The Workbench

Re: Workshop: BeoMaster 3400 - addition of Pre-Amp-out RCA Sockets for Subwoofer

Steve at Sounds Heavenly — Sat, 28 Mar 2009 16:23:42 GMT

Very nice!

You may hate me for saying this, but there is an another (possibly easier) way of adding your subwoofer! Attenuated speaker cables can be used to connect an active (ie. powered) subwoofer directly to the 2 pin speaker outputs of the amp without damage (by reducing the amplified signals back down to a variable line level).

This will allow your subwoofer volume to vary automatically with that of your other speakers. (I'm quite proud of this solution!)

I do like your approach as well!

Best regards,

Steve.

Re: Workshop: BeoMaster 3400 - addition of Pre-Amp-out RCA Sockets for Subwoofer

yachadm — Tue, 17 Mar 2009 12:01:47 GMT

And here is the finished product from the rear, not B&O original, but it does the job admirably of feeding my Sub.

Re: Workshop: BeoMaster 3400 - addition of Pre-Amp-out RCA Sockets for Subwoofer

yachadm — Tue, 17 Mar 2009 11:55:19 GMT

Here is the rear bulkhead, showing the Phono and Tape DIN Sockets, with their new wiring after the "accident".

The 2 new RCA sockets are on the extreme left, the Right channel socket on top, the Left channel socket on the bottom.

You can see a sheet of rigid cellophane, which I added as an insulator between the tops of the components on the lower PCB, and the exposed solder points on the bottom of the upper PCB.

Re: Workshop: BeoMaster 3400 - addition of Pre-Amp-out RCA Sockets for Subwoofer

yachadm — Tue, 17 Mar 2009 11:49:44 GMT

Here is the underneath of the PCB, showing the wiper contacts of the 2 Volume Pots.

Blue is the right channel, White is the left channel.

Workshop: BeoMaster 3400 - Pre-Amp-out RCA Sockets for Subwoofer

yachadm — Tue, 17 Mar 2009 11:04:44 GMT

A while back, I restored my BeoMaster 3400 Quad, with the upgrade of all capacitors, much soldering of dried joints, and general cosmetic cleanup.

The sound improvement was so drastic that I kept looking at my 600W TC2000 subwoofer, and thinking "What if....."

So, I finally got down to it.

The objective was to set up 2 RCA sockets, off the wiper of the Volume Control potentiometers.

It was not without pitfalls, however.....

A split-second's distraction cost me an extra full day's work - When I was drilling the 2 holes in the rear panel (very slowly), the drill bit broke through the panel unexpectedly and wound around itself a whole harness of 16 wires, thoroughly destroying them.

I had to build a new harness, matching the colours as close to the original as possible.

Here is the "2nd storey" PCB on the left side of the BM3400, with the Right and Left Volume Pots on the extreme left of the picture.

The observant among you will notice that this was taken before the "accident" - it still has the original wiring harness at the DIN sockets.