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Inputs 

– Slave amplifiers 

The S121 and S251 slave amplifiers accept a LINE IN via 2 x RCA connectors at the rear and the same signal can 
be sent out to further amplifiers from the LINE OUT pair of RCA connectors. Since the amplifier is mono, all stereo 
inputs are summed together. 

Inputs 

– Mixer-amplifiers 

A microphone can be connected to MIC1 channel by either 6.3mm jack or XLR to the front panel combo input. If 
required, there is also a 6.3mm jack connection on the rear panel for MIC1 channel. A further microphone can be 
connected to MIC2 channel via a 6.3mm jack on the rear panel. 

Line inputs (e.g. CD, DVD, mp3 players) can be connected to LINE1 and LINE2 channels via pairs of RCA 
connectors on the rear panel. Alternatively, for the USB/FM/AUX channel, a stereo 3.5mm socket on the front panel 
can be used instead 

– ideal for portable mp3 players etc. 

There is also a USB type A connector on the front panel for playback of digital audio files stored on a USB pen. 

The overall mix can be connected to further amplifiers via the OUTPUT pair of RCA connectors. 

Operation 

With all volume levels and VOX control turned down, connect the amplifier to the mains supply (ensure correct 
supply voltage) using a suitable IEC lead (as supplied) and switch POWER on. 
 
HIGH and LOW EQ controls should 

be initially set to the vertical “12 o’clock” position. 

If microphones are being used, turn up the MASTER control approximately half way and gradually increase MIC1 
rotary level control whilst speaking into the microphone until the required volume is reached. Repeat for MIC2 
volume control. Adjust HIGH and LOW EQ controls to alter the overall bass and treble response of both 
microphones as needed. 

For any line level devices connected to line input channels, adjust the LINE1 and LINE2 level controls in the same 
way as for the microphone channels. Overall tone of the line inputs (including the USB/FM/AUX) can be adjusted 
via the HIGH and LOW controls. 

For the USB/FM/AUX channel, pressing MODE toggles between the USB device, FM tuner or AUX input as a 
sound source. Turning the USB/FM/AUX level control increases the level of the playback through the amplifier 
For the FM tuner, an initial channel search can be performed by pressing “CH –“ followed by “PLAY/PAUSE” .  

Summary of Contents for A121

Page 1: ...908 S251 Slave amp 250W 952 911 User Manual Features 2 Mixer amp models and 2 Slave versions Transformer coupled output for 100V or 4 16Ω operation USB FM audio player on mixer amp models Compact 1U rack mount format Dual fan cooled High efficiency toroidal transformers 32V phantom power switchable www avsl adastra com ...

Page 2: ...cover or obstruct cooling vents or fan grilles Placement Keep out of direct sunlight and away from heat sources Keep away from damp or dusty environments When rack mounting secure firmly in place and avoid positioning heavy items directly on top of the unit Ensure adequate access to controls and connections and pay attention to cooling air flow Cleaning Use a soft cloth with a neutral detergent to...

Page 3: ...250W system 100Vmax 250W 100V 2 5A so the speaker cable should be rated to 2 5A minimum Each speaker must be connected in a parallel chain and the total wattage for all speakers should not exceed 90 of the amplifier s rated output Please see the diagram below to show an example arrangement 25 FM antenna connection Cooling fans 26 OUTPUT 2 x RCA line output 27 LINE1 LINE2 2 x RCA line inputs 28 MIC...

Page 4: ...imum impedance of the total speaker load connected to either or both of these sockets must be no lower than 4Ω The impedance is calculated using an inverse calculation as shown below _________1________ _________1________ _________1________ Impedance Speaker 1 Impedance Speaker 2 Overall Impedance therefore for 2 speakers each 8Ω impedance _1_ _1_ _1_ 8Ω 8Ω 4Ω so the overall impedance is 4Ω for bot...

Page 5: ...via the OUTPUT pair of RCA connectors Operation With all volume levels and VOX control turned down connect the amplifier to the mains supply ensure correct supply voltage using a suitable IEC lead as supplied and switch POWER on HIGH and LOW EQ controls should be initially set to the vertical 12 o clock position If microphones are being used turn up the MASTER control approximately half way and gr...

Page 6: ...cking of the other channels when MIC channels are used SPECIFICATIONS Model A121 A251 S121 S251 Power supply Switchable 110 240Vac 50 60Hz IEC Output RMS 4Ω 120W 250W 120W 250W Mic input front MIC1 combo connector XLR jack N A N A Mic inputs rear MIC1 MIC2 6 3mm jacks N A N A Line input front AUX stereo mini jack 3 5mm N A N A Line inputs rear LINE1 LINE2 RCA pairs N A N A Mic controls MIC1 MIC2 L...

Page 7: ... file types standard compressed digital audio files required Check memory device works on a PC or Mac for standard playback Output is very loud or LIMIT LED is on constantly Check level of input signal is not too high Reduce channel volume and EQ settings Reduce MASTER level until LIMIT light stops flashing Ensure Hi Z line level input s not connected via MIC1 or MIC2 Output is working but at very...

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