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Before we put those mids back in, I noticed something that needs mentioning. The gaskets for the mids looked reusable except for one. One was not properly installed in the first place and was too messed up to re-use. I ended up putting on new foam gaskets myself for all drivers. Adhesive foam strips work well for this sort of thing as they can’t move out of the way during installation.
Sealing is an important topic and I suggest those of you reading this to take a closer look at old gaskets and seals in your speakers. Leaks (even small ones) can lead to strange noises and buzzes etc. Most of all they lead to the acoustic system not working/performing as intended.
Now safely back at home, the mids are ready to go back in!!
Things were going well. ….until they weren’t! The outer flange of the surround was starting to wrinkle and not lay flat so I frantically ran around to try and find something to hold them down while the glue set. Luckily we are a well equipped office and have drink vessels of the exact-right size for this job.
While the glueing-up was taking place, I also made sure that I ran some signal through them to ensure no nasty misalignment and coil rubs were to take place.
One of my favorite view from the office. We are very fortunate that our company values engineers and doesn’t shove the soldering station in the basement somewhere!
This is usually just our random electronics area. Soldering, buzz-up station, general debugging typically goes on here.
Working in a speaker company means we usually have all the tools for the job haha! In this case it was nice to have a small turntable to spin the drivers on when applying the glue for the surrounds.
We had a long, three-day weekend here in the US and everyone but myself cleared out early on Friday. After everyone took off, I connected my phone to the monitors on the shelf, started jamming and getting on with the work.
About an hour or so later, I have a full set, ready for the re-foam job.
After swapping out all the parts in the amps, I also set the bias voltage and DC offset and called it a day. They seemed to be tip top!
Now to switch tracks a bit and get over to sorting the acoustics. Classic Penta story here – all eight midrange transducers need new foam surrounds.
This particular chapter takes place in the office lab. A lab where new loudspeaker prototypes are brought to life so it is the perfect place to do this kind of work.
Starting with a shop vac, I carefully vacuumed up the large chunks that were basically just falling off. Then alcohol to remove the remaining residue in preparation for the new surrounds.
I’ve never seen such terrible foam rot before!
After a few hours, I had a modest pile of old caps out and replaced with fresh electrolytic goodness.
Again – absolutely amazing opportunity to marvel at some truly epic packaging / design engineering.
Now for all the little caps inside plus trimmers and a fresh Burr Brown OPA134 op amp. Hope you like working with a flashlight.
New power caps are finally in. I always appreciate finding all the little B&O branding elements throughout old systems like this. I’m guessing these were all made by suppliers but still nice to see.
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.
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!
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.
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.
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.
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.
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.
Looking forward to seeing/reading some more on this project.
Hey Pepps – I’ll write up a thread on it in a little while (have many more photos). I’m in the home stretch and just might finish it this weekend!
However I will tease one thing… Yesterday I did embark on the re-foaming of the midrange drivers. Mission was successful.
I’m back in the US for a little while so I’m trying to sort out one of my other previous acquisitions, BL Penta MK2. They need the full overhaul so I bought all 3 cap kits and new foam surrounds. These will be the main L/R channels in the master bedroom and the basis of a surround system (eventually!).
