META42 Headphone Amplifier

What's a META42?

The META42 was the predecessor to the PIMETA. Its main features were:

• Small board size: 2.9" × 2.4" (61mm × 74mm)

• The board should work with most FET-input dual-channel op-amps. (Or a pair of single-channel op-amps, with adapters.) DIP and SOIC packages work directly with the board.

• Elantec EL2001 or EL2002 buffers on the outputs. These are typically configured in a Jung multiloop topology, but there are other possible topologies.

• Strong power supply circuit, for such a small amp: multiple levels of capacitors for reservoir/bypass, lots of space on the board for power caps, virtual ground buffer driven from a precision voltage divider, etc.

• Reverse power supply voltage protection

• If you use a suitable low-voltage op-amp (e.g. the AD823), minimum supply voltage is 3V on a minimal feature set. A conservative minimum is 6V with all of the features of the board enabled.

• The op-amps can be biased into class A.

• The board will accept several commonly-available volume controls, including the popular, small and cheap Panasonic EVJ potentiometer or the nice, big and expensive ALPS RK27 series potentiometer.

• All resistors are on 0.100" × 0.300" spacing. This means that you can put a DIP socket in their place and socket the resistors for easy experimentation. Similarly, many other holes are placed on 0.100" centers to allow the use of socket strips.

• It strikes a careful balance between spaciousness for things like large, premium capacitors, while still keeping the board small enough to fit in small, portable cases like the PacTec HML and the Serpac H-65.

• The board's layout is optimized for minimum trace length. There are no vias and no layer changes at component pins.

• A lot of attention has been paid to usability for the person populating the board.

• Several other points of flexibility have been designed into the circuit. We're not expecting that the amp design will be all things to all people, but we'll give it a try anyway. :)

These pages are being left up mainly for historical reasons, as the META42 is a dead end design and no more of the professional boards I made are available. The Elantec EL200x buffers the boards depended on were discontinued. I did make a new version of the META42 with the Burr-Brown BUF634 buffer; that version does work well, and you can download the design files from this site. I abandoned that line of development because I found that changing the topology to be more like that of the PPA gave even better results. The result is the PIMETA.

Where To Next?