Hi

I just wanted to say thanks for the info on the mod to improve the sound

I removed the four capacitors c 215 c 216 c 415 c 416 and the sound has improved ten fold

there's much more depth to the sound.

Regards Henry

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:

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...

I only started this post to thank the guys on the

workbench for this mod.

At no time have I said anyone should do it as it's there choice.

I done it and have had no probs what so ever thats all I was saying.

I understand what your saying about feed back but I can't see how

it can feed back through a broken circuit. Which is what happens

when you remove the caps.

I'll post back on this post in 6 months and let you all know it still works.

Like I said anyones welcome to come and look at what i have done.

I am confident in what I have done. Just PM me and I'll give you my number

and address over the phone.

I have a broken back and play music for long periods of time everyday

on average 6 - 10 hrs a day during the day at loud volume.

OH and like I said in an earlier post these amps have protection in

them to switch off when overheating. In actual fact it nows seems to

be running cooler.

Your talking about the mic and amp theory the closer you get to the amp with the mic

the more the feed back but if you was to cut the wire the feed back stops. The same as removing

the caps. Thats the simplest way to explain it.

Henry

"I understand what your saying about feed back but I can't see how it can feed back through a broken circuit"
- It's not broken - that's part of the problem. I admit, it may not be the easiest circuit to look into but
the caps introduce a high-frequency path from base to collector of their respective feedback
transistors, providing a certain blockage for amplification of high frequencies, partly through the low impedance
base leads (output stage emitter resistors).
The self-oscillation can start as early as the predriver (BF423 in this case) and is sometimes even traceable
back a couple of stages further (in severe cases probably through the power rails).
By removing the caps, the transistors run more freely and you no longer
have the blockage (less the microscopic parasit cap inside every transistor which is only a few pf and of
no use in this regard).
The transistors are fed back directly from across the emitter resistors of the output stage.
At least that's how I read the circuit.
Please correct me if I'm wrong.

"these amps have protection in them to switch off when overheating"...
- Yes, if there are time enough to heat up the cooling fins.
This protection is to protect the Beomaster from extended periods of
overload (Parties or too heavy/many speakers driven).

"In actual fact it nows seems to be running cooler"...
- Then the idle currents are no longer at the same setting.
Worth checking ! If they are too low, you will put excess stress on the output stage
transistors and introduce cross-over distortion, your speakers will not like it in the long run
plus it will sound cold and harsh.
If the amplifier is in good condition, those caps will have no influence
on the temperature of the cooling fins whatsoever, at least if running normally...

Don't misunderstand me. Its your amplifier.
If you think the constructors at B&O made a mistake by introducing those capacitors in the output stage, or
simply like it better this way, then fine with me.

I just wanted to state my opinion which I've done and as a technical advisor here at Beoworld I cannot
recommend this modification.

Martin

Well time will tell and I will be honest if it goes wrong,

but with the load I have on it at the moment 2 pairs of pentas,

1 pair cx100, cona sub and a 500 watt sony sub which is set to

kick in between 60 - 70 hz and I have pummelled eveyday since

I did the mod on friday.  I do appreciate what your saying but

I was ready to throw this amp until I came across this mod

so I thought what the hell I'll give it a go I had nothing to loose

but everything to gain. I'm not an electronics engineer but before

my back went I was a Motor Mechanic and done auto electrics

and rebuilt ecu units and upgrade them so I just apply common sense

to the understanding of what I'm doing. I don't mean any disrespect by common sense

it's just the way I look at things. Its a pleasure to have these discussions as I learn from them.

Henry

henrykin:

Well time will tell and I will be honest if it goes wrong,

but with the load I have on it at the moment 2 pairs of pentas,

1 pair cx100, cona sub and a 500 watt sony sub which is set to

kick in between 60 - 70 hz and I have pummelled eveyday since

I did the mod on friday.  

I have no electrical knowledge, but isn't this overloading the amp somewhat? It's not the most powerful after all.

I have one pair of Pentas and a Cona on a BM 8000!

That's my point it would have gone bang by now .

henrykin:

 Its a pleasure to have these discussions as I learn from them.

Exactly the correct attitude!  

I've worked in and around consumer/pro audio most of my life, and I've learned a lot from Beoworld - even if I've sometimes looked a bit daft when I'd got it wrong.  

