RoXX-Series

301 Personal Headphone Amplifier / Line Checker Manual

The RoXX-Series 301 by ASL is a versatile professional stereo headphone amplifier for personal and portable use. The unit is battery powered and accepts all commonly used audio signals: balanced and unbalanced signals at microphone, line or speaker level.

This Personal Headphone Amplifier has been designed with great precision. However, designing equipment like this is always a matter of finding compromises between: max. gain, noise, max. output power, distortion, power consumption, flexibility, mechanical aspects, costs etc. The starting point of this design was to make a versatile unit, which can be used for many purposes in different circumstances, with long battery life and as little as possible controls. We hope we managed to meet your requirements. Read this user manual first.

Applications for the ASL RoXX - Series 301 Personal Headphone Amplifier

Practicing through headphones

An electronic instrument (guitar, keyboard) or a CD player can be connected to the (stereo) Jack input(s), and a dynamic microphone can be connected to the

XLR input. These signals can be mixed to the stereo headphone output to practice. Even two headphones can be connected in order to allow a singer to practice together with an instrumentalist.

Checking microphone signals

Very usefull to, for instance, boom operators.

Trouble shooting

A sound engineer can check lines, microphones or outputs, to locate signals or to solve problems.

Routing two headphone outputs to one headset

For instance the monitor outputs of two mixing consoles, or the monitor output of a mixing console and an intercom signal.

Creating a monitoring system for studio or on stage use

An output of the mixing console can be connected to the stereo input of the PHA, and a microphone or instrument can be connected to the XLR input with a loop through to a mixing console input. The performer can make his own mix between his own voice / instrument and the signal from the mixing console.

Headphones can be used in a studio, ear plugs on stage.

Boosting a headphone output

Whenever the headphone output power of any equipment is not sufficient, the Personal Headphone Amplifier can be connected to that headphone output.

The output power of the PHA will be high enough for most circumstances/purposes.

Setting up a (battery powered) two station intercom system

A dynamic (headset)microphone can be connected to the XLR input of each of the two PHA’s. The loop through XLR’s are interconnected. The two users can hear eachother (and themselves) through the connected head(set)phones. Two identical microphones need to be used, and the microphone signals are summed by there output resistance.

Sending an audio signal to many headphones

Two headphones can be connected to one PHA.

Personal headphone amps can be interconnected using the loop through connectors.

More applications to be discovered by yourself!

A S L C O M M U N I C A T I O N S Y S T E M S RoXX-Series 301 Manual

FRONT PANEL

1 Power switch

With this switch the unit is turned on and off.

2 Power-on LED indicator

This LED illuminates green when the unit is switched on.

* When the Personal Headphone Amplifier is prepared for charging Ni-MH batteries within the unit, this LED also indicates fast charging of the cells. During fast charging, while the unit is switched off, this LED lights up burns red. During fast charging, while the unit is switched on, this

LED lights up orange.

3 Stereo headphone 3,5mm mini jack

Two headphones can be connected to this headphone amplifier at the same time. A headpone with a 3,5mm mini jack can be plugged in this connector.

Both high and low impedance headphones can be used (when using 2 headphones at the same time, use headphones of the same type). The internal power amplifiers are short-circuit and overload protected.

4 Stereo headphone jack 1/4”

A headphone with a 1/4” jack can be plugged in this connector.

5 -20dB switch

With this switch the gain of the unbalanced inputs can be reduced by 20 dB for monitoring speaker or high level line signals.

In the normal position the input impedance of the unbalanced inputs is very high (1M Ohms), enabling the monitoring of electric guitar signals (or other pick-ups).

6 Stereo/mono switch

In mono position a stereo signal on the unbalanced input(s) is made mono.

7 Unbalanced input Volume control

With this knob the volume of the unbalanced input signal can be controlled

8 Balance control

With this knob the left / right balance of the unbalanced input signal can be adjusted.

9 Mic / Line switch

With this switch the sensitivity of the balanced input can be selected.

10 Balanced input Volume control

With this knob the volume of the balanced input signal can be controlled.

11 Pan control

With this knob the left / right panning of the balanced input signal can be adjusted.

A S L C O M M U N I C A T I O N S Y S T E M S RoXX-Series 301 Manual

REAR PANEL

12 Balanced input + loop thru XLR’s

These XLR-3 female and male connector are paralleled and are the input & loop thru for a balanced signal (mic. or line level).

13 Mono left / stereo input jack

This 1/4" jack connector is the input of the left signal of a stereo signal when a mono jack is used

(input 14 is the right input), or the left and right signals when a stereo jack is used (input 14 is not used). It accepts signals of line or speaker level.

