Amplifier project, need suggestions/recommendations!

[TheMG]

Hi all!

I'm in the last term of Electronics Engineering Tech and for one of the courses I have to construct a project. I've decided to construct a 5.1 receiver/amplifier.

Since this is for the micro controllers course, all controls on this amplifier will have to be digital and using the 68HC11 MCU. That is a must.

Currently I've been doing some research and have come across the TDA7439 digitally controlled audio processor which seems like it would work. For 5.1 channels I'll have to use 3 of those. I want one 5.1 input and at least 2 stereo input. Using a DSP is out of the question since I do have limited time and would kind of defeat the purpose of having to use the 68HC11. Now, what I'm wondering is is there a better way to go about this?

Second thing is, a receiver is not very useful without some kind of digital input, so what I need is some kind of SPDIF-to-analog module/converter. Does such a thing exist and at a reasonable price?

As for the amplifier chips themselves, haven't quite decided on anything yet. I want to get the signal processing part out of the way before I start worrying about the actual amps. But I do have a few STK4221II chips kicking around I might just use. I don't like how much heat those things give off though.

If this 5.1 idea doesn't work out I might just scrap it and make it a stereo amp.

Thanks for reading!

[Speedskater]

The December 2007 issue of AudioXpress magazine had an article by Andreas Schilloff "A Home Theater Preamp" it is a 6 channel unit controlled by a PIC16F57. The web site may have more info:
http://www.audioxpress.com/magsdirx/...enda/index.htm

[AndrewT]

Hi,
reading between the lines of other posters it is my understanding that decoding the 6 analogue channels from a 5.1 datastream is not a diy proposition. I think the message is that one has to have a license to decode the information.

You could make the digital side of your project into control of analogue channels, for volume , balance, selection and muting of inputs, auto muting if the telephone rings (or the door bell), soft start, remote trigger, auto off and auto on, auto detection of analogue or digital input.
The list is nearly endless.

[TheMG]

The site didn't have much info at all about it. Just some source code and a flow-chart.

Anyways what I was hoping to do is basically what AndrewT suggested, controlling the analog side of things. But what I was hoping is that there would be some kind of a digital-to-analog decoder module I could purchase.

[huy5005]

Build a simple gainclone with 68HC11 controller as a Volume attenuator and accept remote control?
Even this simple project will takes you a lot of time though.
I think your project is so hug for a term? Anyway, it's just a suggestion :P Hopefully, it helps.

Alex

[error401]

Originally posted by TheMG
The site didn't have much info at all about it. Just some source code and a flow-chart.

Anyways what I was hoping to do is basically what AndrewT suggested, controlling the analog side of things. But what I was hoping is that there would be some kind of a digital-to-analog decoder module I could purchase.

Unfortunately not. The technology is tightly wrapped in licensing and patents, so no IC manufacturer will sell you the necessary parts without a proper license. It can be done in software on a sufficiently powerful microcontroller (probably ARM7 or better), but your 68HC11 is definitely not going to cut it. The only other option is to rip the decoder part out of a DVD player (if this is possible) and hack into it to provide the digital data and get the audio data out. You're probably better off just keeping the inputs analog and using your DVD player to decode the 5.1 stream.

As for the rest of it, that IC you found seems to fit the bill; its specs are a bit on the low side for a 'hi-fi' system around here, but it would definitely serve for most non audiophiles.

I think I would recommend keeping the bits you need to design yourself down to a minimum. Designing the amplifier stages, input selection & control and digital sections, then getting boards fabbed and writing code are each going to be a fair bit of work; I wouldn't want to have my grade riding on getting all of them done. I'd recommend you buy ready made amp modules, or at least kits, and focus on the 'preamp' part of the project. It's more than enough work, I promise . I'd point you in the direction of gainclone (LM3875/LM3886) or tripath for your power amps as there are plenty of kits out there (see chipamp.com or 41hz.com).

If you want some inspiration, check out Mark Hennessy's beautiful DIY preamp at http://www.mhennessy.f9.co.uk/preamp/index.htm

[TheMG]

I don't have a DVD player that outputs analog 5.1, nor have I seen one in while.

All stand-alone decoder units I've seen are also way expensive for whatever reason. I guess analog and 5.1 don't really fit together very well, nearly everything in that category is moving to DSPs nowadays.

But yeah as far as the actual power amplifiers go, either I'm going to use some Hypex UCD modules or some STK4221II ICs, for which I have a board layout I can easily copy and put together.