Audio Engineering

264 Chapter 8

Second, the outputs of crossovers or consoles, or misconnected amps, which are kaput
and have DC faults, so the output voltage might range from  /–10 V to up to  /–30 V for
line sources, and up to /–160 V DC for power amplifi ers, but more typically  /–30 to
 /–90 V DC.

25. 00

PA–DCS–1.CIR Temperature  27

20. 00

15. 00

10. 00

5. 00

0. 00

100 m 1000 m

dB(v(V 0 )) dB(v(V 02 ) 1Hz) Frequency (Hz)

Frequency response

Phase response – linear scale

Usual

C3P

10 100

Gain

dB

10. 00

8. 00

6. 00

4. 00

2. 00

0. 00

Phase

Degrees

0. 10 20. 08 40. 06 60. 04 80. 02

ph(V 0 ) ph(V 02 ) Frequency (Hz)

100

Usual

C3P

Figure 8.8 : Direct current servo circuits cause at the very least the same phase and delay

error as using a DC-blocking capacitor conventionally. The upper graph shows the frequency

response of a standard two pole servo (2  { 1 M.O  470 nF } ). The lower graph shows

the phase shift, which is clearly nonlinear below 85 Hz—place a ruler against the line. The

curvature indicates a frequency-dependent signal delay, hence smearing (after Deane

Jensen). An alternative, custom three-pole compensating type (C3P) is plotted. This

overcomes the smearing, as the phase shift is much less than 0.1º above 5 Hz, but the

amplitude (upper) is now peaking below 1 Hz.