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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!
Loving this thread
Glad you like it! Had to take a lunch break, now back at it.
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!).
Thanks, Tignum! Nothingness is one of my go-to test tracks. Apart from it being an awesome song, the distant thunderstorm effect at the beginning is particularly difficult to render for some speakers so I like to use it in my usual test material.
Ok deviating from main topic now but this is an interesting rabbit hole I’m heading down… I did a few more measurements at my listening position of the ‘RT60’ test (on REW this time instead of Audacity) and indeed my room is pretty live. Roughly 40% more live than prescribed in the REW manual. I made two tests, one at left position and one at right position to mimic the speaker locations (I used a sound source different to the speaker as I couldn’t pipe a stimulus to the system just yet). My mind is properly blown as REW is able to do this with a log-chirp and not a noise decay like the usual test method. Anyway, for the “left” test I averaged 416ms.
