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Bandwidth Audio 22A3, Owner'S Manual, Page: 9 / 17

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Bandwidth Audio 22A3 Owner'S Manual Download Page 9

22A3 Monaural Amplifier Rev 1.0                                                                                                               

9

 

2.3

 Top Features 

 

 

 
 
 
 

12. Negative  
      Feedback  

Feedback switch to select between “Open Loop” mode for feedback

-free 

operation, or “Closed Loop” Mode for operating the amplifier wi

th feedback. 

Closed Loop Mode is suggested for higher output power close to the 
amplifier

’

s rated output. This will reduce distortion (THD + N) and help to 

maintain linearity.  
 

12. Negative Feedback                                 13. Hum Balance      14. Hum Balance 

Summary of Contents for 22A3

Page 1: ...22A3 Monaural Amplifier Owner s Manual www bandwidthaudio com sales bandwidthaudio com ...

Page 2: ...gged and not in use Do not remove back cover unless you are a qualified service technician For service contact Bandwidth Audio High Vacuum Tube Temperatures Vacuum tubes get extremely hot with bulb temperatures capable of reaching 200 degrees Celsius Do not touch or attempt to remove the tubes while hot Amplifier Bias With the volume turned all the way down the bias should be set between 50 60mA T...

Page 3: ...before powering on See Section 3 3 Biasing 1 1 Amplifier Placement For the best operation and longest life of components the amplifier should be set up and used in a well ventilated area with good air circulation Do not use the amplifier in enclosed furniture as this may result in a fire Overheating can damage the amplifier and diminish tube life 1 2 Setting The Load Impedance Never turn on your a...

Page 4: ...mplifier illuminates when powered on Tube warm up time is typically 30 seconds It will take at least this long for music to play from speakers Best performance is achieved after amplifier has been running for a period of time and up to a steady temperature typically 30 minutes When powering off music may still play for a few seconds This is normal While the tubes are hot make sure not to move or k...

Page 5: ...ng the input signal Rather than a normal rotational potentiometer a stepped attenuator is used A stepped attenuator eliminates noise during rotation and also maintains volume balance between a pair of amplifiers driving separate speakers Due to its construction the volume knob will click into each slot giving precise volume control 1 Volume 2 VU Meter 3 Power ...

Page 6: ...ut power rated at approximately 5 Watts of output power when it is indicating 0dB Driving the output beyond this region will cause amplifier distortion Although this is not harmful to the amp there is a significant increase in the average output power as distortion increases This can damage speakers rated close to the amplifier s maximum RMS output power 3 Power Switch The power switch is used to ...

Page 7: ...s current to protect the user and amplifier from various short circuit failures 6 Cathode Fuse Use only Amp Slow Blow Fuse Fuse is in series with V3 and V4 output tubes to protect the output transformers and other circuitry from a shorted or bad tube If blown check performance of the output tubes before replacing the fuse to prevent damage from a failed tube 4 Mains 5 Mains 6 Cathode 7 Bias Curren...

Page 8: ...voltage ground to lower the AC filament noise This is usually set in the middle and requires no adjustment However if hum is discernable through the speakers try rotating the potentiometer clockwise and counterclockwise from the center position to minimize it If no change occurs the hum is being picked up by another source 10 Speaker Outputs Used for connecting the speaker load to the amplifier Ma...

Page 9: ...en Loop mode for feedback free operation or Closed Loop Mode for operating the amplifier with feedback Closed Loop Mode is suggested for higher output power close to the amplifier s rated output This will reduce distortion THD N and help to maintain linearity 12 Negative Feedback 13 Hum Balance 14 Hum Balance ...

Page 10: ...t and correcting for error Increasing the volume back after moving to Closed Loop mode will still realize all of the benefits of a feedback topology 13 14 Hum Balance Screwdriver adjustable potentiometers that form the center taps for filaments on output tubes V3 and V4 Since the 2A3 tube is a directly heated triode the center tap of the firmament forms the cathode connection for signal ground Thi...

Page 11: ...ld be followed Tubes should always be installed and removed by handling the base of the tube rather than the glass Match the keyway in the tube socket with the key in the tube and install with a slight and gentle circular rocking motion until the tube is fully seated against the socket Follow the same procedure for removal 3 2 Replacing Tubes Vacuum tubes should be replaced when a lack of power be...

Page 12: ... change unless reliability is a concern and the amplifier has seen a lot of vibration from transportation Moving the amps when they are on or hot can damage the rectifier and other tubes Always re bias your amplifier after changing the power tubes The bias of the amplifier should be checked immediately after replacing the 2A3 Power tubes V3 and V4 Hum Balance adjustment potentiometers may also nee...

Page 13: ... The bias reading for the power tubes can made off of the two analog ammeters located on the back face of the amplifier Bias Set Point 50 to 60mA With the volume turned all the way down the bias should be set between 50 60mA by the screwdriver adjustment potentiometer labeled Bias on the back of the amplifier This range is based on sound preference as well as desired output tube life The lower the...

Page 14: ... fact the power tubes can last longer However distortion will rise steeply causing significant distortion figures less power and bad sound Running the amplifier with a bias setting over 53mA will decrease the life of the power tubes A bias well over 53mA will cause red plating or glowing of the internal metal plate structure of the tube due to excessive heat This can be so excessive that the glass...

Page 15: ... at 1 Watt 1KHz 0 5 Open Loop 0 35 Closed Loop 1 Watt Bandwidth 13Hz 23KHz at 3dB Open Loop 13Hz 32KHz at 3dB Closed Loop Input Voltage for Rated Output 1 3V RMS Open Loop 1 7V RMS Closed Loop SNR 1 Watt into 8ohms 600 ohms source impedance volume set to maximum 90dB A Weighted Open Loop 91dB A Weighted Closed Loop SNR 5 Watts into 8ohms 600 ohms source impedance volume set to maximum 95dB A Weigh...

Page 16: ...osed Loop Only 2 dB Input impedance 100K ohms Speaker Taps 4 8 16 ohms Power Tubes 2x 2A3 Preamp Tubes 1x 6SL7 1x 6SN7 Rectifier Tube GZ34 Power Consumption 100 Watts Dimensions 20 x 13 x 9 5 Due to the open loop design of this amplifier actual performance will vary depending on vacuum tube quality ...

Page 17: ...______________ Bias Current V3______________ V4_____________ Notes ___________________________________________________________________________________ ___________________________________________________________________________________________ ___________________________________________________________________________________________ _________________________________________________________________...

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