Digital stream switching - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 24th January 2006, 07:05 PM   #1
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Default Digital stream switching

Hi all,

I am looking at a way to switch different CD digital outputs to a D/A converter without degrading the signal. I am looking at RF coaxial switches at the surplus market, but the ones I found are all 50 ohms characteristic impedance, while an AES/EBU connection should be 110 ohms IIRC.

Would there be a signal degrading if I used the 50 ohms switch? Do you have another solution?

Thanks,

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 24th January 2006, 08:00 PM   #2
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
What is the frequency of the signal?
  Reply With Quote
Old 24th January 2006, 08:03 PM   #3
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally posted by poobah
What is the frequency of the signal?

Ehhh... I'm an analog man basically. I think the AES/EBU is 11.something Mhz digital stream. I'll look it up.

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 24th January 2006, 08:22 PM   #4
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
11 Mhz may be a bit too enthousiastic:

"The [AES/EBU] data transmission is sent as a Bi-Phase mark mode to minimise the DC content of the data stream. A logic '1' is represented by a transition in the middle of the data bit and a logic '0' doesn't have a transition. The end of each bit time also has a transition regardless of the data level. This method of encoding requires that the data clock is two times the data rate. For 48kHz sample rate data the clock would therefore be 6.144MHz (2 channels x 32 bits per sub-frame x 48kHz)"

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 24th January 2006, 08:36 PM   #5
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
OK,

At that frequency your wavlength is somewhere between 30 - 50 meters.

A 50 Ohm switch in a 110 Ohm line will cause reflections back toward the source... in theory these reflections should die when they return to the source amplifier/driver (if it has a 100 Ohm Zout). So your signal between the driver and the switch (and down stream for that matter) is the original with the reflection superimposed.

On paper it doesn't sound to well... but in reality 6Mhz is really pretty slow, the reflections are not 1 to 1 in magnitude (not even close), and digital is very forgiving.

Is there a real price advantage with these surplus switches?

As an alternative I'm sure there are silicon switches for this purpose. You would terminate each line with 110 ohms; feed this to a switch, and reamplify with 110 Zout and be on your way down stream. If the distance between your switch and the DAC is very small, you could avoid the transmision line completely.

Do you have a complete description of the signal standard or its "name"?

  Reply With Quote
Old 24th January 2006, 08:41 PM   #6
moamps is offline moamps  Croatia
diyAudio Member
 
Join Date: Oct 2002
Location: Croatia
Hi Jan,

I once used two-pole two-position reed relays (one for each input) for switching between three inputs, with satisfactory results. The coaxial relay is unsymmetrical and it isn't apropriate for switching symmetrical signals. Have you considered an active switcher?

Regards,
Milan
  Reply With Quote
Old 24th January 2006, 08:48 PM   #7
diyAudio Member
 
Join Date: Oct 2001
Location: .
Default Re: Digital stream switching

Quote:
Originally posted by janneman
Hi all,

I am looking at a way to switch different CD digital outputs to a D/A converter without degrading the signal. I am looking at RF coaxial switches at the surplus market, but the ones I found are all 50 ohms characteristic impedance, while an AES/EBU connection should be 110 ohms IIRC.

Would there be a signal degrading if I used the 50 ohms switch? Do you have another solution?

Thanks,

Jan Didden

Why not do what is done in the broadcast arena and switch after SPDIF decoding.
  Reply With Quote
Old 24th January 2006, 08:55 PM   #8
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally posted by poobah
OK,

At that frequency your wavlength is somewhere between 30 - 50 meters.

A 50 Ohm switch in a 110 Ohm line will cause reflections back toward the source... in theory these reflections should die when they return to the source amplifier/driver (if it has a 100 Ohm Zout). So your signal between the driver and the switch (and down stream for that matter) is the original with the reflection superimposed.

On paper it doesn't sound to well... but in reality 6Mhz is really pretty slow, the reflections are not 1 to 1 in magnitude (not even close), and digital is very forgiving.

Is there a real price advantage with these surplus switches?

As an alternative I'm sure there are silicon switches for this purpose. You would terminate each line with 110 ohms; feed this to a switch, and reamplify with 110 Zout and be on your way down stream. If the distance between your switch and the DAC is very small, you could avoid the transmision line completely.

Do you have a complete description of the signal standard or its "name"?


Hi-quality HP coax switches (DC to 18GHz) are < 50 $, which is a steal really, but as I said they are 50 ohms.

I really would want to keep this as simple as possible to use for listening A/B tests of different CD players digital output. If I used silicon switches everyone would say that they would mask any differences .

As to the signal specs, is this what you are looking for:

"The [AES/EBU] data transmission is sent as a Bi-Phase mark mode to minimise the DC content of the data stream. A logic '1' is represented by a transition in the middle of the data bit and a logic '0' doesn't have a transition. The end of each bit time also has a transition regardless of the data level. This method of encoding requires that the data clock is two times the data rate. For 48kHz sample rate data the clock would therefore be 6.144MHz (2 channels x 32 bits per sub-frame x 48kHz".

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 24th January 2006, 08:56 PM   #9
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Default Re: Re: Digital stream switching

Moamps and rfbrw:

See my post above. really need to keep this as simple as possible for psychological reasons...

Thanks for the inputs,

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 24th January 2006, 09:00 PM   #10
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Like so (but with BNC connectors):

Jan Didden
Attached Images
File Type: jpg hp8761btyp1.jpg (16.1 KB, 401 views)
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
FS: SMC Ex-Stream SMCWAA-G naz Swap Meet 2 28th December 2008 08:16 PM
Sound Stream Mc-245, No Power!..help! JT_mechanic Solid State 0 27th May 2008 10:37 PM
Audio Stream to Power amp on and off masaclaw Parts 2 10th July 2006 01:43 PM
sounds stream? subarusteve Car Audio 0 1st May 2005 01:53 AM
sound stream any good? 1needforspeed Car Audio 6 20th March 2005 02:09 PM


New To Site? Need Help?

All times are GMT. The time now is 04:56 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2