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Beloab 150 / Penta Upgrades

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machineage
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machineage Posted: Sat, Mar 22 2014 12:27 AM

Hi all Smile

I've decided to carry out some work on my ageing Beloab 150 amps / Pentas. They were originally Beovox Penta Mk1's to which I later added Beloab 150's when they turned up.

Anyway they have given good service over the years - and they are currently running cool. I feel though they are of an age where I should now carry out preventative work by way of replacing some components - and upgrade as I go. I'm on a budget so I intend doing the amps first - then possibly the Xovers at a later date.

First the electrolytics which I will replace with 105°C rated components. I wonder if anyone could recommend what electrolytic manufacturer / series I should go with - Panasonic / Vishay / Nichicon ?

I understand most of these are not in the signal path - but some of the caps are. Which ones are in the signal path and what should I replace them with? WIMA MKS2?

I will also replace the 10,000uF caps. There seem to be loads of Elna & Nippon caps on eBay, but I've read a lot about them being fakes Sad

I wonder if these too are fakes: http://www.proaudioservice.co.uk/oscommerce/catalog/product_info.php?products_id=29

I read it is a good idea to replace the Op-Amp with a Burr-Brown alternative - which would be recommended?

I will replace the trimmers too - are there any recommendations that will still allow access to trimming without taking out the transformers?

Finally are there any other components I should replace whilst I'm in there?

Thanks! Smile

cordobaman
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I've attempted this upgrade, replaced C1, C2, C5, IC2.  Also R65, R66, R73 because they looked like they got hot.  Plus the caps in the power supply.  Now the amps will turn on, put I get zero output...not even hiss. 

Suggestions on where to look?

machineage
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machineage replied on Sat, Mar 22 2014 11:42 PM

Can anyone help with my questions Smile

In the meantime I've ordered replacement foams for the midranges from Good HiFi. Mine are all still intact - but I daren't touch them Cool

 

I read too on the archived forum about a mod to get rid of the 'pop' on power up - but the link to the mod doesn't seem to work:

http://archivedforum.beoworld.org/forums/t/34895.aspx

 

Thanks Smile

BO
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BO replied on Sun, Mar 23 2014 2:57 PM

machineage:
but the link to the mod doesn't seem to work

http://archivedforum.beoworld.org/forums/p/14677/108526.aspx#108526

//Bo.
A long list...

Beobuddy
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Beobuddy replied on Sun, Mar 23 2014 7:28 PM

machineage:

In the meantime I've ordered replacement foams for the midranges from Good HiFi.  

 

Don't! Audiofriends has the right ones!

machineage
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Oh Sad

It's a bit late as i've already paid for them...

 

Are they completely wrong for the drivers? Should I ask for a refund?

BO
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BO replied on Sun, Mar 23 2014 8:54 PM
Beobuddy:

Don't! Audiofriends has the right ones!

I can confirm this!

//Bo.
A long list...

machineage
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Oh dear 

 

There's not much I can do now - unless I ask for a refund if they haven't already beens sent.

 

I will ask

Beobuddy
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Beobuddy replied on Mon, Mar 24 2014 7:19 AM

Even then, I wouldn't doubt investing in another set of foamsurrounds.

You will have the opportunity to compare the surrounds. You will notice the difference!

Again, I'm repeating myself, do not use the Good Hifi version. Among the more then hundred drivers I've done so far, there where several with the wrong surrounds fitted. They became loose around the chassis where the coil-wiring goes in. Or were simply bad placed caused by the wrong dimensions.

Beobuddy
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Beobuddy replied on Mon, Mar 24 2014 7:22 AM

And order some speakerglue with it. You will get glue which stays elastic. Don't use PVA as I've seen which gets hard.

machineage
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machineage replied on Mon, Mar 24 2014 10:04 AM

They haven't been shipped - so Good HiFi have said they will refund me Smile

 

I will buy the foam surrounds & glue now from Audiofriends!

Beobuddy
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Beobuddy replied on Mon, Mar 24 2014 2:25 PM

Let us know how you went! Pictures...

machineage
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machineage replied on Tue, Mar 25 2014 10:35 AM

Ordered the foams & glue from Audiofriends - and awaiting a refund from Good HiFi

 

Here's a picture of the mids as they are now. Surprising they have survived this long - but you can see some fuzz emanating now - and I daren't touch them Unsure

machineage
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OK - the foams arrived today!

The auction did say 2 x glue & 2 x brushes - but I only received one of each? So I have asked about that.

