BThe Acoustic People
Manual amp two
bottom line
amp two
Operating Manual
1. Introduction
2. Safety precautions
3. Concept
4. Controls
5. Operation summary
6. Technical specifications
7. Disposal regulations
1. Introduction
Welcome to AER. It took us quite some time – so we are all the more happy
that you have opted for the amp two.
You have chosen a professional, compact and powerful amplifier which was
designed especially for handling electric basses.
When talking about authentic tone, not just the instrument but the entire signal chain is our reference. Instrument, pickup, cable, preamplifier, power amplifier and loudspeakers will create what you understand as ‘your tone’.
We would appreciate if the amp two should become a vital element for you
and wish you lots of enjoyment with it.
2. Safety precautions
Please read and check if you have understood all instructions in this manual.
down on dynamics, since the power amplifer, power supply or components
hit their performance limit too early.
Always take some basic safety precautions when using your amp two in order
to minimize the risk of injury through fire or electric shock.
By now it should be clear how complex the problem is and why we have taken
quite a different approach to realise our tonal ideas, letting the ‘bass’ sound
the way it wants to sound.
Pay attention to all warnings, instructions and additional texts on the amp
• An analogue 200 watts power amplifier with high dynamic reserves and a
massive power supply provides the required output power.
Always use an earthed power supply with the correct mains voltage. If you
are in doubt about the power outlet’s ground, have it checked by a qualified
• The analogue signal processor monitors the signal so that the full output
power can be called on without an ample ‘headroom’ which would be required otherwise. This will spare you space and weight, save the loudspeaker
and provide constant, defined power amp conditions. Since this is a ‘closed
system’ (power amp, processor and loudspeaker), all components can be perfectly matched while ensuring maximum efficiency without overstraining the
system. We go to the limits, but not beyond.
Use only fuses with the same current rating and trigger characteristic as replacements. Never mend fuses! Should a fuse blow again after a short while, the
device needs to be checked.
Pay attention to an unhindered air circulation in the amplifier’s surroundings.
Never obstruct the air vents or grilles.
Do not install or use your amp two in close proximity to water or if you are
soaking wet yourself.
Use your amp two in a safe place where nobody can step on cables or trip over
and damage them.
Do not install your amp two close to devices with strong elec­tromagnetic
fields such as large mains transformers, revolving machines, neon illumination etc. Do not lay signal cables parallel to power current cables.
Cable up your amp two only if it is powered off.
Always pull out the mains plug before you clean your amp two. Use a damp
cloth for cleaning. Avoid the use of detergents and do not let any liquids enter
into the unit.
There are no user-servicable components inside your amp two. All maintenance, adjustment and repair works should be carried out by qualified staff
only. Any unauthorized tampering will void our 2-year warranty.
Keep this manual in a safe place!
• We have chosen a 10” Sica instrument speaker chassis. This loudspeaker is
highly suitable for a good bass response, especially in small ported cabinets.
However, response characteristic, power handling and efficiency are interdependent factors so that dedicated bass chassis are always a bit lower in volume (approx. -3dB) than all-purpose speakers. The chassis has been tested for
electrical and mechanical dependability according to AES standard.
• The cabinet must withstand an enormous strain. It is made from 18 mm slotted, waterproof laminated birch plywood. The speaker chassis sits in a separate ported chamber to provide optimum uncoupling from the electronics.
• Additional features:
- Compressor
- Adjustable XLR DI out
- Line out, tuner out, headphones out
- Footswitchable >Mute< and >Effect on/off< functions
- Pre and post EQ inserts
- Effects loop
- Ground lift
3. Concept
It was our ambition to put a professional unit with tremendous power, great
features and outstanding tonal qualities into a small portable cabinet to make
the ‘whole bass’ really happy.
It’s been known for a long time how innovative today’s bass players are and
how they love trying out new things.
No doubt has the electric bass evolved into a ‘solo instrument’; for this reason
the acoustic and technical requirements have gone up steeply and consequently the demands on the engineers as well.
Straight talk
A distortion-free, rock-solid and deep bass reproduction finds itself in constant opposition with physics, human perception and what product costing
still accepts as in line with market conformity.
A lot more energy is needed to give the fundamental bass notes the same volume as midrange or treble frequencies. The aim is a harmonic reproduction
of the instrument’s pure tone, irrespective of resonance and formant ranges.
In theory several problematic issues can add here in a negative way:
• The human ear is far more sensitive at middle frequencies than at any other
tonal ranges.
• The instrument shows a very uneven reproduction of its individual spectrum.
There are big differences in level, dispersion characteristic and sustain which
produce frequency cancellations and peaks.
