The Workbench

Re: Project: Beolink / AUX multiplexer

Stoney3K — Sun, 21 Mar 2010 21:18:57 GMT

Die_Bogener:

It's much easier to build than you think.

Use a 4052 multiplexer for selecting the input channels. You can control the inputs by a switch or by a programmed Atmel Microcontroller.

Use caps 1-10uf for decoupling inputs and outputs, your design is dc coupled and will have various problems with dc offsets.

If you use the powerlink ON signal, there is even no power supply necessary. The 4052 needs almost no power ;)

Right now, I decided to drop the decouplers for a minute because I'm still testing the circuit. It's just a step up from passively hard-wiring line input sources together (which works, but loses 6dB of signal), and the trouble with DC offsets would affect the Beomaster as well if the circuit was NOT in place here. All gains are unity, so DC offsets (if any) would pose little issues.

I'll add the caps if I'm confident they won't screw up my bass response. I could have used a 4052, but this little circuit also has a few more flexibility options (like, adding an RIAA preamp in a phono stage, or adjusting gain for a specific source), and I intend to develop it into a matrix box which has several outputs for link rooms as well. In my home setup, I've got 6 audio sources as well as 4 audio sinks, so having a way to intelligently tying them together (without using a huge mixer with a ton of AUXes) is a plus.

Using the Powerlink signal is out of the question in my case: I've got a Beomaster 2000 which only does Datalink on the TP input, no Powerlinks out supplied. I am going to throw in an Atmel (ATMEGA8), so I can hack into the Datalink and automate the system from remote.

Re: Project: Beolink / AUX multiplexer

Die_Bogener — Sat, 20 Mar 2010 13:31:22 GMT

It's much easier to build than you think.

Use a 4052 multiplexer for selecting the input channels. You can control the inputs by a switch or by a programmed Atmel Microcontroller.

Use caps 1-10uf for decoupling inputs and outputs, your design is dc coupled and will have various problems with dc offsets.

If you use the powerlink ON signal, there is even no power supply necessary. The 4052 needs almost no power ;)

Re: Project: Beolink / AUX multiplexer

Silou — Sat, 20 Mar 2010 04:28:45 GMT

A possibility for the Ouverture / BS9000, ...:

http://cgi.ebay.ch/ws/eBayISAPI.dll?ViewItem&item=120545826831&ssPageName=STRK:MESELX:IT

Project: Beolink / AUX multiplexer

Stoney3K — Wed, 10 Mar 2010 18:34:56 GMT

I've been working on this project for about a week now, here's the deal:

Lots of Beomasters and Beocenters only have one available TAPE input. On some systems, there's actually no additional input available, or it's built with RCA jacks. Now with the advent of new media devices like HTPC's, set-top boxes, Blu-Ray players and a various arrangement of game consoles cluttering the living room, I deciced to start drawing some things up and find a way to plug all of that stuff into our existing B&O audio rigs.

I took a little bit of artistic freedom (eh, cheat) and looked at simple examples of audio mixing desks, which are simple adder circuits to combine several audio inputs.

The current ("version 1") design I intend to use for testing with my own system, is a multiple input, active mixer circuit. It offers mixing of stereo line sources, such as a tape player, CD player, BluRay deck or console, and throws everything onto the main output at the same level. If you're familiar with op-amps, the circuit should look fairly straightforward and easy to construct.

The easiest way to do this is to tie all of the sources together with resistors, which works, but you will lose 6dB of signal with each source. An active mixer design, like this, works better, can be expanded to an unlimited amount of signal sources (at the L*_IN and R*_IN points), and can even be converted for differential signal output if you really need it.

Obviously, this is a preliminary design, so it has a few drawbacks as well. First of all, the Datalink is tied together in quite a dumb fashion. This isn't really an issue if you have devices that have no or only one-way communication capability, but might cause a few hiccups if you connect more devices and they start having quite extensive conversations with each other. 2 Beocords on this line might start a serious argument. A smarter way of handling Datalink (with outside communication, either wired or wireless) is on the way. Hurray for the magic of microcontrollers in this case!

Secondly, and this is currently the most important drawback: If you have an unconnected source, its level is fixed, so the 'fader' for that source will stay open. Which may be causing noise to arrive at the amplifiers input, ruining your pretty signal you just got out of that expensive 192KHz/96-bit D/A converter, without having a clue how it got there. Again, a muting circuit for each input is being worked on.

The inputs are standard LINE inputs and can be built with 7-pin DIN plugs (recommended if you want to connect B&O gear), or any other plug you prefer for your line level signal. RCA is a popular choice, but 5-pin DIN and TRS are not uncommon, and I'm personally a fan of RJ45 plugs and CAT5 cabling to carry audio and digital control signals around the house in a neat, inexpensive fashion.

The power supply isn't quite that impressive. It takes 9VAC from a standard wall plug adapter (available at music stores to power guitar stomp boxes) and straightens it out for +/-5VDC. Any more voltage swing is not required anyway.