Beogram 4002 (5523): Replacement of Corroded RCA Plugs

The Beogram 4002 (5523) that I am restoring right now was outfitted with RCA plugs and a grounding wire instead of the standard DIN 5 connector. As usual the plugs and the grounding terminal were grimy and corroded:

I replaced the RCA with all-metal gold plated plugs and I installed a new grounding terminal:

For some reason these nice compact RCA plugs do not come with a color coding, so a while back when I started using them in my restorations I designed 3D printed inserts that close off the back of the plugs and give them a distinguishing mark for the left and right channels:

On to the final adjustments and a test drive of this lovely Beogram!

Beogram 4002 (5513): Installation of New Gold Plated RCA Plugs

No Beogram 4002 restoration is complete without replacing the original DIN or RCA plugs. The original plugs are usually a bit corroded since they were not gold plated. It is a great idea to install modern all metal plugs with gold plated terminals. This increases protection against EMI interference and also ensured low contact resistance to let those small MMC20 signals travel to your amplifier unimpeded. This gives an impression of the original RCA plugs that were on the Beogram 4002 (5513) that I am restoring right now:

Pretty grim...I cut them off and installed nice Amphenol plugs with a full metal body and plated contacts:

And fully assembled:

Very nice! 

Unfortunately, this Beogram also had its grounding wire shortened:

What is it about cutting off cables?? A significant number of Beograms that found my bench in recent years had severed cables, either the power cord or the output cables. How about just curling them up into a neat coil and leaving them alone if they are too long?? Oh well, I replaced the cable fragment with a new pristine 16 gauge wire matching the RCA cables in length. All good again!

Beogram 4002 (5513): New Gold Plated RCA Plugs

Most Beograms have corroded DIN or RCA plugs at this point in time, and so it is a great idea to replace these connectors with new gold plated units. This particular Beogram 4002 (5513) was originally outfitted with RCA connectors.

I usually use modern quality big all metal plugs as replacements, but in this case an additional boundary condition was that the Beogram will be connected to a Beolab 5000, which has all connectors in a small compartment integrated into the bottom of its enclosure. While this is very elegant and hides the cables under the unit, it also is very restrictive with regard to what types of plugs can be used.

I finally settled on some all metal plugs made by Rean that are gold plated. They are short enough to fit into the Beolab compartment. However, like so many of these plugs they have gargantuan exit openings for the cables, which may be a concession to the modern trend to use very thick cables (which in my opinion is another snake oil concept to extract money from unsuspecting enthusiasts, but that is a different topic...;-). I did not like the looks of this, and so I decided to design small 3D printed inserts that would solve this issue and also allow me to color-code the plugs in an elegant way:

Then I soldered the plugs on:

This is how they look assembled:

Beolovely! Here is an impression of plugging them into my Beolab 5000:

A close fit, but leaving just enough room to get the cables out. The final job on this Beogram is to restore the hood which has a few bad scratches.

Beogram 4002 (5523): Installation of New Gold Plated RCA Plugs

The final item to exchange in the Beogram 4002 (5523) that I just rebuilt were the old somewhat corroded RCA plugs. This shows the original plugs:

Here is an impression of the new Amphenol gold plated RCA plugs during installation:

I really like the clean design of these plugs. It makes installation easy and results in reliable solder connections. And here the end result:

Now we need to wait a bit until I get the PCBs for my new RIAA phono pre-amp design (here is an impression of the prototype board). This Beogram will be the second unit to receive this new Beolover upgrade.

Beogram 4002: Replacement of Rusty RCA Plugs

Today I replaced the old grimy and rusty RCA plugs on the Beogram 4002 (5513) that I am finishing up right now. Here is a picture of the old plugs:

I used some nice heavy duty Amphenol gold plated RCA plugs that will do a fine job transmitting the low voltage MMC signal to the amplifier. These plugs are nice since their housing is metal, which improves their shielding properties to keep the signal path insulated from the EM environment. Here is a picture after soldering them on:

And closed up:

Pretty, aren't they??

