Yamaha P-2200, P-2200/2201, P-2201

bridging transformer box should be used. While matching

or step up transformers like those just described would

maintain a balanced feed, several such boxes could over-

load the source device. By using a transformer which has

a high impedance primary and a high impedance

secondary, the source can feed several P-2200 inputs

without being overloaded. Use one box for each

P-2200 input, paralleling the primaries (the primaries

are then fed from the single, balanced source; the

secondaries are connected to the P-2200 inputs). Con-

struct the box in a similar manner to the Step Up

Transformer Box, or the Matching Transformer Box.

Fig. 42 - Bridging Transformer Box Schematic. Construction

is similar to Photos in Figures 40 or 41.

Input Impedance Matching for the P-2200

While the input impedance of the P-2200 varies

somewhat with the setting of the input attenuator, for

practical purposes, it is fixed at 25K-ohms. This means

that any source device feeding the P-2200 must be

capable of driving a 25K-ohm load without overload,

distortion, or failure. Any professional device, most

semi-pro equipment, and most hi-fi devices meet this

requirement.

When a single source device feeds the inputs of

several P-2200 amplifier sides, the effective load on the

source is equal to the parallel combination of all the

P-2200 input impedances. To avoid overloading a high

impedance source, use a resistor matching network, an

impedance matching transformer, or insert a line

amplifier with a lower output impedance between the

source and the P-2200's input.

Figure 43 shows the voltage division diagrams for

the output impedance of a source device and the input

impedance of the P-2200, when various impedance

matching devices are used.

Fig. 43 - Voltage Division Diagrams

Level Matching and Headroom (also see Page FIVE 2)

Headroom is the amount of level available above the

average (nominal) signal for peaks in the program. Noise

floor is the average noise level at any point in the

system. The difference in level between the peak output

of the system and its noise floor is the system dynamic

range.

Careful level matching can optimize the dynamic range

of the system (minimize the noise) and maximize the

headroom.

First choose a headroom figure. For maximum fidelity

when reproducing music, it is desirable to allow 20dB of

headroom

above

the

average

system

output.

While

some

extreme musical peaks exceed 20dB, the 20dB figure is

adequate for most programs. A 20dB headroom figure

represents a peak level that is one hundred times as

powerful as the average program level. This means that

for an 8-ohm load, and a 20dB headroom figure, even an

amplifier as powerful as the P-2200 has to operate at an

average 2.3 watts output power. In some systems such as

studio monitoring, where fidelity and full dynamic range

are of utmost importance, this low average power may

be adequate. In other situations, such as 70-volt back-

ground music systems, a 20dB headroom figure is

undesirable and costly.

The choice of a headroom figure, then. depends on

the type of program material, the application, and the

available budget for amplifiers. For a musical applica-

tion where high fidelity is the uppermost consideration,

15 to 20dB of headroom is desirable. For most sound

reinforcement applications, especially with large

numbers of amplifiers, economics play an important

role, and a 10dB headroom figure is usually adequate.

For

these

applications,

limiter

will

help

hold

program

peaks within the chosen headroom level, and thus avoid

clipping problems. For the extreme situation where

background music and paging must be heard over high

continuous noise levels, such as a factory, yet danger-

ously high sound pressure levels must be avoided, a head-

room figure of as low as 5 or 6dB is not unusual. With

this low headroom figure, and the extreme amount of

compression and

limiting

necessary

achieve

without

distorting, the program may sound unnatural, but the

message

will

get

through.

Fig. 44 - Headroom Adjustments

After choosing a headroom figure, next adjust the

incoming and outgoing signal levels at the various

devices in the system to achieve that figure. For the

simple system in Figure 44, the adjustments for a 20dB

headroom figure would be made as follows:

1. Initially, set the attenuators on the P-2200 at

maximum attenuation (maximum counter clockwise

rotation). Feed a sine wave signal at 1000Hz to the

mixer input at an expected average input level