14 Mono right / mono input jack

When no signal is connected to the left jack input

(13), the mono signal on this input is sent to the left and right cans of the headphone. When there is also a mono signal connected to the left jack input

(13) the signal on this input is sent only to the right input (input 13 is the left input). It accepts signals of line or speaker level.

15 Stereo loop thru connector

This jack connector is always configured as a stereo loop thru for the signals connected to the unbalanced inputs 13 and/or 14.

When a stereo signal is connected to input 13 this connector provides a stereo link. When mono left and mono right signals are connected to inputs 13 and 14, this connector outputs those signals as a stereo signal (left=tip, right=ring). When a mono signal is connected to input 14, this connector outputs the mono signal (on tip and ring). This connector is especially useful for connecting multiple headphone amplifiers to one source.

Powering the Personal Headphone Amplifier

Battery Operation

SIDE PANEL

16 DC adaptor input

An external DC adaptor can be used to power the

RoXX-Series 301. The internal batteries will automatically be switched off. The unit accepts DC voltages from 9 V to 24 V.

* When the Personal Headphone Amplifier is prepared for charging Ni-MH batteries within the unit, the external DC voltage can range from 12 V to 18 V. The adaptor must be capable of delivering a current of at least 700 mA.

17 Internal battery compartment

Accepts 4 AA-type 1.5 volt batteries or 1.2 volt rechargeable cells.

The Personal Headphone Amplifier can be modified so that Ni-MH cells can be charged in the unit. Consult your distributor for more information

18 Beltclip

Open the battery compartment on the side of the unit

A S L C O M M U N I C A T I O N S Y S T E M S RoXX-Series 301 Manual

by turning the knurled screw anti-clockwise. Take out the battery holder. Insert four AA-size 1.5V batteries in the holder. Put the holder back into the unit, with the holders connection terminals pointing to the side where the beltclip is mounted. Close the battery compartment by putting back the little coverplate and turning the screw clockwise. The Personal Headphone Amplifier is now ready to operate on batteries.

Always choose four identical batteries of the same age. Rechargeable NiCd or Ni-MH 1.2V cells can be used as well. The RoXX 301 is protected against reverse voltage.

The ASL RoXX -Series 301 can be switched on by pushing the power button (1). The unit will start whenever the total battery voltage is higher then 4.0V.

The unit will work until the total battery voltage drops below 2.5V.

When the unit switches off because the battery voltage is lower than 2.5V, the batteries will start to recover a bit. The battery voltage rises, and when it exceeds 4.0V, the unit will switch on again. By then, the battery voltage will again go down, resulting in switching off the unit at 2.5V. This frequently and automatically switching on and off means that the batteries are empty and that they should be replaced.

The ASL RoXX -Series 301 Personal Headphone

Amplifier can be modified for charging four Ni-MH cells in the unit. Consult your distributor for more information. Whenever a RoXX 301 is prepared for charging Ni-MH cells, normal batteries should not been used anymore and reverse voltage protection for the cells does not work anymore!

Mains Operation

The ASL RoXX -Series 301 Personal Headphone

Amplifier can be powered by mains by using a mains adaptor (not supplied with the RoXX 301). Choose an adaptor with an input voltage that matches the local mains voltage. The output of the adaptor needs to supply a DC-voltage between 9 and 24V at a current of 500mA (12 to 18V DC at a current of 1A when the

RoXX 301 is prepared for charging Ni-MH cells). The

DC-voltage can be either unregulated or regulated.

Connect the adaptor via an appropriate plug to the

DC-in socket (16) at the side of the RoXX 301. The inner pin of the socket is hot (+), the sleeve is ground

(-). The unit is protected against reverse voltage.

Warning !

Always turn the unit on and off without the headphone on your head.

Connecting and Monitoring Balanced Signals

The ASL RoXX -Series 301 Personal Headphone

Amplifier has an independent section for balanced signals and one for unbalanced signals. Balanced signals can be both microphone and line-level signals.

Speaker signals should not be connected to the balanced input (they are mostly unbalanced and can be monitored with the unbalanced section of the ASL

RoXX -Series 301).

Before connecting any balanced signal to the XLR connectors, turn the Balanced input Volume control

(10) down. Press the Line/Mic. button (9) if you plan to connect a microphone level signal. Release the

Line/Mic. button if you plan to connect a line-level signal. Connect the balanced signal to one of the XLR connectors (the other one is for loop thru, the male and female connectors are paralleled). Turn up the

Balanced input Volume control (10) carefully and you will hear the connected balanced signal.

