Hooking up BDA-1 short interconnects or short digital cable?

john1970 · « **on:** 5 Oct 2008, 09:50 pm »

Dear Bryston or other Byrston users,

I will be purchasing a BDA-1 in the forthcoming weeks and would like to know if there is a preference to using a short digital cable vs. a short XLR interconnect. This will determine whether I place the BDA-1 underneath my CD player which will be used as a transport or underneath my BP25 preamp. The longest cable would be three feet so we are not talking that long of a length.

Thank you in advance for the advice,

John

mcullinan · « **Reply #1 on:** 5 Oct 2008, 11:01 pm »

For some reason I remember reading that your digital cable should be a meter long... Longer is better in this sinstance. Why dont ask me. I read it on the internet and its all true. Really.
Mike

James Tanner · « **Reply #2 on:** 5 Oct 2008, 11:55 pm »

Hi John,

It is important that you use the correct cable with the correct connection(s). The 'Source' Impedance -the 'Cable' Impedance - and the 'Load' Impedance are all critical in getting accurate transfer of signal from one point to another. The wavelengths of digital signals are 'very short' (squarewaves) so the lengths and terminations are much more critical than with analog signals.

When the wavelength of the signal the cable is used for approaches 1/30th of the length of the cable then transmission line effects start to appear and much more attention has to be paid to the connection and termination. If not then reflections and cancellation of data is a real possibility.

For instance the AES/EBU digital connection on the back of the Bryston BDA-1 and BCD-1 should be used with a cable having an impedance of 110 ohms.

james

vegasdave · « **Reply #3 on:** 6 Oct 2008, 01:11 am »

Ok, here's a question. Optical or coaxial?

James Tanner · « **Reply #4 on:** 6 Oct 2008, 01:29 am »

Quote from: vegasdave on 6 Oct 2008, 01:11 am

Ok, here's a question. Optical or coaxial?

COAXIAL - there are 2 more conversions (SPDIF to Light ---Light to SPDIF) required for Optical which can increase jitter. Optical is good if your having ground loop issues.

james

denjo · « **Reply #5 on:** 6 Oct 2008, 01:43 am »

Quote from: James Tanner on 6 Oct 2008, 01:29 am

COAXIAL - there are 2 more conversions (SPDIF to Light ---Light to SPDIF) required for Optical which can increase jitter. Optical is good if your having ground loop issues.

james

Hi James

More conversions no doubt, but I seem to prefer my Nordost Whitelight optical to various RCAs I have tried! My ears don't seem to mind the extra conversions!

Maybe I just have not got the "right" RCA cable yet!

Best regards
Dennis

vegasdave · « **Reply #6 on:** 6 Oct 2008, 02:52 am »

Quote from: James Tanner on 6 Oct 2008, 01:29 am

Quote from: vegasdave on 6 Oct 2008, 01:11 am
Ok, here's a question. Optical or coaxial?

COAXIAL - there are 2 more conversions (SPDIF to Light ---Light to SPDIF) required for Optical which can increase jitter. Optical is good if your having ground loop issues.

james

Thanks for clearing that up, James. I always figured that optical was superior just by the nature of the beast.

James Tanner · « **Reply #7 on:** 6 Oct 2008, 02:55 am »

Well I think we are dealing with very small amounts of diffferences here so go with what sounds best.

james

vegasdave · « **Reply #8 on:** 6 Oct 2008, 03:09 am »

Sounds good.

NewBuyer · « **Reply #9 on:** 7 Oct 2008, 08:09 am »

Quote from: denjo on 6 Oct 2008, 01:43 am

Quote from: James Tanner on 6 Oct 2008, 01:29 am

COAXIAL - there are 2 more conversions (SPDIF to Light ---Light to SPDIF) required for Optical which can increase jitter. Optical is good if your having ground loop issues.

james

Hi James

More conversions no doubt, but I seem to prefer my Nordost Whitelight optical to various RCAs I have tried! My ears don't seem to mind the extra conversions! Maybe I just have not got the "right" RCA cable yet!

