UralTone Subwoofer Amplifier – building instructions

UralTone Subwoofer Amplifier - Building Instructions

UralTone Subwoofer Amplifier is equipped with versatile controls, featuring a 300W active crossover / amplifier for passive subwoofer speakers.

Follow the component list made for the series during construction. We occasionally update the connections of the series, and over time there will be improvements or changes, for example, according to the availability of parts. Therefore, deviations from the image series in this guide are possible. In case of changes, we strive to add notes to the text of this guide.

Before starting construction, it is advisable to check the version number of the parts list from the links below. If the provided series contains documentation of an older version, ensure which instructions to follow before beginning the construction.

UralTone Subwoofer Amplifier - BOM - bill of materials

Always first check that all parts are included in the delivery. If you find any shortages, contact us via email or through the "contact us" form on the website. Note that the components may look slightly different than in the photos. Also, note that the voltage ratings of the parts may be higher than listed; the values of the parts may have been rounded down/up where the exact value is not crucial. We strive to keep the component models the same, so sometimes due to poor availability, we have to change the manufacturer or model of a part. So if a part is slightly different in color, don't be alarmed, each component has the necessary values marked on its side. Read any notes on the parts list carefully.The colors of the supplied wires may also vary. If the color shown in the images is not available in the partial delivery, replace this color with another. While the color does not matter, the type of wire does. Use a thicker wire for the speaker outputs and the mains power input wiring.

Subwoofer Amplifier circuit board. Each part's part number (e.g., R4) is printed on the board. Each part number corresponds to the component value given in the parts list (BOM). In this photo series, the parts are placed in order from the lowest first. This technique facilitates work as the components automatically press against the board's surface when the board is flipped for soldering.

The circuit board has reserved spots for components that are not used in this project. If a component with a part number printed on the board does not have a corresponding numbered component in the parts list, it is not installed.

Note: When assembling circuit boards, it is advisable to always compare the previous and next image if the components are not familiar by name and appearance.

Note 2: After the preparation of the photo series, an optional EQ circuit Q-value selector switch and the necessary components for the connection have been added to the circuit board.

Solder the resistors onto the circuit board. The installation direction of the resistors does not matter, but as shown in the picture above, they can be placed in the reading direction relative to the prints. This way, the value of the part is easier to read from the board.

Solder the IC sockets onto the board. The IC socket and the IC chip to be installed later also have a specific installation direction. At this point, align the socket according to the prints so that the semi-circular notched end is aligned according to the board markings. In the image above, this notch points to the left.

Solder the ceramic and plastic film capacitors onto the board. These components do not have a specified installation direction.

Solder the electrolytic capacitors onto the board. The round cylindrical electrolytic capacitors must be installed on the board in the correct orientation. The stripe printed on the side of the part / shorter lead should be aligned with the pad marked with a white semicircle on the circuit board.

Solder the pin header cut to two pins with jumpers onto the board. JP1 controls the sensitivity of the crossover. When closed, the gain of the circuit is 15dB, and with the jumper open, it is -4.5dB. It is recommended to keep the jumper closed initially. If the range of the volume control is insufficient, try opening the jumper.

The potentiometers in the preamplifier section are implemented with trimmer potentiometers, which can be connected as dual or quad potentiometers if needed. The parallel-connected trimmers should be mounted on their shaft and soldered as a single unit. This way, the shaft acts as a guide for the installation, and the trimmers align on the same line. When installed this way, the control becomes easier to turn since the shaft does not have to bend when rotated.

Push the knob/shaft through the first trimmer and turn it counterclockwise if necessary. Then push the knob into the next trimmer and turn the knob again so that this trimmer's position is also turned counterclockwise. If the trimmers are not aligned, remove the last trimmer from the shaft and install it in the same direction as the previous one. Repeat this step as needed depending on the total number of trimmers. The position of the potentiometer shaft's slot does not matter at the beginning of the installation; this can be corrected later. When the trimmer is turned to zero, the slot has rotated 65° counterclockwise from the top position.

Note: Before soldering, ensure that all trimmers on the same axis are aligned. If one or more trimmers are soldered onto the board at an angle/twisted, their electrical value will not match the others. Similarly, the adjustment range of the controller will slightly shrink.

Attach the trimmers to the board and ensure that all trimmers on the same axis are aligned and flush with the board surface before soldering them to the board. You can use the device's front panel as an aid in positioning and adjust/correct their position if necessary.

The device's LED is installed on the component side of the circuit board. Bend the LED legs at a 90-degree angle. The bend is made so that the shortest lead of the LED goes to the pad on the right side in the picture. In this task, it is also advisable to use the front panel as an aid to find the correct installation dimensions. Solder the LED from this side of the board.

Cut the LED legs on the back side of the board close to the board surface so that the LED pins do not touch the toggle switch body.

Note: the pictures show the toggle switch soldered onto the board. It is advisable to solder it only after the LED installation.

Same work phase from the side.

Attach the toggle switch to the board. Ensure that it is flush with the surface of the circuit board before soldering.

Finally, install the IC circuits into their sockets. Pay attention to the installation direction of the components.

The soldering work on the crossover is now complete, and this can be set aside for a moment.

The back panel of the kit uses an auxiliary circuit board to attach the screw terminals of the speaker-level input to the panel. This same board also reinforces the back panel.