The volume control button not only acts as a volume control but it in fact controls the gain of the preamplifier and the signal level send to the poweramps at the same time. This reduces noise and creates the capability to handle a great range of input signals with only one knob.

Connecting and Monitoring Unbalanced Signals

The ASL RoXX -Series 301 Personal Headphone

Amplifier has an independent section for unbalanced signals and one for balanced signals.

A S L C O M M U N I C A T I O N S Y S T E M S RoXX-Series 301 Manual

The Pan control knob (11) can be used to pan the signal between the left and the right channel of the

RoXX 301.

The unbalanced input is DC and overvoltage protected

(except for speaker signals with the Line/Mic. button in the Mic. position).

Monitoring phantom powered signals

The ASL RoXX -Series 301 Personal Headphone

Amplifier is not equipped with a phantom-power facility. Nevertheless, sources which are phantompowered by another device can be monitored.

Connecting the RoXX 301 to the circuit of source and phantom-powering device will cause clicking of both the headphone amplifier and the other device (the input capacitors of the RoXX 301 need to be charged).

To reduce or prevent this clicking, a so-called groundlift cable (e.g. pin 1 not connected in one of the XLR connectors of that cable) can be used.

Unbalanced signals may be signals produced by instrument pick-ups (electric guitar), line outs of mixers, CD-players etc. or speaker signals. They can range from -16dBu to (almost)+ 4 . For your own safety

do not connect AC-signals higher than 40Vrms (e.g.

outputs of power amps >200 Watt into 8 ohm; a 1/4” jack is not a safe connector for these kind of signals).

Before connecting any unbalanced signal to the 1/4” input jacks, turn the Unbalanced input Volume control

(7) down.

There are three possibilities of connecting unbalanced signals:

* Suppose you want to connect an unbalanced mono signal on a mono 1/4” jack. This signal should be connected to the Jack input labeled "Right/Mono"

(14). The input labeled "Left/Stereo" (13) should be left unused. The mono input signal will be sent to both left and right channnels of the Personal

Headphone Amplifier.

* Suppose you want to connect an unbalanced stereo signal on a stereo 1/4” jack. This signal should be connected to the Jack input labeled

"Left/Stereo" (13). The input labeled "Right/Mono"

(14) should be left unused. The stereo signal will be sent as a stereo signal to the left and right channel of the Personal Headphone Amplifier.

* Suppose you want to connect an unbalanced stereo signal on two mono 1/4” jacks (e.g. Left and

Right). Connect the left signal to the input labeled

"Left/Stereo" (13) and connect the right signal to the input labeled "Right/Mono" (14). The signals will be sent to the corresponding channels of the ASL

RoXX -Series 301.

When the connected signal is higher than +6dBu, the

-20dB button (5) needs to be pressed. Turn up the

Unbalanced input Volume control (7) carefully and you will hear the connected unbalanced signal(s). The balance of the signal can be controlled by the Balance control knob (8). A stereo signal can be made mono by pressing the Stereo/Mono knob (6). This is usefull when a single muff headphone is used or when you want to pan the unbalanced signal to one side of your headphone.

The unbalanced inputs are DC and overvoltage protected.

Linking the unbalanced signal(s) to another ASL RoXX

-Series 301

The connector labeled ‘Unbal. Stereo Loop Thru’ (15) will allways provide a stereo signal of the signals connected to the input connectors. The unbalanced input signal(s) can be linked to another Personal

Headphone Amplifier (or other device) by connecting a stereo jack-jack cable between the Unbalanced

Stereo Loop Thru (15) connector of the first and the

Left/Stereo (13) of the second. Never use a 1/4” mono jack on the loop thru connector (the right input signal will be short circuited).

Using the RoXX 301 with an electric guitar (or any other instrument with pick-ups)

A pick-up will sound best if the load of it is very low

(e.g. input impedance is very high, like an active DIbox). ASL RoXX -Series 301 has a very high input impedance on the unbalanced inputs (as long as the -

20dB button is not pressed). So an instrument pick-up can be connected to the RoXX 301! Normally the

Right/Mono input connector would be used for this mono signal. But then the pick-up is loaded by both the left and right input amplifiers of the Personal

Headphone Amplifier, making the input impedance half its value. It would be better to connect the pick-up to the Left/Stereo input and pressing the Stereo/Mono button. The input impedance is now 500k ohms and the pick-up will sound best.

Volume Control

The unbalanced input section and the balanced input section both have their own volume control knob as descriped in the above sections. The unbalanced input(s) and the balanced input can be used at the same time with the possibility to make a mix between the signals with the two volume control knobs (and the balance and pan knobs).

