A while ago I contacted Peter from this forum thinking my 70's 3800's were a match for his Pentas. I was wrong. At anything other than low volume the Pentas rock. They rocked so much I went and bought some. I still have them, and consider them to be better than anything else I've heard (I've not heard the 5's though).

Of course the problem is driving the buggers at high volume. I disregarded the optional beolab 150 and 200 because it's class AB, the transformers are known to melt over time, and it's just plain old technology. I bought a Cambridge Audio amp and drove at a maximum 100W. Something was missing.

I'd tried a Tripath Class T amp and was blown away with by the clarity. But I needed 150W of Class D/T. No I can't afford B&O's latest Active stuff, and anyway, the Pentas are still considered by many to be the best speaker design they've made. It would be a shame to get rid of them.

Solution

In a couple weeks I will show you how to upgrade the Pentas so that you can bin the powered amp if you have one and install two B&O IcePower ASC 200's. The panel is replaced with a simple dual colour LED, and the board snugly fits between the crossover units.

I've measured it and done the research, I'm just waiting on the boards. I have a supplier doing them for just $235 delivered.

So bookmark this thread because if you have a pair of Pentas and want audiophile defination you'll want to do this mod!

You will have 150W of Class D power, the same series of modules that power B&O's latest stuff, and it'll cost you no more than 200 quid.

Specification (for driving 8ohm pentas):

IcePower, 81% efficency

150W 10% THD (penta max rated volume)

130W 1% THD

100W 0.001 THD

Fully thermal & overload protected.

Automatic standby and wakeup.

How-TO

Coming soooooooon :)

Hi Snoopy.  Thanks for this post.  I personally think the actual driver and crossover arrangement is severely holding back the speakers, and I don't know if investing in the amps is worth the effort before the driver and crossover setup is corrected.  I was writing a post on an audio website to someone who had just acquired a set of penta 2's, so I'll copy and past some of what I wrote:

"As you can see, you have 3 sets of drivers. It is technically a 3.5-way arrangement since the 4 midrange speakers have slightly shifted crossovers. The inner two are shifted slightly higher, while the outer two are shifted slightly lower in the frequency range. Unfortunately, in the case of the pentas, the drivers weren't matched all too perfectly, in either frequency range or quality. The tweeter you'll be happy to hear is a high quality SEAS 19mm ferrofluid unit. I don't remember the model number off the top of my head (you can look at the back of it). The model is discontinued but you can still see the info in the discontinued section of the SEAS website. An equivalent SEAS tweeter is about $30 to $40. Now, the standard SEAS version was a 6-ohm nominal impedance driver. If you look at the back of your tweeter though, you'll see "BO" at the end of the SEAS model number, and underneath it will says "8 ohms". The tweeter is an 8-ohm version made for B&O. We'll get to why later.

Now you're midranges I'm sorry to report are junk. They're made by Haes, a German oem manufacturer for german car speakers, such as those found in your standard bmw. I actually found the same speakers on partsexpress.com a couple years ago for $5 each. They're very low quality. Furthermore, B&O has arranged the crossover to drive these speakers outside of their intended frequency range. This explains the fuzzy mid range you're hearing.

The crossover design isn't anything to celebrate about. I've forgotten most of what I learned about crossovers several years ago when I was trying to design one, but I still remember one of the major issues I saw with the penta design. The crossover was first used in the Penta 1 in the 80's, and only changed slightly all the way to the Penta 3 in the 90's. A good crossover impedance matches drivers. You can use a 6-ohm driver with an 8-ohm driver without an issue. Those numbers are fairly deceiving anyway though, as the impedance actually changes across the frequency range. The Penta crossover doesn't impedance match the drivers. Instead, they just tried to match the nominal impedances of the drivers themselves, which as I said aren't very meaningful numbers anyway. The main woofers are 8 ohms. So, they had SEAS modify their 6 ohm tweeter to be an 8 ohm tweeter. The midranges are 4 ohms each, so what did they do with those? They put each pair in series. The two center midranges are in series, and so are the two outer, yielding 8 ohms total they thought. Unfortunately this reasoning works fine with resistors, but with speakers you don't just mix and match so that their nominal impedances add up to the same number and call it a day."

About 2 years ago I spent tons of time studying crossover designs on sites like diyaudio.com and www.zaphaudio.com.  Those are two I remember off the top of my head, but can pull up others from my bookmarks if you're interested.  I learned that a good 3-way crossover is incredibly difficult to design, and that the penta crossover was far from a shining example.  Someday when I have time I plan on replacing the midrange units and perhaps woofers with higher quality SEAS or Peerless units, and then attempting to use driver and acoustic chamber modeling software to pull together some semblance of a suitable crossover design.

Austin

While B&O may sometimes seem like they design to a budget I think that implying they didn't appreciate the significance of connecting the drivers in series a little unlikely. They would have also tested the resulting speaker extensively (their speaker test facilities are among the best in the world).

If the Penta's do have limitations then I believe it was with the full knowledge of B&O, the chances of them not understanding are, IMO, zero.

