300b

[ledzep]

Ok,my brother again has been offered a a pair world audio design 300b pp monoblocks,but they have a slight hum in the back ground,any ideas what it could be and its in both amps and are they any good? £500 the pair his mate wants for them

[hifi_dave]

Has your Brother heard the amps with his chosen speakers, playing his music ?

[John]

This are lovelly amps but as Dave is hinting need the right speaker match to sounf good

[lurcher]

How old are the valves in them? Hum can always be fixed with a bit of work, but a quad of 300b will add another £200+ to the price to get them working well.

[ledzep]

Yep he bought a apir of impulse lalis,very nice speakers,but he is worried about the hum coming through both speakers,i havent got a clue what it is,its very quiet in the back when no music is on but its there

[ledzep]

The chap told him the valves are not very old,but i think they are.he has a receipt for a new one,but they look fairly old and used

[John]

its likly to br transformer hum someone like Lurcher (nick) should be able to sort it out

[ledzep]

Yeah thats what i said it would be transformer hum

[lurcher]

There is a good side and bad side from your post. The fact that it hums is bad, and needs fixing, the good side is if you can hear it it means the speakers are probably sensitive enough :-)

Hard to say at a distance, but as its a push pull output stage, the hum could well be coming from the driver stage, which is why the hum can't be null'd by the hum pots.

[ledzep]

yep speakers are impulse lalis 91db rating,great speakers

[hifi_dave]

Things is, it could be poor design, poor build or faulty components including the valves. Then again, it could be a combination of all of these and is likely to be expensive to fix.

Why not go with your first thought and get a Croft Integrated - job done.

[ledzep]

Thats what i keep telling my brother but he wants to go the down the monoblock road