Evan's MK2 BeoLab Pentas

33 replies
Hey everyone! It's been a long time since I've written a thread like this but it seems I have some time to do so and I shouldn't keep all my delicious build photos to myself. Here is the long (and still running!) saga of my 2022 rescue of a pair of MK2 PentaLabs. But first some context! I kind of live in two places - San Francisco, CA and Bridgend, Wales. It's a long story that mostly involves work. Work is speakers, and speakers are life so everything has blended into one and the same. So if some of the details in this story don't make logical/logistical sense then that is most likely due to my frantic, time-impoverished, trying to keep everyone happy, expat lifestyle I currently find myself in. Like many of you, I religiously browse Facebook marketplace, craigslist and eBay just looking at all the B&O gear I could buy. I found a listing for a pair of MK2 Pentas in the East Bay area and kept my eye on the listing for a few months. Definitely didn't need them as I already have a pair of MK3's (in a storage unit, 2500 miles away, might as well be on Mars) but then again, the bedroom in SF needs some floor-standers for movie watching and to play music from my then recently acquired BS Moment that the PrizeDrawBot himself sent my way. Turns out luck was on my side as the girlfriend and I found ourselves in the east bay at a lunch gathering. This was a group of my girlfriend's colleagues so I was naturally, silently plotting to grab those Pentas on the way home. And snag them we did. I even planned ahead for this and made sure we took the larger of our cars in order to accommodate them and carry them home. Naturally the confident seller stated that they were a flawless pair of Pentas that had zero foam rot. The seller was a restauranteur and used them as PA speakers for wedding receptions and that sort of thing so in hindsight they had lived a pretty tough life. We arrived at the restaurant and I shined my phone light through the fret to show him what foam rot really looked like - the surrounds were literally falling out and collecting in a neat pile behind the fret. The seller also decided to stop using the amps themselves and very inconveniently extended a pair of speaker wires through them amp (yes, he fished the wire THROUGH the amp) instead of just disconnecting the amps altogether and running wire out the back. But at any rate, they seemed savable and both made music so I made a deal. I think in the end I paid $450 for them. Here they are in our old bedroom connected up to the Moment for sadly what was only a very brief moment. The amp started cutting out on the right BeoLab and I realized that the tweeter wasn't even playing. So out they went into the garage as I ordered parts and prepared for my departure to Wales.

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
I quickly ordered all the cap kits from BeoParts and a new set of surrounds from good hifi (I think). Both took a long time to arrive in CA and sadly not soon enough for me to do anything about it. I was flying out to Wales in order to start my next assignment at work. They stood in the corner of the garage not doing anything for about 3 months. I finally returned from Wales in November and finally had the chance to sink my teeth into these babies. First things first - lets get the mids out.

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
After taking the mids out and taking those to the office (more about that later), I decided to pull out the crossovers and start there. Lets get started with the fun, easy soldering of putting new caps into the crossover.

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
One thing I didn't notice until I started the re-cap was this burned resistor. I suspect this artifact is evidence to their history of being thrashed in a large restaurant but this seemed to be the limit to the damage on the crossover. Anyway, needed to order this resistor from Mouser and do some waiting. So I moved on to the amps themselves while waiting for a pair of these resistors to arrive.

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
Now time for the amplifiers. Man do these things need a lot of disassembly before you can really get to the matter at hand. Not to mention the actual task of working inside a pentagonal heatsink. However that was also something to marvel at. The engineer in me is very impressed that this amp even exists. The heat sink is clearly just big enough to hold the transformer and there seemingly isn't a single right angle among any two components. Packaging this thing mist have been hell. If anyone from the original Penta project team is reading this, I'd love to know more about this. Did you guys/gals use CAD to develop this package?! Even if you did, I'm impressed. Never mind the poor photo, this was mostly just to keep track of cable routing. Now that the gray trim pieces and power cord are off, its time to pull out those power supplies.

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
See what I mean?? This is amazing. Yes, those power supplies actually fit in there! This level of disassembly is unfortunately necessary, the power caps (and all other caps to be honest) live in the core of this beast.

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
Loving this thread  :)

Location: Kent, UK

My B&O Icons:

BeoCenter-9500.png BeoCenter-9500.png
Beoremote-Beo4.png Beoremote-Beo4.png
Beosound.png Beosound.png
Beoplay-H3.png Beoplay-H3.png
Beomaster.png Beomaster.png
Beofan for many years with a penchant for 1990s audio systems.
Glad you like it! Had to take a lunch break, now back at it.

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
First thing was to get the main power caps swapped out. Seemed easy enough! Turned out, like many things in this amp, to be a highly-tedious process due to the cramped nature of this beast. The cable routings are exact. No real wiggle room to get things in and out and the lack of extra wiring harness made it extremely tough to get the connections made without burning things nearby with the soldering iron. In the background I was watching the AutoAlex series on his new Jag XJR-6. Highly recommended! Judging by the coffee hardware in the background this was clearly an AM session!

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
A closer look at what I mean. No slack in the wires and they are nearly tied in knots through those solder lugs. I tried to surgically remove the wiring exactly as it was by de-soldering with a pump and painstakingly maneuvering the wires out but in the end it wasn't worth it. In order to get the new caps to fit in the black plastic holder, I needed to add some wire so I soldered on some extensions ultimately.

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
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