Beolab Penta MK1

[NickNS]

Hello everyone,

Today I just got a pair of speakers from the headline. I expected a miracle, but was heavily disappointed. The sound is awful. The bass is all over the place covering almost everything else. Overall sound is ‘closed’ if I can call it that way, vocals can hardly be heard, all in all – rubbish.

They are connected to Beomaster 5000 which worked excellent with my S45.2 – the sound was heavenly 😉

I have tried connecting via line from pre-amp outs, and also connecting via speaker out to the available terminals. The second option is slightly better, but still nowhere near what it should be.

Speaker settings are fine, all is set-up according to the Penta MK1 manual.

Seller told me that amplifiers were re-capped, and mids have new (rubber) surroundings.

I’m seeking an advice on where to start looking for the potential issues.

Thank you all in advance,

NickNS

[filip_kbh]

Perhaps the crossover filter needs a recap. Since the sound is not great regardless of using the amps or not, it points to either the crossover filter or the mid foams IMO. The placement and distance to walls can also affect the sound.

[Glitch]

I assume that you didn’t have the opportunity to audition them before purchase. On the off chance that you did, do they sound different now?

NickNS wrote:

Seller told me that amplifiers were re-capped, and mids have new (rubber) surroundings.

Did you get the feeling that the seller knew what they were doing for these repairs?

The first thing that I would test is the speakers and amps separately. Remove the Penta amps and use them to drive the S45.2’s. It sounds like you have already done the “BeoVOX Penta” test by driving them directly from the BM5000 amp?

Check that the all of the internal speaker driver connections are correct. You might have one or more drivers that are hooked-up with reverse polarity. You should check ALL of the connections.

I would also try to test each of the mid-ranges individually. All eight midranges should sound exactly the same. If they don’t, the refoam job was likely botched. Hook up two drivers directly to a amp (at low volume), run a frequency sweep, and listen/compare to the results of left versus right. Of course, if you have better test equipment like microphones, etc. you can run better tests.

filip_kbh wrote:

Perhaps the crossover filter needs a recap

Maybe, but not as likely as something else being messed up.

As a note, the more detailed the explanation/description of your test/results that you provide will make it easier for people to provide meaningful advice.

…and, of course, pictures are always appreciated…

Glitch

 

[NickNS]

Thank you both so much for the ideas and suggestions!

Let me reply ‘shortly’.

I didn’t have the opportunity to hear them prior to purchase, I just took a leap of faith. Not a smart move, I know, but what’s done is done.

I can not test Beolab amps with S45.2 because I gave them in exchange to the guy who sold me Pentas (plus some money). But, I did take the amp off and connected Beomaster directly to the speakers, and the sound did not change (BeoVOX test). Therefore, I assume I can disregard the option that amps are causing this issue, at least for now. Also, I didn’t have a feeling that seller actually new what was done with the amps, he is the dealer of used audio equipment and has ‘his service guy’, and he seamed like the person who doesn’t get involved much in the ‘service’ part.

Placement of the speakers is in the corners, 40 cm from each wall, about 3 1/2 meters from each other and about 3 meters from me. And I’ve tried all of the settings provided on the speakers, starting with factory suggestions from manual, and then combining different levels of sensitivity and bass, as well as Power Mode.

So, following your suggestions, I plan to check polarity of midrange drivers tomorrow and test them with frequency sweep connected directly to the amp. On that occasion, I will take some pictures and post them along with results. If I don’t find any faults that way, I will consider re-capping the crossovers.

At some later point, I do plan to take the amps to my service guy who already did an excellent job with my Beomaster 5000. I want them checked, measured and serviced if necessary, even if I find that something else is causing current issue.

Thanks again to both of you, hopefully I’ll post first results and pictures tomorrow.

 

[Die_Bogener]

Bad sound Penta?

• Dead mids
• misaligned refoamed Mids
• blocked mids
• scratching mids
• wrong wirement of the mids, reversed, + = – ?
• wires not marked during rework… and you have a very nice day
• there are only 5 of 8 orange wires on the mids, which one is the right one???
• dead tweeter
• burnt tweeter resistor
• dead tweeter cap
• wrong recap of the crossovers, bad material
• recap is not recap, sometimes recap is badcap… good material out, worse material in
• broken coils in the crossover…

… and we did not talk about the amp. Just the box.

[Glitch]

Die_Bogener wrote:

… and we did not talk about the amp. Just the box.

Nice list.  An addition is …

• other intentional modifications intended to make the speaker “sound better” (i.e. substituted drivers, changed cap values, etc.)

The positive news is most everything can be resolved. Pentas are worth the effort to make right.

