Vibro Champ Preamp - Pictorial Build Guide
Vibro Champ Preamp - Pictorial Build Guide
The Vibro Champ Preamp is a guitar preamp housed in a cast aluminum enclosure. The circuit remains faithful to the original Vibro Champ, featuring a Blackface-era tone stack with a mid control and a tube-driven tremolo. The Vibro Champ Preamp can be used either as an alternative preamp connected to the return of a guitar amp’s effects loop or as a standalone effect. It runs on a 12V / 1A power supply, and the high voltage required for the tubes is generated using a boost regulator.
This article walks through the construction process in detail, with both images and text. Carefully review the pictures and instructions before starting — this will give you a clear understanding of the nature of the task. Familiarizing yourself with the process in advance will also help you understand what is being done later on and why certain steps are carried out in a specific way.
Follow the parts list provided for this specific kit during the build. We occasionally update the circuits in our kits, and over time there may be improvements or changes, for example due to parts availability. Therefore, minor differences from the photo series in this guide are possible. When such changes occur, we aim to note them in the text of this guide.
Before starting construction, it's a good idea to check the version number of the parts list using the links below. If the documentation provided with your kit is for an older version, make sure to verify which set of instructions is most appropriate for your build.
UralTone Vibro Champ Preamp - BOM - bill of materials
UralTone Vibro Champ Preamp - Schematics
Always start by checking that all components are included in the shipment. If you find any missing parts, contact us by email or through the "Contact Us" form on our website. Please note that components may look slightly different from the ones shown in the photos. Also, note that voltage ratings may be higher than listed, and some component values may have been rounded up or down to the nearest E-series standard value (e.g., 250pF = 220pF). We strive to keep component types consistent, but due to supply issues, we may occasionally need to substitute a part with a different manufacturer or model. So if a part looks a bit different in color, don’t worry — the required values are marked on each component. Be sure to read the notes in the parts list carefully.
The colors of the supplied wires may also vary. If a specific color shown in the pictures is not included in your kit, substitute it with another color. While the color doesn't matter, the type of wire does. Use thicker wire when wiring the DC jack.
Building the preamp consists of three stages: preparing the enclosure, populating and soldering the circuit board, and finally installing and wiring the board into the enclosure. The first two steps can be done in whichever order suits you best. However, we recommend following the assembly sequence shown in the photos below. This way, the build process is structured and follows the rhythm of the article.
1 - Drilling the Enclosure
Use the front panel plate to mark the holes to drill on front panel with following dimensions:
- Potentiometers: ø 7mm
- Toggle switch: ø 6mm
- Screws and LEDs: ø 3mm
- Footswitches: ø 12mm
The hole sizes can be slightly larger. The front panel layout ensures that all components align properly. For example, M3 screw holes can be 3.5mm in diameter. If the drill bit has drifted off-center while drilling, the hole can be "adjusted" into place using a round file.
Drill the input and output jack holes into the back panel as well. The jack holes should be 9.5mm in diameter, and the DC jack hole should be 12mm. The positioning of the connectors is not critical — in the example shown, the holes are centered vertically on the enclosure. Horizontally, they are roughly aligned with the potentiometer holes.
Clean off any burrs and make sure no metal shavings remain inside the enclosure.
NOTE: PCB version 1.03 has minor fault missing the two holes for the spacer mount. See the additional info placed in the end of this article
2 - Laying Components to Main PCB
Vibro Champ Preamp circuit board. Each component position on the board is labeled with its part number (e.g., R4). Each part number corresponds to a component value listed in the bill of materials (BOM). The build also uses smaller auxiliary PCBs for mounting the tube sockets and footswitches.
Note: When assembling the circuit boards, it's a good idea to compare the previous and next images if you are not familiar with the components by name and appearance.
3 - Main board - Resistors
Solder the resistors onto the circuit board. The kit includes two types of resistors: metal film resistors (blue) and carbon film resistors (light brown). Do not mix resistors of the same resistance but different types. Resistors do not have a specific installation direction. In the image, they are all oriented the same way, meaning the color codes can be read either from bottom to top or from left to right.
Resistor R22 is a jumper wire. Use a piece of leftover lead trimmed from another resistor for this.
Note: In the image, R23 is a smaller 0.6W resistor. In the parts kit, it is supplied as a 2W version.
Note: R15 is omitted kits supplied after September 2025.
4 - Main board - Diodes
Solder the three diodes onto the board. Diodes have a specific installation direction. A stripe is printed on one end of the diode’s body — this stripe should be aligned with the markings on the circuit board.
5 - Main board - Non-polarized Capacitors
Solder the ceramic and polyester capacitors onto the board. These components do not have a specific installation direction.
For this type of capacitor, the value is indicated using a three-digit code in picofarads. The first two digits are the base value, and the third digit is the power of ten. For example, 221 means 22 × 10¹ = 220, and 473 means 47 × 10³ = 47,000pF, which is 47nF or 0.047µF.
6 - Main board - Polarized Capacitors
Solder the electrolytic capacitors onto the board. These components have a specific installation direction. A white half-circle is printed on the circuit board to indicate the negative lead. The component itself has a stripe on the same side, and the negative lead is also shorter.
7 - Main board - Transistors, Regulator, Coil and Trimmer Potentiometer
Solder the transistors and the regulator socket onto the board. The orientation of the components is printed on the board. For the transistors, the direction is determined by the shape of the casing or the flat side marking. The IC socket has a notch at the pin 1 end, and this notch is also shown on the board silkscreen. Once the socket is soldered in place, insert the IC chip into the socket. Pay attention to the orientation — the notched end and the small circle marking pin 1 should face the same direction.
The coil (L1) can be installed on the board in either direction.
