Layout, making holes, screwing screws

When planning out which enclosure to go with, I made a listing of the dimensions of all the traditional rackmount mixers. I realized that while the Rane MP2016 is very shallow (too shallow for a DIYer to jam everything into that space), I could match the dimensions of the Urei 1620, and that was good enough for me. Still, it took a lot of planning and small adjustments to get everything to work. Set up like this, most of the things fit and work as I originally planned.

Back Left Bottom: PSU (AC to DC +/-)

Back Left Top: phono preamps (2)

Left, Front: VU meter circuits

Center, Rear: relays

Center, Front: audio/power distribution

Back Right Bottom: main audio board

Back Right Top: cue/headphone board

When looking at the mixer this way (from the inside), inputs will be at back left, and outputs will be back right, and the fx loop will be somewhere in the middle. So this way, the boards line up mostly pretty nicely with what they'll be routed to.

Masking the base and marking off points to drill for standoffs:

Aaaand first layer drilled and mounted, shown with mostly completed rear panel and a small amount of wiring completed:

Some uninteresting notes on the rear panel:

Inputs are on the left. Each channel will have 2 input options with a switch at the front panel (channels 1 and 4 will be Line/Line, and channels 2 and 3 will be Phono/Line). Phono jacks have a grounding post below them. The tape out has a switch below it and that'll be to switch the tape output between pre- and post-fx. Versatility/why not. There are 2 linked power plugs, one of which will allow the same wall wart plug to be used to power the isolator I will eventually be adding..

Back in the saddle; a total repackaging

Some updates in case anyone stumbles across this:

First, obviously this project was shelved for a while. Literally. I moved about 5 years ago, and the mixer (until very recently) has sat on a shelf in my new house since then. As I found myself lusting after many of the new boutique rotary mixers coming out (E&S, Taula 4, Condesa Lucia, Mastersounds, and so on), I realized I should probably get my own project finished and I could end up with something on par with these (save some shortcomings on the fit-and-finish).

I was never really happy with the enclosure, or the layout, and I had half-assed some of the wiring with the idea that I'd re-do it to a better standard later (hah). I mean, check out this mess:

So all the boards got torn out of the old box, a new rackmount enclosure from Hammond Mfg was ordered, and new connectors and some various other parts were ordered from Tayda Electonics.

And thus, re-construction began. First, using a couple small stripboards, I made up these distribution boards for audio and power. The signal needs to pass through caps before each main channel volume knob, and resistors after, then the resistors need to join into just one set of L/R outputs. There is also a 2-ch strip for audio distribution post-fx-return, a 2-ch strip for cue audio distribution, and a 3-ch strip for power distribution (+, ground, and -). Still a couple caps and connectors to be installed here, I think they were still on order at the time.

For the cue select, I previously had a rotary dial for cue select, and an LED on a each channel which would come on if that channel was selected for cue. But I wanted something more slick. So I ordered some relay boards off Amazon, and found a good price on some illuminated pushbutton switches on AliExpress, and plan on having push-button cue select running through relays. I will also use a relay for turning the FX loop on and off. My hope is that since these relays seem to use the appropriately placed diodes, there will be minimal "pop" and one will be able to turn the FX on and off without much fuss in the middle of playing music. I will hopefully eventually be using the loop with an isolator, but we're not there yet. Here are the relay boards:

Next up: laying it out and mounting PCBs

Test Mix #1

Wiring more bits, and a shot of the faceplate

I'm mostly at an impasse right now until I receive some shielded audio cable I'm waiting for Fedex to deliver, which may take a while. Apparently the package arrived in Chicago a week ago, then went up to Wisconsin, and is now back in Chicago and "In Transit" as of 4 days ago.

In the meantime, I'm trimming the shafts on the pots down so that the knobs sit at the proper height, and I wired the cue select LEDs. I'm not sure which knobs I'll be using for volume yet, so I am waiting to cut those down. One thing I discovered is that it's extremely difficult to cut something that rotates with a hacksaw, especially if you don't have a vise. The cutting wheel on my Dremel made quick work of the shafts though.

The cueing will be 1 channel at a time, with a blend between cue and master. The channel is selected via a rotary knob. Here's a shot of the LEDs in action, but obviously no audio yet (but at least I'm on track). This is the first visible sign of life from the mixer.

Primer, paint, sanding, etc

I decided to go with flat black for the base of this mixer, and a gloss ivory for the top. All of the features on top (knobs, dial plates) will be silver and black, so it should look pretty sharp against the off-white.

Just a tip: make sure your primer is compatible with your topcoat. Mine weren't, and I had to completely take the base and faceplate back down to bare metal with steel wool and a sanding block. It was not very enjoyable. I started with some generic old primer, and when I used a Krylon top coat it just dissolved the primer and everything wrinkled up and cracked. I ended up using a combo primer/topcoat from Krylon on the sanded metal, and everything is looking good so far. Here's a shot of the base with a couple connectors installed for the photo op.



Below, you can see the faceplate. I'm still adding layers to this one, I want to take my time and get a nice finish on it.



The vertical lines of holes on the left will be for the vu meter LEDs, mounted in metal bezels. The 4 holes on the bottom will be for the main volume knobs for the 4 channels, with the cue select LEDs mounted above them. Above that are the pilot holes for bass EQ, which will come later. The top 3 holes on the right are master, booth, and headphone volume, and under that is cue select and cue/master blend.

Case prep

The case is from Hammond Manufacturing. They had plenty of options. I would have liked something more compact but I thought it best to err on the side of having too much room to work with rather than not enough.

I started by designing the mixer layout in Illustrator - took a while for me to decide on spacing and arrangement on the faceplate. The rear was pretty easy. I used a sharpie to mark the protective coating on the aluminum case, then made pilot holes with my Dremel.



Then, the drilling of the holes. This led to a lot of tiny aluminum shards on the floor of my apartment, one of which hitched a ride in the bottom of my foot for a couple days.

Boards soldered

A quick shot of the soldered audio boards and the power supply, sitting in the unprepped case. Not too exciting yet. More to come.