Raspberry Pi I2S to SPDIF Hat

Hands is 100% correct. BNC was designed for, and tested at 50 or 75 ohm impedance, and up to 1,000Mhz frequency. RCA jacks are not. Which would be fine if you could at least get 75 ohm high frequency RCA cable. That would reduce the effect of the small discontinuity at the connector. Finally, at the receiving end you would still need a transformer to match the 75 ohm impedance. This matters because at 24-Bit/192Khz frame rate the encoded data is running at 24.576Mhz! RCA is designed for audio frequencies of 10Hz to 20Khz.

From the Coax Wiki:

"Coaxial cable differs from other shielded cable used for carrying lower-frequency signals, in that the dimensions of the cable are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line."

As an engineer this is one of those times I can whole heartily agree with the Audiophile folks!

Cheers,
Michael

 

Well I got my Digi+ (Transformer model) and I must say it sounds really good. After just some casual listening there is nothing glaring missing or wrong compared to the usb out from my fully tweaked PC. The one thing I noticed with music from the Digi+ or the usb output of the Pi3, is an emphasis on the mid bass, giving the music a meatier sound. I feel like the loudness button was pressed. I am running rca coaxial out from the Digi+ to my Mutec 3+ reclocker. If the Digi+ sounds pretty good I can only imagine that the SPD will be even better. As if I was not already excited...

 

I greatly appreciate your feedback.
This is totally unexpected to me. I mean... if a fully tweaked audio computer is (in your opinion) more or less on the same level of the digi+\Pi3 combo, what is the message here? I can't help wondering a about fancy audio PCs, usb centipeds, and other things. But I keep my thoughts to me until further experimentation.
I could take your comment also as a compliment on the mutec (for the reclocking ability) and\or on the hdplex power supply (which I assume is powering the Pi). Maybe the mutec is levelling differences, Maybe the psu is.

I can tell you this in my experience: The Pi2\digi+ combo (with a good psu) is an astounding performer at the price but inferior to good old cd transports I tried like a 20+ year old micromega duo cd 3 owned by a friend. And it is not the best cd transport around.
Maybe you would have liked more the chinese digipi, which lacks a little of bass\midbass bloom compared to the swiss digi+.

 

In all its simplicity, I don't think I've every used anything this easily affected by external things since using a 47 Lab Gaincard. I use a 20000 mah lithium ion battery pack with the pi and DIGI+ and the sound changes as the output and electrical noise varies. Still worth evaluating, but there is a 3 hours or so sweet spot. Looking forward to reading about your continuing power investigations. I agree with older transports, interested to know if you have found affordable ones?

 

Vastx,
I admit I was initially surprised as well until I really thought about it some more. In my experience with audio, simpler usually is better. Even though my pc is fully tweaked its still a big noisy device that is way overkill for what I am using it for, a simple network renderer. If you read about the playback software HQplayer, they actually recommend a simple device like the Pi3 to send the audio signal to the dac. Sonore has their microrendu device. I also believe in separating the audio computing pc from the renderer.

Another thing to consider here is that perhaps the spdif output of the digi+ is whats making it sound good compared to the mobo usb of my pc. I was considering getting an audiophile usb card from Paul Pang but just felt it and the various other usb helpers are just band aids. This is why I started to look for a simpler solution for my renderer.

By the way, I agree with you sentiments about transports. A while back I had the Esoteric P3 D3 transport and dac which sounded fantastic. I am not sure what made it sound so good. Perhaps it was the clock or lack of jitter or good power supply implementation or? There are just so many factors that impact the sound quality. That's why this whacky hobby is so fun and frustrating!

 

Hey guys check this thread out over in the RuneAudio forums. A member measured the THD out from the Pi3 usb and Digi+ SPDIF. The THD is orders of magnitude higher than the output from his laptop. @Michael Kelly, not sure what kind of measuring device you have but it may be interesting to compare the SPD to the Digi+. Is this a limitation of the Pi or the Digi+? If its the Pi, is there anything that can be done to improve it?

Here are the test results:


Here is a link to the original thread:
http://www.runeaudio.com/forum/post14590.html#p14590

 

If he's measuring it correctly (hard to do)... maybe that's why it (digi+) sounds so average before linear power. I skimmed thru quickly, it looks like he tested with ethernet cable, a pi3, and cheap switching power thru usb (not GPIO)

Also ethernet is a known noise problem on the pi: http://www.crazy-audio.com/2013/10/tracking-down-noise-sources-on-a-raspberry-pi/ (This is Daniels at hifiberry's blog)

Edit: UTP ethernet cable may not have this problem... so do not have to use wireless. Haven't tested this on my own though.

He should use the piZERO.

 

Thanks Scott. That was a very informative link. I am going to try a wifi dongle and compare to my wired connection.

 

I'm following that thread now.. hopefully they don't find out the rpi is just not suitable for digital out for some reason. fingers crossed they are measuring wrong

 

Talked about that in this thread: https://support.hifiberry.com/hc/en...-legit-Re-jitter-and-i2s-on-the-raspberry-pi-

Not a problem when the pi runs as clock slave

 

Scott, pls educate me. In the link you posted that is talking about jitter and how the Digi+ can act as a clock master thereby helping to improve on the Pi's internal clock. The meausrements taken in the RuneAudio post was done from the Digi+ SPDIF and Pi USB outputs. Both had similar THD. So it seems at least in the measurements taken that running the pis as a clock slave to the Digi+ didnt really help. Perhaps I am not understanding correctly?

 

The THD must be coming from somewhere else, if we even trust those tests-- the scummy switching supply he uses comes to mind

And the numbers are so close and high in each case, he has other problems to fix before looking at subtleties like jitter or spdif errors. I wouldn't be surprised if he hears an audible 60Hz hum or something thru the speakers

Frankly, we know what we have here... that guy has more work to do

 

I may be totally nuts but I think I perfer the sound when I use a usb to ethernet converter to receive music versus the built-in ethernet port. What got me thinking about trying the usb port instead was the above post talking about how noisy the ethernet port is.

I had a Cable Matters usb3.0 to ethernet adapter laying around so I decided to try it. Initial impression is that music is smoother. I need to compare more though. I want to also try a usb wifi adapter but the signal strength in my music room is very week, esp on the 2.4ghz band. In the past when I tried a wireless N usb adapter I would get dropouts. I currently use a wireless AC wireless bridge on the 5ghz band in this room to stream music to my server and Pi3/Rune renderer.

FYI, I use my Pi3 and Rune as a renderer on my network. I also use a HifiBerry Digi+ board outputting via coaxial to my Mutec 3+ reclocker.

 

Update on 503SPD1 and 503SPD2 - PCB's went to fab yesterday, due a week from this Monday. Build time will be 2-3 days to fit them into our schedule. I'll update when we build them up. Once complete we'll circle back around to get contact info for the crash test dummies who foolishly (or is that Audiophoolishly) agreed to help us with this.

Cheers,
Michael

PS Not to brag or anything, but our Hybrid Tube Amp Kickstarter campaign hit $75K today! Just saying.

 

Is the D1 RCA/TOSLink and D2 BNC/XLR?

Your PDF 3D drawings are blank for me...

 

So awesome! I am beyond excited! I should just send you money now for a D2 and case. And congrats on hitting $75K!!!!!!

 

Yes, 503SPD1 is TOSLINK in and out, and RCA Coax with isolation transformer. 503SPD2 is BNC out with isolation transformer, plus balanced XLR out also with isolation transformer.

Screen caps:





Cheers,
Michael

 

@Michael Kelly in the first rendering I see SPDIF in and out, not Toslink as you mentioned. However, why have any input at all?