Simple parallel composite amplifier with balanced input, based on the article "High Precision Composite OP Amps", John D. Yewen, El and WW, Feb 1987 and the application bulletin AB-051, Morgan Monks, Burr-Brown Corp., Mar 1993.
The ZD-50 power amplifier was taken as a basis, as well as the output stage of the RME ADI-2 DAC headphone amplifier. DC voltage protection at the output was partly taken from the Omicron headphone protection.
The R250 amplifier consists of: an input buffer U1, U2 (OPA1656), a differential amplifier/filter U3 (OPA1656) with A=-1, a composite amplifier U4 (OPA1612), U5-U10 (OPA1688) with A=-2.
The secondary power supply U14 is SEPIC on the TPS61175 converter, with an operating frequency of about 1 MHz. The linear voltage regulators U12, U13 of op-amps (except for the OPA1688) are built on the TPS7A47 and TPS7A33.
Schematic diagram:
Assembly:
Thermal picture:
Open Loop:
The main design idea of the R250 amplifier is minimal phase distortion.
To achieve this, the open loop gain must be maximal and linear, the phase must be as flat as possible in the range 300 Hz - 20 kHz.
The ZD-50 power amplifier was taken as a basis, as well as the output stage of the RME ADI-2 DAC headphone amplifier. DC voltage protection at the output was partly taken from the Omicron headphone protection.
The R250 amplifier consists of: an input buffer U1, U2 (OPA1656), a differential amplifier/filter U3 (OPA1656) with A=-1, a composite amplifier U4 (OPA1612), U5-U10 (OPA1688) with A=-2.
The secondary power supply U14 is SEPIC on the TPS61175 converter, with an operating frequency of about 1 MHz. The linear voltage regulators U12, U13 of op-amps (except for the OPA1688) are built on the TPS7A47 and TPS7A33.
Schematic diagram:
Assembly:
Thermal picture:
Clip (1 kHz):
Clip (20 kHz):
Square (20 kHz / 2V input):
Square (20 kHz / 10V input):
Clip (20 kHz):
Square (20 kHz / 2V input):
Square (20 kHz / 10V input):
Open Loop:
The main design idea of the R250 amplifier is minimal phase distortion.
To achieve this, the open loop gain must be maximal and linear, the phase must be as flat as possible in the range 300 Hz - 20 kHz.
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