The amp becomes much faster with this mod, but it can become instable, causing spikes or oszillations on high frequencies.

These caps are used for the damping in the feedback loop of the amp. I could imagine to make them smaller but i would not recommend this mod to remove them in total.

They have 220nF, try 100nF or 150nF, there should be some audible effect, but do not remove them.

How can it feed back through a broken circuit ?

 I did it on friday and have had no probs !

Not broken, maybe it will and can work with your amp. But it is a high risk to remove parts out of the feedback loop. Maybe you are lucky and it works with your amp...

I have a BC9300 here for repair which does not play a certain CD, but on a other BC9300 it works perfectly. It has nothing to do with the drive, it's the sound of the music causing an instable amp, there are audible distortions on one of the beocenters, even if connected by an AUX Link. The CD is mastered with signals lower than 40Hz and higher than 20kHz.

So it could be that you play a CD with bass lower than 40Hz and your amp makes smoke signals...  

I got the info for this mod from this site in the workbench.

I have a 500 watt sub woofer thats set to kick in at about 60 - 70 Hz

and it 's been pumping all day with no ill effect and no smoke.

I also have 2 pairs of penta's 1 pair of cx100 and a cona sub connected up

and I have played one cd after the other with out a break since this morning.

There is no distortion what's so ever.

The improvement is unbeliveble. I was ready to dump my BM 7000 before I found and done this mod.

I honestly would have thrown it out as I was so disappointed with the sound.

As an example I have played the dance by Fleet wood Mac if you know it you'll know the peaks that that hits.

I took this from the work bench and i comfirmed it with B&O,

If you have owned a lot of B&O equipment then you will have probably noticed that these models give a slightly disappointing sound when used witha passive loudspeakers when compared  to some of 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 Beomaster 7700 (amongst many others), all of which give very satifactory performance.

The Beomaster5500, 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 problem, the same arrangemaent is used in the Beomaster 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 the 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 or the circuit it seemed safe to remove them and see if the performance improved. With the capacitors in the circuit the sound from the 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 the 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. (Beomaster 5500,6500 and 7000)

Hope this answers your questions.

You are right, the caps are shown in the manuals of the BM 5500 - 6500 - 7000, but missing in the manual of the BM5000.  

The BM5000 does not have these caps, i checked it, yes, they are definitly missing. Also the BM5000 board does not show any hints to these caps.

Congratulations, you found another mod. :)

Thankyou

But all credit to the guys in the work bench not me

Congratulations ?
Sorry but I don't agree on this mod.

It may improve the sound in some way but you removed a modification B&O introduced
to stabilize the amplifiers and keep them from eventual self-oscillating. Probably depending on
output impedance (low impedance/heavy loads/link speakers etc.).
You were about to remove them on your BM5500 as well to improve that one too, but
found that they were not installed.
I haven't tried this mod. myself but wouldn't dream of doing so.
I also have my doubts with regards to the difference when you set off to remove
the caps from an amplifier that didn't have them in the first place...
Surely the difference can't be that huge, then.
Yes, there are many amplifiers running without the caps but B&O added
them for a reason - like many other aftermarket changes.

Rant over.

I think I would go another way;
Put back those caps and then upgrade the preamp section instead. Die_Bogener
did an excellent write-up of this modification. It is really worth doing,
adds a whole new sound spectrum, headroom and air to the sound and it bears no
risk of damage to anything.

Trust me, a self-oscillating DC coupled amplifier running at 100KHz at full
power until something goes wrong, is not something you would like to experience.
It goes off with a bang. Your tweeters won't like it either.

Martin

Dillen wrote:

Trust me, a self-oscillating DC coupled amplifier running at 100KHz at full
power until something goes wrong, is not something you would like to experience.
It goes off with a bang. Your tweeters won't like it either.

Martin

...or the local bat population... 😁

Seriously though, while I've long been an advocate of snipping and binning the filter caps on CD player outputs (and the corresponding amp inputs) with excellent results, I'd be very wary of pulling caps from a power amp.  Inputs can't do any harm  - if something goes wrong, it will just sound awful - but as Martin says a self-propagating power amp can really ruin your day (and your speakers, and upset the dog too).

Maybe it is a perfectly safe mod, that really does make a world of difference to the sound, but I'd want to have a good look at someone else's amp that has been running like this for a while before I did my own - your amp/speakers are too expensive to be guinea pigs...

The preamp is well worth looking at though, because no matter how good the power stage is, it can only amplify what is being fed to it, and if detail has been lost already, no amount of power amp fettling will bring it back....

Just my 10 rubles...