Handbook for Sound Engineers

Grounding and Interfacing 1205

32.6.2.2.1 For Unbalanced Interfaces

STEP 1: Unplug the cable from the input of Box B and

plug in only the dummy as shown below.

i Output quiet?

No—The problem is either in Box B or farther

downstream.

Yes—Go to next step.

STEP 2: Leaving the dummy in place at the input of

Box B, plug the cable into the dummy as shown below.

i Output quiet?

No—Box B has a pin 1 problem (see Section 4.3 to

confirm this).

Yes—Go to next step.

STEP 3: Remove the dummy and plug the cable directly

into the input of Box B. Unplug the other end of the

cable from the output of Box A and plug it into the

dummy as shown below. Do not plug the dummy into

Box A or let it touch anything conductive.

i Output quiet?

No–Noise is being induced in the cable itself.

Reroute the cable to avoid interfering fields (see

Section 32.4.2 or 32.4.4).

Yes—Go to next step.

Figure 32-40. Block diagram of example system.

TV

receiver

CD player

Cassette player

Preamplifier

Crossover and

subwoofer

power amplifier

Main

power

amplifier

ac power safety ground

Entry lightning

ground

CATV 3' 20' 15'

3'

3'

Figure 32-41. Balanced ground dummy.

Figure 32-42. Unbalanced ground dummy.

2

3

1

For balanced audio XLR

P1/J1 = Switchcraft S3FM adapter

with QG3F and QG3M insert

All resistors 1%, ¼ W metal film

For balanaced audio 3C phone

Use Switchcraft 383A and 387A

adapters with XLR version

2

3

1

49r4

S1 39r6

604

Close S1 for CMRR test only

Unbalanced interfaces

For audio RCA

P1 = Switchcraft 3502 plug

J1 = Switchcraft 3503 jack

R = 1 k 7 , 5%, ¼ W resistor

For audio 2C phone

Use Switchcraft 336A and 345A

adapters with RCA version

P1

R

J1

R

Output

Box A Box B

Cable Input

From

upstream

devices

To

downstream

devices

Output

Box A Box B

Cable Input

From upstream

devices

To

downstream

devices

Output

Box A Box B

Cable Input

From

upstream

devices

To

downstream

devices