can anyone confirm that the bass drivers are 16 ohm, and wired up in parallel pairs to give 8 ohm ?

can anyone confirm that the 4 ohm midrange are wired up in serial pairs to give 8 ohm load ?

can anyone confirm that the tweeter is 8 ohm ?

I like a project like this, the Penta is really a fantastic speaker and these suggested improvements are really something you can hear.

I have a suggestion to take the upgrading even further. Coating the cones of the speakers will have a good effect on the sound. Also the individual speaker will perform a wider frequency response, leading to a total of a good frequency response for the Penta.

The coating I am using - see the picture here.

/Frede

Hi, I've just acquired a pair of Pentavox and, as expected, the midrange drivers are rotten. 

Looking at this thread, can someone please tell me the reference /specs of the midrange drivers, old & new? I'm trying to find a replacement for those, having no B&O dealer around. If not, could Peter Pan please take a picture of the midrange drivers, as zooming on the previous pics isn't that great?

Thanks in advance!

As far as I know, the Thiele parameters for the midrangedrivers are not known (except to B&O). So finding replacements is not easy. I will post a picture of mine later on.

I would suggest to replace the rotten foamsurrounds with new ones. It is very easy to do yourself, and it is cheap. I did several Penta's myself, and all functioned fine after the repair. I used to replace the rotten surrounds with new foam surrounds, but recently I found a supplier which can also deliver rubber surrounds. I did one pair of Penta's with the rubber surrounds and compared them directly with a set of Penta's using new foam surrounds. I could not hear any difference, but the rubber surrounds will almost last you a lifetime.

Here you can order the rubber surrounds: http://www.speakerrepairshop.nl/index.php?item=&action=page&group_id=10000014&lang=NL

The foam surrounds can be found here: http://www.speakerrepairshop.nl/index.php?item=&action=page&group_id=10000013&lang=NL

(The site is in Dutch, but delivers worldwide)

Hi and thanks for the info,

I checked the website selling the replacement rubber surrounds, someone can do it for me, my main concern was whether the new drivers would bring any audible improvement, looks like not..

In that case indeed, it will be much cheaper to replace only the surrounds!

I recently refurbished a set of Penta's for a client, who insisted on having the mid-units replaced, instead of refoaming. So I replaced all 8 units with new ones (ordered directly from B&O). After finishing the job, I was able to compare a refoamed Penta, against the replaced Penta. I (and my colleaques) could not hear any difference between the two sets.

So in my view refoaming is as good as replacing (provided the refoaming job is done well)

That's good news for me, thanks, I ordered the rubber rings in Netherlands and hope to get them next week, I'll let you know how easy (or not..) the job will be!

Yesterday, I was cleaning the bottom of my PentaVox and found a masked Powerlink input: do you guys think that this feeds the display directly?

Question is: if I can find a display (or 2, one for each BeoVox), mount it in the BeoVox cabinet and plug it via Powerlink, will the display be powered from Powerlink, or do I need an AC power source to make it work?

Yes this feeds directly to the display. Behind the plastic front (inbetween the two front grills) you'll find the other end, with a connector attached. If you can find the original LCD display's, you can connect them directly to that connector and mount them behind the translucent front. Plug the bottom connector directly in a powerlink and the display's will work. No soldering or external AC required!

Regarding the rubber surrounds:

It is very easy to do, providing you take your time and don't rush the job. The visually most appealing way of mounting the surrounds, is behind the speakercone. Mounting them on top of the cone is easier, but does not look as proffesional. Soundwise there is no difference between the two ways of mounting the surround.

Example 1: Here the inner edge of the surround is mounted on top of the speakercone:

Example 2: Here the inner edge of the surround is mounted on the back of the speakercone:

Mounting the inner edge of the surround is a bit harder to do, but absolutly not impossible. I would advise you to use waterproof woodglue. This takes a bit loner to dry, so it gives you some time to adjust and if necessary refit the surround. As the glue dries, it becomes transparant, so if you spoiled some, or used to much, it is hardly visible.

Succes with your project!

Great, thanks for the advise and the detailed pictures!

I found on Internet a pair of BeoLab 200 at a reasonable price, is it possible to simply screw them at the bottom of a BeoVox, and make the BeoVox become a true BeoLab Penta with proper Powerlink connections? Or is it not so easy to do...?

You wrote:
"The visually most appealing way of mounting the surrounds, is behind the speakercone. Mounting them on top of the cone is easier, but does not look as proffesional. Soundwise there is no difference between the two ways of mounting the surround."