Attach the back panel and the auxiliary circuit board together with M3 screws.

Attach the RCA connectors to the board. Leave the insulating plate inside the RCA connectors uninstalled. This way, the copper grounding on the circuit board runs to the screw terminals.

Place the screw terminals in position and solder them in place. Finally, solder the resistors to the end of the screw terminal as shown in the picture. Leave the soldering on the RCA connector side undone for now.

Note: These resistors are used for attenuating the speaker-level input. Their size can be adjusted if necessary, depending on how sensitive the speakers are when using the subwoofer amplifier, in case the amplifier's volume control range is not practical. With the 150kΩ resistors supplied with the set, the speaker input attenuation is -20dB. (Av=0.1) See the circuit diagram notes for comparison.

Attach the speaker output banana plugs in place and insert the IEC connector-fuse holder-switch combination in place. M8 ring terminals can be installed under the nuts of the banana plugs if the soldering iron available does not have enough power to solder the wires directly to the connector bodies.

The back panel is ready for final assembly.

Attach the 12mm spacers for the preamp and the 8mm spacers for the power amp. Install the star washer between the spacer and the enclosure. This way, the front panel potentiometers will be at the correct height.

Attach the ICEpower module to the base plate.

Attach the rubber feet to the corners of the base plate with M4 screws and nuts.

The seven- and eight-pin conductors of the ICEpower wiring harness can be connected as they are, with the shortened conductors soldered to the preamp board from the corresponding ends. If you want a slightly simpler and neater wiring, unnecessary conductors can be removed from the connector housings and the shielded conductors can be replaced with unshielded ones that are left over. The wiring is relatively short and the signal cabling between the preamp and power amp does not need to be shielded.This optimization is not mandatory and the wires can be soldered unmodified to the preamplifier board. In this case, also shorten the wires to the correct length.

Individual wires are easy to remove from the wire bundle. Use a knife or similar tool to release the crimp connector from the connector body. Disconnect the top three input wires from the 8-pin connector in the picture, as well as the fifth white wire from the top.From the 7-pin connector, you can remove all except the sixth wire (if the connector is viewed from the same direction as above).The 3-pin cable does not need to be changed.

Push the detached wires into the connector housings as shown in the picture. The new wires in the 8-pin cable are the top three (white, yellow, and black) and the second from the top in the lower section (light green).

Model the appropriate wire lengths.

Solder the wires onto the board as shown in the picture.

Attach the preamplifier and connect the wires to the ICEpower module.

Shorten both the power and speaker connection wires of the ICEpower wiring harness to the appropriate length. It is easiest to measure this on a lightly assembled base again.

In the image, the outer sheath of the network conductor has been completely removed. The cable is quite stiff, and assembling the amplifier is somewhat easier when the wires bend more. Measure the separate protective ground KE/VI conductor a few centimeters longer than the amplifier module's network cable.

Below is a more detailed guide for soldering the wires to the back panel:

Solder a short conductor for the Network / IEC connector between the fuse holder and the power switch. Solder the protective ground KE-VI conductor, to which an M4 ring terminal is crimped at the other end. The connection of the ring terminal can be secured by soldering. Finally, solder the conductor pair going to the ICEpower module to the same connector.Feed the speaker wire pair going to the ICEpower module into the speaker terminal.

Finally, solder the shielded wires to the RCA connectors.

The same work phase seen from the side.

Solder the wires coming from the RCA connectors to the preamplifier board, attach the ground ring terminal to the chassis, and connect the quick connectors of the power and speaker terminals to the amplifier module.

Slide the amplifier into the case. Press the front panel into place and attach it as shown in the picture with two screws on the top side (bottom side in the picture).

The base plate is secured in place using the screws on the underside. At this stage, it is important to ensure that the base plate is attached to the front panel. It is best to install the screws on both sides simultaneously and tighten them alternately. This way, the screws grip the base plate evenly and the plate is centered correctly.

The back panel is installed in the same way, first from the top edge and finally from the bottom side, tightening alternately.

Finally, install the fuse into the fuse holder on the back panel.

Note: The front part of the fuse holder sled is reserved for a spare fuse, the actual fuse in use is attached to the back of the sled.

The subwoofer amplifier is ready!

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Instructions and Notes:

The amount of attenuation at the speaker level input largely depends on how the subwoofer amplifier is used with sensitive loudspeakers. Less sensitive speakers require a larger signal to achieve the same sound pressure as sensitive ones, resulting in a similarly large signal being fed to the preamplifier. The size of the resistors soldered to the screw terminals on the back panel can be changed as needed. The resistors R43 and R44 supplied with the kit have a value of 150kohm, providing an attenuation of -20dB, meaning only one-tenth of the signal from the speakers reaches the preamplifier. (The line-level input impedance is 15kohm, resulting in a voltage divider of 150k/15k.) Sensitivity can be increased by soldering additional resistors in parallel or decreased by replacing them with larger ones. The appropriate resistor can also be determined using a trimmer, whose value is measured and replaced with a resistor of the same size, or the trimmer(s) can be left in the circuit as is. When using a trimmer, it is important to remember not to turn its resistance range to zero, as this risks damaging the input at high signal levels.

Another or parallel method to the one presented above to control the gain is either to bridge or open jumper JP1. When closed, the device's sensitivity is higher. An open jumper reduces the circuit's gain by -20dB.