ESOTERIC SOUND Re-Equalizer Manual de usuario descargar pdf (Pagina 6)

MODEL 408A – HOW DOES IT WORK?

In Figure 1, the dual, low-noise opamps (U1 and U2) provide all the preamp gain and frequency

response shaping with the RC networks. Because of the circuit design, the gain and frequency

response of each stage (U1 and U2) are independent. The value of R3, R10, R15 and R22 can be

changed by moving jumpers on jumper-blocks (JB1 through JB4) to set the maximum gain to 52,

56 or 60 dB. All jumpers should be set to the same gain or the frequency response will not be

correct.

To eliminate ground loops (for lower output noise), the circuit board common (ground) is connected

to the aluminum enclosure at only one point: at the left input connector.

Response shaping is done by the RC networks with rotary switch S1 controlling the Turnover

frequency and S2 controlling the Rolloff gain at 10 kHz. Many texts detail calculating the

component values for these networks so we wrote a couple of computer programs to make the

calculations easier (they are freely available on our website under Downloads).

U3 with its associated components are the Rumble filters with corner frequencies of 20 Hz. They

may be switched in or out (bypass) with toggle switch S3. U5 buffers the output of the dual Volume

control and provides the stereo signal to the output connectors when the output lowpass filters are

bypassed. The filter is switched IN or to bypass with toggle switch S4. Figure 3 shows the output

lowpass filters that are used only when they are switched IN by S4.

The 24 VDC from the wall power supply is very noisy so it enters the preamp into a separate

shielded enclosure that contains noise filters and voltage regulators (Figure 4). The 24 volts is “split”

into positive and negative levels of about ±12 volts. These voltages are then regulated to ±6 volts

with U6 and U7.

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ESOTERIC SOUND Re-Equalizer Manual de usuario Pagina 6