• The reproduction of low bass frequencies requires more ‘energy’ and puts
a lot more stress on the material as well as the components – the more so if
extra amplification is made using equalization (e.g.: +15dB at 80 Hz equals the
5.6-fold voltage at this point or 31.6 times more power).
Tonally speaking, the ‘bass’ is a very demanding instrument. Its reproductive
capabilitiy extends over the entire audio spectrum. The level-relevant distribution, however, is very disproportionate. In general the lows and particularly the highs are greatly boosted to achieve a well-balanced signal which can
then be further processed by sophisticated tone controls.
The random interaction of pickups, pre and power amplifiers, each with numerous controls and varying quality degrees, will soon reveal limitations that
will entail a mediocre signal-to-noise ratio of the whole audio chain and cut
- Adjustable AUX input
4. Controls
Left to right:
input Instrument input (mono jack)
middle Midrange control
high / low Sensitivity selector switch
high: high sensitivity
low: low sensitivity
freq. Center frequency of midrange control (200 … 2000 Hz)
wide / narrow Bandwidth of midrange control (wide / narrow)
gain input level control
treble Treble control
clip Overload indicator
mute Amp mute (also controllable via footswitch)
tone balance EQ balance shift (allows bass or treble accentuation or a
combination of both.)
compressor Dynamic compressor (for narrowing dynamic range)
threshold Sets the level above which the compressor becomes
active (clockwise lower level, i.e. higher compression).
ratio Sets the compression ratio
(clockwise higher compression).
active Control indicator. Lights up when the compressor becomes active (depending on input signal)
off / on Turns the compressor on/off.
equalizer 3-band equalization (see also technical specifications)
colour Midrange contour filter. Boosts presence range and
slightly cuts low mids.
bass Bass control
bass boost Additional lower bass boost
balance Alters the type of equalization as follows:
Left stop: bass boost
Center setting: bass and treble boost
Right stop: treble boost and bass cut
intensity Controls the intensity of the balance EQ
Left stop: no effect
Right stop: full effect as described under ’balance‘
master Overall volume control
power Operation indicator
Rear panel
Left to right
line out
pre/post masterSwitches the line output pre or post master
volume control
headphones Caution! Use only stereo headphones.
Please insert no mono cables!
line out Preamp output
sub out Unfiltered output for an active subwoofer
footswitch Stereo footswitch socket,
TIP = mute, RING = effect on/off
send Output to an external effects unit
return Input from an external effects unit
insert pre eq Insert loop pre EQ
insert post eq Insert loop post EQ
aux in Stereo input jack for connecting a CD player e.g.
tuner Output to an external tuner.
May also be used when input is muted
aux level Aux signal level control
hf level Additional treble control (has only effect
on the onboard speaker)
DI pre/post eq Selector switch for the DI output signal;
pre or post equalizer and effects
DI level Signal level control at DI output
DI out Balanced XLR output, pre master
ground lift Disconnects signal ground from protective ground,
thereby eliminating hum problems with so-called
ground loops. However, this button should normally
remain switched off (i.e. not pushed).
power on Combined power switch with fuse holder
and mains input socket
5. Operation summary
• Cabling and startup
Check if your local mains voltage (e.g. 120 V in the USA, 230 V in Euro­pe) complies with the required operating voltage for your amp two. The proper mains
voltage is printed on the rating plate on the rear panel of the unit, e.g. AC 230V
(AC means alternating current).
Please take care that the master and intensity controls are set to zero (left
stop) and all other controls to their center positions. Don’t forget the unobtrusive hf level control on the rear – it has a strong effect on the treble response!
The pushbuttons should be switched off (not pushed in). Next make all the
necessary cable connections (mains, instrument etc).
Now you may turn on your amp two with the power-on switch located on the
back. The green power control LED will indicate operational readiness.
• Level adjustment
Using the high/low switch and the gain control you can adapt different pickup systems or other signal sources to the amp two.
The best possible sound quality is achieved when the gain control is set neither too high (distortions) nor too low (noise, too little volume). While playing
with a strong attack, turn the gain control clockwise until the clip indicator
flashes momentarily. Now turn back the gain control slightly (and also the
instrument’s volume control, if needed) to ensure an undistorted reproduction. The clip control LED should now only rarely flash. In case you have problems with that because the input signal is too strong, press the high/low
button as well.
Finally set the desired overall volume with the master control. With the mute
switch you can mute the amplifier as required.
• Equalization
Hopefully we have designed the filters in such a way that you can use the EQ
network as a flexible and universal tool which lives up to the great variety of
basses and voices. One more note: Adjusting the EQ controls can also affect
the level setting. Whenever you see the clip indicator flashing frequently, you
should slighty correct the gain setting (see ’Level adjustment’).
