Build Tips

Before you start building your SR-909, here are a few tips and procedures to avoid mistakes from the outset!
I have divided the whole thing into different steps to make it easier for you to get started.


Check all components for completeness using the BOM. Don’t necessarily rely on the sticker for this. With this amount of parts, small mistakes can always occur during packaging.


Before you get to the assembly, one more note. For some components such as diodes or capacitors, the polarity must be observed! For each board, start with the flattest parts. So first the diodes, then the bridges, the resistors, etc.

The circuit boards are labeled with the components on both sides. This has the advantage that you can check again before soldering whether you have inserted the components in the right places! Take advantage of this opportunity!
In addition, make sure that you solder the components on the correct side! Some boards are labeled „Part side“ on the edge, others are not. For those that are not labeled with this, check with the housing to see how around they have to be inserted! It is better to double-check the position before you solder on the first component!

Try to assemble your SR-909 conscientiously and calmly so that you have to find and fix fewer errors afterwards!

Power Supply

In order to have the right voltages during construction and completion, it is advisable to solder the power supply first. This is also a good start because it is easy to build.
Important: You are working here with high currents that are life-threatening! It is advisable to consult a specialist to build the power supply!
After setting up, check the voltages at the output according to the voltages printed on the circuit board.
„R“ is the reset supply. It is switched a few milliseconds after the 5V output to ensure a direct 5V supply. Here is also 5V.

IO and MIDI Board

It’s a good idea to build the connector boards as the next step. This has the advantage that you also have this available during the test. These boards are also easy to build because they only need a few parts that are also easy to assemble.

Sequenzer Board

You cannot address the mainboard without the sequencer board. So it makes sense to move on to that next.
With the board it is important that all chips can be provided with a socket! The processor of the SR-909 can be equipped with a socket so that you don’t have to solder it in directly. That is also recommended.
The chips are only put on the board when it is completely soldered!
With the buttons you have to pay attention to the polarity of the LED. The small buttons are plugged onto the main board with the adapter boards. The pins look through very little, but with enough solder and flux you can make a clean connection.
You should first plug in the LED for the clock display, insert the sequencer board into the housing and adjust the distance between the LEDs so that they sit well on the front panel and then solder them on.


The mainboard is the most complicated and important part of the SR-909. As with the other boards, first solder in the diodes. With the clipped legs you can then insert all bridges in the board. IMPORTANT, there is a resistor (R405) on the board, it looks like a bridge, but it is a resistor!
Here, too, all iCs are socketed! Even the operational amplifiers. The set includes bases that you still have to cut to size.
Pay attention to the polarity of all components.
Without exception, all iCs are set with Pin1 at the top or left. With the OpAmps and the Matched Transistors, the lettering is on the left! There is no component which is oriented to the right or below!