Interesting thread Snoopy - I wait eagerly to see how you get on with this project!

I think that Bulgarien attempted something similar a year or so ago, and was very pleased with the results. I have an easier way of driving my Beovox Pentas to my satisfaction though - it's called a Beomastger 8000 :)

Of course these speakers can be driven by anything (Beo 8000) but I'm after the glorious sound that comes from a proper Class D. In a nutshell I'm upgrading the speakers to B&O's latest technology but shifting the active filtering to passive filtering.

Regarding the Pentas, I believe the reason they sound so good is to do with the phasing introduced by the crossover, and because of reduced harmonics between the drivers given they are all doing a different job. At the end of the day they sound stunning at mod to high volumes - my mid-range certainly doesn't sound "fuzzy". It's easy to say B&O cut corners but in reality they never do - and especially not on a flagship product.

I'm collecting most the bits this week and the IcePower's are on the way!

Andrew

j0hnbarker:

I think that Bulgarien attempted something similar a year or so ago, and was very pleased with the results.

Yes, here it is.

Hi Puncher!

I know several crossover experts have said that the 3-way crossovers are still ridiculously hard to design even today, and also that crossover designs have definitely changed in the past couple decades.  I wasn't really implying that b&o alone didn't know what they were doing; I'm saying I think there was an overall lack of knowledge in good 3-way xo design in the speaker industry 20 years ago.

Edit: I just noticed something Peter had said in a PM about the Pentas.  He said that they are amazing because they sound far better than would have been expected of their constituent parts.  This I totally agree with.  For the given set of parts in the Penta, we may have close to the best configuration.  What I'm wondering though is 20 years later whether the design can be tweeked with new parts.  Of course, at some level I suppose it's not really worth arguing until I actually get up off my seat, try it, and then test it with a calibrated microphone.

Austin

Oh yes, Bulgarien's page was very good.  If replacing the capicitors with polypropylene ones, the actual brand or quality doesn't really matter though.  The only problem with cheaper made in China polypropylene caps is that sometimes they aren't truely polypropylene.  Using inexpensive ones is fine as long as you buy them from a reputable supplier.

Austin

You're never going to hear the difference unless they are on the input side, it's the same old snakeoil argument for speaker wire. His capacitors were blown, and how his drivers looked like that I don't know (mine are perfect and been playing since 1989). The original capacitors and crossover must be fine if the Pentas sound this good. Yeah I thought of active amps but there is no need to destroy a crossover network that appears to be brilliantly designed.

A big argument for active amps is using surplus capacity to enhance the bass on smaller diameter cones and smaller volume cabinets. The 6000 shows the limitations of this, the Beolab 1 needed 400w to do 125w and the Penta doesn't need any of this because it's a true sized cabinet based on mathmatical formulas.

That's my argument for keeping the Pentas.

LED's have arrived. Stage 1 shall be up shortly. :)

Snoopy, I certainly don't believe in speaker wire snake oil (as my signature says - 'skeptic').  Electrolytic capacitors can certainly degrade enough over 20 years to create an audible difference.  It's a somewhat random degredation though, and it's very likely that electrolytic caps from 30 years ago are still working fine.  If you only plan on keeping the speakers for a couple years it won't matter, but if you plan on holding onto them there's no reason not use the polypropylenes.  Plus they're pretty cheap anyway as long as you don't buy a boutique brand.

Which crossover are you saying was brilliantly designed?  The crossovers changed across the different pentas.  At one point even the zobel filters were removed, I think when going to the penta 3.  I only know what my penta 3's sound like though, so I've never been able to listen to the different versions.  By the way, I found the main site I stuck to when studying crossovers.

http://sound.westhost.com/lr-passive.htm

Also, I think producing active crossovers would be too much of an undertaking without having the frequency response plots of the drivers.  As I said, I've only been able to source the graph for the tweeter.

Austin

Mucho agreeance on the active amp side of things.

I didn't know the Pentas crossover changed I thought they were all the same. It makes sense since the amp changed from Beolab 150 to 200 and they were probably tweaking to meet the new characteristics.

I'm working on the original Beovox from 1989 (e.g mk1). I don't see any reason to put polypropylene's ones in as the sound is still as close to perfect as I've heard from a set of speakers.

Nice link btw :)

snoopy:

I'm working on the original Beovox from 1989 (e.g mk1). I don't see any reason to put polypropylene's ones in as the sound is still as close to perfect as I've heard from a set of speakers.

I believe (literally, with no facts) that the aging of the original caps depends on how much (and how loud) the speakers have been used over the years.

I recently rebuilt my Beovox Pentas with Intertechnik MKT caps, and I'm still not sure how much difference it made (but at least I feel better...).

However, the MKTs will have a lower ESR than electrolytics even when the electrolytics are new. One can argue if this is actually a change for the better, or if the original characteristics have been accounted for in the calculations and tests when the speakers and crossovers were designed. In the same time with the Pentas, I did the same treatment for a pair of RL60.2's I have at the office, and the difference was very, very clear - even so much that I think they sound overly sharp now.

