AMB Laboratories DIY Audio

[goldkenn]

Any recommandation of online seller who offer IRFP9140N/IRFP140N in MATCHED PAIR or MATCHED QUAD?

[amb]

I doubt that you'd find any.

Unless you have a very large number of devices to pick from, it's going to be very hard to find matched N and P channel devices (much less a quad). Due to the manufacturing process the Vgs of the P channel device tends to be higher than the N channel.

The β24 does not need to have matched MOSFETs, or for that matter, the BC550C/BC560C BJTs. The only devices that need matching are the 2SK170BL/2SJ74BL JFET quads in the input differential stage and the common-mode feedback section. This is because the input stage and CMFB stage are where the most gross DC offset problems would occur if they're not matched, and the DC offset trimpot might not have enough adjustment range to compensate. For the rest of the devices, the trimpot will null out any imbalance, and due to the cascode topology in every stage of the amp, the transfer characteristics of all amplification devices are linearized, so matching is unnecessary to achieve best performance.

[goldkenn]

I just think matched always better and more safety.

I did have purchase the matched JFET from you already.

Years before I did found an online shop from Germany selling many matched stuffs and claimed at minimum 3% matched, from small SMD transistor to big MOSFET, the price was not cheap, such as a pair 2SK30 COST EUR8.00 excluding shipping, but this still far much cheaper then buy punch of transistors to do the matching by myself, plus need to handle those left after matching, that's why I want to try to ask is there still such kind of online shop exsist.

[amb]

I just think matched always better and more safety.

It certainly won't "hurt" to match them, but it's not necessary on this amp due to the reasons stated above. For other designs matching might be more important to minimize DC offset and distortion.