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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 4:43 pm 
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Benjamin
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I used the Yiddish method of reading, didn't see the need to go further.

But now that you have pointed it out!!!!!!!!!!!!!!!!!!!

Oy vey.

Jocko


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 6:22 pm 
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Sheep

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Jocko Homo wrote:
I used the Yiddish method of reading, didn't see the need to go further.

But now that you have pointed it out!!!!!!!!!!!!!!!!!!!

Oy vey.

Jocko


Rather that focus strictly on this circuit's technical merits why don't we look at the 'big picture'. Given this circuit's low cost and complexity, combined with its ease of assembly. Will it provide any 'subjective' improvement for the average DIY'er persuing this low-cost transport? This solution may have already taken its first step towards improvement with the suggested replacement of the SC944 with the Neweva S22083.

Is the glass half empty or half full?

Regards,
Dan :good:


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 6:59 pm 
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Benjamin
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I think the glass is broken. All of those problems are easily corrected.

Step one: pico-gates.

Jocko


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 7:49 pm 
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Sheep

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Jocko Homo wrote:
I think the glass is broken. All of those problems are easily corrected.

Step one: pico-gates.

Jocko


Is that the limit of your e-altruism? ;)

Regards,
Dan


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 9:23 pm 
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Benjamin
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How much of this am I expected to redesign?? All of the clues have already been posted by me. And also by Phred.

OK, maybe you weren't here then. Maybe if I get time, I will elaborate.

Jocko


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 9:29 pm 
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Sheep

Joined: Mon Feb 23, 2009 3:34 pm
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Dan Twomey wrote:

Is the glass half empty or half full?

Regards,
Dan :good:


Depends. Am I drinking, or pouring?


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 9:45 pm 
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Sheep

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Location: Ontario, Canada
Jocko Homo wrote:
How much of this am I expected to redesign?? All of the clues have already been posted by me. And also by Phred.

OK, maybe you weren't here then. Maybe if I get time, I will elaborate.

Jocko


That wasn't a solicitation, only a little friendly kidding around. :wave:

Regards,
Dan


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 9:46 pm 
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Steve Dunlap wrote:
Dan Twomey wrote:

Is the glass half empty or half full?

Regards,
Dan :good:


Depends. Am I drinking, or pouring?


Good one! :rotfl:


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 10:52 pm 
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Dog
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...and btw what's that coupling cap doing there after the transformer, on the S/PDIF output?
As Jocko previously said, those output impedances are all messed up.
I wonder why reclock and then do something this bad in the end.

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"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 10:57 pm 
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Benjamin
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I thought the same at first, and then I remembered some POC, like the LHH1000 (or whatever it was called) had DC on the input.

As for fixin' the problems:

It is a matter of time. Seriously, I don't have it these days. I might get time to fill in some details.

Jocko


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 Post subject: Re: Very Nice Transport
PostPosted: Wed Feb 03, 2010 11:49 pm 
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Jocko Homo wrote:
Step one: pico-gates.

Jocko


As long as they are the right pico-gates. I've had very poor results with the AUP family, the LVC are WAY better.

John S.


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 Post subject: Re: Very Nice Transport
PostPosted: Thu Feb 04, 2010 4:36 am 
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Benjamin
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Never tried the former; only the latter. What is its shortcomings? Not that it will work in my 5V designs.........

Jocko


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 Post subject: Re: Very Nice Transport
PostPosted: Thu Feb 04, 2010 8:54 am 
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I use Fairchild HS & TI AHC picogates in digital audio circuits.
For the bigger logic ICs ('393, '164, '157, also '74 using one part per package) I always use good old HC, and VHC if I need smaller propagation delays mantaining not too fast rise/fall times.

I used LVC only one time, it has very fast rise/fall times ...RFI Alert!!
AUC? :scratch: Isn't it optimized for very low voltage high speed operation?

I also put 100n PPS // 1n C0G smd caps before and after the newava.
I prefer a linear stage to drive the SPDIF line, and also to receive it, and some other things in between that help with the TDR.

the following figure shows some TI little logic families transition times 20-80% driving 50kohm//50pF


You do not have the required permissions to view the files attached to this post.

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Roberto


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 Post subject: Re: Very Nice Transport
PostPosted: Thu Feb 04, 2010 3:06 pm 
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Goat

Joined: Sat Mar 04, 2006 5:26 pm
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Dan Twomey wrote:
Jocko Homo wrote:
I used the Yiddish method of reading, didn't see the need to go further.

But now that you have pointed it out!!!!!!!!!!!!!!!!!!!

Oy vey.

Jocko


Rather that focus strictly on this circuit's technical merits why don't we look at the 'big picture'. Given this circuit's low cost and complexity, combined with its ease of assembly. Will it provide any 'subjective' improvement for the average DIY'er persuing this low-cost transport? This solution may have already taken its first step towards improvement with the suggested replacement of the SC944 with the Neweva S22083.

Is the glass half empty or half full?

Regards,
Dan :good:

It's not a bad starting concept, but it's got a few bugs (RF impedances not right, AHCT14 clock generator, etc). Work those out and you'll have a better system.

Here's what I'd do:

-- Make the oscillator using a 2-gate HCU04 tinylogic part with a well-filtered power supply. Make sure your filter provides plenty of attenuation at SPDIF frequencies - my usual recipe is a separate linear regulator with a passively filtered input. Also make sure your PCB design keeps ground currents out of the oscillator. (There's better ways to build a clock and feed it power, but I'll leave that to the experts)
-- Buffer the oscillator output to the CDP with its own gate (another HCU04 tinylogic part works fine)
-- Change the 74xx74 to a softer family (VHC/AHC are nice, nothing with a T)
-- Series-terminate all logic outputs. Especially the one feeding the CDP.
-- If you're not using AES/EBU, rip out that output. If you are, that's another post.
-- On the SPDIF driver, get rid of the transformer. Build a new circuit that looks like:

74xx74 Q --> resistor pad 1 --> 75 ohm video amp (5V rail) --> resistor pad 2, with AC coupling --> BNC

Resistor pad 1 gets the 5Vpp level from the 74xx74 down to something sensible for driving the video amp without saturating its input. Depending on logic family speed and video amp speed, a stray C can't hurt in this pad. Resistor pad 2 provides RF matching, AC coupling and gets the voltage level down to a suitable level for SPDIF. For a video amp, just hit up the Analog Devices website and find something with enough bandwidth for component video. Study the datasheet well, these things require good layouts and decoupling.

I'll stop before I design the thing entirely for everyone. I'm just teaching, do your own homework...


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 Post subject: Re: Very Nice Transport
PostPosted: Thu Feb 04, 2010 3:10 pm 
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Goat

Joined: Sat Mar 04, 2006 5:26 pm
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Location: Nova Scotia
Another thought: it can't hurt to put an "optional" inverter on the clock, with a jumper or a pair of resistors which select whether a normal or inverted clock feeds the 7474.

Just to make sure that the SPDIF coming back from the player has a good setup'n'hold time going into the 7474. Compare the 7474's D and clock inputs with a scope, you don't want D changing when the clock rises, you want it changing when the clock falls. Metastability from poor retiming of signals is probably the worst kind of jitter (insert rant on asynchronous reclocking here)


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