Overview: B & K amps became notable with the introduction of the original ST-140 model, which today remains very well thought of by audiophiles. Many complained of the weakness of the design even though they liked the overall sound of the unit. Later came the more powerful ST-202, the EX-442 and many others. B & K later added multi-channel units with a some of the same sonic integrity.

Our modifications address the shortfalls of the amp and gives the owner of his "new" modified amp a large scale improvement in all areas, but with the basic sound intact. We make it a much more polished and natural version of that original musical sound.


Details: M-140LX mod has a number of interesting features. We add a capacitance upgrade/upsize to the input circuitry. Our mod uses new input caps, several small value compensation caps, new resistors in critical positions and added power supply bypass caps. We dramatically increase the low frequency capability of the amp with a larger time constant in the loop feedback. New output caps are used in the Zobel output filter. Fast film caps are paralleled with the large can filter caps to improve their effective bandwidth by lowering inductance in the high frequency range.

Elite circuitry uses the famous Muse capacitors within the the front-end of each amp. Sublime soft-recovery rectifiers are used as the power rectifiers for the power supply. Special attention is lavished on the front-end power supply. Our Elite version has added bypass caps, double bypassing in some cases. 


LX Sound: The brightness is gone! You enjoy a much lower grain structure, more dynamic "sock", greater transparency and much improved musicality. Bass is tighter, cleaner and more three dimensional. The feeling of neutrality, dynamics, sweetness and transparency is enhanced.


Elite Sound: The Elite has superior bass and greater detail. At the same time, it is clearly more natural and musical. The superb audio grade capacitors yield a dramatic increase in silky smoothness, level of detail and naturalness. Carefully chosen soft recovery diodes complete the feeling of smooth, solid image recreation. Elite sound is transparent, fast and clear while retaining the essential sweetness of the performance.



M-140 LX Mod

$399 installed for B & K stereo amps. 

M-200 mono amps LX mod - $599/mono/pr  Multi-channel amp mods are $699 for 5-ch.



M-140 LX Elite Mod

This mod is for old and new stereo amps except as noted

with Muse audio grade caps, soft-recovery rectifiers, added power supply bypasses:

M-140 LX Elite modification is $599 installed for B & K stereo amps, except as listed below.*

* for M-200 amps $779/pr, for 5-ch amps $999



LX Mini-Platinum Mod

Add this upgrade to an Elite mod for even more natural sound. Platinum grade resistors, deployed in strategic locations, offers superior naturalness, micro-detail and clarity.  Add $250 to stereo Elite mod prices, $300 to mono pair pricing



Performance Notes: Many of the older B&K amps are still using large can filter capacitors that are well beyond a reasonable service life. We strongly suggest that these be replaced, not just for the health of the amp, but your treasured speakers. Power supply failure can be dramatic in some cases. Naturally we’d like to beat our drum a little and suggest that the PS-200 board is the logical choice where it can be fitted. If that’s not affordable give your speakers a break and at least acquire some new replacements. Buying used or ‘new old stock’ caps can be worse than keeping what you have. Know the possible consequences when you make that buying decision.

B&K Power Amplifier Modifications