Tell us if we’re right!
However, we feel that it takes more to give the instrument a round, well-balanced sound. An extreme treble boost (inharmonic reproduction characteristic, especially in connection with active bass electronics) will also increase hiss
and noise, of course.
• Compressor
All our amplifiers offer a dynamics control (limiter). Furthermore you can also
activate a compressor in the instrument channel (aux-in remains unaffected).
Besides using it as a mere bass effects device, the compressor can also help to
level out dynamic contrasts between different signal sources.
• Additional Connectors
headphones: Allows the connection of a stereo headphone set. Caution: can
only handle stereo jack plugs, please do not insert any mono jack plugs!
line out: This output provides the master signal including equalization and
ef­fects, e.g. for connecting an active extension speaker cabinet. The line out
pre/post master switch lets you select if or not the output signal level shall be
independent from the master volume control.
sub out: Allows the connection of an active subwoofer.
The footswitch jack allows the connection of a standard dual footswitch by
means of a stereo cable. With this the external effect (send / return) may be
switched on or off, in addition the mute function may be remote-controlled
(see also technical specifications).
send and return: Using these jacks an external effects unit may be linked in
‚parallel’, i.e. the effect is blended with the original signal.
insert pre eq and insert post eq: Using these jacks an outboard device may
be linked pre or post equalization „in series“, i.e. the signal path will be interrupted and the signal entirely fed through the outboard device. Connection
is normally made with a so-called splitter cable (stereo to 2x mono) – see also
technical specifications.
aux in: Stereo jack input (left and right channel are summed) for a playback
signal (e.g. CD).
tuner: A tuner may be connected to this signal output. Thus any sound degredation is prevented as the tuner is no longer connected directly to the instrument. The tuner output may also be used after the amplifier has been muted
with the mute switch.
DI out: Balanced pre master XLR output (suitable for linking the amp two directly to a PA system or for recordings). The DI out pre/post eq switch determines if the signal shall be output with or without equalization and effects.
6. Technical specifications
Single-channel amplifier for electric basses
Inputs (notes 1, 4)
inputHigh-impedance instrument input
Mono jack, ¼” (6.35 mm) Sensitivity: 22 mV (-33 dBV)
Impedance: 1 Megohm
Equivalent input noise: 2 µV (–114 dBV),
high / low switch: 10 dB attenuation
aux inStereo jack, ¼ “ (6.35 mm)
L + R mixed and added pre master,
but post tone controls.
Level control.
Sensitivity: 2 x 185 mV
Impedance: 22 k (each channel)
Return for parallel effects loop
Mono jack socket, ¼” (6.35 mm)
Sensitivity: 400 mV
Impedance: 10 k
tone balanceNo effect if intensity is set fully to the left. The following
values apply if intensity is set fully to the right:
balance left:
+10 dB at 50 Hz
balance at center position:
+8 dB at 50 Hz, and +7 dB at 10 kHz
balance right:
-3 dB at 50 Hz and +8 dB at 10 kHz
(shelf-type frequency response in all cases)
hf level+6/-19 dB at 10 kHz, effective on built-in
loudspeaker only.
Compressor (note 5)
threshold range 1 mV … 350 mV at instrument input
ratio range
1:1 … 10:1
Time constant
38 ms
Outputs (note 2)
Indicator LED
Lights up at approx. 1 dB gain reduction.
headphonesOutput voltage: 1.1 V (20 mV input)
Power: max. 100 mW into 32 ohms
Internal speaker is muted when headphone is plugged in.
Stereo jack, ¼” (6.35 mm)
For use with stereo headphones only.
Please do not connect anything with a mono jack plug.
line outSwitchable pre / post master
Mono jack, ¼” (6.35 mm)
Output voltage: 2.3 V
sub outSubwoofer output without filter
Mono jack, ¼” (6.35 mm)
Output voltage: 2.3 V
Power amp
240 W / 8 ohms, discrete bipolar transistor design
Limiter threshold 220 W
Analog signal
Subsonic filter, low distortion RMS limiter
Speaker system12“ (300 mm) woofer with neodymium alloy magnet,
bass reflex enclosure
4” (100 mm) mid-high direct-radiating speaker
Mains powerMains voltage (depending on model):
100, 120, 230, or 240 V AC, 50–60 Hz
Power consumption: max. 700 W
sendSend for parallel effects loop
Mono jack, ¼” (6.35 mm)
Output voltage: 900 mV
Mains fuse5 x 20 mm
slow 3.15 A for 230 and 240 V models
slow 6.3 A for 100 and 120 V models
tunerTuner output, not affected by mute
Mono jack, ¼” (6.35 mm)
Output voltage: 900 mV
0.7“ (18 mm) birch plywood
waterbased acrylic, black spatter finish
DI out
Dimensions500 mm (19.7 “) high
420 mm (16.5 “) wide
350 mm (13.8 “) deep
re-master, switchable pre / post tone controls and
effects, level adjustable, balanced XLR output.