Visually appealing maybe, but technically quite important to get it right, I'm afraid.
The surrounds need to let the cone rest perfectly unstressed (with no signal). The cone should not be pulled out
or pushed in for the surround to grip the cone edge.
If it's offset to one side, you will get distortion since the cone will move easier one way than the other
because of the introduced pre-tension.
Since this is a midrange driver with fairly small coil movements when playing, even the slighthest offset
will cause distortion and in this case you have a whole millimeter or so, which is quite a bit of offset
for a midrange. A midrange distortion of 4-5% (often more) is far away from anything you could call high-end.
Not hard to understand, I think.

I've bought from a large dealer in Holland a couple of times and am not impressed.
Two different sets of surrounds, both guaranteed to fit 100% on the same B&O woofers was returned and
it was not the first time, I got my money back.

The cheap china surrounds that you often see listed on Ebay and elsewhere are mostly no good.
I've tried several and had surrounds with inner lips pointing upwards (from Holland), 8-inch surrounds that
were more than 10mm oval, loads of surrounds with incorrect sizes plus some with wrong
axial placement of the inner lip, making it impossible to axially set the cone at rest.
You cannot do a satisfying job with any of this.
I am not saying that all Ebay sellers sell junk but a good handrule is that a good quality surround
is in the GBP 15-20 range/each (plus packing/postage/customs/VAT etc.) and typically comes with proper cement
and a new dustcap to mount after coil aligning.
This is not too far from the cost of having the drivers done by a pro, which is what I would recommend to anyone.

BTW: How did you realign the coil/spider ?
I'm asking because the dustcaps look undisturbed.

Martin

Chrisreunion:

Great, thanks for the advise and the detailed pictures!

I found on Internet a pair of BeoLab 200 at a reasonable price, is it possible to simply screw them at the bottom of a BeoVox, and make the BeoVox become a true BeoLab Penta with proper Powerlink connections? Or is it not so easy to do...?

Fitting the Beolab 200 is extremly easy. Unscrew the bottom mirror (5 screws). Connect the speakercables from the 200 to the terminals on the bottom of  the penta's, and hook up the Beolink cable. Screw the 200 to the bottom of the Penta, using the same mounting holes which held the mirror bottom in place. Screw the mirror bottom to the bottom of the 200 and you are done! 30 min job max per speaker.

Chasepoes:

Chrisreunion:

Great, thanks for the advise and the detailed pictures!

I found on Internet a pair of BeoLab 200 at a reasonable price, is it possible to simply screw them at the bottom of a BeoVox, and make the BeoVox become a true BeoLab Penta with proper Powerlink connections? Or is it not so easy to do...?

Fitting the Beolab 200 is extremly easy. Unscrew the bottom mirror (5 screws). Connect the speakercables from the 200 to the terminals on the bottom of  the penta's, and hook up the Beolink cable. Screw the 200 to the bottom of the Penta, using the same mounting holes which held the mirror bottom in place. Screw the mirror bottom to the bottom of the 200 and you are done! 30 min job max per speaker.

Only problem is you lose the displays, as the Beovox Pentas' display panels are empty. Maybe it would be easier just to find some Beolabs?

But he already found some display's if I'm not mistaken.

In reply to Dillen. Realligning the spider is not necessary with these units, 98 times out of a 100 times. The spider in these units is strong enough to hold the conus in place, even without a surround. I've refurbished hundreds of speakers (Used to work at a speaker\stereo repair\refurbish firm) and spiders usually only need realligning in big woofers). If you replace the surrounds the way it should be done, there is no way of introducing 'pre-tension' in the speaker. If done right, it's done exactly the same way as the manufacturer does.

The units I repair now for my hobby (I've moved to a differnt proffesion some time ago), undergo rigorous test and are driven wel beyond what they would encounter in everyday use, before they are claimed to be repaired. I've yet to come across a Penta mid-unit that was not repairable ore needed a realignment of the spider. (not to say, they don't exist). I've ABX repaired Penta's many times against Penta's with replaced units. So far, no one has been able to tell the difference.

Repairing costs about $5 in materials per unit (and about a day's work, mostly waiting for the glue to dry), as replacing costs about $50 per unit. A no-brainer in my opinion. I can't comment on the quality of E-bay surrounds, because I never used them. The surrounds I order from the formerly posted webshop fit fine and are consistent in quality and finish (I'm no affiliate by the way). There is another supplyer that I use, but it does not deliver overseas. The surrounds posted fit extremly well, the only 'but' is, that the outer diameter is about 1mm to small, compared to the original surround. This however posses no problems what so ever in fitting the surround. The inner diameter and all other dimensions are spot on.