But...nobody jumped on me and started laughing, which again is one of the things that makes this site so good.  Some audio forums are downright nasty places to be - very unfriendly and some people there are more interested in scoring points off other people than the audio, which is a shame.

Every modification has to be tried by someone at the start.  Some turn out to be fantastic, and soon everyone's saying "of course you should do ABC", when it goes right, as if they invented it.  If it goes bang they laugh and say "Well I wouldn't have done XYZ - it was bound to fail"...

I always tell people "It's your equipment - you must decide" and that's certainly the case here. I'm sure I speak for everyone in saying I hope this goes well and that we will hope you are good enough to share your results honestly with us.  

Maybe it will become a "must do" mod, or maybe it will go pop, but either way we'll be thanking you for sharing your results with us.

henrykin:

That's my point it would have gone bang by now .

Does it sound any good? Surely not with all the speakers running at once - unless they're at a low-ish volume...

I will be honest and let everyone know exactly what the out come is.

 If it blows I shall be the first to say don't do it .

Tomorrow I'm going to really try to push it to it limits.

I'm going to connect up a 500 watt technics as a pre amp

and if that doesn't blow it, I think it will be alright.

I hope it doesn't blow as the sound is now so much better

and is much richer and fuller .

Henry

Yes it sounds great with all the speakers running

no distortion just perfectly clear pure sound.

henrykin:

 

Tomorrow I'm going to really try to push it to it limits.

I'm going to connect up a 500 watt technics as a pre amp

and if that doesn't blow it, I think it will be alright.

Henry

Hi Henrykin

Can you explain what you mean?  I'm confused as to how you're going to connect the Technics and the Beomaster....

Connecting the preamp-out of the Technics to an input on the Beomaster will give it the same level input as plugging in the source directly to the beomaster.

Plugging the speaker outputs of the Technics into the Beomaster's input is going to result in fireworks....

Please enlighten me!

What I did was to use the technics as pre amp by jack plug from technics to 5 pin din

into BM 7000 aux B&O said to use  this port. Set both vols to 0

I increase vol on 7000 TO 12 and then incresed the vol slowly on the technics

and the vol increased nicely on my 7000 to sound like the vol of my 5500.

Here's the e-mail I recieved

We are pleased to see that you are the owner of Beomaster 7000. You can connect a pre-amplifier to the Audio AUX connection. However we are not able to recommend a model.

Kind regards
Bang & Olufsen a/s

Mette Krabbe Helmholt
BeoCare
 

and no fireworks.

Now waiting for a preamp from the US

henrykin:

Sorry lads no fireworks

Hello Henrykin

Nobody wants fireworks!  

I just wanted to know how you were going to connect the Technics and the Beomaster.....

I think I can safely say that none of us want to hear of a piece of B&O going up in smoke, and certainly not so someone can say "told you so..."

Sorry if I appeared rude.

Interesting discussion to follow but I am not in a position to make a technoical judgement! Happily my Beomaster is the 5000 so I don't have the extra caps to start with.

Perhaps the clincher is the fact that the Beomaster 7000 is question was unlikely to be used without the mods, so in the case leaving the  the amp unmodded  wasn't an option.

Simon

henrykin:

What I did was to use the technics as pre amp by jack plug from technics to 5 pin din

into BM 7000 aux B&O said to use  this port. Set both vols to 0

I increase vol on 7000 TO 12 and then incresed the vol slowly on the technics

and the vol increased nicely on my 7000 to sound like the vol of my 5500.

Here's the e-mail I recieved

We are pleased to see that you are the owner of Beomaster 7000. You can connect a pre-amplifier to the Audio AUX connection. However we are not able to recommend a model.

Kind regards
Bang & Olufsen a/s

Mette Krabbe Helmholt
BeoCare

and no fireworks.

Now waiting for a preamp from the US

Aha, mystery solved!

Yes, this is the correct way to connect them - all that talk of 500W output had me confused, as of course the preamp output of a 500W amp is the same as the preamp output of a 1W amp....

Other than some more inputs (probably including digital) what have you gained by using the Technics?  The signal still goes through the Beomaster 7000's preamp, so I'm not sure what you've achieved...

Have you got any speakers attached to the Technics, or are you just using it as a preamp?  Some amps don't usually like playing into no load at all, it confuses them...

Plus this brings me on to one of the things that always annoyed me about the Beomasters that take passive and active speakers: when connected to actives, that poweramp is still working, which is a waste of energy really...