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NJM2706

3D Surround Audio Processor with Dynamic Bass Boost

Japan Radio Corporation  

NJM2706

sAPPLICATION NOTE

1. Fine-Tuning the ealaBASS

The NJM2706 has quite sophisticated NJRC’s original dynamic bass-boost technology. Both of the level and the

frequency for bass-boost moves automatically corresponding to the input signal level. This dynamic filtering action

prevents the signals over boosted, and provides less distortion and wide dynamic range bass-boost processing.

In addition, if you want to fine-tune the bass-boost effect for your system, you can modify the bass-boost effect by

changing the external parts value as described below.

1-1. Modify the Boost Center Frequency

This plot shows the frequency response for NJM2706 ealaBASS.

Frequency Characteristics (eala Bass)

V+=12V Vin=-20dBVLch Vout=Lch RL=4.7k Ω

Rg=25Ω

10

C4=0.1µF

5

C4=0.15µF

C4=0.18µF

0

-5

10

100

1000

104

105

Frequency [Hz]

The Boost Center Frequency can be adjusted by changing the value for the external capacitor, C4.

If your speaker system has more than 100Hz of f0 (= Lower Frequency Response Range), or, if you would like to

get more powerful bass-boost effect than the typical settings shown on the page 9, increasing the Boost Center

Frequency higher could be a good idea. We strongly recommend you to determine the actual capacitance value by

testing and examinations on your actual application.

1-2. Modification for the LPF Cut-off Frequency fCL

This picture shows the equivalent circuit for NJM2706’s LPF.

20k

Lch

20k

Rch

R1 20k

2pin

3pin LPF

16k

1pin

MONO Amp. C1

0.1µ

* The pin numbers apply in DMP24 and SSOP24's case.

The LPF Cut-off Frequency fCL is given by the following equation:

1

1

fCL= 2πCR = 2πC1×16k

Set the fCL as same as the Boost Center Frequency, which is determined as above (The Boost Center Frequency =

the frequency of which the gain is +3dB). In the typical application circuit shown on the page 9, the LPF Cut-off

Frequency fCL is set to 100Hz.

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