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Uraltone Mixer and Spring Reverb (and some synth literature...)

DIY kits and literature

Bjooks and DIY kits

Every now and then I had seen pictures of the beautiful and super interesting Push Turn Move book by Kim Bjørn: https://www.pushturnmove.com/. Unfortunately it's not available as an eBook and the price has been too high for me because of the shipping costs. Some time ago Bjørn launched the Kickstarter campaign for his third book Pedal Crush. All the buzz it generated in social media led me once again to the Push Turn Move web page. This time I was delighted to find our local DIY music electronics store Uraltone in the reseller list. Of course I had to buy both of the already published "Bjooks" immediately and while at it I decided to buy some Uraltone eurorack DIY kits too. I have wanted a spring reverb since the days I got my first electric guitar and another mixer in my eurorack wouldn't harm. After a short bike ride to Uraltone I had my back bag full of reading and soldering! Support your local!

Uralkit Spring Reverb

Here's a link to the kit: https://en.uraltone.com/kits/synth-kits/uraltone-euro-rack-series-spring-reverb-kit.html

Building a project from a kit with high quality PCB and all parts included was nice for a change. I have recently had my share of sourcing headaches and more or less crappy stripboard builds. The kit has a main pcb and an additional connector pcb. They are cleverly joined together with angled connectors. Everything was perfect until I got to the point where potentiometers needed to be soldered. PCB and panel was done for pcb mounted pots but one of the pots was normal wire connector type pot. A nasty hack had to be made to mount it and I wasn't able to make it that robust. I hope it doesn't fall apart anytime soon.

Starting point. Big reverb tank with 3 springs, a panel and a PCB.

So far so good. Fast and easy build...

...until potentiometers came along. Notice the non-PCB-mount type pot in the middle. Molex connectors for reverb tank also still in place.

Hacky modification to mount regular pot directly into PCB.
Unfortunately that one pot wasn't the only painful potentiometer issue in this module. At least on my kit there were several different types of potentiometers included. One 9mm mini pot with plastic shaft, 2 pots with knurled shaft, 2 pots with D-shaft and one with the 6.3mm shaft. It's nearly impossible to mount same type of knobs on all of these! I ended up using my default choice, the green Davies 1900h clones but had to mount them in a weird angle on the D-shaft pots. I should probably get proper pots for this one but I'm lazy and will probably just get used to this weirdness. My synth is anyway full of ugly and weird panels and potentiometer knobs.

6 potentiometers, 4 different shaft types. What knob type would fit all of them?
The final source of pain in this build was the spring tank cable. Molex KK connectors were provided but trying to crimp those into a coaxial cable ground wire that has no insulation around it was just too damn difficult for me. After several failures I just took connectors away and soldered the cables. It's less reliable and moving the module is now really difficult but I'll just have to live with that and re-solder if something breaks.

After several frustrating retries Molex connectors were thrown out from the board.

Mounting the Reverb Tank

The problem with every spring reverb module is that it's not really a module that can be easily moved around. There's always a big reverb tank that has to be mounted somewhere. When ordering the kit I chose the biggest Accutronics 9AB2C1B tank because it was recommended over the smaller ones and my rack had plenty of room on the sides. Only when building the kit I learned that spring tank mounting orientation matters and there's slightly different tank models for different orientations. Mine was supposed to be mounted horizontally with open side facing down. (Last B in the part code tells the orientation). I was worried that it wouldn't work and I would have to do some tricky carpentry to install it but after some testing I just ended up mounting it vertically like I had originally planned. I didn't hear much difference so didn't bother with extra work. My ears aren't that accurate so this works for me just fine.


Reverb tank mounted completely against the specification. Sounds just fine to my ears.

Ready! Unfortunately the only way to install these knobs to D-shaft pots was so that the indicator shows completely wrong position compared to the other pots. I should probably order more suitable potentiometers for this one.

The Result

Even though pots and spring tank wiring caused some pain I enjoyed building this kit a lot and the result is stunning! It sounds really good and I'm probably going to use this one a lot. I need to try it with guitar too.

Uralkit Tube Sounding Mixer


It was originally designed as a standalone mixer for guitar and synth applications and later converted to eurorack format.

Heavy metal!

This board is definitely the heaviest pcb I have ever built. It is full of potentiometers, jacks and switches packed as tightly as possible.

It was really straightforward build. There were some errors in the silkscreen because component holes had eaten some of the markings away but luckily the layout is really logical because all mixer channels are identical etc. so I didn't have any problems figuring out correct places for components.
Resistors and one IC soldered.

Crowded! This must be the heaviest PCB I have ever built. So much iron attached!

6.35mm sockets had to be wired to pcb.
Ready! This module offers so many possibilities. 6.35mm sockets make it ideal for hooking to external gear.

Distortion!

As the name suggests this mixer is not about super clean hifi sound. It's really evident that the module has its roots in electric guitar world. There's so much gain that it's easy to add lots of really good sounding distortion to the sound. And if that's not enough there's a switch to add diode pair for some serious clipping!

Thanks to generous gain and 6.35mm jack sockets its possible to connect external gear to eurorack and vice versa with this module. There's also stereo out, aux bus and inserts so this module offers almost endless amount of possibilities. I'm pretty sure that this will end up as being one of the modules that I use in every patch.

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