I want a bigger S/PDIF ! - Page 2 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, 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 5th May 2009, 12:34 AM   #11
Tenson is offline Tenson  United Kingdom
diyAudio Member
 
Join Date: Feb 2006
Location: Kent
Thanks for all the replies!

I have got a little further with this now. It seems there were two reasons my DAC was loosing lock. Firstly as I said the S/PDIF output was too low. However, even when boosted with the switch-box it kept loosing it. It turned out that I needed to ground the switch-box because both my sources and my DAC had floating inputs/outputs. So I grounded the input of the DAC, that in turn grounds the switch-box.

Now, it does seem to be working reliably, but there are a few things I wonder if you can help clear up?

Firstly, removing the voltage divider on the output of the switch-box did boost the level, and I now get about 500mVpp on the output. However, something that I find puzzling is that changing the feedback resistors R8 and R6 do nothing to the output level. In fact even bypassing R7 does nothing. It seems that no matter what the level of the input signal, and no matter what the feedback resistors are, the output is always spot on 500mVpp. Why is this??! I'd like to make it about 1V if I could, then I can add a 75R series resistor after the gate to get the impedance right and still have a good level. At the moment there is no source resistor, it just connects the gate, via a cap to my DAC with a 75R input load.

Secondly, there seems to be some ringing when the signal is connected to the switch-box.

If I have the S/PDIF output from my CD player going through a coax wire unloaded or loaded with a simple 100R resistor it does ring a little, but interestingly this can be reduced with a change in cable from a coax to a twisted pair balanced cable. See the comparison below.

Click the image to open in full size.

Now the bit I don't get - when I connect it to the switch box, it rings no matter what cable I use, and it does so on the input, and the output! (p.s. I changed the scope range from 500mV to 1V when looking at the switch box output)

Click the image to open in full size.

So why does the cable suddenly make no difference, and how can I clean up that ringing?

Thanks for your help!
  Reply With Quote
Old 5th May 2009, 11:57 AM   #12
diyAudio Member
 
Join Date: Jun 2004
Location: Warsaw
Default AES3 driver

-> EC8010

Could you share with us the circuit diagram of your AES3 driver? Did you used something similar to SPDIF to AES/EBU converter shown on http://www.epanorama.net/documents/audio/spdif.html ?
  Reply With Quote
Old 5th May 2009, 12:09 PM   #13
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Default Re: AES3 driver

Quote:
Originally posted by buble_corp
Could you share with us the circuit diagram of your AES3 driver? Did you use something similar to SPDIF to AES/EBU converter shown on http://www.epanorama.net/documents/audio/spdif.html ?
Close, but not quite. I picked up the signal inside the player where it came from the oversampling chip, so I didn't need the AC coupling and diodes in your reference. I did connect three inverters in parallel (like your reference) to drive the output. Then I added a series resistor and a series 1uF capacitor to drive the AES3 transformer. I'd draw it, but for various reasons, my scanner isn't working.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 5th May 2009, 12:15 PM   #14
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Tenson, you're going to need a better oscilloscope than that to see what's going on. As it is, your lack of analogue bandwidth or sample rate could be concealing all sorts of things. I think the best you can do is to set your source impedance to 110 Ohm, use 110 Ohm twisted pair and hope that everything is correct. Fortunately, you can still check your source impedance by seeing if adding a 110 Ohm halves the open-circuit output voltage.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 5th May 2009, 03:03 PM   #15
diyAudio Member
 
Join Date: Jun 2004
Location: Warsaw
Default AES3 driver

-> EC8010

What kind of AES3 transformer did you use? Whas it balanced transformer with 1:2 ratio or standard 1:1 for spdif i.e. PE65612 from elfa.se ?
  Reply With Quote
Old 6th May 2009, 07:00 AM   #16
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
The transformer was a 1:1 DIL type made by Newport Magnetics. I should warn you that although I've made this circuit a few times, the values of the series resistors may need to change depending on the individual inverters to get the right output resistance.
Attached Images
File Type: gif cd5400 aes3.gif (7.5 KB, 345 views)
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 6th May 2009, 11:00 AM   #17
diyAudio Member
 
Join Date: Jun 2004
Location: Warsaw
-> EC8010

Thanks for schematic, I see that you didn't use inverters to create balanced signal, you only used gates to buffer/amplify the signal.

I read the topic where Jocko Homo was teaching someone how to build correctly spdif output so I know about matching impedance, but still are there any datasheets telling you what the output impedance of chip's spdif digital output? Of course you can calculate it after measuring output voltage on different load, but to do it precisely you need a really good oscilloscope.
  Reply With Quote
Old 7th May 2009, 08:05 AM   #18
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Quote:
Originally posted by buble_corp
... but to do it precisely you need a really good oscilloscope.
Yes.

Actually, if you do the sums, you'll realise your oscilloscope doesn't need to be that good. Provided you compare open circuit with half amplitude (by adjusting a trimmer to give half amplitude), you can then just measure the trimmer with a DVM and the result will be good enough.

There's no way you can determine the inverter's output resistance from theory - they use FETs and FETs have enormous device to device tolerance. Also, the transformer adds resistance. It really is best to determine that series resistor by experiment.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 7th May 2009, 04:55 PM   #19
gmarsh is offline gmarsh  Canada
diyAudio Member
 
gmarsh's Avatar
 
Join Date: Apr 2004
Location: Halifax, NS, Canada
Use a 74HCU04, not a 74HC04.

Putting feedback on a HC04 (non-U) is asking for spurious oscillation.
  Reply With Quote
Old 7th May 2009, 05:12 PM   #20
Tenson is offline Tenson  United Kingdom
diyAudio Member
 
Join Date: Feb 2006
Location: Kent
Quote:
Originally posted by gmarsh
Use a 74HCU04, not a 74HC04.

Putting feedback on a HC04 (non-U) is asking for spurious oscillation.

Hi,

The circuit in my first post seems to use a HD74HC04, and has some feedback resistors. Removing them seems to do nothing to the output level, so should I remove them? Do gates like these not have a near infinite open loop gain, like an op-amp?
  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
S/PDIF Optical to S/PDIF RCA Replacement PrecisionAudio Digital Source 2 11th February 2007 10:35 PM
Why STK is bigger than TDA..?! Dj BASS AMP Chip Amps 2 25th July 2004 06:08 PM
Big, bigger, .. Nielsio Planars & Exotics 7 20th December 2003 12:55 PM
Characters getting bigger and bigger Elso Kwak Everything Else 11 31st May 2003 11:43 PM
Is bigger better? Pete Fleming Solid State 8 29th September 2001 02:54 PM


New To Site? Need Help?

All times are GMT. The time now is 08:09 AM.


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