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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
I'm sharing with the Beoworld community my recent Beovox M70 restoration project. I bought them last fall from Canadian auction site and since they don't come by often, I still bought them despite their "fair" condition. I was looking for a pair for more than a year so I took the challenge to bring them back to their best.
This one fell from the third floor I guess, oh my... The corner was filled with body panel putty, we'll see if we can save it.
This is another reason why I bought the M70's, the optional trumpet stands! Agreed they need little care to get rid of the corrosion.
Front grills completely destroyed...
Lets start!
Both speakers were completely dismantled for an entire restoration, I mean from A to Z. First let's take care of that corner. Once the putty was removed, luckily the rosewood veneer was still there but the corner was severely damaged.
With a precision knife, the veneer was separated from the wood. This revealed that the corner was in terrible shape and only a whole reconstruction would make it right.
Many Many hours later with a lot of TLC, the original veneer was put back and finished the best I could.
Both cabinets gently sanded and polished with 0000 steel wool
The final touch, 3 coats of satin varnish...
Let's take care of the drivers now. The original SEAS woofer in the M70's suffer from badly assembled terminals on the speaker housing. The terminals come lose and the spacers are rattling against the cone. Eventually, the leads are breaking leading to speaker failure. I was lucky to have all good drivers requiring little repairs.
Terminals epoxied solidly to the speaker frame
The filler driver also suffers of problems. Often, the magnet will separate from the speaker basket leading to coil damage. Again, chance was on my side and both filler drivers were good however I still epoxied the magnet avoid future problems...
The crossover was completely rebuilt and only the original coils were kept. The layout was made on AutoCAD first in order to optimize the space. The original resistors were replaced with MILLS MRA of the same values, woofer and filler capacitors were replaced with Mundorf NP electro, midrange and tweeter benefited of ClarityCAP PX. I choose these instead of the SOLEN, I tried previously, because I was really disappointed by their harshness and limited top end.
The original speaker grills were unrecoverable so I decided to make my own replica. This part was the longest of the entire restoration process. To start with, I cut to size 3 pieces 1/8" thick of high density wood fibre.
Openings practiced same as the original.
The angle plastic pieces were saved from the old grills and glued to the replicas. Then, using a steam machine, a clamp bar and patience, the panels ere shaped in an angle like the original. I had to do it process at least 3 times were the panel kept the desired shape.
I couldn't save the original cloth so it was replaced with high quality speaker fabric made for that purpose. Since this new fabric was expandable, I had to make a wood frame to stretch it first, then I painted the panel flat black, applied spray adhesive on the replicas and finally laid down the panel inside the frame. Final result is just amazing!
The front of the cabinets were flat black painted and drivers mounted into their location using sealer
Time to fill the cabinets with dampening material. Inner walls were covered with speaker dampening wool.
The rest was filled with the original material.
The stands were brought to a local machine shop were they were re-finished using the same grit as the original. Then I painted them using glossy clear laquer.
After too many hours of hard work... Here is the front
The side...
And the back...
The process described here was much longer and required a lot more steps however if you wish clarifications, feel free to ask.
Oh, btw, the sound is quite amazing, extremely detailed and spectacular imaging.
MrRoast:Good work! I’m impressed with how you handled the trumpet stands 👌🏻
Thank you for the encouragement! The above pictures and process description represent a fast forward from, at least, 3 months of work. The stands were actually mounted onto a large swing lathe and sanded from the outer edge to the middle shaft by very small increments to match the exact same original grit and circular finish.
Little details here and there combined make big differences at the end
Really good job! Congratulations for giving a new life for those amazing speakers!
Theomaster
Vintage Bang & Olufsen
the_o_master: Really good job! Congratulations for giving a new life for those amazing speakers! Theomaster
I should have paid the same attention to my writing like I did for the speaker restoration but I can't edit the text now...
But yes, they are truly amazing speakers and actually Jacques (Chatz) convinced me to look after them without knowing it, Merci Jacques!
Very nice work indeed!
Martin
Impressive work Jean........and I can see you got real pleasure from the work ;¬)
Craig
Dillen: Very nice work indeed! Martin
Martin, when I started the project, I knew exactly what to look for and what to do because most of the information came from the THIS forum. When starting a project, people should really search and extract every piece of information from this website; it is an endless valuable resource. And you as a person, really helping DIY’s like me to bringing back to life those old reputable piece of engineering; thank you for that!
Thanks Graig!
If you ask my wife, yes too much fun doing this hobby, as I'm slowly filling the house with my stuff!
Very nice job!
Those M70s are our living room speakers and they sound so nice and unfatiguing.
And they have that prodigious bass too. We use a Beomaster 4400 on linear mode.
Jacques
Thanks Jacques,
Guess what's on the workbench right now? And who inspired me the most? You have a lot to with all this Jacques!
Just missing the Beogram 4002 but working on it as we speak!
Were the output trannies fried?
chartz: Were the output trannies fried?
Hi Jacques,
0 0 1 147 842 Compass-NAV inc. 7 1 988 14.0 Normal 0 false false false EN-CA JA X-NONE Unfortunately yes, two TIP141 on the right channel that I find very strange by the way, but I think I have pinpointed the problem. You see, I consulted the site many times to find the common anomalies for this amplifier before beginning the restoration of mine. In all cases, some output transistors were defective and that, in my opinion, it's really not normal, because this amp is very well protected at the output stage. I have never seen, in all my restorations, damaged output transistors without any damage in the upstream output circuit either through abuse, "visible" component failure or something else... In my case, everything is good, but two failed TIP141 ... ??? As you know, the number one cause of chip failure is heat. I very much suspect that the heat dissipation from the back plate, where the trannies are mounted, to the heatsink is very bad because of the modular design. I do not want to dwell on it here, but you can see the details on my post here: https://archivedforum2.beoworld.org/forums/t/30193.aspx
Rich:Welly welly welly done! Welcome to the M70 club! You seem the perfect person to take on P45s with stuck woofers....
You seem the perfect person to take on P45s with stuck woofers....
Thanks Rich, you've been there right?
No thanks for the P45, I have enough on the workbench right now
Great job!!
Now I have a few questions as I am doing some work on my 70's.
Did you replace the foam on the front of the speaker? Did you epoxy all of the drivers?
It looks like you have to remove the mid range driver from the inside and not touch the nuts you see on the front?
How did you reattach the grills?
Mine sound great now and I want to make sure they do for a long time.
Thanks, Jim.