Here is one set of mid's before I start. My drivers are the ITT variant. I placed one of the foams on top of one of the drivers as pictured below - and they are indeed an excellent fit Big Smile

I also noticed that my tweeters are different Surprise More about that later.

Work to do first!

 

 

 

Beobuddy
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Beobuddy replied on Fri, Mar 28 2014 7:51 PM

So, some work to do indeed.

Start by proper cleaning the old drivers without sanding paper. 

I've shimmed the last 5 or 6 sets as the dustcap sometimes isn't placed corrrectly in the middle. I mark each position of the caps. At last I glue them back in its original position. By shimming you are guaranteed that the conus is placed in the middle. So, the voice-coil will move freely without making a scraping sound.

The tweeter is changed during the period the mk3 was sold. Early mk3's have the same tweeters as yours, and the onces placed in the later versions have a different dustcap.

machineage
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machineage replied on Fri, Mar 28 2014 10:31 PM

Thanks Beobuddy Smile

Have removed and cleaned up four drivers so far. The worst part is removing the glue from the basket - I found a good solvent that does the job without affecting the plastic basket.

How did you remove your dust caps without damaging them?

cordobaman
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cordobaman replied on Fri, Mar 28 2014 11:42 PM

I too found it troublesome to remove the glue from the frames.  Here's a picture of my refoam using AuioFriend's kit.  My skill is not as high, but it worked well overall.  It took many hours of break-in, then there was a nice improvement in sound.

 

I have also rebuilt the crossovers using polypro foil caps and good resistors. On the tweeter resistor, I went with a 1.5 ohm rather than the original 1.8 ohm.  I had always though the tweeters could use a little boost.  But now after the rebuild they are too loud!  Probably will go back to the 1.8 ohm.  On the caps, the 68 uF ones were too large to fit on the board, had to use extension wires and glue them inside the Penta's cavity.  Overall a BIG difference in clarity!

machineage
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Great job there Cordobaman Smile

I will get to the crossovers at some stage - my plan of action is midranges / amplifiers / crossovers in that order.

I've stripped all  but one now. A time consuming job - and great delicacy is required - most especially when removing the foam glued to the cone.

Beobuddy I would like to shim them - to get them as centred as I can. How did you remove your dust caps? the adhesive used is different for the caps. Is there a solvent that will loosen them - or a little heat maybe? I could slice them off - but that will require some very careful handwork in order not to damage them or the cone.

 

Orava
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Orava replied on Sat, Mar 29 2014 4:59 PM

I found cluing surronds easier to do when speakers were back in frame. They were more stabile in it.

 blah-blah and photographs as needed

Beobuddy
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I've made a special carrousel the turn the mids. It's easier and esssential to glue both parts before putting them together. 

 

I've made a picture when cutting the dustcap. Just take a bare piece of knife to cut a close as possible to the conus without cutting through the conus itself. After glueing back you will hardly notice the cut.

 


Beobuddy
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Beobuddy replied on Sat, Mar 29 2014 6:52 PM

Mind the mark I made just above the knifeblade. This way the dustcap always comes in place.

Beobuddy
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This is why shimmen is necessary. Look how the dustcap is placed.

 

 


DMacri
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DMacri replied on Sat, Mar 29 2014 8:58 PM
I have had success with leaving a small section uncut and just fold the dust cap out of the way of the shims. Then when I was done I just glued them back in place.

Dom

2x BeoSystem 3, BeoSystem 5000, BeoSystem 6500, 2x BeoMaster 7000, 2 pair of BeoLab Penta mk2, AV 7000, Beolab 4000, BeoSound 4000, Playmaker, BeoLab 2500, S-45, S-45.2, RL-140, CX-50, C-75, 3x CX-100, 3x MCL2 link rooms, 3x Beolab 2000, M3, A8 earphones, A3, 2x 4001 relay, H3, H3 ANC, H6, and ambio 

Beobuddy
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Beobuddy replied on Sat, Mar 29 2014 9:23 PM

That does also work. In my case it doesn't as I have specially made rings to rest upon the surrounds during the time the glue dries.

But, indeed, without these, you can keep about 1,5-2 mm uncut to open the dustcap.

Beobuddy
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Beobuddy replied on Sat, Mar 29 2014 9:23 PM

That does also work. In my case it doesn't as I have specially made rings to rest upon the surrounds during the time the glue dries.

But, indeed, without these, you can keep about 1,5-2 mm uncut to open the dustcap.

machineage
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Ahh I see - so you leave the glued part of the dust cap alone.

Has anyone tried cutting between the glue and successfully removed the cap without any damage?

I wonder also if there are replacement dust caps available of the same size - the colour though is quite unusual.

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