Mixer 1

This unkempt box is the first DJ mixer I built years ago, and has served my living room without trouble since then. The whole thing is just a mishmash of opamp circuits from Douglas Self’s Small Signal Audio Design, even the headphone amplifier is just made up of 2 cascaded NE5532 ICs.

This started its life as a six channel Realistic 32-1210 audio mixer intended to accompany a home video editing setup. I was given it and pulled it apart without any idea what I would do with it. It loitered in a box for a few years until I was having a party and wanted a DJ mixer for it. Rather than borrow anything I whipped this up in a few days, which is more of a testament to how basic it is rather than to my skills as an engineer. Every single part was taken from my junk boxes, except for the main piece of veroboard which I purchased at a local shop. The power supply is external and was built into a industrial junction box. I think the transformer I used was originally in a Roland SH-3A monosynth…

The signal flow is very basic, two phono preamplifiers and a line buffer take care of the inputs. These are run into a summing amplifier and then sent to the output jacks. This signal is tapped for the meter amplifiers. Each channel also runs to the cue selection switch then to the headphone amplifier. I was actually surprised at how well it worked considering the shambles inside the box. I didn’t pay much attention to well thought out grounding and the wooden case isn’t even shielded. Four or so years down the line and I never actually screwed the thing together properly so it was very easy to open up and take embarrassing photos of. I never even screwed the PCBs in to place. As you can see the front panel is pockmarked with holes from its previous life as a line mixer, pretty ugly.

Anyway, hopefully this will inspire people to see what you can do in a weekend if you need to. It is always kind of humbling to open up an old project and realise just how crappy it is.

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Mixer 1 – Summing Bus
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Mixer 1 – Phono preamplifier 1 of 2
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Mixer 1 – Main PCB, from left to right: Summing Amplifier, Line Buffer, Meter Buffer and trim, Headphone Amplifier.
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Mixer 1 – The mixer in its messy glory.
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Mixer 1 – Front Panel and Enclosure.

Enjoy!

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