The Workbench

Re: Beolab Penta 1 revidieren

Die_Bogener — Wed, 28 Oct 2009 15:25:53 GMT

Hi,

there are two 68uF caps on this pcb, but just one is used in the audible signal path. The second is just for the linearisation to the amp, causing a constant load for the amplifier => nothing audible, just to make the amp stable for all frequencies. So it makes no sense to spend a lot of money for this one, it's something like a dummy load... use the original one.

Audyn MKP QS are pretty expensive, but really very good :)

If you have trouble with the distance pcb - caps, this is not a real problem. If you use a good copper wire, then there is no problem. There is no need to make it much stronger than the wires of the used caps.

If you dont get the necessary caps in the right size (e.g. 27uf), then you can combine 2 caps. 27uf= 22uf + 4,7uf.

Combining caps has an advantage, that the resistance of 2 parallel caps is much lower than a bigger single cap. So you wont have trouble with combining caps... it maybe sound even better, using 2 caps instead of only one.

There is also a additional high end mod possible. Some people add a small mkp/mks/mkt or even a 4700pF (!) glimmer cap to a much bigger other cap. Small signals use the 4700pF= 4,7nF = 0,0047uF cap, bigger signals the bigger cap. My ears are not good enough to hear this difference, but some people think they can hear it.

Martin

Re: Beolab Penta 1 revidieren

Tuinkoelie — Wed, 28 Oct 2009 11:07:33 GMT

Hi Die_Bogener,

first of all, I would like to thank you and everyone on this forum for sharing their knowledge on this forum. Without people like you, I would never have taken the effort to revive my penta's like the way you did.

I have a few questions though, if I look at the pictures of the modded PCB, I notice that you did not replace every single cap, especially the second 68 uF one next to the replaced one. Is this because the PCB was not finished at that time, or is there a reason for replacing only specific caps?

At this time I have replaced all caps on both PCB's with Audyn MKP QS caps. Because of the size of these caps (way bigger in size than the MKT's) I had to mod some stuff. I used high end speaker cable and soldered it to the PCB and to the huge 68 uF caps and stuffed the cap in the space above the PCB location in the speaker shaft. I know this is far from ideal, but I did not see any other way..

Am I causing any severe loss of sound quality by creating a certain distance from cap to PCB? I am not noticing it, the two revised penta's sound awesome.

Another question, I am now thinking of revising the other two (I have four ) with the MKT ones because I will use the other two for rear surround speakers and I am not feeling like it to perform those forced modifications for those two. I noticed that there is no 0.68 uF MKT, however there is a 0.68 MKP QS. Is it possible to mount two different types of caps on the same PCB, or would you advise to keep the original ones in combination with the new MKT's?

thanks in advance, if people are interested I can figure out on how to post some photo's of my work.

best regards

Re: Beolab Penta 1 revidieren

Frank Rizzo — Sun, 06 Apr 2008 10:54:20 GMT

Thanks Austin..!!

I'll wait....yes the speakers are in south america....but i'm going to have someone bring the amps back to the USA.....as the II's are not working... Do you know someone..(or do you) offer a rebuild (refurb) service...of these amps??

THanks...

Re: Beolab Penta 1 revidieren

camshaft — Sat, 05 Apr 2008 23:35:30 GMT

Keith, I'll be picking up my Penta 3's on Friday. After that I'm going to start a long thread on modifications, which will encompass many of the mods that have been mentioned on this site, along with some new ones. I'll include pictures, and since it'll be in english, you may want to just wait till then. I don't know what suppliers are in your area (didn't you say before you're in South America?) but here in the US, there are major electronics parts suppliers such as digikey.com and newark.com.

Re: Beolab Penta 1 revidieren

Frank Rizzo — Fri, 04 Apr 2008 01:51:11 GMT

Hi guys...

I've got a set of Penta I and II's...

I'd like to do this amplifier mod and the filter mod.... where can i buy all the parts, etc.??