For the moment I found a pair of BeoLab 200 that would fit below the BeoVox, I'm still looking for second hand displays, if they exist, otherwise I might follow the route with Ridax's displays, hoping one of them will fit inside the Penta and the wiring is not too complex; this will be step 3, for the moment I'm waiting for the midrange rubber rings, to focus on the speakers, silver soldering all cables at the back of each unit, refoaming the mids, and reversing the mid-treble cabinet in one Penta (to make it completely symetrical, and this was so easy, I wonder why B&O didn't pair the speakers from the beginning..).

2nd step will be adding the BeoLab 200 (I presently have a BeoCenter 9000, will it really make a big difference? I guess you will all say "yes, huge difference"!!).

3rd step will be the displays.

Final step would be replacing the Lab 200 amps by ICE amps if one day they "melt" like the ones found in this thread..

Second hand display's are few and far between. They can be ordered at B&O, but it'll cost you. I've never worked with the Ridax display's, so I can't comment on them, nor on how easy or hard it is to fit them into the Penta's. Regarding your other steps in upgrading the Penta's, I've got a very different opninion then that of the topic starter.

Directly soldering the wiring to the unit with silver soldering, will not give you any audible inprovement. It is stated that the resistance of the connectors is very high, and that of silver solder is very low. This is true in a way, but the differences are to small to be heard. Fact of the matter is, that altering the resistance does in no way alter the soundquality. The resistance of the connectors is absolutly lineair in the audiospectrum, just as the silver solder is. The only influence a lower resistance has, is that he speaker will play measurably louder then the connector version at a given input signal when using silver solder. But the difference is very small and can easily be corrected by turning the volume up a very tiny amount. The only thing you will accomplish, is that the resoldered Penta unit is just a minute tad more sensitive then the connector version. But given the fact that Penta's are a relativly sensitive speaker already, you gain no substantial benefit. This we tested in many different ABX hearing sessions at my former company. But that is just my 2 cents.

Adding or replacing your amplifier will also not give you much improvement. It is often stated that the Penta's need a very beefy amplifier to really shine. I've got no idea who started that statement, but it is ridicilous. The Penta's are very sensitive for a cone-speaker system (91 dB versus 86-88dB for an average speaker), so no need for power in that respect. The impedance curve is also very amplifier friendly, so no need for power there either. I drive a set of Penta's using a 12 Watt OTL Tube amplifier at home, and this combo can play loud enough to make windows rattle. Ok, the Penta's are capable of earthshaking volumes, if you drive them with a 200 Watt per channel amplifier, but I doubt one will ever reach those volumes in normal live in there home setup.

But hey, those are just my 2 cents on those matters. I am a trained electrotechnician, so I normally use to smile when audiophiles claim outragous improvements, which have no electronical or physical explanation what so ever. I just want to let you in on the other side of the coin so to speak. Believe who you want to believe, and make your own discissions.

Good luck with your modding project. Hope it works out for you!

Chasepoes:

Yes this feeds directly to the display. Behind the plastic front (inbetween the two front grills) you'll find the other end, with a connector attached. If you can find the original LCD display's, you can connect them directly to that connector and mount them behind the translucent front. Plug the bottom connector directly in a powerlink and the display's will work. No soldering or external AC required!

How did/would you do that?

All the penta display's get there power (10V AC, type mkI, II, III) through the powerlink, which comes from the main transformer.  

Imho a wrong suggestion.

Beobuddy:

How did/would you do that?

All the penta display's get there power (10V AC, type mkI, II, III) through the powerlink, which comes from the main transformer.  

Imho a wrong suggestion.

What I meant was: If you connect the original display's to the connector found behind the plastic panel (situated inbetween the two front grills), the display is connected correctly. Offcourse you have to hook the Penta up with a Beolink capable amplifier, using a Beolink cable for them to work. There is no need to 'change', rewire or solder anything inside the Penta to make it work, that was my point.

The idle current trimmers go bad and the idle current can run astray, that's a common fault.
Seeing Penta amplifiers melted down, like the one pictured, is not common.
The "melted" plastic in the penta amplifier is just a sign of an ignorant or unaware owner, who let the amplifier
run even if it started to hum (which BTW was noted by the owner) got red hot and presumably started to smell of burning
dust and warm electronics in either order.

Regarding refoam'ing, I am not worrying too much about the spider alignment - the cone is not too heavy in
these speakers so not very prone to distort the spider - but rather the coil/pole piece.
You may be able to center everything correctly without shim'ing anything, you also tell that you have a huge
experience which presumably lifts your success rate but trust me when I say that far from
all owners can do the same.
I have lost count of the failed DIY-jobs arriving here. Something either "didn't quite fit" or "didn't
quite come out as planned" or the speakers "for some reason" started to distort after a DIY refoam.
Some owners stop when they realise that they are in too deep and while things can still be saved - others don't.

