Looking for stuff I could do the next time I'm bored, I was reading yet another of Die_Bogener's excellent workshops, this time on the Beogram 6500 internal RIAA amp.

In the schematic, I don't quite understand what the designers were trying to achieve with the mess including the 4066 analogue switches, as I'm not a big fan of routing signals through them... Looks like it is supposed to drop the signal gain for a while after power up - perhaps to prevent pops and bangs - but isn't the muting switch going to do it anyway?

Do these decks leave the stylus on the record in the event of a power cut? (I get the impression they do).

Indeed they do - just tried - and the circuit keeps the Beogram muted for maybe 4-5 seconds after you plug the power back in, well long enough for it to get up to speed before the sound comes back.

But, still I don't see the point for this complication... it's not like people go about unplugging (only) their Beograms all the time, and during a normal power cut the Beomaster would turn off as well.

Thanks for the link - I'm inside this deck now, and may take the time to do more than just figure out what's wrong with the transmission to the tonearm assembly.

Yes - haven't yet tried it myself, but replacing the caps alone would be easy and probably very much worth the time and trouble.

I'm not so sure about the opamp replacement, but it can always be left to a later date.

Does the amp return to previous operation when power is restored? If so to me it would seem that the circuit simply lasts long enough to remain mute once the amp is powered and ready and everything else is stable (the RIAA amp itself).

I would have thought the record player would reset the arm after a powercut if it was unable during!

All Beomasters (the ones I have anyway) stay in standby once power is restored.

Anyway, even if this was the only purpose, the implementation seems totally silly. Once "on", the feedback loop of the buffer opamps - which essentially should be a straight connection for unity gain - goes through two series connected 4066 switches (with a 10k resistor in parallel). Either the designers had just come back from a weekend trip to Amsterdam, or this circuit has some odd side effect I just can't think of...

I did the cap and opamp upgrade on my BG7000 recently. Used Die_bogeners excellent article on the upgrade process as a reference. The improvement in sound quality is very noticable. Removing the SMD opamps requires a lot of patience but well worth the effort!

There is also a very good article on upgrading the Beogram here:

http://www.condoraudio.com/wp-content/uploads/Projects/BeoGram-4500-Turntable-Restoration-Repair.pdf

Not sure about the configuration of the 4066 chip. Perhaps Die_bogener could shed some light on that?