Is there any detailed instruction?? with pics...??

Do all pretty much agree that this will really improve the imaging??

Thanks alot,

Keith

Re: Beolab Penta 1 revidieren

magnushj — Mon, 31 Mar 2008 09:36:07 GMT

Does anyone know where I can buy the two big 10000uF 80v capacitors for the power supply? They seem to have been replaced in one of my speakers by a previous owner, and now i think the old ones in the other speaker are bad...

Re: Beolab Penta 1 revidieren

Die_Bogener — Tue, 29 Jan 2008 13:01:40 GMT

I would never use a knife or any tool to remove the frets. Most B&O equipment/covers is designed to be openend without any tools to prevent scratches.

I have opened these frets some dozen times and none of them was ever breaking. I would hate it to have a scratch on the copper trim lines... and attaching the frets is also very easy, i really dont know what should be difficult with them. There are small hooks on the rear side, they can be felt through the cloth. Press them a little bit and the freds snap on. With a little bit feeling the frets can be removed in 15 seconds and mounted in the same time.

Ok, maybe they can break when the pentas are very old and have had a lot of sunlight. Then plastic becomes very hard and can break easily, maybe the same problem like the midrange loudspeakers.

Re: Beolab Penta 1 revidieren

tournedos — Tue, 29 Jan 2008 04:38:30 GMT

There are apparently two schools regarding the fret removal; this is what I was taught:

http://forum.beoworld.org/forums/thread/73105.aspx

I believe using a blunt knife behind the fret would be more friendly to the clips, and Martin's method more friendly to the fabric. Your choice

-mika

Re: Beolab Penta 1 revidieren

joostdeclercq — Mon, 28 Jan 2008 16:27:58 GMT

Hello Martin,

Thanks for the quick advice. It were indeed the displaycovers that bothered me. I'll give it a try on a rainy sunday :)

kind regards

Joost

Re: Beolab Penta 1 revidieren

Die_Bogener — Mon, 28 Jan 2008 16:15:21 GMT

Hi Joost,

the displays are not difficult. Use both hands at the same time and pull the glass on both sides straight from the Pentas. Pull a little bit outwards on the sides with the fingernails. Then it will snap of. Pulling from only one side will break the hooks.

And watch out for the orientation, there is a upper and a lower side... that's why they break.

Or did you mean the boards inside? They are sometimes rally very hard to remove...

The freds are easy: begin to pull on one side next to the display. Dont use any tools, your hands are good enough. It will snap of. There are a lot of hooks inside the fret. If you dont bend the frets too much, they will all open and not break.

Start here and continue pulling on one side, then change to the other side...

http://img221.imageshack.us/img221/5851/p1010004co0.jpg

Martin

Re: Beolab Penta 1 revidieren

joostdeclercq — Mon, 28 Jan 2008 15:30:46 GMT

Hello,

I've done the amplifier and crossover mods and with great result. But can anybody give me some hint on how to remove the frets of the pentas so I can access the drivers? I've read on several post that the display often don't survive this operation.. :-(

Kind regards

Joost Declercq

Gent (B)

Re: Beolab Penta 1 revidieren

Beobuddy — Sun, 27 Jan 2008 13:14:34 GMT

Turbo:

But I still can not help thinking that there is more sound quality to get out of these speakers...

If you have the time and money you could buy an ICE power module/amplifier(s) and design a 24dB active crossover filter to drive each bass/midd and high range seperate.

Maybe you can use the idea of ABL from the Beolab 6000/8000 to create a lower -3dB point at the bass section.

The only thing is, you won't get it into the foot of the penta.

I think the modifications I've made so far are affordable and you can do it yourself.

These modifications can easely be heard and will raise the feeling of joy.

But I try to be careful not to loose myself in replacing wires with ones made of gold of eg 1000 euro each.

There are lots of other forums where people drive themselves crazy with cables and other sort of stuff to improve the sound quality.