Glitch

[Beobuddy]

NickNS wrote:

. Seller told me that amplifiers were re-capped, and mids have new (rubber) surroundings.  NickNS

If you would take replacing the mids with rubber surrounds”” as reference for the complete service what has been done, then I don’t have much confidence in the quality what has been done.
Often the so-called and mis-used term “refurbished” is used by some who barely can handle a solder iron and just start replacing all the caps and call it job done at that point.

Occasionally I get sets from new-(secondlife) owners who just bought their set which starts malfunctioning. Sometimes it’s eye sobbering how bad the quality of soldering is. “Let’s put just some extra solder there on that joint” seams to be thought resulting in nice floating solder balls just above the joints. I’ve seen it on some throughout compplete boards.

But just wondering whether the BM5000 ever has had some attention. What output is used? The speakersockets or the pre-amp level output. Due to aging in the relays that also might affect the quality of the sound. As with lots of other possible causes.

[NickNS]

Hi everyone,

Thank you once again for taking the time to help me with this.

Here are the results after taking midrange board off one of the speakers.

First I checked polarisation with voltmeter, it was correct on two drivers and incorrect on other two.

Disregarding polarisation at this point, the real result is this – when connected to Penta, neither one of midrange drivers is working at all. When connected directly to the amp, all four work as they should. Tweeter works fine when connected to speaker.

So, I suppose the issue has to be somewhere in the tower.

If you have any further suggestions on my next step, I’m here to listen 🙂

NickNS

[Beobuddy]

If you have no sound from the mids that means your mids has been wired the wrong way. Sometimes only 1 driver produces sound.
There are 2 sets consisting of 2 drivers. Each set are in series. The first set are the outer ones. These 2 are in series. 1 orange wire goes from the (+) to the (-) on the other side.

Then the 2 middle drivers are in series. Again one (+) connected with the other one (-) with a orange lead. The blue and orange leads are connected correctly. The orange wires which goes down the tower can be interchanged without problems. These 2 end both at the same junction at the board. If wiring is correctly done but you still have hardly any sound from them (outer 2 drivers deliver less sound than the 2 middle ones due to the filtering on the board), then check L3 on PCB 15. It happens that these are burned.

[NickNS]

Ok, I’ll try what you said. It’s still possible that they were incorrectly wired after re-foaming.

[Beobuddy]

As I look more closely, your wiring is wrong.

[NickNS]

Can you please re-iterate once again the correct wiring 🙂 ?

[Glitch]

NickNS wrote:

First I checked polarisation with voltmeter, it was correct on two drivers and incorrect on other two.

I’m not quite sure what you mean by this… Did you mean to say continuity or resistance?

It looks like your the polarity of the drivers are marked with the “+” stickers. Check the wiring against the schematic.

NickNS wrote:

If you have any further suggestions on my next step, I’m here to listen

There are spade connectors at the crossover boards. One (or more) of these may be either disconnected or misconnected. Also, many possible crossover issues could be identified if you provide pictures.

All of the drivers look to be original, which is a good start.

Glitch

 

[NickNS]

Thank you Glitch, I think at this point I need to try to correctly wire them. Beobuddy’s explanation is a bit confusing at first reading, so I’m now trying to understand what is the correct position for each wire.

If correct wiring doesn’t help, I’ll take out crossovers and send pictures.

[Beobuddy]

I searched a drawing of the wiring. It is taken from behind. So looking at the sockets.

[Beobuddy]

I hope this will be enough. I made it ages ago 😉
Looking towards the drivers when placed, the tweeter sits at the right side.
I understand it can be sometimes a bit confusing.

[Beobuddy]

If you look at the diagram from PCB 15. The drivers are placed the way they are drawn from top to bottom.

[NickNS]

Ok, got it. Working now. And we have an overwhelming improvement in sound 🙂

Now I’m moving on to polishing and changing grill cloth, which is going to be a great pleasure now that I know they are working.

Of course, in the near future, I plan to refresh crossovers, and check what that guy did with amps.

Thank you all very much for your help, this is a great community and I’m happy that I joined. We will certainly talk more 🙂

Nick

[Glitch]

It is good to hear that you have made progress.

One tip related to changing the grill cloth is to use two sided tape to attach the new material. This makes it much easier to get the tension just right versus using glue.

There are a many other tips that people can provide for Pentas. You probably have already figured out that B&O enthusiasts are pretty passionate when it comes to Pentas ;-).

Glitch

 

[NickNS]

You just caught me trying to get rid of the glue applied by previous owner 🙂

I have also prepared the glue :)))

Well, I guess I’ll get rid of it, and starting looking for the tape.

Thank you for the advice!

Nick

[Author]

Posts