Audio Engineering

364 Chapter 11

proposed that eight secondary segments should be placed in the gaps left between 10
primary windings. This increases the stray capacitance,C 1 , across the primary winding
and between primary and secondary coils. However, the HF phase errors introduced by
these will probably be unimportant within the design frequency spectrum.

11.8 Effect of Output Load Impedance .........................................................................

This is yet another area in which there is a confl ict in design requirements, between
output power and output stage distortion. Figure 11.17(a) , shows the output power

40

20

0

0 4K 8K 12K 16K 20K

Load resistance a-a (ohms)

2%

1%

Power output (watts)

KT66VaVg2 400 V U/L connected

Figure 11.17 : (a) Power output vs THD. (b) Power output curve.

0

0

0.4

0.8

1.2

4K 8K 12K 16K

Load resistance (ohms)

Power output (watts)

12

10

8

6

4

2

0

6AK6 Va  180 V

Power output

THD

3rd harmonic

2nd harmonic

THD percent