’ve added my own thoughts and experiences:
- output level control – “Who is playing loud on those damn Monotrons! Turn down the volume!” – very usefull on synth meets if you don’t want - to run every 10 minutes to main mixing console,
- no channel mute if it can’t be done right (without loud pop sound) – I’ve got kicked out from one synth meet for this confused So, pop generation chance should reduced to minimum,
- all connectors on top to avoid unnecessary mess with cables going on different sides of device,
- power supply from 9F22 batteries – quite cheap, popular, gives plenty of headroom and you can buy at as USB rechargeable!

Thats how 4sum portable audio mixer was born smile

Circuit is very simple and is based on dual opamp (TL072), you can check the schematic here: Schematic of 4sum mixer

PCB & enclosure

PCB size is 93×60 mm and was mostly defined by comfortable distance between potentiometer centers (16 mm). There are not many components but I’ve tried to place them in a way that no additional description is needed. The unusual battery holder (I am very proud of) is build into PCB and takes advantage from devices “sandwich” design.



I also made few enclosure prototypes, dissed in a nasty way by my girlfriend. I loved the look of a real simulated wood, but I dumped this idea and moved to plexiglas panels.




The final device

I wanted my mixer to be clean and elegant, with basic functionality. There is no description of front panel, I tried to make everything clear from the first look.




I don't want to put to much boring cat/synth stuff here, the full story of design, errors and testing is on my blog: https://syntherjack.net/portable-audio-mixer/

Features and specs

Main features:
- 4x mono inputs,
- 1x stereo (double mono) output,
- long battery life (average 100 hours),
- output in phase with input,
- designed for portability,
- LED on/off indicator.

Mechanical data:
- size:
- - without knobs : 93 x 60 x 29 mm,
- - with knobs : 93 x 60 x 35 mm,
- weight:
- - without battery: 90 g,
- - with battery: ~120 g.

Electrical data:
- max. input signal level: 6 Vp-p,
- max. amplification x2 (+6 dB),
- power supply: single 6F22 battery,
- current draw: ~5,5 mA @ 9V,
- battery life:
- ~100 h (average cheap battery),
- up to 200 h (lithium battery),
- works with rechargable USB batteries.

Full kit can be ordered via patch.audio shop: https://patch.audio/en/product/syntherjack-4sum-full-diy-kit/
Hope you like it!
Cheers
Jack
patch.audio
I can recommend that product! wink
grenert
syntherjack wrote:
I don't want to put to much boring cat/synth stuff here, the full story of design, errors and testing is on my blog: https://syntherjack.net/portable-audio-mixer/

Of course, once I saw that, I had to go look for the kitty on your blog and found cute Totoro!
Very nice little "useful" project! hihi
I appreciated all of the testing data; thanks for sharing it.
patch.audio
grenert wrote:
Of course, once I saw that, I had to go look for the kitty on your blog and found cute Totoro!
Very nice little "useful" project! hihi
I appreciated all of the testing data; thanks for sharing it.


Yep, he is THE MAN! wink) There will be much more portable devices projects from Syntherjack available at https://patch.audio soon. Follow us on facebook to have latest info!
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