The schematic for the Naim power amp appearing on sites such as Acoustica and Neil McBride usually show the Vas and its associated current source using ZTX653 and ZTX753 transistors.
However, these transistors have a relatively high Cob of 30pF, compared with around 3pF for the MPSA42/92. My simulation shows that the distortion drops by about 10dB using the MPSA pair, but is the choice of the ZTX devices crucial to achieving the 'Naim sound' ?
However, these transistors have a relatively high Cob of 30pF, compared with around 3pF for the MPSA42/92. My simulation shows that the distortion drops by about 10dB using the MPSA pair, but is the choice of the ZTX devices crucial to achieving the 'Naim sound' ?
if the amplifier is working leave as is...simulation can be different from real world plug and play...if you wish try these transistor out and see if you hear any differences in sound...doubtful...
I've used such transistors as 2n5551/ 2n5401 and mpsa42/91's in may amp stages and found them very good.
happy trails.
I've used such transistors as 2n5551/ 2n5401 and mpsa42/91's in may amp stages and found them very good.
happy trails.
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