I recently purchased a used PEACHTREE DAC-IT (S/N 107010). My first DAC. It brought a truly weird phenomenon to light. Using my Rega Planet as a transport (digital coax out) it will not recognize a signal when the cable is shorter than a couple meters.
Yep, you read that right...I've tried about a dozen different coax cables (MIT, BlueJeans, Acoustic Research), both traditional audio (unbalanced) and a 12" Blue Jeans purchased especially for it (a BJ Belden 1694A digital cable - 1 foot). Nothing. I double checked the output connector, seemed fine with no intermittents when I jiggled it.
My NAD CD player, on the other hand, does just fine from it's digital out to the DAC.
On the other hand, I just happened to have bought a 12' long sub cable (Blue Jeans LC-1) the other day and that worked fine. Longer is better? Thought that wasn't true.
My first assumption was that the cables I was trying were older except for the sub cable,BJ LC-1. Nope. Found an ancient, super cheap 15' Acoustic Resarech that worked fine, too.
Thinking it might be an issue of digital cable design versus analog optimized cable, I purchased a BJ digital cable...nope, didn't work.
BTW, my NAD CD player plays just fine with the DAC at any length.
Now it gets really weird. I hooked up a splitter on the digital out of the Rega, ran my new digital cable to the DAC (no sound) and then hooked the 12' sub cable to the other output on the splitter but left the other end of that cable unterminated. Got sound.
So, is there someone who can suggest what might be going on? Even better, how to fix it?
Thanks!
Yep, you read that right...I've tried about a dozen different coax cables (MIT, BlueJeans, Acoustic Research), both traditional audio (unbalanced) and a 12" Blue Jeans purchased especially for it (a BJ Belden 1694A digital cable - 1 foot). Nothing. I double checked the output connector, seemed fine with no intermittents when I jiggled it.
My NAD CD player, on the other hand, does just fine from it's digital out to the DAC.
On the other hand, I just happened to have bought a 12' long sub cable (Blue Jeans LC-1) the other day and that worked fine. Longer is better? Thought that wasn't true.
My first assumption was that the cables I was trying were older except for the sub cable,BJ LC-1. Nope. Found an ancient, super cheap 15' Acoustic Resarech that worked fine, too.
Thinking it might be an issue of digital cable design versus analog optimized cable, I purchased a BJ digital cable...nope, didn't work.
BTW, my NAD CD player plays just fine with the DAC at any length.
Now it gets really weird. I hooked up a splitter on the digital out of the Rega, ran my new digital cable to the DAC (no sound) and then hooked the 12' sub cable to the other output on the splitter but left the other end of that cable unterminated. Got sound.
So, is there someone who can suggest what might be going on? Even better, how to fix it?
Thanks!
My guess is the added capacitance from the longer cable is somehow filtering the digital signal in a way that allows the DAC to receive it cleanly, but only a guess. Obviously, for whatever reason, they aren't playing together nicely. You could try adding a small capacitor across the DAC input to see if it does the same thing, maybe a COG/NPO ceramic in the low hundreds pF range, but it's probably indicitive of deeper issues and may need further investigation.
Mike
Mike
Mike - thanks for the suggestion. Not sure how to do that, however I did email both Rega and Peachtree. The Rega people claimed that a digital cable shouldn't be less than one meter...?! but it was probably the DAC's fault. The Peachtree folks suggested testing (grounding the shield) for galvanic isolation which I think is corrosion. Will try that since it's easy and report back.
Ken - I wondered if something like that might be possible. Since I just bought the 12' cables for my subs (and they take up lots of room), I'm hoping the Peachtree suggestion will work. Rega did (again) suggest trying another DAC, which I don't have but will explore if I can find one to borrow. Thanks, Dan
Any chance of a scope shot of the rega output, I would suspect that that is at fault here, as SPDIF should work with any length cable, and using longer cables is a load of rubbish.
To find out what is happening with the two SPDIF outputs a picture of the waveform from an oscilloscope is what we need to look at, if you havn't got a scope (as many don't have) we are working in the dark regarding the problem.
Looking at the Rega's stuff and notes I suspect either the rise time is to fast or the level is incorrect. The fast rise time is my first suspicion as this would cause excess reflections and possibly a non monotonic leading edge at the DAC causing it not to latch on.
http://www.ami.ac.uk/courses/ami4822_dsi/u02/
Figure 2.12 shows a non monotonic wave, but the whole article is probably relevant to your problem.
Do you know what is inside your DAC where the SPDIF enters, is there a transformer or resistor?
Looking at the Rega's stuff and notes I suspect either the rise time is to fast or the level is incorrect. The fast rise time is my first suspicion as this would cause excess reflections and possibly a non monotonic leading edge at the DAC causing it not to latch on.
http://www.ami.ac.uk/courses/ami4822_dsi/u02/
Figure 2.12 shows a non monotonic wave, but the whole article is probably relevant to your problem.
Do you know what is inside your DAC where the SPDIF enters, is there a transformer or resistor?
Ha. Been several decades since I touched a scope. Not that I knew what I was doing even then. Someone in my search suggested that inappropriate reflections were a suspect and sent me the following link: spdif. While I'm unwilling to pop open or mod the Peachtree DAC, the Rega is fair game. The Peachtree guys have been really responsive and suggested lifting the ground on the Rega. Haven't figured out quite how...since it's a two prong. However, since longer cables (12') pass the signal, I do have a work around. Problem is, there's very little sound difference between the Rega's analog output to my Bryston pre/amp and the digital output via the Peachtree DAC when I A/B them. Soooo, that, to me, can mean the 10+ year old Rega's got a nice DAC built in or the long cable & Rega digital out combo with the DAC is degrading the digital out. To check that, I've ordered an optical cable...wanted to play with that anyway. All this because I put my vinyl collection in storage during home construction...:8(
- Status
- Not open for further replies.