Dana wrote: > Couldn't the TO-92 part (2N3904) be soldered down instead? > * * * > John speaks of high dissipation, which is a good point. The first- and second-stage NPN amplifiers in the TNS-BUF dissipate about 225mW each, and the output stage NPN dissipates about 425mW. The TO-92 part is rated to dissipate from 500 to 625mW at 25C ambient, and from 175 to 250mW at 50C ambient (in both cases, depending on which manufacturer's datasheet you consult). With around one watt being dissipated inside, 50C is probably a low estimate of the worst-case ambient temperature inside an enclosed TNS-BUF. My personal design limit would be a dissipation of no more than 150mW for each TO-92 (less if h/w tests showed internal ambient temperature > 50C). Even the TO-223 part (PZT3904) in the output stage exceeds its comfortable dissipation limit unless it is mounted on a substantially larger foil pad than the 2.5 sq inches specified in the ratings. Best regards, Charles