I agree on the connectors. They are not as bad as some people might think and I also doubt that soldering the
connections will improve the sound quality. Indeed the change in resistance would be microscopic and the introduction of
a small resistance will not affect sound quality - only volume - and unless a connector is really bad, lose or burned, you won't
ever notice any difference.
The connectors solder joints in the board is a different matter though. They can crack and that can indeed
cause sound problems so they should definitely be attended and solder with a hint of silver would be what
I would choose too since it doesn't tend to crack as easy as the standard 60/40 or 63/37.

The Pentas are wonderful speakers and they are worth restoring.
The capacitors in the crossovers are important for sound quality and they will have started to dry out by now.
The same goes for the capacitors in the amplifier section of the Beolab versions. Here the problem is not specifically sound
quality related but rather a matter of stability. Important none-the-less.
There is, however, a few capacitors in the signal path that needs attention and also a couple of op-amps that can be replaced
with better modern types as also suggested by Die_Bogener in another Beoworld thread.
A convenient kit is available, put together with Die_Bogeners friendly assistance and partly
based on his superb suggestions. Improvements you can actually hear.
The Penta amplifiers are some of the better discrete amps built by B&O. They are not as bad as some owners
think - they just need the usual 20+ year service like any other electronic item.

Martin

Hi & thanks for the very valuable comments & suggestions , which adds even more confusion & hesitation about what to do, but at least gives a better idea of what can change (or not) if one replaces something by something else.

I guess my only urgency at the moment is the midrange drivers being rotten, after that I'll be able to do proper listening sessions & find out if something else needs to be improved.

Chasepoes:

Directly soldering the wiring to the unit with silver soldering, will not give you any audible inprovement. It is stated that the resistance of the connectors is very high, and that of silver solder is very low. This is true in a way, but the differences are to small to be heard. Fact of the matter is, that altering the resistance does in no way alter the soundquality. The resistance of the connectors is absolutly lineair in the audiospectrum, just as the silver solder is.

Sure, but the resistance between different connectors is not constant. I'm not claiming that would be audible either, measurable just perhaps...

Adding or replacing your amplifier will also not give you much improvement. It is often stated that the Penta's need a very beefy amplifier to really shine. I've got no idea who started that statement, but it is ridicilous. The Penta's are very sensitive for a cone-speaker system (91 dB versus 86-88dB for an average speaker), so no need for power in that respect. The impedance curve is also very amplifier friendly, so no need for power there either.

Just what I have been saying... Pentas are excellent speakers for silent listening. No need to make them jump before the music "opens up". Hooking them up to a Beomaster 900 was very enlightening.

In another post:

What I meant was: If you connect the original display's to the connector found behind the plastic panel (situated inbetween the two front grills), the display is connected correctly. Offcourse you have to hook the Penta up with a Beolink capable amplifier, using a Beolink cable for them to work. There is no need to 'change', rewire or solder anything inside the Penta to make it work, that was my point.

But the Penta displays need power to work. It will not come over Powerlink, you have to supply it from somewhere else if the Penta amp is left out of the equation. So not quite as simple as "hooking them up".

tournedos:

resistance between different connectors is not constant. I'm not claiming that would be audible either, measurable just perhaps...

Ok. I thought the soldering was done to improve the sound. Simply disconnecting and reconnecting them again will make them have perfect contact again.

tournedos:

But the Penta displays need power to work. It will not come over Powerlink, you have to supply it from somewhere else if the Penta amp is left out of the equation. So not quite as simple as "hooking them up".

Your right. I just thought that the previous poster intended to mount some Beolab 200's. The auxilary power is not necessary in that setup.

Hi, I've just received the new rubber rings by mail today, so tomorrow being a bank holiday in France, I'll start refoaming the midrange drivers and hopefully at the end of the day I'll discover a better "Penta sound"

Well, I've just completed refoaming one of the Pentas, didn't expect it to be so easy, once you know what to do and where to glue, it's like making pancakes, only the first one is a mess, then the others are great!

The sound improvement is obviously noticeable, now I'm going to silver solder the filter wires and keep working on these beauties..Just finished cleaning the frets as well, now they start looking great!

Someone in the first messages on this post showed pictures of the "original" Nokia midrange drivers, and guess what? Mine are not Nokias! 

They were made by a German company called SEL, I couldn't find any info about them on the net..see for yourself: