The DIY Arp 1600 Sequencer Clone
The 1601 Clone kit from Synthcube
The ARP 1601 was a 2×8 or 1×16 step sequencer that could utilize three separate gate busses. It also had a built in quantizer so voltages which would ensure that output always in the 1 volt per Octave standard to keep everything sounding “in tune”. When released in the early to mid 1970s, it was considered state of the art in an analog world. By today’s standards however, so much more can be done with microprocessor controlled sequencers you really have to love analog to justify the costs of building this beast. An Arturia BeatStep Pro does far more at 1/6th the cost.
There have been a few different PCB designs over the last few years from different DIY builders. All of them are pretty much based on the schematics found in the ARP 1601 service manual. This particular version was designed by J.R. Daniels in 2014. It has been updated a few times since then, and the latest version 6a came out in early 2020. The PCB is available through Synthcube. This PCB is designed to rely mostly on through hole components however for a couple of the semiconductors that are no long in production for DIP packages, the designer has utilized surface mount versions instead.
Component side of the main PCB
Hardware side of the main PCB
The other differences between an original ARP 1601 and the clone can be found in the power supply. The original utilized a linear power supply with 110VAC mains. The clone utilizes an AC wall wart and DC to DC power regulators. Building the 1601 clone, is not a technically difficult project, with the hardest part being soldering the mechanical switches and sliders to the PCB. Many DIY’ers who may lack experience soldering sliding potentiometers can ruin them if too much heat is applied. The two SMT devices are easily handled with a generous amount of flux and a standard pencil type soldering iron. There really is no assembly instructions, just the ARP 1601 service manual to go by. I would not recommend this as a project for beginners.
You can buy the entire parts kit from Synthcube, including a couple of case options. The kit is mostly correct however, there are two areas that I found incorrect with the Synthcube supplied components. The first is that there are 12 resistors used for the quantizer circuit. This is nothing more than a resistor ladder or voltage divider, but it has to be accurate. The original ARP sequencer utilized a 12 way resistor network that was accurate to 0.1%
The Synthcube supplied kit came with standard 1% resistors, that were not selected to be within 0.1% with each other. To remedy this, you can select 12 for a few dozen by measuring them with a resistance setting on a multimeter. Most multimeters however, are only accurate to within +/- 2%. Another method is by purchasing 0.1% precisions from Mouser or Digikey. I find this to be the best way, as they were only a few pennies more expensive than standard 1% resistors. If you do nothing and just go with the arbitrary 1% as supplied, you will most likely hear the difference in some tonal frequencies as they will be a few cents off from being in tune.
The other issue with the Synthcube kit are the 1/2 Watt resistors. The ones supplied with the kit are 1/4Watt yet are marked with the appropriate part number from the Bill of Materials (BOM). I ordered the correct part using the exact same part number from Mouser and got the correct 1/2 Watt resistor. Note the size difference. These are used with the LEDs in the sliders. 1/4 Watt may work, but they most likely won’t last long.
Finally, there is one major difference between this version and the original version and that is the addition of a voltage divider (see the far right hand side of the first image). For those that wish to use this feature, you need to purchase the optional voltage divider PCB. Note that all of the resistors, capacitors, and semiconductors are all SMT devices. They are however a manageable size and can easily be hand soldered with a standard soldering iron.
