U 8A - Subwoofer Helix - Free user manual and instructions

Product Type	Ultra-compact 8" active subwoofer
Brand	Helix
Model	U 8A
Woofer Diameter	8" / 200 mm
Power Output RMS / Max	180 / 360 Watts
Frequency Response	45 - 150 Hz
Lowpass Filter	50 - 150 Hz adjustable, 24 dB/Oct slope
Subsonic Filter	16 Hz / 12 dB/Oct
Phase Adjustment	0° / 180° switchable + 0-180° continuous shift
Input Sensitivity (Highlevel)	1.2 - 20 Volts
Input Sensitivity (Line/RCA)	0.3 - 4 Volts
Input Impedance (RCA)	10 kOhms
Input Impedance (Highlevel)	33 Ohms
Signal-to-Noise Ratio	>92 dB (A-weighted)
Distortion (THD)	< 0.4%
Operating Voltage	10.5 - 16 Volts
Fuse Rating	25 Ampere (Maxi-fuse APX)
Dimensions (H x W x D)	78 x 245 x 345 mm / 3.07 x 9.65 x 13.58"
Housing Material	Diecast aluminum
Included Accessories	Mounting brackets, cable remote control, connection cables
Protection Features	Overheating, over/undervoltage, short-circuit protection (Protect LED)
Auto Remote Function	Automatic turn-on via high-level input (switchable on/off)
Inputs	2 x RCA/Cinch, 2 x Highlevel speaker, 1 x Remote In, 1 x Remote Control
Recommended Wire Gauge (Power)	4 mm² / AWG 12 (short runs) or 6 mm² / AWG 10 (longer runs)

Frequently Asked Questions - U 8A Helix

What is the power output of the Helix U 8A?

The Helix U 8A delivers 180 Watts RMS and 360 Watts max.

What are the dimensions of the U 8A subwoofer?

Dimensions are 78 x 245 x 345 mm (H x W x D) or 3.07 x 9.65 x 13.58 inches.

How do I connect the high-level inputs?

Use the included 6-pole connector with flying leads. Connect left to front left speaker output and right to front right. Ensure correct polarity. When using high-level input, the Auto Remote switch should be set to On for automatic power-up.

Can I use both high-level and low-level inputs simultaneously?

No, it is strictly forbidden to use both inputs at the same time. Doing so may damage the low-level outputs of your radio.

How do I adjust the phase?

First use the Phase switch to select 0° or 180°. For fine-tuning, adjust the Phase Shift control continuously from 0° to 180°.

What does the Protect LED indicate?

A red Protect LED indicates a malfunction due to overheating, over/undervoltage, or short circuit. The subwoofer shuts off automatically. Check connections and settings; if problem persists, contact an authorized dealer.

What fuse rating is required?

The subwoofer uses a 25 Ampere Maxi-fuse (APX). Replace only with an identical rating to avoid damage.

How do I connect the remote control?

Connect the included cable remote to the Remote Control input (⑦) on the subwoofer. This allows you to adjust the volume remotely.

What is the recommended crossover frequency?

A good starting point is 100 Hz (center position of the Lowpass control). Adjust between 50-150 Hz to match your system.

How do I install the subwoofer safely?

Disconnect the battery negative terminal first. Use the included mounting brackets to secure the subwoofer. Ensure the mounting surface is flat and free of obstructions. Check behind for cables, brake lines, or fuel tank parts. Use proper wire gauge and install a main fuse within 30 cm of the battery.

USER MANUAL U 8A Helix

Two black HELIX audio amplifiers with labeled buttons and ventilation gauges (no text or symbols on the devices themselves)

U 8A / U 10A

Ultrakompakter 200 / 250 mm Aktiv-Subwoofer

Ultra-compact 8 / 10" active subwoofer

Close-up of a black electronic device component with a highlighted orange section and mounting holes (no text or symbols visible)

① Power & Protect LEDs

① Power & Protect LEDs

⑥ Input Level

Kanal L = Links vorne

Congratulations on your purchase of this innovative and high-qual ity HELIX product.

The active subwoofer was developed according to the latest technical findings and is characterized by excellent workmanship and convincing sound.

Thanks to more than 30 years of experience in research and development of audio products this active subwoofer generation sets new standards.

We wish you many hours of enjoyment with your new HELIX active subwoofer.

Yours,

AUDIOTEC FISCHER Team

General instructions

General installation instructions for HELIX components

To prevent damage to the unit and possible injury, read this manual carefully and follow all installation instructions. This product has been checked for proper function prior to shipping and is guaranteed against manufacturing defects.

Before starting your installation, disconnect the battery's negative terminal to prevent damage to the unit, fire and / or risk of injury. For a proper performance and to ensure full warranty coverage, we strongly recommend to get this product installed by an authorized HELIX dealer.

