My battery powered Eurorack

My battery powered Eurorack

I wrote previously about being inspired by people using battery powered erorack systems to make electronic music in nature. I tested it out at the Eurorack SF cafe jam meetup. It worked great! If you’re in the bay area join this Meetup!

Power supply

Most Eurorack modules run on +12 volts, -12 volts, and +5 volts. You can’t get this from a single wall wart or power brick. Usually the rack or a module will convert a DC voltage to +12/-12/+5v.

If you can’t plug into the wall you will need a battery. A wide variety of batteries are available but most supply 5 to 9 volts, some will supply more. None will provide the +12/-12 volts that runs your modules. To get this you’ll need a Eurorack power supply that can run from DC power supplied by a battery. Here are a couple options.

Synthrotek USB Power: This is a small power converter that runs from a USB connection. That means you can power this with any USB battery.

MMI USB Power: Another USB power solution.

USBPowerThingy: Another USB power solution as a PCB kit. Build it yourself!

4MS power 25, 35, and 45: these are modules that supply power. you’ll need a battery that can supply 15-20v DC.

Befaco Excalibus: heres a power bus that runs on 9 to 18v. you can build it as a kit.

I’m using the Intellijel 62hp Palette case which takes 15v DC in and converts that internally. I needed a 15 volt DC supply to supply power for this case.

Batteries

I used a USB battery from Amazon. It’s a PowerADD 2300. Looks like they don’t sell this model any more. It’s a few years old there is a probably an improved model available now.

Battery Type: Li-polymer Battery
Capacity: 23000mAh / 85Wh
Input: DC 15~24V/2A
Output: DC 9V/12V/16V/19V/20V 4.5A(MAX)
USB1: 5V, 2.5A
USB2: 5V, 1A
Dimension: 18.28*12.44*1.52cm
Weight: 558g

The important stats are the output of 9, 12 and 16 volts and the capacity of 23000mAh. “mAh” is milli Amp Hours. The battery above shows:

Output: DC 9V/12V/16V/19V/20V 4.5A(MAX)

If you’re using a USB power option the USB information becomes important. The battery above shows:

USB1: 5V, 2.5A USB2: 5V, 1A

Using ModularGrid.net you can mock up your rack and calculate the power consumption of all of the modules in the rack. The modules I put together showed:

Power Consumption: 661 mA +12V | 254 mA -12V.

That’s 661 mA on the positive rail and 254 mA on the negative rail for a total of 915 mA. The battery supplies 23000 mAh. The battery would ideally power the this rack for:

23000 / 915 = 25.1366120219 hours!

That’s an ideal estimate.

The jam at the cafe was about 1.5 hours and the battery showed 76%. That estimates about 6 hours of total use which is much lower than the 25 hour number. The case’s internal power circuit generates +/- 12v and +5 from 15v DC, there is a cost there (not in the estimate), the case also has a buffered multiple with lot of LEDs which use up more current (not included in the estimate). The battery also probably uses current faster in the 16v mode. And, the current usage estimate for the modules is probably idle current, they use more when you are sending CV in.

The case

The case is a 62HP Intellijel Pallette. It comes with a built in power supply and an external brick that supplies 15v power.

These cases are well made and work well. I give them high marks! That said there are three things to look out for.

The power cables are hard to reach under the panel at the top. The space is really tight and the connectors are packed in pretty close together. I disassembled the case and added all of the connectors. I don’t disconnect the cables from the case! Instead I connect one of the cables in the case to the back of a module!

Second, the depth of the case is 51.3mm / 2.02″. Modules taller than this will not fit. I only have one or two modules that don’t fit so this is generally not an issue.

Narrow modules tend to be deeper. In a small case you are often looking for narrow modules to get the most out of your space. Check the depth before you buy anything.

Last, be aware that the 1U row uses the Intellijel standard. Pulplogic 1u modules won’t fit.

The modules

The 62HP size is a limit that also inspires creative decisions. You can’t fit everything but there is enough room for plenty of fun music making. The contents of a small case will change over time.

The modules I chose for the current rack were:

The 1U row has:

Here is the rack on ModularGrid.net (note the modules have updated since I wrote the list above!)

I got some of these Befaco Knurlies to attach modules to the case. While costly they do make it easy to change modules without need for tools. They come with a little washer. The washer and the fact that you’re hand tightening these means you’re not over tightening and marring your front panels!

These are great when you switch modules often. With a small case like this you will be likely to swap modules.

The Knurlies come in M2.5 and M3 sizes. Check your rack and buy the correct size! The Intellijel case uses the M3 size.

Here’s an alternative on Etsy.com.

By the time I had written this far I had already updated my case a couple times.

The two Piston Hondas gave me three oscillators which is useful but took up a lot of space (34hp) and didn’t offer any utility. I took out the Piston Honda Mk I, and added µClouds (8hp granular delay sampler ambience generator) and Prizma (6hp sequencer). Then found I wasn’t using either of these. In the end I was happy with:

The Befaco A*B+C is a great utility module, especially for a small case. You can use it as a 4 channel mixer, dual VCA, attenuverter and offset, and use it for amplitude and ring modulation.

I have mixed feeling about the 2hp Delay. The size is great and it works well. It just barely fits this case. It feels very delicate like it could break easily.

Temps Utile is a great clock source. The Intellijel Noise Tools has a single clock. Having a dedicated clock seemed to open up more possible rhythmic options.

Overall I was very happy with this selection of modules. These allowed for two quantized voices. The wave table oscillator has a variety of sound options which doesn’t quite make up for the lack of having a dedicated filter but is a compromise. Between Temps Utile, Ornament and Crime, Noise tools, and Quadrax I’ve got plenty of CV and modulation options.

If you really enjoy playing modular and nature inspires you a battery powered case might be for you.

Noodling in the backyard no need for an extension cord! All of the music here was generated with battery power. The recordings were done with an iPhone and the Roland Go Mixer Pro. See my post about the Go Mixer.


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