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Old 30th January 2011, 04:06 PM   #1
Doz is offline Doz  United Kingdom
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Default Dolby AC3 coming on nicely.

Just some pics of the latest build

24 valves in total. 8 EY500A rectifiers
6 6N6P's in driver duties
10 EL84's in push pull.

Modular construction. Waiting for output bottles and transformers.

The whole thing will be mounted in a 19" 4U case

Photos here:

Dolby AC3 ... with vacuum tubes | Facebook
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Old 30th January 2011, 07:26 PM   #2
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Oh...

I thought with a title like that, you had built the DECODER in valves...

So, youv'e done a 6 channel Power Amp, not a Dolby AC3, or Dolby-Stereo/Pro-Logic Decoder.....

I did a Dolby Stereo Decoder in Chips and discretes, from the original Dolby research docs...

I used summit like 20 odd dual op-amps, and four VCA chips.....

Still got it round here somewhere, Worked pretty well, but the Dolby Pro-Logic has its limitations. Far Prefer Circle-Surround, MUCH better spectral representations--Even of Dolby recorded stuff....

Sorry, personally dont like Digital AC3, way too 'lossey' Much prefer Analogue decoding done Properly, But--Thats just MO!

Last edited by Alastair E; 30th January 2011 at 07:29 PM.
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Old 1st February 2011, 10:22 AM   #3
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Could you picture it! I suspect there's more computing power in the Dolby decoder than put a man on the moon!

There are 5 power amps and one line amp. The firmware is my own.
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Old 1st February 2011, 12:31 PM   #4
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Err....

Not being funny, But...

If the 'Firmware is your own' (and I'm assuming the decoding algorithm) Then it cant be Dolby AC3....

Dolby AC3 is a Propriety algorithm of Dolby Laboratories....

TBH if it IS your own, Its prolly a damnd site better than AC3!
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Old 1st February 2011, 05:03 PM   #5
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The firmware that is used to talk to Mr Dolby's IC.. it drives the LCD display/remote control etc. Basically only reads and writes to the relevant registers.
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Old 1st February 2011, 05:04 PM   #6
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I would image Mr Dolby would be very upset if I'd reverse engineered his proprietory protocol!
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Old 1st February 2011, 05:19 PM   #7
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Quote:
Originally Posted by Doz View Post
I would image Mr Dolby would be very upset if I'd reverse engineered his proprietory protocol!
Oh, Yes!

They are a very 'funny' company that way! You wouldnt believe how much I had to go through to get the design notes for the then, 'Dolby-Stereo' decoder used in Cinemas. --What the CP-50 and CP55 were based on....

This was before they released 'Pro-Logic' on the scene for the domestic market....

Everything is guarded most securely!
Even the actual 'Dolby-Digital' sound-track between the sprocket-holes on a movie 35mm print has the Dolby Logo in its centre, on each and every one of the millions in a release 35mm print!

Out of curiosity, what DSP are you using? Years ago, A.D. had a pretty nice one that AC3 would run on.....
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Old 5th February 2011, 12:22 PM   #8
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http://www.hsav.com/englishdoc/da32/hsavd216.pdf

all done for you ...
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Old 18th April 2011, 01:00 PM   #9
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And all finished at last... sounds great ... need to fabricate a top that's more ventilation than cover. Dolby AC3 ... with vacuum tubes | Facebook
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Old 18th April 2011, 05:40 PM   #10
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That's pretty awesome! I've always wondered about doing something like this; its way beyond my skill level at the moment, but it's still cool to dream.

Is this for a home theater setup or a multi-channel music setup? What speakers are you using? Power output is 15 watts per channel?
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