Don't forget to enjoy

Re: Beolab Penta 1 revidieren

Die_Bogener — Sun, 27 Jan 2008 11:32:24 GMT

I'm very glad to hear this. Now i know, some more people can hear the difference

So, that's the proof, B&O and Audiophil is possible

Re: Beolab Penta 1 revidieren

Beobuddy — Sat, 26 Jan 2008 14:37:49 GMT

Hi Martin and other interested guys,

The caps I've used are shown above and are from Audyn, type MKP-QS.

The salesman, who also build's speakers was convinced that you can here the difference between the Audyn and other regular types.

I also replaced the 3,9uF cap (C5) in the tweeter section. B&O used already a MKT type, but then again, caps can lose their function and probably won't work as they should do. This is something you already showed us in other topics about capacitors which where leaking aleady.

First I started to replace the 2,2uF cap with a 4,7 uF as you suggested. But as I did some studying on the schematic diagram, I replaced it with the original value of 2,2uF from Audyn.

As it appears, the high pass tweeter section is a 4th order filter, and it is more delicate than a 2rd or 3rd. So changing the value from 2,2 uF to 4,7 or 5,6uF will affect the crossover frequency. The larger the value, the lower the crossover-frequency. And at that point it didn't feel right, because by lowering the crossover-frequency you are entering the terrain from the midrange section.

So I've choosen to maintain the original values and not to shortcut the resistors. My penta's are connected through powerlink and are supplied with 3 stage swith for the bass section. So I've set it to the lowest position.

Shortcutting the resistors means basically "boosting" the mid and high range compared to the bass range.

My idea about the filters is that they are specially designed in combination with the speakers units,

As I was curious about the diffrence between the modified speaker and the old one, I made a cd-r with the help from Adobe Audition.

I took some some favourite tracks I know well and changed them with Adobe to mono.

So this was the way to use your balance from the stereo knowing that the left and right chanel have the same audiosignal.

By using your balancefunction you can hear very easy the difference. And there is!!

I even invited my old man to come over to hear the diffrence.

I didn't mentioned which one was modified, but my dad could hear the difference within a second!

He also ownes a pair of penta's , so he's thinking about modifiing it also.

If your using the original tracks from the cd's then your ears are like a magnet to the modified penta.

So, I did modify both filters in each speaker.

But there is more.

Now I'm replacing the condensators and the IC2 in the amplifier and the wires which are used.

I also bought the Wima (red) caps and the Opa 2134 ic and changed the original wire to 4 mm2 in the amplifier.

At the speakerside I replaced the wires from the bass units to 2,5 mm2 and soldered them directly on the bass units.

I've changed the supplying wires from both filters to 2,5 mm2 and attached them directly to black bottom panel.

So the bass section will interfere the midrange less by suppling them seperatly.

Bulgarien already mentioned this earlier on the old forum, and he is right about that.

An 200 RMS amplifier connected through a 1-1,5 mm2 wire [:'(]

After this modification I again used the cd-r to hear the difference. And again you can hear it. Man I'm proud of the progress I've made !

So I only have to modify the other speaker.

I know for certain that men really can enjoy the music again.

I even dare to say that the can stand the BL9 easily. It feels likes the artist is really performing in your livingroom with the clarity from the mid and high range and the direct punch from the bass section.

So I would like to say, spend some money on the pentas, they are worth it

Re: Beolab Penta 1 revidieren

Die_Bogener — Sat, 26 Jan 2008 06:24:58 GMT

Ok,

if you just replaced the original caps by similar looking caps, then you have almost the sound of a "new" Penta. The MKS MKT mod goes much further, the typical problems of a magnetic electrolyt cap are gone.

So if you really want another improvement, use these Audyn caps (they are really one of the best) or any other MKS or MKT type cap like WIMA or Intertechnik.

Martin from Bogen (Die_Bogener)