Beomaster 8000: The Mystery of Swapped Tape 1 and 2 In- and Outputs and a Broken Damper Arm (Sad Story)

A Beomaster 8000 that I recently restored showed a strange phenomenon when I hooked it up to my Beogram 8000 and Beocord 9000 for in-situ testing: When I pressed start on the Beocord, the Beomaster came on with the Tape 1 input selected as it should due to the Beolink connection between the two. However, there was no sound from the tape (and no recording either as I found out shortly after). However, I was able to hear the playback signal very faintly when I cranked the Beomaster up to full volume. This indicated that there was something fundamentally wrong with the Tape inputs. The plot thickened when I hooked my iPad up to the Tape 1 input and only got sound out of the receiver when selecting Tape 2. Then I connected it to the Tape 2 input, and, you guessed it, I needed to select Tape 1 to be able to listen to it.

It appeared that the inputs were swapped...very strange!

The Beomaster went back to the bench, and I opened it up. Then I traced the signals to plug P3 on PCB3 (preamp). And indeed both in- and output leads were swapped on this plug, effectively connecting Tape 1 to the Tape 2 connections on ICs 202/102, while Tape 2 was connected to IC4.

I removed the terminals from the plug housing and replaced them in the correct order. I made a schematic for future reference:

After this I thought everything was fine, and I tested the inputs. And indeed, now I plugged in the source to Tape 1, and it played when selecting Tape 1 as input. The same for Tape 2. Great! (I thought!). But then I played with the 'input level presets' (potentiometers accessible from the outside of the Beomaster that allow to attenuate the inputs if a signal source is too strong). This yielded another surprise: Now the Tape 2 presets affected the Tape 1 input, and the Tape 1 presets affected the Tape 2 input...very strange! But of course much better than the original situation where I was not able to use my Beocord properly. Still strange!

After scratching my head a bit, I remembered that some Beomasters come with a different connector box, where the tape RCA connectors are connected to the Tape 1 input instead of Tape 2. At that point it dawned on me what probably happened to this Beomaster 8000 of unknown ebay provenance:

The previous owner swapped the original input box that had the RCAs on Tape 1 with an input box  from an other Beomaster that has the RCAs on Tape 2, and it seems that these two configurations have Tape 1 and Tape 2 swapped on P3 that connects to the circuit board.

Here is a pic that compares the two boxes and shows their P3 terminal arrangement:

Note the different arrangement of the Tape in and out RCAs on top and the input level presets labeled below. Tape 1 and 2 are swapped. At this point it escapes me why B&O would have changed the P3 pinout...there is really no reason, they could just have connected the RCAs to Tape 1, relabeled the box and been done with it.

It is interesting to note that all Beomaster 8000 circuit diagrams that I so far have seen show the "standard configuration", but there is a significant percentage of Beomasters that have the "RCA on Tape 1 configuration"...

Anyway, this Beomaster is working now as it should (as long as one remembers which input level presets to use) and my Beocord works happily with it.

Some bad news: While putting the left side of the Beomaster back together after rearranging the inputs, a 'petit malheur' happened: When I bolted the control panel lid back onto place, and closed it a loud crack occurred, and then the lid was undamped. first I thought the linkage broke, as it has before, but no, a more spectacular problem arose:

The damper arm cracked into two pieces:

This picture shows the arm fragment still attached to the linkage with the broken off part:

Here is a shot of the two cracked parts assembled with the damper:

And the broken arm separately:

I guess it is time to fire up a 3D printer...;-). Small parts like these are an interesting printing challenge to get the proper fit and stability. Stuff for another blog entry.

Beogram 4002 (5513): Replacing the DIN 5 Cable with a Cable Featuring RCA Plugs

The Beogram 4002(5513) that I am currently rebuilding will be used together with a McIntosh Preamp, i.e. the DIN5 connector that is standard on Bang & Olufsen equipment is inconvenient. The best solution with regards to shielding and lowest-possible EMI is to install a new cable with RCA connectors right at the source of the signal inside the turntable. Adapters are never a perfect solution.

Aiming for excellent sound quality, we decided to go with an solder-ready open ended RCA cable supplied by Sounds Heavenly in the UK. This cable features individually shielded left and right cables using a twisted-pair arrangement between signal and return path. At any rate, it looks very 'audiophile'...;-). I made a short video discussing the original DIN 5 arrangement, the installation of the RCA cables, and the differences between the 4002, 4004, DIN and RCA grounding and shielding schemes:

Here are a couple pictures of the installation. This one shows the new cables installed into the original plug of the DIN 5 cable:

And this shows the cable entry to the Beogram and the RCA plugs: