The Cooperation between Uraltone and J. Paasonen is continued again in the form of this kit.

As the name suggests, the new build series is based on the Mk3/Mk4 Tone Bender circuit introduced in 1968 with slight updates. This was the first model of the Tone Bender product family with a Tone control. It is precisely the tone pot that makes the MK4 a very versatile Fuzz Pedal. There's plenty of adjustments to be made from Doom growl to loud Surf. The circuit humbly respects the original, excluding the necessary changes required by the transistor model chosen for the task.

The circuit is made with high-quality NOS Valvo AC127 transistors, which enable the use of current standard power sources in addition to a fantastic sound. The transistors have been adapted to work with this circuit without wasting time or materials. Other mechanical and switching components have also been selected from the high-quality end of the range, like the best boutique pedals.

The Mk4 offers strong sustain, but also many shades of milder distortion. Tone adjustments makes it easy to calibrate the frequency band according to the user's preference and the needs of the playing environment. In my own use, I'm used to limiting too much bass humming with one turn of the button. The Rouhi MK4 is exceptionally well suited as a fuzz pedal for various amplifiers, effects devices and guitars.

Enjoy your building process, Janne Paasonen, 15 December 2020

Features

Knobs: Tone, Fuzz, Volume
Switches: by-pass
Power supply: 9V battery or 9VDC power supply (center negative)
Size: 80x55x21mm (box measures)

  1. UralTone Rouhi MK4 by J. Paasonen - kit ('68 Tone Bender MkIII/MkIV)
    UralTone Rouhi MK4 by J. Paasonen - kit ('68 Tone Bender MkIII/MkIV)
    €45.00
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    As the name suggests, the new build series is based on the Mk3/Mk4 Tone Bender circuit introduced in 1968 with slight updates.

    NOTE! AC127 sets are out of stock; sold without transistors.

    Learn More
    SKU: 950P-ROUHI-MK4

Always check first that all parts are included in the delivery. If you find any problems please contact us by email or through the "contact us" form on the pages. Note that the components may look slightly different than in the photos. Also, note that the voltage specs of the parts may be higher than what is listed. Read all the notes at BOM (bill of material) carefully.

Bill of materials

Soldering instructions

Identifying Components


Building ROUHI MK4 pedal

Follow the order in which the images below are assembled. We try to keep component manufacturers and types same, but sometimes we have to change the manufacturer or model of a part due to poor availability. SO if a part is a slightly different color or higher voltage rating, all is good, each component has the required values ​​marked on the side of the part.

Rough MK4 Wiring Circuit Board: The locations of all parts with their designators are printed designators can be found in the parts list supplied with the kit.

It is a good idea to start with low profile parts, so that the parts press against the surface of the PCB as they are soldered to the PCB. Start by population the resistors on a plate. Resistors are marked R1, R2, etc. Resistor values ​​are marked with colored rings. To identify these, see the BOM provided with the kit. The correct values ​​can also be measured or compared to the color rings in the image above. The mounting direction of the resistors does not matter, but for readability, it is always a good idea to mount them in the same direction.

NOTE: R7 has been reduced to 2.2kohm to increase the trimmer adjustment margin.
Updated 5/20/2020.

The following low parts are soldered to the diode. The mounting direction of the diode is determined: The cathode ring of the diode is aligned with the ring printed on the circuit board.
Note: The Germanium diodes has poor heat resistance. Do not heat the component unnecessarily. The diode may also be black, depending on the image.

Solder the trimmer RV2 in place.

Solder the Ceramic and Plastic Film Capacitors (C1, C2 ...) in place. The values ​​of the ceramic capacitors are indicated so that the first two digits indicate the value of the first two digits. The third indicates the number of zeros. For example, 471 is 470pF, 472 is 4700pF, or 4.7nF. These can be mounted in any direction because there is no polarity..

Install the electrolytic capacitors on the plate. Note the mounting direction of the part, the white stripe on the negative terminal corresponds to the white print on the circuit board.

Solder the Germanium transistors to the board.

Please note: installation space is small, so these should be installed slightly skewed. Leave about 5mm of wire on the legs of the transistors between the housing and the board. Germanium transistors (like ge diodes) are poorly resistant to heat so work quickly. The transistors in the series are selected, so please take into account their installation locations.
Note: The pads on the board and the legs of the transistor do not always line up . The legs of the transistor are in a triangular housing. When viewed from the top / through the transistor, the 90-degree angle of the triangle, the middle leg comes to the right. Cf. in the image below.

Transistors from the side. Note the order of the feet. Transistors can also be of a different type from what you see in the pictures. Please check correct pinout (feet position) if your kit uses something else than AC127.

Solder the DC jack, battery clip, and jack wires to the disc. Presents stripped wires. The wires in the battery clip can be shortened by about half.

Same step from another angle

Solder the potentiometers in place. Note. As with all our three-button kits, remove the center potentiometer from the guide pin. This is done by twisting with tip tongs or cutting with a side cutter.

There is little space under the pots. Make sure the transistors do not contact with the potentiometers.

Solder the Jackets to their wires.

The UralTone effect kits are delivered with two different types of input jacks. Please refer how to solder instructions found here:
https://en.uraltone.com/blog/input-jack/

Mounth the footswitch to the disk. The installation is a bit cramped, but with determination, it works. You may need to press the part with moderate force onto the PCB. The switch does not break easily, so no worry. Screw one nut into the footswitch so that the installation height is the same as the rest of the connection. Pay attention to the installation direction, the groove of the threaded part comes upwards. Thread the led into place. The shorter leg comes in a square pad. Don't solder these yet.

Thread the connection into the housing. Attach the Jackets first. These can be left a little loose so you can rotate these to a suitable position later. Drop the led through the front panel. If you are using the optional front panel, install it now. With the plate in place, tighten the front plate nuts.

Once the front panel nuts are tightened, solder the footswitch and led. Install the battery and test.

The effect is complete.

Finally, adjust the trimmer RV3. Connect a guitar cable to the input jack. Measure the voltage between the point on the image and the housing. Adjust the trimmer until the measuring point has a voltage of about 2V. You can also try playing and leaving the trimmer in the best sounding position.

Congratulations! You have a high quality boutique Fuzz pedal in your hands that is built by you! If you have any question, please do not hesitate to contact us!