Welborne laurel 300B single ended amp

This my famous American counterpart and he is usually very highly rated. I have to admit the products look gorgeous almost makes me jealous! He is more commercial then I am and I have to hand it to him, he runs a great business.

This amp ended up in my workshop because the owner is a highly critical guy and he felt that it was not as good as it should be.

And since he already bought new speakers, high sensitive TAD monitors and even was using an active 2 way crossover he still felt that he was not getting all out of the combination.

After I lend him my Mario Magnificent he knew where the problem was, his dear laurels needed some surgery.

Another reason is his amps hummed to much for the horns ( 110dBor more /w/m ).

First I studied what was going on and to my surprise the circuit used the very highly acclaimed µ follower stage ( which I don't like )

and otherwise it uses very nice components caddock resistors, Black Gate and KR tubes ( when they fail in warranty don't expect them to honor that )you want to kill just to have one. It also uses paper in oil caps and solen mkp capacitors.

The Allen Bradley resistors are not of this age anymore, and the cheap electrolytic could damage at this level.

Original Schematic :

Schematic Modified

Some pics of inside before the mod :

After the MOD: Please notice many small chokes for smoothing used

It was tough to cram it all inside the chassis, but listening immediately proved how much of an upgrade this really was.

Measurements show 1 amp to be dead quiet = less then 0.5mV hum, the other channel had 4-5mV hum probably due to imbalance in the PP driver stage.

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