Use your Ears to Bal DC

 


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Last Edited:
12-Sep-2004

 
This is the DC Balance Adjustment procedure for the 222D Integrated Stereo Amplifier, quoted directly from the H.H. Scott "Service Bulletin."

"To make this adjustment a short audio cable with an audio (RCA -phono) plug on one end and bare wires on the other end is needed.

Insert the (RCA phono) plug into the RIGHT (B) Channel Tuner Input, and connect the two bare wires to the LEFT (A) Channel Speaker Terminals (High and 0).

Connect a loudspeaker to RIGHT (B) Channel Speaker Terminals (High and 0).

Connect the Green wire that comes through the chassis grommet to the RIGHT (B) Channel speaker impedance terminal which matches the impedance of the speaker being used.

Remove V3 (ed note: the phase-splitter tube for the LEFT or A Channel). Set the Controls as follows:

Input Selector Tuner
Power Switch Off
Stereo Selector Stereo
Bass & Treble 0
Stereo Balance 0
Loudness Control (Vol pot) 0
Compensator Loud
Tape Out
Scratch Filter Out
Speakers On
Equalization Either Position

Insert the power line cord into an AC outlet and turn the unit on. Wait a few minutes for the amplifier to completely warm up.

Slowly turn the Loudness Control clockwise until you can just hear a low hum in the loudspeaker. (If you turn the volume up too high, the amplifier will oscillate and produce a motor-boating noise).

Take a small screwdriver and adjust the LEFT (A) Channel DC balance control for minimum hum. (Hum is a 120 cycle low frequency noise -- do not confuse it with any high frequency noises present.)

Turn off the amplifier and replace the tube V3.

Connect the audio cable to the RIGHT (B) Channel speaker terminals (High and 0) and insert the (RCA phono) plug into the LEFT (A) Channel Tuner Input.

Connect the loudspeaker to the LEFT (A) Channel Speaker Terminals (High and 0).

Connect the Red wire that comes through the chassis grommet to the LEFT (A) Channel speaker impedance terminal which matches the impedance of the speaker being used.

Remove V103 (ed note: the phase-splitter tube for the RIGHT or B Channel). Keep the Controls the same as before.

Turn on the unit, and adjust the RIGHT (B) Channel DC Balance control for minimum hum. 

Turn off the amplifier and replace the tube V103."

 

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