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Old 30th October 2010, 04:35 PM   #201
sendler is offline sendler  United States
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Default 75 ohm Tpad

So I will try these 75 ohm T pads on both ends of the cable to hear what it sounds like.
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File Type: jpg 6db attenuator 75in 75out.jpg (43.9 KB, 177 views)
File Type: jpg 11.5db attenuator 75in 75out.jpg (46.0 KB, 170 views)
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Old 30th October 2010, 05:21 PM   #202
sendler is offline sendler  United States
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Default Cost 30 cents

Quote:
Originally Posted by jkeny View Post
Sendler, remember this use of RF attenuators is only possible if your SPDIF signal can withstand some attenuation & your DAC can still lock to it without any problems. This works with the Hiface because of it's high output but has also worked on other devices - the Shigaclone, some soundcards, Teac VRDS-10 CDP, etc.
The worst that can happen is that I will lose lock or it will sound worse. At which point, I will have only wasted 30 cents worth of resistors. It may also improve my 110R to 75R XLR to RCA conversion from the AES/EBU output of my DEQ2496 to the RCA input of the Big Dac Board.
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File Type: jpg 12db attenuator 110in 75out.jpg (50.3 KB, 165 views)
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Old 30th October 2010, 05:25 PM   #203
jkeny is offline jkeny  Ireland
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That's the spirit - go for it & let us know how it works out.
 
Old 30th October 2010, 07:59 PM   #204
sendler is offline sendler  United States
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Default 110-75 ohm converting cable with attenuators

My new XLR to RCA converting digital cable with built in attenuators is playing. Neutrik silver XLR, Belden 1701a wire, Cardas rhodium RCA. Lock from the XLR digital out of my DEQ2496 into the Big Dac Board configured with DIR9001/ CS43122 running direct out seems to be no problem. 7db attenuation in the XLR input and 6db built into the RCA output gave me the resistor values shown below which I had on hand. Sonic comparisons with my old, otherwise identical cable to follow after some hours of break in tomorrow.
Attached Images
File Type: jpg 7db attenuator 110in 75out.jpg (47.1 KB, 155 views)
File Type: jpg 6db attenuator 75in 75out.jpg (43.9 KB, 153 views)
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Old 30th October 2010, 11:17 PM   #205
jkeny is offline jkeny  Ireland
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Sendler,
I just noticed that your RCA side impedance is 75ohm but RCA is NOT 75ohm (maybe 35- 50 ohm?) so you will have an impedance match between this & your RCA connector.
 
Old 30th October 2010, 11:27 PM   #206
sendler is offline sendler  United States
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Default Digital cables with T pads sound better!

Quote:
Originally Posted by sendler View Post
My new XLR to RCA converting digital cable with built in attenuators is playing. Neutrik silver XLR, Belden 1701a wire, Cardas rhodium RCA. Lock from the XLR digital out of my DEQ2496 into the Big Dac Board configured with DIR9001/ CS43122 running direct out seems to be no problem. 7db attenuation in the XLR input and 6db built into the RCA output gave me the resistor values shown below which I had on hand. Sonic comparisons with my old, otherwise identical cable to follow after some hours of break in tomorrow.
OK. I sat and read every post in this thread. 200+ posts, countless hours of theoretical conjecture, and not one person other than the original poster and his compadre doing the excellent scope shots ever actually built and listened to the simplest and cheapest circuit ever proposed on DIYAudio. Sad. You all could have saved a lot of time. It sounds better! I will be rebuilding all three of the digital cables in my signal path.
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It is surprising how much difference adding the attenuators to both ends of the cable makes to the sound even when running into the DIR9001 receiver which has it's own clock. The differences are also very apparent into the same dac when the DIR9001 receiver module is changed to CS8416. My application might be more revealing due to the attenuator on the input of the cable also improving the adaptation from the XLR standard 110R to an RCA 75R output. In this application, adding the attenuator to convert the input/ output impedance is a no brainer compared to a $30 transformer which will save about... $30. I will also do listening tests with an RCA/ RCA cable from my FireWire410 to the SRC2496 upsampler and with an XLR/ XLR digital cable from the SRC to the DEQ2496.
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The digital cable with T pads on both ends sounds more natural and layered. On Natalie Merchant live San Andreas Fault, the vocal and instrument images float free in a blacker background. Using the standard cable makes the crowd noise sound less realistic and more like white noise. Janis Ian Live, Tatoo, has more body to the vocals and the eerie steel guitar set way back in the soundstage is more fleshed out. The standard cable is flatter and less 3d, less composed. Her live Acousticville shows the only hint of a trade off sounding slightly more dynamic and exciting with the standard cable. None of the other 10+ recordings I played had anything superior to show about the standard cable. The padded cable generally has more ease to the presentation that analog devotees will appreciate. The intro to No God from the Exteme, Waiting For the Punch Line disc clearly favors the new cable as it gives much more body to the drums and bass guitar. On track 7 from Ian Anderson's Secret Language Of Birds, the old cable makes everything sound very artificial by comparison.
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Adding pads to your digital cable is a clear winner as long as the signal stays strong enough to provide a reliable lock. It will be interesting to hear if the effect can sound even better with the excellent Susumu surface mount resistors replacing the Yageo through hole parts I am using now.
Any recommendations to tweak my values before I order the parts?
Attached Images
File Type: jpg 7db attenuator 110in 75out.jpg (47.1 KB, 26 views)
File Type: jpg 6db attenuator 75in 75out.jpg (43.9 KB, 23 views)
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Old 30th October 2010, 11:33 PM   #207
sendler is offline sendler  United States
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Default Connector

Quote:
Originally Posted by jkeny View Post
Sendler,
I just noticed that your RCA side impedance is 75ohm but RCA is NOT 75ohm (maybe 35- 50 ohm?) so you will have an impedance match between this & your RCA connector.
Should I match the inherent impedance of the RCA connector or the 75R termination behind it?
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Old 30th October 2010, 11:51 PM   #208
jkeny is offline jkeny  Ireland
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God help you reading through all this thread - it must have been agony
You are the first from here to actually try this out - well done - it's shameful that 20 pages were spent arguing the theory without one person trying it. Anyway, all in the past!

As you probably read, the way that the attenuators work in this situation seems to be by reducing the reflections caused by impedance mismatches encountered by the SPDIF signal along the signal path (this includes transmitter, outputs stage, connectors, cable, receiver, input stage, etc). The attenuator does a double attenuation of the reflections because they pass through the attenuator twice on the journey back to the DAC where they can cause jitter. So if you have 6dB attenuator the reflections will be reduced by 12dB. Even so it's probably beneficial to try to minimise impedance mismatches as much as possible & where practical.

You would probably need to measure the characteristic impedance of your RCA connectors & make one side of your T-pad match this impedance. This may be just theoretically optimal & the in the real world you may not hear any difference.
 
Old 30th October 2010, 11:55 PM   #209
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Quote:
Originally Posted by sendler View Post
The digital cable with T pads on both ends sounds more natural and layered...
Excellent listening report sendler Thanks, this is the kind of stuff we need to begin to understand why these pads are making a difference.
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Old 31st October 2010, 12:17 AM   #210
jkeny is offline jkeny  Ireland
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Yes, abrax, many thanks to sendler. This was always meant as an experimental effort that I hoped would be taken up & advanced by enquiring minds & we could all have learned something.
 

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