Subsonic Filter; Limiter Circuit - Ecler APA600 Bedienungsanleitung

The "STK OUTPUT" (18, 20) are in parallel with the inputs and are used to supply the
same input signal to other amplifiers or sound systems. This signal output connectors are of jack
1/4" type. The pin assignment is as follows:
The input impedance is 22KΩ (balanced) with a nominal input sensitivity of 0dBV(1V).
This impedance makes possible to parallel several amplifiers without loosing audio quality.

3.4. Subsonic filter

This filter cuts off inaudible frequency components which when amplified suppose a
risk of damage to the low frequency speakers as they generate excessive excursions of the
woofer's diaphragm. The APAs feature a switchable, Butterworth shaped Subsonic Filter
located inside the unit (see figure 1) with a 25Hz cut-off frequency and 18dB/oct slope.
Subsonic filters are very important when playing back vinyl records because the
phono cartridges are specially sensitive to feedback and acoustic coupling at very low
frequencies.
APA amplifiers are delivered with switched ON Subsonic Filter.
CAUTION: Changes on the Subsonic Filter have to be performed by a qualified
technician.

3.5. Limiter circuit

This system is an always active protection inside the APA series of amplifiers. The
ANTICLIP circuitry constantly analyses harmonic distortion caused by excessive signal
excursion at the power amplifier's output and automatically reduces the input level in order
never to exceed 1% total harmonic distortion. The APA range of amplifiers are delivered with
the anticlip system adjusted at a threshold of 1% THD (hard limiting). However, this value can
be switched to a softer limiting (5% THD) via an internal jumper (see figure 2).
The great convenience of such a circuit in any kind of installation has to be remarked:
The clear advantage of a limiting system in front of conventional compressors is that the former
does practically not alter the dynamic range, acting only when the distortion threshold is
reached.
CAUTION: Changes on the ANTICLIP configuration have to be performed by a qualified
technician.
HOT or direct signal
COLD or inverted signal
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