Balanced Headphone Operational Amplifier

A high powered differential headphone amp with a focus on modularity and prototyping. Inspired by the Schiit Audio Magni Heresy.

Features

• All sections of the amp should be modular (Filter, VA, CA, Output protection)
• All sections should be accessable via pin headers
• Output power >1W per channel

Schematic

The Amp consists of a simple differential input filter for very high frequency noise, an instrumential amplifier input stage for differential voltage amplification and 8 paralelled opamp sections in buffer topology per channel (of which there are 4 for differential amplification for a total of 16 opamps(!!!). Mental, I know).

The instrumental amplifier in the prestage was chosen, because it is really easy and straight forward to set the gain with just a a single resistor per channel.

Furthermore the output is protected via muting relays driven by a mosfet and a turn on timer for a startup delay.

The power supply is off board to stay in the limits of JLCPCBs cheap 100x100mm PCB service. It can range from +-5V to +-18V (or how much the Opamps will take). The output relays are 5V, a simple 78l05 so8 IC is supplying them with 5V.

TODO

• Improve stability of current amplification. Maybe high value resistors to ground to give a reference for the inputs. Also cascaded topology might be a better CA stage as per SBOA553A
• Improve output protection. Firstly ADD some DC protection and improve the circuit for setting delay time.