8 - Main board - Tube Socket Brackets
Tubes mounted horizontally require adapters to secure the tube sockets to the board. For this purpose, the kit includes two smaller circuit boards as shown in the image above.
Shorten the angled IDC connector by one pin pair and solder the connectors on the PCBs. We recommend to solder these only by one pad and checking the proper alignment of the connector pins parallel to the PCB. If needed the single solder point can be reheated for realignment. When the wanted position is found solder the rest of the 17 pins.
Solder the novel socket on opposite side of the PCB.
Attach the soldered boars together with two M3/20mm spacers and four M3x6 screws. Insert the combination into main board pads. Here as well soldering by single pin first is recommended to make sure the bracket is secured against the main board.
When positioning is as wished solder rest of the pins. Lastly cut short the pins extruding the solder side of the main PCB.
Same step seen from another angle.
9 - Main board - Potentiometers
Solder the potentiometers onto the circuit board. Before soldering all three pins, make sure the back of the potentiometer is flush against the circuit board. Any height mismatch will make it difficult to install the board into the enclosure.
Note: RV6 is changed to C20k (was B250) after September 2025.
Cut off the excess leads. The metal is fairly thick, so sturdy side cutters are necessary. It's best to cut only one pin at a time.
There is a small metal alignment tab on the edge of each potentiometer. Bend and break it off from all six potentiometers. The tab is made of cast aluminum, so it will snap off when bent.
10 - Main board - Pin Strips for Foot Switches
The preamp circuit uses the same footswitch PCB as most UralTone effect pedals. With a separate board, the mounting height of the footswitch can be adjusted appropriately, and it also makes repairs or replacements easier if needed.
Solder a 5-pin header and two loose pins for the tremolo footswitch as shown in the image. To align the pins correctly, use the footswitch PCB as a guide by temporarily pressing it into place.
Only the 5-pin header is soldered for the bypass switch.
Note: Unlike in the image, the kit includes headers with longer pins. This makes installation easier and allows the footswitch to be mounted slightly deeper.
11 - Enclosure preparations - Toggle Switch
Attach the toggle switch to the enclosure and front panel. You can adjust the switch height to be level with the panel by turning the inner nut (inside the enclosure) to the desired position at the base of the switch. Once the correct height is set, secure the switch in place, and then install the preamp circuit board into the enclosure.
Same step seen as inside of the enclosure.
Solder small hookup wires between the solder lugs of the switch and the circuit board. The two lower solder lugs are bridged.
12 - Enclosure preparations - Foot Switches
Solder the current limiting resistor of the led on the foot switch board. There's two of these boards used in the preamp.
Press the footswitch through the pads of the footswitch PCB. This requires a bit of force. Do not solder the switch yet — when unsoldered, there is a bit more room for adjustment. Remove all nuts and the plastic washer from the switch shaft, leaving only the star washer in place.
Insert the LED into the board through its pads, but do not solder it yet. The LED has a specific orientation: align the shorter lead with the pad marked K or –.
Press the footswitch into the enclosure. The installation is done from underneath, so the footswitch is lifted into place while the enclosure is upside down. This way, the washer won’t fall off.
Once the footswitch has aligned with the mounting hole, guide the pin headers through the pads on the footswitch board and secure the footswitch to the enclosure with a nut.
Push the LED through the circuit board into the hole drilled in the enclosure. Solder the LED, pin headers, and footswitch to the board.
The kit should look like this at this step.
And from outside like this.
13 - Enclosure preparations - Rear Panel Connectors and wiring
Attach the input and output jacks as well as the DC jack to the enclosure. The input jack has three solder lugs, one of which is a switch. This switch grounds the input when no cable is connected. More detailed wiring instructions can be found below:
The input and output wires are soldered to the bypass footswitch circuit board. The output pads are on the right in the picture, and the input pads are on the left.
On the input jack (left), the black ground wire is bridged between the leftmost and the center solder lugs.
Solder the DC jack as shown in the picture, so that the jack’s positive terminal is in the center. If desired, the polarity can be reversed by reversing the wire order.
14 - Enclosure Finalizing
Attach the tubes into sockets.
Fasten the potentiometer knobs. Vibro Champ Preamp is ready!
15 - Inspections and Testing
Before turning on the power, carefully check the wiring. Make sure the voltage adjustment trimmer at the bottom right is turned counterclockwise.
Measurement and adjustment are easiest when one probe of the multimeter is connected directly to the enclosure (the circuit ground). Measure the voltage at the cathode of diode D1 (the striped end). Adjust the trimmer clockwise until the meter reads 260V.
Addition to the instructions
The tremolo footswitch operation corresponds to the original Vibro Champ circuit. In this design, the tremolo oscillator is controlled, being switched off when the tremolo is not in use. This implementation is actually found in nearly all Fender designs. Presumably, the idea here is to move the control away from the audio path to avoid interference (cf. the Fender reverb circuit).
In the Vibro Champ circuit, the tremolo modulates the cathode of the output tube with a DC-coupled signal. For this reason, the position of the Intensity potentiometer affects the amplifier’s volume even when the tremolo is switched off, because the tremolo’s cathode follower output still carries a DC component. This implementation may not necessarily match builders’ expectations, but this choice was made out of faithfulness to the original circuit.
The circuit can be easily modified toward a “more normal” behavior—if not completely—by moving the footswitch control from the oscillator to the Intensity potentiometer: Cut the jumper wire from the left side of the vibrato footswitch to the circuit board. Solder a jumper wire to the outermost lug of the Intensity potentiometer. Viewed from the component side, this is the left-hand pad.
Version 1.03 pcb has minor fault missing the M3 holes for spacer mounting.
The installation of the PCB can be done by leaving the screws on pcb side of M3 spacers between the pcb and enclosure uninstalled.
Alternatively the missing hole on left can be drilled and used as instructed.