ESL audio First One
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Thermal considerations
To ensure proper operating conditions to the
First One amplifier module, temperature of the
main heatsink should never exceed the limit
value of 75°C (Table 1). This is even more
important since module has only two output
transistors, so it is of utmost importance to
keep them at low temperature range at all
times to get best out of their performance.
Therefore heatsink's power dissipation
efficiency must be high, resulting in thermal
resistance of Rth=0,5 K/W or less. Module
(four drivers and two output transistors) is
fixed to the heatsink surface with four M3x12
mm and two M3x16 mm bolts (obligatory use
M3 washers) tightened to M3x10 mm threaded
holes in the heatsink. Output transistors must
be isolated from the heatsink by mica insulator
washer, driver transistors are already isolated.
All six transitor's bottom surfaces needs to be
coated evenly with silicon thermal grease
before fixing the module to the heatsink.
Optional calibrations
Although First One M module is pre-calibrated
in the production, it is highly recommended to
check and recalibrate it prior initial or any new
installation into the chassis. Thus the module's
vital parameters are set to optimal working
conditions in accordance with power supply
selected. Three electrical parameters should be
checked and adjusted if necessary:
VAS idle bias current (18 mA)
output DC offset voltage (0 mV)
supply idle bias current (280 mA)
Calibration adjustments will be correct only if
performed 20-30 min after powering on, when
optimal operating temperature of the module's
heatsink settled around 42-45°C, measured
close to the output power transistors.
Schematic diagram of calibration adjustment
procedure is shown below (Fig.2), using three
digital multimeters (DMM) will ease the
measuring job substantially. Please be careful
to set all DMM to proper measuring range and
connect them as shown in the schematic.
Trimmers TR1, TR2 serves to adjust VAS idle
bias current to 18 mA (180 mV measured
between TP1-TP2, same between TP3-TP4)
and at the same manner to adjust the output
DC offset voltage to 0 mV.
Description of TR1, TR2 trimmers rotating
adjustments explained as follows:
to increase VAS idle bias current rotate
TR1 or TR2 clockwise
to decrease VAS idle bias current rotate
TR1 or TR2 counter-clockwise
to increase output DC offset voltage
rotate TR1 clockwise or TR2 counter-
clockwise
to decrease output DC offset voltage
rotate TR1 counter-clockwise or TR2
clockwise
Observing the display values of DMM1 and
DMM2 simultaneously will clearly show the
resulting effect of rotating TR1, TR2, so both
preferred target values could be set easily.
Trimmer TR3 serves to calibrate output bias
current, correct value is achieved when
complete idle current consumption of the
module shows 280 mA (DMM3).
If TR3 adjustment changes setting of VAS bias
current or output DC offset, readjust TR1, TR2,
so the correct target values are gained back.
Technical specifications
Connectors to use with module
Voltage gain:
+27,5 dB
J1 – Molex 08-55-0110, contact, crimp
Input impedance:
10 kΩ ll 100 pF
Molex 22-01-2035, case housing
Output impedance: 10 mΩ (DC to 20 kHz)
J2 – Fast On 6,3 mm, contact, crimp
S/N ratio:
> 110 dB (input shorted)
J3 – Fast On 6,3 mm, contact, crimp
Output DC offset:
+/- 10 mV max.
J4 – Fast On 6,3 mm, contact, crimp
Power bandwidth:
DC to 100 kHz (-3 dB)
J5 – Fast On 6,3 mm, contact, crimp
Output Power:
160 Wrms/8 Ohm max.
J6 – Fast On 6,3 mm, contact, crimp
240 Wrms/4 Ohm max.
Overall height:
40 mm (rest of dimensions – Fig.3)
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