Studer A1 - A3: Input Common Mode Rejection Ratio (CMMR); A3: Quiescent Current Setting

A Series Active Monitor Speakers
E4/16 Service Date printed: 29.02.00
4.4.1.6 A3: Input Common Mode Rejection Ratio (CMRR)
• Connect the generator in common mode to the input – i.e. “hot” generator
output to both input terminals no. 2 (+) and 3 (–), “cold” generator output
to input terminal no. 1 (GND).
Steps Generator Measurement
No. Description Id Value Test pos. Type Value Limits
1 CMRR 50 Hz G1 0 dBV/50 Hz/sine wave M1 Level < –60 dBV
2 CMRR 1 kHz G1 0 dBV/1 kHz/sine wave M1 Level < –60 dBV
3 CMRR 10 kHz G1 0 dBV/10 kHz/sine wave M1 Level < –40 dBV
4.4.1.7 A3: Quiescent Current Setting
Procedure: 1. Measure the primary current:
A1
1
= 40…50 mA
AC
(for 230 V), or 80…100 mA
AC
(for 115 V),
and note the measured value;
2. Adjust RT390 (turn carefully clockwise) for a reading of:
A1
2
= A1
1
+ 3 mA
AC
(for 230 V), or A1
2
= A1
1
+ 6 mA
AC
(for 115 V),
and note the measured value;
3. Adjust RT290 (turn carefully clockwise) for a reading of:
A1
3
= A1
2
+ 6 mA
AC
(for 230 V), or A1
3
= A1
2
+ 12 mA
AC
(for 115 V),
and note the measured value;
4. Connect both dummy load resistors (10 Ω/10 W each) and check the pri-
mary current again:
A1
4
= A1
3
±0.5 mA
AC
(for 230 V), or A1
4
= A1
3
±1 mA
AC
(for 115 V).
Common mode rejection
–100
0
–90
–80
–70
–60
–50
–40
–30
–20
–10
[dBV]
20
20 k
50 100 200 500 1 k 2 k 5 k 10 k
[Hz]