JBL EON15 G2, Technical & Service Manual

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High Frequency Amplifier
Voltage measurements are at frequency of 10Khz with –25dB on input at XLR (not shown).
This is the high frequency power amplifier used in the EON15-G2 after serial number 27225. It uses a
TDA7293 operational power amplifier in a non-inverting configuration with the normal peripheral
components to provide proper equalization and operation. The nominal operating voltage of
±
40Vdc is
applied to the IC via pins 7,13 and pins 8,15.
The negative feedback resistor, R8, in conjunction with R7 determine the amplifier’s closed-loop gain.
Signal output from pin 1 of U3A is capacitively coupled by C1 and serially reduced by R1 and
connected to the non-inverting input of U1 at pin 3. Operating stability is increased by adding the
supersonic frequency input filter through the shunt of R7 and C2 and by adding filter C14 and R29 on
the output. These circuits dampen possible resonant oscillations.
Peak output/dc offset voltage from the IC output pin 14 travels to D1 and traverses through connector
P1 is detected at U6 pin 9 on the Signal Input PCB.
The EON15G-2 has thorough IC thermal protection/muting circuitry. Comparator U5 (located on
power supply description) toggles if sensor RT1 (on same) detects a heatsink temperature in excess of
≥
60
°
C. or Q14 (on same) detects a loss of ac power. This resultant shutdown signal is sent to bias Q1
into conduction, which, ultimately, mutes the amplifier preventing possible driver damage.