Whenever only one input section is used turn the volume control of the not used section down (anti clockwise).

Warning !

Always turn down the volume controls down before connecting any headphone or input signal and turn up volume carefully. The output levels of the RoXX -

Series 301 can be ear damaging and destructive to your headphone.

A S L C O M M U N I C A T I O N S Y S T E M S RoXX-Series 301 Manual

Choice of the Headphone(s)

The choice of the headphone(s) is highly individual.

However, the ASL RoXX -Series 301 can handle almost any headset.

The headphone impedance should preferably have a value higher than 32 ohms. The headphone outputs of the unit are short-circuit proof so loading the outputs with a headphone-impedance lower than 32 ohms won’t damage anything (it may eventually cause clipping of the output amplifiers before the built-in limiter begins to operate).

In general, low-impedance headphones create a higher Sound Pressure Level on your ears (also depending on their efficiency), but using them will reduce battery life. These headphones can be a good choice in noisy environments. High-impedance headhones (>200 ohms) often have a lower SPL, but will increase battery life.

In case you want to use two headphones with the ASL

RoXX -Series 301, choose headphones with the same impedance (> 50 ohms) and efficiency.

Please check the specifications of your headphones if they can handle the output power of the Personal

Headphone Amplifier.

The Built-In Limiter

The ASL RoXX -Series 301 Personal Headphone

Amplifier has a built-in stereo limiter to prevent the output amplifiers from clipping.

The limiter range is 30 dB for the balanced input and

25 dB for the unbalanced inputs. So when the output level of the RoXX 301 reaches the threshold level of the limiter, the input signals can become 25 or even

30 dB higher before the output amps will actually clip.

If clipping occurs in one of the input stages of the ASL

RoXX -Series 301, the limiter can’t do anything against it. Carefull fixing of the -20dB button, the Line/Mic.

button and the volume control knobs remains necessary (the balanced volume control knob also controls the gain of the preamplifier)

The stereo limiter is combined for the balanced and the unbalanced signals. This means that whenever the limiter limits for instance the balanced signal, the unbalanced signal will go down in level even when the unbalanced signal itself still has not reached the limiter threshold level.

A S L C O M M U N I C A T I O N S Y S T E M S RoXX-Series 301 Manual

SPECIFICATIONS ASL RoXX - Series 301

Frequency response

Balanced input

Unbalanced input

50 Hz - 36 kHz +0, -3dB

40 Hz - 40 kHz +0, -3dB

Total Harmonic Distortion

< 0,3% (20 Hz - 20 kHz, 3 dB below limiting)

< 0,5% (100 Hz - 20 kHz, 10 dB over limiter threshold)

Equivalent Input Noise

- 125 dBu (22 Hz - 22 kHz, Rsource = 50 Ohm, max.

gain)

Headphone output Impedance

< 2 Ohms, Short Circuit Proof

Limiter

Limiter Threshold

Limiter Range

2,5V rms (10,4 dBu)

(measured at headphone output)

Balanced input 30 dB

Unbalanced input 25 dB

Power

Internal 4x 1.5V AA-Battery or 4x 1.2V rechargable NiCd or Ni-MH AA-Cell

External 9 - 24 V DC

Supply Current (idle) 80 mA with 4x 1.5V AA-Battery

Battery Life 24 hours under normal conditions with 4x 1.5V Alkaline Batteries

Dimensions

Weight

43 mm H x 94 mm W x 138 mm D

500 grams nett

Maximum Voltage Gain, Input Impedance and

Maximum Input Levels before clipping

Maximum

Voltage gain

Balanced Input

@ mic level

Balanced Input

@ line level

Unbalanced Inputs pad @ 0

71 dB

36 dB

26 dB

Unbalanced Inputs pad @ 30 dB

7 dB f = 1 kHz, Rsource = 50 Ohm

Input

Impedance

28 kOhms

20 kOhms

500 kOhms

23 kOhms

Maximum Headphone Output Level + Power

Max. Output Level

R load = 200 Ohm

R load = 32 Ohm

4.1 V rms

3.2 V rms

Maximum

Input Level

-10 dBu

+34 dBu

+12 dBu

+

4

Output Power

84 mWatt

320 mWatt

ASL COMMUNICATION SYSTEMS

Zonnebaan 42

3606 CC Maarssenbroek

HOLLAND tel. : +31 - (0)30 - 241 19 01 fax.: +31 - (0)30 - 241 06 38

ASL reserves the right to alter specifications without further notice.

A S L C O M M U N I C A T I O N S Y S T E M S RoXX-Series 301 Manual