1. Check that the space between the active subwoofer and other parts, such as the car seat etc., is sufficient.
2. Take care that the mounting surface is flat and free from all obstructions.
3. Ensure that the active subwoofer is correctly connected (phase), i.e. plus to plus and minus to minus.
4. For safety reasons, the U 8A / U 10A must be professionally installed. Therefore, use the four mounting brackets which are included in delivery. These are attached to the bottom of the active subwoofer with two short screws which

are included in delivery, too (see following picture).

Close-up of a black electronic device component with a highlighted mounting bracket (no text or symbols visible)

When screwing the active subwoofer to the vehicle chassis, carefully examine the area around and behind the proposed installation location to ensure that there are no electrical cables or components, hydraulic brake lines or any part of the fuel tank located behind the mounting surface. Failure to do so may result in unpredictable damage to these components and possible costly repairs to the vehicle.

1. Do not mount the active subwoofer where water may splash on it or close to heat-radiating parts and electronic controls of the vehicle.

2. The quality of the installation has a significant effect on the overall performance of the active subwoofer. Treat each installation step with a high degree of attention.

General instructions

General instructions for connecting HELIX activesubwoofers

The active subwoofer may only be installed in vehicles which have a 12 Volts negative terminal connected to the chassis ground. Any other system could cause damage to the HELIX U 8A / U 10A and the electrical system of the vehicle.

The positive cable from the battery for the complete system should be provided with a main fuse at a distance of max. 30 cm from the battery. The value of the fuse is calculated from the maximum total current input of the car audio system.

Use only suitable cables with sufficient cable cross-section for the connection of the active subwoofer. The fuse may only be replaced by an identically rated fuse (25 A) to avoid damage of the active subwoofer. Higher values can lead to dangerous consequential damage!

We recommend that you perform a short function test at low volume to ensure that the active subwoofer is functioning correctly before final installation.

Prior to installation, plan the wire routing to avoid any possible damage to the wire harness. All cabling should be protected against possible crushing or pinching hazards. Also avoid routing cables close to potential noise sources such as electric motors, high power accessories and other vehicle harnesses.

Attention: Ensure that the active subwoofer is correctly connected (phase), i.e. plus to plus and minus to minus.

Connectors and control units

① Power & Protect LEDs

These LEDs indicate the operating mode of the active subwoofer.

② Phase

This switch allows to switch the phase between 0^ and 180^ .

③ Auto Remote

This switch allows to activate / deactivate the automatic turn-on feature via the highlevel inputs of the active subwoofer.

④ Lowpass

Control for adjusting the lowpass filter from 50 Hz to 150 Hz.

⑤ Phase Shift

Control for continuous fine tuning of the phase from 0° to 180°.

⑥ Input Level

Control for adjusting the input sensitivity of the lowlevel Line and Highlevel Inputs.

⑦ Remote Control

Input for connecting the included cable remote control for volume adjustment.

⑧ Highlevel Input

Highlevel speaker inputs for connecting a factory radio or an aftermarket radio without lowlevel line outputs.

⑨ Line Input

RCA inputs for connecting lowlevel line signals.

⑩ Fuse

Input fuse - 1 x 25 Ampere.

11 Power Input

Connector for the power supply and the remotecable.

Initial start-up and functions

① Power & Protect LEDs

The Power & Protect LEDs indicate the operating mode of the active subwoofer. If the Power LED lights green, the active subwoofer is switched on and ready for operation.

If the Protect LED lights up red a malfunction has occurred. A malfunction may have different causes as the HELIX U 8A/U 10A is equipped with different protection circuits. These protections shut off the active subwoofer in case of overheating, over- and undervoltage and false connection. Please check for connecting failures such as short-circuits, wrong connections, wrong adjustments and over temperature. If the active subwoofer does not turn on it is defective and has to be send to your local authorized dealer for repair service. A detailed description of the malfunction and the purchase receipt has to be attached.

② Phase

This switch is used to toggle the phase between 0^ and 180^ . This allows to match the phase of the active subwoofer with the other speakers thus avoiding any cancellations in the frequency response due to phase shifts. If the changeover does not lead to the desired result, a ne tuning can be done with control 5 (Phase Shift).

③ Auto Remote

The U 8A / U 10A will be turned on automatically if the Highlevel Input is used or if a signal is applied to the remote input (REM) terminal of the Power Input. The Auto Remote switch allows to activate / deactivate the automatic turn-on feature of the Highlevel Input. The feature should be deactivated (Auto Remote = Off) if there are e.g. disturbing noises while switching on /off the active subwoofer.

Note: If the automatic turn-on function is deactivated it is mandatory to use the remote input to power up the active subwoofer! The highlevel signal will be ignored in this case.

