Polish the Gem within!

Overview: B & K amps became notable with the introduction of the original ST-140 model, which even today remains very popular with audiophiles. Many complained of the weak areas of the design even though they liked the overall sound of the unit. Later came the more powerful ST-202, the EX-442, the M-200 monos and many others.

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 B&K sound basic qualities. We make it a much more polished and natural experience without losing the original musical sound that launched its popularity.

Details: M-140LX modification has a number of interesting features. We add a capacitance upgrade to the input stage circuitry. Our mod uses new input caps, new resistors in critical positions and added power supply bypass caps. We dramatically increase the low frequency cut-off capability of the amp with a larger time constant in the loop feedback. New shunt 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 famous Audio-Grade capacitors within the the front-end of each amp for power supply and feedback circuits. Sublime sounding 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 superb sounding added bypass caps in some cases. 

Ultra uses exotic parts to get you closer to the musicians.

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 audio grade capacitors yield a dramatic increase in silky smoothness, level of detail and naturalness. Imaging is deep with a good degree of solidity and the feeling of each instrument possessing focus and more of a shape of its own 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.

PA-7: Wait the PA-7 is a Hafler amp mod, right? Well Hafler is the primary focus but some B&K models with internal heatsinks work great with the PA-7. Those amps use the same mosfet output devices as the Hafler amps so the PA-7 is a natural. Yes, the install is more difficult so there is a labor up-charge compared to Hafler models but you get that Best of Our Art sound quality. Call or email for more info.

Options? Visit these pages - PS-100/220/500 power supplies

See our "Connector" page for RCA jacks, binding posts, IEC sockets!

M-140LX Mod

$399 installed for most B & K stereo amps. 

M-200 mono amps LX mod - $599/mono pair  

M-140LX Elite Mod

This mod is for vintage and newer stereo amps except as noted

with Elite level audio grade caps, fast 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 mono amps $799/pr

>>>Important 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 you replace them, 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-220 mod or even the LC series of caps are the logical choice where they can be fitted. See those here. 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.