Best regards
Dennis

A little late for me to join this thread, but I'm with denjo on this. Paradoxically, and even though the engineers/designers swear that good coax implementation must always certainly be better, I have found that a quality glass optical cable consistently results in a nicer overall sound aspect than coax (even expensive coax choices) with nearly every DAC and every situation I've tried so far. I've just chalked it up to the complete and total galvanic isolation that optical provides, in spite of the theoretical jitter hit and the additional conversions that optical brings.

(Oddly, the only digital connection that to me has ever bested good optical, has occasionally been AES/EBU...)

NewBuyer · « **Reply #10 on:** 7 Oct 2008, 08:17 am »

(Whoops - double post)

ian.ameline · « **Reply #11 on:** 7 Oct 2008, 07:32 pm »

Given how the BDA-1 locks on to and re-clocks the incoming signal, I highly doubt that there would be any audible difference between digital cables -- either optical vs coax, or between different co-axes. As far as the BDA-1 is concerned it's either getting the bits, or not. Nothing in-between. This is how it should be, and equipment that doesn't work this way are just examples of poor engineering/design.

The good news is that I will soon be able to test this theory in person -- I just ordered a BDA-1

vegasdave · « **Reply #12 on:** 7 Oct 2008, 07:34 pm »

That's cool. Please report your findings.

mcullinan · « **Reply #13 on:** 7 Oct 2008, 07:39 pm »

Umm... I do notice a difference between digital cables. I had a Stereovox XV2 which sounded horrific with the BDA-1. I went back to the Morrow dig-1 and it sounds much much better. Maybe an incomaptibility of some kind. And all cables make sound differences. I dont want to get into it though

The BDA-1 is one fantastic DAC. You guys are in for a treat!
Mike

ian.ameline · « **Reply #14 on:** 7 Oct 2008, 07:54 pm »

Firstly, we are talking about the digital interconnect, right? (Not the analog outputs.)

I'm curious, can you reliably tell which is which in a blind listening comparison? (someone else switching the inputs, and not telling you which is which)

mcullinan · « **Reply #15 on:** 7 Oct 2008, 08:11 pm »

YEs, digital.
And the sound was obvious.

Mike

ian.ameline · « **Reply #16 on:** 7 Oct 2008, 08:25 pm »

After looking at that cable, it appears that they took one unshielded twisted pair from a cat5 cable and soldered on good quality RCA conectors.

Right out of the gate there's something wrong with this approach -- Wrong impedance -- SPDIF is speced at 75ohm (+-5%) impedance -- the isolation transformers at each end expect this. Twisted pair without any shielding will not have the correct impedance.

What you want is a pair of good gold plated rca connectors soldered to a high quality 75 ohm cable that can handle the frequency range needed for spdif -- 100khz to 25 Mhz (the latter for 24 bit, 192khz samples) A good example would be Belden RG59U or RG6U (the latter has a larger center conductor, but Belden tests both up to 3ghz -- and over a short run (under 10m.), the smaller conductor of the RG59 will make no difference -- both are solid center conductor co-ax.)

These guys smell of snake oil to me.

mcullinan · « **Reply #17 on:** 7 Oct 2008, 08:40 pm »

I believe the Stereovox XVs is shielded and has good connectors, is 75 ohm but sounded really bad... The Morrow sounds pretty good to me.... The other cable I have is an old MIT digital cable. Im not trying to sell anything, just saying they do sound different, one being worse than the other.
Mike

ian.ameline · « **Reply #18 on:** 7 Oct 2008, 08:42 pm »

It may be obvious, but I wonder if you could tell if someone *else* was switching the inputs and not telling you which was which -- could you correctly identify which was which more than 60% of the time? (To perform this test scientifically you need to repeat the test at least 10 to 20 times -- without communicating in any way with the person selecting the cable -- both of you just write down which cable you believe it to be (the one actually selecting the cable should be right

, and he should use a coin toss to determine which to select each time.)

You might be surprised at the results of such a test.

Jon L · « **Reply #19 on:** 7 Oct 2008, 10:38 pm »

Quote from: mcullinan on 7 Oct 2008, 07:39 pm

I had a Stereovox XV2 which sounded horrific with the BDA-1. I went back to the Morrow dig-1 and it sounds much much better.

That's very strange about XV2. How exactly did Morrow sound "better"?

I've made enough thin-AWG, twisted, unshielded digital cables to expect a forgiving/soft, ethereal/"airy" sound with warmish bass balance.