④ Lowpass

This control is used to adjust the crossover frequency of the lowpass lter from 50 Hz to 150 Hz. As a reasonable initial value for adapting the active subwoofer to the other loudspeaker systems, we recommend a setting of 100 Hz (center position of the control).

⑤ Phase Shift

This control is used to one tune the phase from 0^ to 180^ if the phase adjustment with the Phase switch (see item 2) did not lead to the desired result.

Note: Always use the Phase switch first to adjust the phase.

⑥ Input Level

This control is used to adapt the input sensitivity to the output voltage of the connected signal source. The control range of the RCA / Line Input (lowlevel) is 0.3 - 4 Volts and 1.2 - 20 Volts for the Highlevel Input.

⑦ Remote Control

This input is used to connect the included cable remote control. The remote control allows you to control the volume of the active subwoofer.

⑧ Highlevel Input

2-channel highlevel loudspeaker input to connect the active subwoofer directly to the loudspeaker outputs of OEM / aftermarket radios that do not have any lowlevel line outputs.

If this input is used the remote input (REM) of the Power Input does not need to be connected as the active subwoofer will automatically turn on once a loudspeaker signal is applied.

Attention: Solely use the connection cable with the 6-pole connector and ying leads which is included in delivery!

Important: It is strictly forbidden to use the High-level Input and lowlevel Line Input at the same time. This may cause severe damage to the lowlevel line outputs of your car radio.

⑨ Line Input

2-channel lowlevel line input to connect signal sources such as head units / radios / DSPs.

Important: It is strictly forbidden to use the High-level Input and lowlevel Line Input at the same time. This may cause severe damage to the lowlevel line outputs of your head unit / car radio.

⑩ Fuse

The input fuse is connected in parallel and provide protection against an internal fault of the device, therefore the system must be additionally protected by a further main fuse located close to the battery (max. distance from battery: 30 cm / 12"). The HELIX U 8A / U 10A is equipped with a 25 Ampere fuse.

⑪ Power Input

This input is used for connecting the active subwoofer to the power supply of the vehicle and for the remote input.

+12 V: The +12 V supply cable must be connected to the positive terminal of the battery. The positive wire from the battery to the power terminal of the active subwoofer needs to have an inline fuse at a distance of less than 12 inches (30 cm) from the battery. The value of the fuse is calculated from the maximum total current draw of the whole car audio system. If your power wires are short (less than 1 m / 40") then a wire gauge of 4 mm² / AWG 12 will be sufficient. In all other cases we recommend a cross section 6 mm² / AWG 10!

GND: The ground cable (same gauge as the +12 V wire) should be connected to a common ground reference point (this is located where the negative terminal of the battery is grounded to the metal body of the vehicle), or to a prepared metal location on the vehicle chassis, i.e. an area which has been cleaned of all paint residues.

REM: The remote lead should be connected to the remote output / automatic antenna (aerial positive) output of the head unit / car radio. This is only activated if the head unit is switched on. Thus the active subwoofer is switched on and off together with the head unit / car radio. This input needn't to be assigned if the Highlevel Input is used.

Option 1: Connecting the active subwoofer when using the highlevel inputs

Note: If the highlevel inputs are used as signal inputs, the remote input does not need to be connected as the active subwoofer will automatically turn on once a loudspeaker signal is applied. To do this, set the Auto Remote switch to "On" position. If there are any disturbing noises while switching on and off the active subwoofer, please use the remote input and set the Auto Remote switch to "Off" position.

Option 2: Connecting the active subwoofer when using the RCA / Cinch inputs

Note: If the RCA / Cinch inputs are used as signal inputs, the remote input has to be used.

Connection of HELIX U 8A / U 10A to the head unit / car radio:

Caution: Carrying out the following steps will require special tools and technical knowledge. In order to avoid connection mistakes and / or damage, ask your dealer for assistance if you have any questions and follow all instructions in this manual (see page 11 et sqq.). It is recommended that this unit will be installed by an authorized HELIX dealer.

1. Connecting the highlevel speaker inputs

The highlevel loudspeaker inputs L and R can be connected directly to the loudspeaker outputs of an OEM or aftermarket radio using appropriate cables (loudspeaker cables with 1 mm^2 / AWG 18 max. ).

Actually it is not mandatory to use both highlevel speaker inputs. However, we recommend the following channel assignment:

Channel L = Front left

Channel R = Front right

Make sure that the polarity is correct. If one connection has reversed polarity it may affect the performance of the active subwoofer and the sound reproduction may be completely suppressed.

When using this input, the remote input (REM) does not need to be connected as the active subwoofer will automatically turn on once a loudspeaker signal is applied.

Important: It is strictly forbidden to use the HighlevelInput and lowlevel Line Input at the same time. This may cause severe damage to the lowlevel line outputs of your car radio.

2. Connecting the lowlevel line inputs

Use the correct cable (RCA / Cinch cable) to connect these inputs to the lowlevel line outputs of your car radio. It is not mandatory to use both lowlevel line inputs. However, we recommend to use both inputs.

