Why are there no Mods to Satellite Receivers - diyAudio
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Old 8th October 2006, 02:14 PM   #1
diyAudio Member
 
Join Date: May 2001
Location: London UK
Default Why are there no Mods to Satellite Receivers

In the UK and parts of Europe, DAB digital compressed radio is very poor compared to FM. However, radio piped thru' satellite is much better.

Aky has such tight control that there is very little information about the digital audio streams in their boxes.

I have successfully tapped the Toslink output of the Sony VTX670 box to enable very good electrical spdif via 75R and a jitter buster.
However, this box is insensitive for fringe areas where I am.

But I just cannot find any technical info/service manual on the more sensitive Pace 26001 or DSN430 boxes.

Why? and why doesn't anyone modify satellite boxes-the standard analog output of the Pace boxes is DIRE, even though the dacs are 18 bit

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Old 8th October 2006, 09:10 PM   #2
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Hi Fmak,

If you pop the lid and look at the chips inside, you should be able to get some info from silicon datasheets to work out I2S lines (although not all STBs use external DACs, most STB decoder chips do output I2S).
The best bet is probably to find the DAC, and then tap off I2S from there, it might be trickier at the stb chip - as it might be BGA.

That may well be the only mod I'd consider doing to a STB.

STBs are full of high frequency signals, typically cheap and with poor SMPS. I personally wouldn't spend too long modding one.
Also, don't think about reclocking them, as the clock signal is typically a drifting VCXO. This deliberate, and is used to ensure audio and video are in sync with each other. Reclocking that would lead to all kinds of problems. If you need to reclock, I guess you'd be able to use a free running clock to reclock the I2S (but I know little about reclocking like that, so check other forums for that).
Perhaps, the drifting clock is the main reason why people don't bother modding STBs?

Cheers,
Phil
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Old 9th October 2006, 06:40 AM   #3
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Quote:
Originally posted by philpoole
Hi Fmak,


STBs are full of high frequency signals, typically cheap and with poor SMPS. I personally wouldn't spend too long modding one.
Also, don't think about reclocking them, as the clock signal is typically a drifting VCXO. This deliberate, and is used to ensure audio and video are in sync with each other. Reclocking that would lead to all kinds of problems. If you need to reclock, I guess you'd be able to use a free running clock to reclock the I2S (but I know little about reclocking like that, so check other forums for that).
Perhaps, the drifting clock is the main reason why people don't bother modding STBs?

Cheers,
Phil

Hello Phil

Thanks for that. I

I have trouble relocking a Sony VTX 750 when I tapped the Tx pin of the Cirrus Chip. Yes only a coarse PLL works.

However, taking the digital out from the Toslink line of the VTX670, I have complete success and very good eye pattern. With twin PLL relock the sound is truly superior on and here I don't care about lip sync.

I shall try the I2S from the Pace units and see what happens.

Do you know where I can buy or download the schematic for a Pace 2600C1 or DSTN430?

Yes, dgiboxes are really nasty hf polluters. In a high end system using Hard Drive as transport, dCS upsampler and dac, I haer a difference when the Sky box and Plasma are switched on; subtle but affects tonality and spacial details!

Fred
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Old 9th October 2006, 09:14 AM   #4
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Hi Fred,

I'm afraid I don't know where to find the schematics. However, if you take the lid off, and note down the chip numbers, you can probably find datasheets for at least some of them online - especially the DAC. From that, you should be able to work out which pins are I2S, and tap off of them and feed something else
Try www.datasheetarchive.com for the datasheets, you should hopefully find something that helps.
Sorry I can't be more precise.

Cheers,
Phil
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Old 11th October 2006, 03:03 AM   #5
dangus is offline dangus  Canada
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Have you tried checking out some satellite-hacker forums? Someone reverse-engineered a bunch of North American satellite receivers and produced an impressive set of schematics. Maybe someone has done that for the European ones.

The Dish network in the USA used something like 128k to 160k bps for their radio channels in MP2 format. I don't suppose other broadcasters are any more generous with bits, so that has to limit the potential quality.
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Old 11th October 2006, 12:58 PM   #6
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Quote:
Originally posted by dangus
Have you tried checking out some satellite-hacker forums? Someone reverse-engineered a bunch of North American satellite receivers and produced an impressive set of schematics. Maybe someone has done that for the European ones.

The Dish network in the USA used something like 128k to 160k bps for their radio channels in MP2 format. I don't suppose other broadcasters are any more generous with bits, so that has to limit the potential quality.

Can you give me some urls?

In UK Satellite radio is 48k 16bit and better than digital audio broadcast which is terrible.
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Old 11th October 2006, 02:22 PM   #7
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Hi,

fmak, I think dangus was referring to the compressed data rate, where I suspect you're quoting the sample rate.
DVB broadcasts for audio are very similar in europe as they are in the US. However, it is highly dependent on the broadcaster (shopping channels typically use far less bandwidth/lower bitrate than pay-per-view sport or movies).

Dangus, not that its important, but nearly all audio broadcast is MPEG1, only the video is MPEG2 (or MPEG4 these days). I think the only exception is AC3.
In fact MP3 audio is actually MPEG1, level 3.

Cheers,
Phil
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Old 14th October 2006, 04:19 AM   #8
dangus is offline dangus  Canada
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This was MPEG 1 layer 2 audio, hence MP2. The radio channels I recorded were extracted directly from the transport stream and saved as MP2. MP2 files would play back with Winamp, and the occasional DVD player. Sound quality seemed inferior to MP3 at the same bitrate... deader somehow, less involving. OK for background music, though, until I got sick of the repetitive playlists.

http://www.audiocoding.com/modules/w...MP2&PHPSESSID=

http://www.dvbapps.com/ for DVB radio tuner/recorder software, and FTA TV. (Broadlogic and Twinhan cards)
http://dvbn.happysat.org
http://www.id-discussions.com
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Old 20th March 2008, 12:33 AM   #9
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Ive looked all over the net for mods to the Sky box and found nothing. Having looked inside my THompson its clear that significant improvements could be made. Especially the power supply. I reckon if I could find the audio output stage then a change of caps there would be worth it.


Anyone done this or any other mods to the sky box?
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Old 23rd March 2008, 09:07 PM   #10
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I just finnished the first mods to my Thompson sky box and got pleasing results

Thread with pics
here: http://www.diyaudio.com/forums/showt...hlight=sky+box
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