The Relay Bypass Module Kit (RBM) is a clever circuit that enables you to have real true bypass switching in virtually any effect pedal! The RBM can be incorporated into new pedal designs or retrofitted into existing pedals that might not have true bypass switching. A lot of thought went into the design of this module and to make sure the switching operation is reliable and noiseless. On top of normal ON / OFF switching capability, there’s also a user programmable momentary mode which allows the use to insert the effect into the signal chain only while pressing down on the footswitch, upon release the effect is bypassed.
Difference Between This Kit And Pre-assembled RBM Modules
The most obvious difference between the products is that this is a kit! You get all the parts in through hole form and you need to assembled them on your own. Some experience in soldering is required. The benefit for you, as a customer, is that you get the lowest cost relay bypass module available on the market. Another difference that is worth mentioning is the program running on the micro-controller. The kit has a user programmable option for normal ON / OFF operation and a momentary mode as mentioned earlier on this page. The default power on for the kit is always bypass mode. If this is something you would like to alter, you need to get one of our pre-assembled modules as they have user programmable power on default (you can see the complete description of these modules by clicking the appropriate link on the right sidebar).
Tools For Assembly
Assembly of the kit is simple if you have the right tools. It would be a good idea to go through the list and make sure you have all the tools and supplies.
- The RBM Kit (obviously)
- Soldering Iron (low wattage is perfect)
- Some solder
- Small Wire Cutter
RBM Kit Assembly
Before you start with the actual assembly. It’s quite obvious, but you should only try assembling the kit if you have some previous experience in soldering. If you don’t you might injure yourself by accident or perhaps burn some of the components in the kit rendering it useless. So onwards… Remove the components from the plastic bag and lay them out in front of you. It should look similar to what is shown in the picture below.
RBM Kit Content
You should be able to identify the following components (from top right in clockwise direction):
- RBM PCB
- 0.33uF Electrolytic Capacitor (black cylinder)
- 0.1uF Ceramic Capacitor (marked with “104”)
- 0.01uF Ceramic Capacitor (marked with “103”)
- 10k Resistor (5 band marking: brown – black – black – red – brown)
- 1M Resistor (4 band marking: brown – black – green – gold)
- Schottky Diode (marked with “4V3”)
- Small Signal Diode (marked with “1N914”)
- 5V Regulator (marked with “L78L05”)
- MOSFET (marked with “2N7000”)
- Relay (marked with “HFD31/5-L1”)
- Pre-programmed MCU (marked with “ATTiny13A”)
Take the 1M resistor and insert it in C3 as shown below.
1M Resistor Inserted in C3
Bend the resistor’s leads on the bottom of the PCB and solder it in place, afterwards snip off the leads using the wire cutter.
1M Resistor With Ledas Bend And Soldered
Take the 0.01uF capacitor (marked with “103”) and insert its leads near the resistor’s leads as shown in the picture below. After that solder the capacitor and resistor leads together as shown.
1M Resistor and 0.01uF Capacitor
After the leads are soldered together you can bend the capacitor upwards so it will be positioned closely together with the resistor and take up little room.
1M Resistor And 0.01uF Capacitor Bent Upwards
Next, insert the 10k resistor to R1 as shown below. After insertion you should bend its leads on the underside of the PCB, solder them and cut off the excess.
10k Resistor in R1
For the following step you should be careful. The diodes are similar looking so you need to recognize the marking on at least one of them to be able to tell the two apart. Look for the Schottky Diode with the marking “4V3” on it. The writing is small, but I can read it without my glasses so you should be able to do the same🙂 After you’ve recognized the diode, insert it in the D2 position. Take extra care to make sure the black ring on the diode’s body is next to the hole with the ring marking. This is the Cathode, if you insert the diode the wrong way the circuit won’t blow up, but it won’t work.
The Schottky Diode Inserted In D2, The Bottom With The Black Ring Marker Is Flush With The PCB
Now it’s time for the other diode that is marked with with “1N914”. The directional feature is the same, you should insert the Cathode side of the diode into the hole with the ring marker in the D1 position in the PCB as shown below.
Small Signal Diode In The D1 Position
Next, grab the 0.1uF capacitor and insert it into the C2 position.
0.1uF Capacitor In C2 Position
Now it’s time to insert the voltage regulator. The MOSFET comes in a similar package (TO-92) so make sure you can read the writing “L78L05” otherwise you are inserting a wrong component! Finding the right orientation is easy as you need to follow the outline drawing on the PCB. Insert the regulator into the Q1 position. While you are at it, take the other device in similar package and insert it into the Q2 position. Please note: because of a last minute component change the pinout of this device is different than the original one that was supposed to be used so you need to insert it revered! You can see the outline on the PCB, don’t follow it – insert the device the other way around as shown below.
Regulator in Q1 And MOSFET In Q2 (Reversed)
We’re almost done now… Take the relay and insert it in position K1 according to the directional line marker. It should be coincide with the line marking on the PCB.
Relay In K1, Note The Direction
Out last capacitor in next, insert the radial packaged device into the C1 position. Please take care to make sure you install it in the correct polarity. The long lead goes into the hole with the small cross marking next to it. Another marking is the white strip on the side the capacitor without should be found on the same side as the white marking in the capacitor’s footprint.
Capacitor In C1 Position
The last component you need to install is the MCU with the code that runs this board. Please observe the package, as shown in the picture below. You can spot a dot indicator in the plastic package. This should be on top of the dot marker on the PCB.
MCU Placed Next To PCB To Show Dot Markers
Insert the MCU into position U1 and solder all the leads. You are done assembling the board! If you followed all the steps you should have a board that looks like in the pictures below.
Completed RBM Kit PCB
The module has two operation modes. “Normal” is defined as the mode that is press “ON”, press “OFF” which is a direct replacement for a mechanical switch. In addition, there’s a “Momentary” mode which keeps the effect bypassed while the footswitch is not pressed and in active while held down. The user can enter programming mode by holding down the footswitch while connecting power to the module. After releasing the footswitch, any additional press will alter between the two operation modes. The LED indicates which mode is selected. LED = OFF means Normal mode is selected and LED = ON means Momentary mode is selected. To complete the selection the power should be removed from the unit. When the power is powered back up the chosen mode will be initiated automatically.