Designed another amplifier after taking apart my Pimeta amplifier. This time its a Pimeta without the use of virtual ground, thus its a two channel amplifier. A real dual supply, + and - voltages and a true ground is used.
The merits of using such a design is covered here by NwAvGuy
The negative voltage supply is generated by a charge pump TPS60403, which is a voltage inverter. The power supply is a 3.7V PSP Lithium ion battery, thus with the charge pump, the voltages supplied is +3.7V and -3.6V.
To ensure that the performance of the charge pump is not affected by PCB layout, the recommended layout in the datasheet is followed closely.
As you can see, the charge pump sits very closely with the ceramic capacitors to reduce parasitic inductance.
The audio amplifier section is also similarly made compact to reduce the footprint and size of the amplifier.
As the charge pump switching frequency is 250KHz, which is within the bandwidth of most opamps. Thus the chosen audio opamp requires a high PSRR to reject power supply noise generated by the charge pump. The chosen LTC6241HV has a minimum PSRR of 83dB when supplied with +-5V.
The input and outputs of the amp is placed above the circuitry to reduce the footprint. The entire amp, including the PSP battery fits inside a hammond 1455C801 aluminium casing.
Power Supply Section
Battery: 3.7V Lithium ion battery
Charge pump: TPS60403
Ceramic Capacitors: 1uF X5R 0603
Voltage Rail Capacitors: 220uF/4V Blackgates PK Series
Bypass Capacitors: WIMA 0.1uF/63V
Audio Amplifier Section
Audio Opamp: LTC6241HV, Gain set at 2.
Volume control: Alps Potentiometer 50K LOG