Elektor's "Ulti Amp"

[Piersma]

The required additional low power supply for the main board.

[Piersma]

Replacing the VAS transistors MJE15031 (T12) and MJE15030 (T13) with transistors 2SA1209 and 2SC2911.

To remain stability with Sanyo 2SA/SC transistors place a 47pF styroflex cap from base to collector for both semiconductors and replace the feedback 220pF cap Cfb for a 100pF styroflex or silvered mica cap.

Lower the idling VAS current to 12mA, by replacing the emitters resistors (R31…) . New resistor value 33 Ohms.

Lower the idling current in the second differential stage to 10mA, this comes down to 5mA per transistor leg.

Replace R51, 100E resistor by a 10E resistor and remove the short to power-ground.

[Piersma]

for your information the 2SA1209/2SC2922 datasheet.

[Piersma]

Original matched dual transistors in this Elektor can be obtained (online) in Germany. Supplier is DSI who still offering the BFX36 and 2N914.

GES GmbH - www.Electronicpool.de - abgekündigte und schwer beschaffbare elektronische Bauteile

regards,
Piersma