Shared Projects by Peef

This board is based on Gary Pimm’s power supply tester. The original article is available here (power supply tester, rev 2):

https://web.archive.org/web/20110514215921/www.pimmlabs.com/web/regulators.htm

The tester acts as an electronic load. A trimpot sets the DC load current while a balanced sound card or audio analyzer can send a test signal such as a frequency sweep as an AC load, allowing for measurement of power supply impedance and noise at the balanced output connector.

This version of the tester uses a single MOSFET rather than a cascode to reduce the voltage compliance. The power supply and DUT connect via Mini-fit Jr connectors.

A daughterboard suitable for replacing a 1/4W resistor with a CCS. The board is designed to accept the LND150 in TO92 or SOT23 and can be used with other pin-compatible parts, such as certain JFETs. There are spots for both a source resistor and gate stopper.

This board is a drop in for the obsolete 2SC3381 and 2SA1349. For a complementary input stage, you will need two boards per amplifier channel, or four for a stereo pair.

The board is designed to accept any combination of BC337, BC327, BC550, or BC560 transistors. The transistor marked “driver” sets the board polarity, e.g. a board filled with BC337 (NPN) drivers replaces the 2SC3381, and requires BC327s or BC560 (PNP) in the remaining position.

Matching the driver transistors for Vbe at 0.5mA will result in better THD.

Resistors R1 and R2 set the idle current of the driver transistor. 2k runs the input device at 0.5mA and is a good compromise between minimizing base current, THD, and noise. For best results, use a thin film, low tempco resistor in the 1206 with a tolerance of 1% or better, such as the Yageo RT.

C1 and C2 are optional. They can be populated if oscillation is observed. Values in the range of 220pF to 680pF work well. The footprint fits the Wima FKP2 film and foil capacitors (5mm lead spacing). Tolerance is not critical. With BC337/327, they do not seem to be needed at 2mA per pair.

Some further information on the sound of Sziklai/CFPs can be found at the following links: http://peufeu.free.fr/audio/memory/