was the BM5500 you compared the BM5000 without the capacitors that Tim Jarman suggests should be removed ?
Beomaster 5500, 6500 and 7000 Article written on 6th January 2009 by Tim
If
you have owned a lot of B&O equipment then you will have probably
noticed that thesse models give a slightly disappointing sound when
used with passive loudspeakers when compared to some of the earlier
designs. This is surprising as the power amplifier circuit is very
similar to that of the Beomaster 2200, Beomaster 5000 and the Beocenter
7700 (amongst many others), all of which give very satisfactory
performance.
The Beomaster 5500, 6500 and 7000 have a rather
basic pre-amplifier circuit compared to that used in the original 5000
model but this is not the cause of the problems, the same arrangement
is used in the Beocenter 9000 where it seems to work reasonably well.
Therefore the power amplifier circuit was investigated to see what
could be causing the trouble.
The only substantial difference
between the Beomaster 5000 circuit and that used in the later models is
the addition of four 220nF capacitors C215, C216, C415 and C416. They
are not shown on all the Beomaster 5500 circuit diagrams but many sets
have them. As these do not appear in any other versions of the circuit
it seemed safe to remove them and see if the performance improved. With
the capacitors in circuit the sound from one Beomaster 5500 was
lifeless, bland and uninteresting, without them it was more similar to
a 5000, engaging and lively with a full, rich tone.
It is not
clear what the purpose of these capacitors is but performance
definitely improves if they are disconnected. Before doing this make
sure that the muting relay 3RL1 is in good condition (contact
resistance less than 0.5R at rest) and that the output bias current for
each channel is correctly set
Tim Jarman