Anyway, the Pentas and their crossovers are very complex, and even with the recent advancements in speaker technology and computer power, I still don't think anyone at their home PC (and home listening room) can really improve on what B&O did with its research budget and facilities in the 80s. Or then it's pure luck

Snoopy if you upgrade your membership you can access all three penta factory service manuals, which have the schematics of both the amps and the crossovers in them.

Mika if you look at that zaphaudio website link I posted earlier, you'll see John as measured some pretty nice frequency response plots in his own living room.  The software he's using is called speaker workshop.  It lets you connect a calibrated studio microphone and preamp to your computer to test the speaker response.  It allows you to do tests and simulations in your own home that were unheard of 20 years ago.  Assuming I can set up the room properly, I could take some baseline measurements of the stock penta.  From there I could start experimenting and if I can't get anything better, then we can simply sit back in revel in the penta's awesomeness   Actually, Snoopy if you feel like it I'd be very interested if you attempted to do the same before and after your amp change.  There's a page somewhere telling you how to make the mic yourself for less than $30US.  I'll see if I can find it.  The software itself is free.

Austin

I'll take a look at the software, might be fun to try it myself. With setups like that, I just always wonder whether we'd be measuring the speaker, the room, the crappy sound card of the PC, or the $30 mic

Well Mika, yes the setup would work much better in an acoustic chamber.  I found the website showing how to assemble the microphone element.  For $3 you're buying just a little capsule element.  If you look around, especially on diyaudio.com, some people sell the mic element along with a calibration file for about $30.  You can then load the calibration file into the speaker workshop program.  Doing so gives you quite an accurate microphone setup (assuming your preamp response is linear).

http://www.speakerbuilder.net/web_files/Articles/diymic/diymicmain.htm

I wonder if you can buy used instrumentation mics such as Bruel & Kjaer from ebay. I sometimes borrow one from work - (it is perfectly flat up to 16KHz).

Lately I have been thinking about another pair of Beovox for my Beomaster 8000 and what John Barker sugest seems to worth trying out at least. However what would be the difference to Beovox MS150 despite the design?

As I've learned with older B&O Beovox Penta's properly needs upgrading of caps and maybe some foamrot to be sounding right.

Most Beovox MS150 needs the same done and its not a problem. What would the difference be in getting Penta's sound wise?

In the afore mentioned speaker test which snoopy and I did, the best speakers on test were the M100s. The control over the bass eclipsed the Penta 3s - more detail and more control. MS150s do much the same though I don't like the top end sound quite so much. You do need a decent amplifier though - BM4400, 6000 or 8000 spring to mind.

Those M100's were really awesome, and really big.

But the edge & control of the Class D IcePower should give the Pentas the edge I reckon.

I'm not too concerned for stats to be honest. I'm taking a speaker that's reknown for it's sound quality (and has no cap/spr problems) and matching it to an amplifier that's highly regarded even by the valve community.

Maybe when it's all done I'll transport them around to Peters and slaughter his Penta 3's

camshaft:

Well Mika, yes the setup would work much better in an acoustic chamber.  I found the website showing how to assemble the microphone element.  For $3 you're buying just a little capsule element.  If you look around, especially on diyaudio.com, some people sell the mic element along with a calibration file for about $30.  You can then load the calibration file into the speaker workshop program.  Doing so gives you quite an accurate microphone setup (assuming your preamp response is linear).

http://www.speakerbuilder.net/web_files/Articles/diymic/diymicmain.htm

I just realized that if I revived my studies a little more, I could probably come up with an excuse to haul the Pentas over to the anechoic room at the university  Too bad I modded them both already

The first and easy stage is to get the display panel working. The IcePower's have two LED outputs, one is standby, one is power on and if both are on there is a fault.

Here I have inserted a dual-colour LED into the original Penta socket. It's a perfect fit. I measured and cut two rubber strips and used a glue gun to secure. You can use anything that comes to hand, but the sag from the rubber places the LED's as close to the centre as possible.

To keep the quality at it's premium I cut shrink wrap and put it around the LED to prevent any splash back. The end result is a single dot and with the covers back on nothing can be seen.

Cant wait! Great idea. Tell more! :-)

Yes! Come on Snoopy, get yer finger out.

Good news!

My kit arrived - I spent 6 hours doing the first one. The components are so tight they need only minor tacking in with the glue gun, they are like a perfect fit!

It's now 00:00hrs so I can't pump it up, however I have quite a large mains hum coming through to the speakers which I need to sort. This could be because only one phono is connected :) but I believe I need to route the cables differently as the IcePower gives out quite a bit of EMI.

It's took a while but I reckon it's going to be spectacular!

Full HOW-TO coming up tomorrow with luck!

A.

Hum solved. I'm running crappy phono plugs until my nice ones arrive tomorrow (I've always used spdif in the past). Grounded the phono plug and can't hear anything.

From a technical viewpoint that means SUCCESS :) :) :)