The automatic turn-on circuit does not work when using the lowlevel line inputs. In this case the remote input (REM) has to be connected to activate the HELIX U 8A / U 10A.

3. Adjustment of the input sensitivity

Attention: It is mandatory to properly adapt the input sensitivity of the U 8A / U 10A to the signal source in order to avoid damage to the active subwoofer.

If you want to change the input sensitivity use the Input Level control (see page 14, item 6). The setting of the control affects both the low-level line inputs (LineInput) and the highlevel speaker inputs (Highlevel Input)!

4. Connection to power supply

Make sure to disconnect the battery before installing the HELIX U 8A / U 10A!

Connect the +12 V power cable to the positive terminal of the battery. The positive wire from the battery to the power terminal of the active subwoofer needs to have an inline fuse at a distance of less than 12 inches (30 cm) from the battery.

The value of the fuse is calculated from the maximum total current draw of the whole car audio system (U 8A / U 10A = max. 25 A RMS at 12 V power supply). If your power wires are short (less than 1 m / 40") then a wire gauge of 4 mm ^2 / AWG 12 will be sufficient. In all other cases we recommend a gauge of 6 mm ^2 / AWG 10!

The ground cable (same gauge as the +12 V wire) should be connected to a common ground reference point (this is located where the negative terminal of the battery is grounded to the metal body of the vehicle), or to a prepared metal location on the vehicle chassis, i.e. an area which has been cleaned of all paint residues.

5. Connecting the remote input

The remote input (REM) has to be connected to the radio remote output if the active subwoofers lowlevel line inputs are used as signal inputs. We do not recommend controlling the remote input via the ignition switch to avoid pop noise during turn on/off.

If the Highlevel Input is used this input does not need to be connected as long as the car radio has BTL output stages.

Installation

6. Configuration of the remote input

The U 8A / U 10A will be turned on automatically if the highlevel inputs are used or if a signal is applied to the remote input terminal. The Auto Remote switch (see page 14, item 3; Auto Remote) allows to deactivate the automatic turn-on feature of the highlevel inputs. The feature should be deactivated if there are e.g. disturbing noises while switching on / off the active subwoofer.

Note: If the automatic turn-on function is deactivated it is mandatory to use the remote input terminal to power up the active subwoofer! The highlevel signal will be ignored in this case. To deactivate the automatic turn-on feature you have to change the position of the Auto Remote switch to "Off".

Technical Data

	U 8A U 10A
Power RMS / max. 180 / 360 Watts 180 / 360 Watts
Woofer diameter 8" / 200 mm 10" / 250 mm
Inputs 2 x RCA / Cinch	2 x Highlevel speaker input1 x Remote In1 x Remote control input	2 x RCA / Cinch2 x Highlevel speaker input1 x Remote In1 x Remote control input
Input sensitivity Highlevel 1.2 - 20 VoltsRCA / Cinch 0.3 - 4 Volts		Highlevel 1.2 - 20 VoltsRCA / Cinch 0.3 - 4 Volts
Input impedance RCA / Cinch 10 kOhms 10 kOhms
Input impedance highlevel 33 Ohms 33 Ohms
Frequency response	45 - 150 Hz	40 - 150 Hz
Lowpass	50 - 150 Hz adjustable	50 - 150 Hz adjustable
Subsonic	16 Hz / 12 dB/Oct.	16 Hz / 12 dB/Oct.
Phase switch	0° / 180° switchable	0° / 180° switchable
Phase shift	0 - 180° adjustable 0 - 180° adjustable
Slope lowpass	24 dB/Oct.	24 dB/Oct.
Signal-to-noise ratio	>92 dB (A-weighted)	>92 dB (A-weighted)
Distortion (THD)	< 0.4 %	< 0.4 %
Operating voltage	10.5 - 16 Volts	10.5 - 16 Volts
Fuse	25 A Maxi-fuse (APX)	25 A Maxi-fuse (APX)
Additional features	Diecast aluminum housing, cable remote control for volume adjustment, Auto Remote switch	Diecast aluminum housing, cable remote control for volume adjustment, Auto Remote switch
Dimensions (H x W x D)	78 x 245 x 345 mm /3.07 x 9.65 x 13.58"	78 x 245 x 345 mm /3.07 x 9.65 x 13.58"

Warranty Disclaimer

The limited warranty comply with legal regulations. Failures or damages caused by overload or improper use are not covered by the warranty. Please return the defective product only with a valid proof of purchase and a detailed malfunction description. Technical specifications are subject to change!

Errors are reserved! For damages on the vehicle and the device, caused by handling errors of the device, we can't assume liability. These devices are certified for the use in vehicles within the European Community (EC).

AUDIOTEC

FISCHER