Output voltage: 0…370 mV
Insert points
insert pre eqInsert loop before tone controls, but after compressor
Stereo jack, ¼” (6.35 mm)
Output voltage: 900 mV
tip = send, ring = return
insert post eqInsert loop after tone controls
Stereo jack, ¼” (6.35 mm)
Output voltage: 900 mV
tip = send, ring = return
23,5 kg (51.7 lbs)
1. Input sensitivities refer to 220 watts into 8 ohms at full gain and volume settings,
neutral tone control settings (hf level in center position, intensity in left position), and
1 kHz sine-wave test signal.
2. Output levels refer to 63 mV / 1 kHz at instrument input, unless stated otherwise.
Footswitch connections
3. Bandwidth of tone controls refers to one half of dB-gain at center frequency. For
example, if center gain is –15 dB, then bandwidth is the frequency band between the
–7.5 dB points.
footswitchStereo jack, ¼” for dual footswitch
tip = footswitch for input muting
ring = footswitch for parallel effects loop on/off
sleeve = common (ground)
mute switch disabled when footswitch is plugged in
5. Compressor threshold refers to 1 dB gain reduction. Threshold tolerance ±3 dB. Ratio
refers to 20 dB gain reduction. Ratio varies with gain reduction due to soft-knee
Tone controls
–1 dB at 300 Hz, +8 dB at 3.7 kHz
±8 dB at 80 Hz
bass boost
+10 dB at 55 Hz
middle±15 dB at 200…2000 Hz (adjustable)
Bandwidth (switchable, note 3):
wide: 1.6 octaves (Q = 0.37)
narrow: 0.6 octaves (Q = 1)
±12 dB at 6 kHz
4. Equivalent input noise voltage obtained by measuring noise voltage at speaker output and dividing by the effective voltage gain of the amplifier. Full gain and volume
settings, neutral tone control settings, input shorted, frequency range 20 Hz – 20 kHz.
Specifications and appearance subject to change without notice.
7. Disposal Regulations
The disposal of electronic equipment in household waste is not permitted. AER GmbH waste electrical and electronic equipment is not
to be taken to public collection points for disposal.
European Union, Norway, Iceland and Liechtenstein
AER GmbH remains solely responsible for the disposal of AER GmbH
waste electrical and electronic equipment labelled with a dustbin.
The disposal of electronic equipment in household waste is not permitted.
To dispose of AER GmbH waste electrical and electronic equipment
that is labelled with a dustbin symbol, please contact us; we will ensure correct and cost-neutral and disposal.
All AER electrical equipment affected by WEEE has been labelled
with the symbol of a crossed out dustbin since 13.08.2005. This is also
applicable for Norway, Iceland and Liechtenstein.
In the case of AER GmbH waste electrical and electronic equipment
that is not labelled with a dustbin, the owner is responsible for correct disposal in accordance with the law.
This symbol indicates that the disposal of the equipment is not permitted with household waste.
However, we are also happy to help in this case and we can present
you with the options of where to dispose of these electrical goods.
The telephone number of AER GmbH: +49 (0)2361 891789
It has been circulated in this form since 13.08.2005.
The European directives of WEEE are anchored in different respective
national laws in all European states. As such, we are unfortunately
unable to provide you with one standard disposal solution.
The distributor or importer for the respective state is responsible for
the observance of the laws of that state and must ensure the disposal
of the waste electrical and electronic equipment in accordance with
national regulations.
The EU directive on the disposal of waste electrical and electronic
equipment (WEEE, 2002/96/EC) has been changed to the electrical
and electronic equipment act.
Other Countries
All AER electrical equipment affected by WEEE has been labelled
with the symbol of a crossed out dustbin since 13.08.2005.
For correct disposal of the electrical goods, please ask the local dealer
or the appropriate authority.
Here, we will provide you with qualified information on the disposal
of AER GmbH waste electrical and electronic equipment.
This symbol indicates that the disposal of the equipment is not permitted with household waste.
It has been circulated in this form since 13.08.2005.
In the German registration department EAR, AER GmbH has been
registered under WEEE registration number DE26301529.
B The Acoustic People
Jan 2009