TLDR – Cable Effects and a Tube Roll
I bought a used Lyr 3. It came with the multibit DAC module, a vintage Crosley-labeled 6SN7 tube and no cords. The input to the module is a USB “B” connector. All computers mentioned in this saga are Windows desktop PC’s, less than two years old, and with maxed out memory.
Installed the Lyr on Computer 1 driving a pair of powered Klipsch bookshelf speakers with a small sub. I ran a Schiit Modi 3 from one USB port and then into the Lyr analog input – this worked fine. I used the Schiit-supplied USB cable that came with the Modi 3. I planned to compare the Modi 3 to the multibit card. Not my best speakers but the computer setup in this room would make the comparison easy.
Then (still on Computer 1), with “USB A-B cable 1” I ran the signal to Lyr multibit module input:
Sound cuts out for 1 to several seconds. Sometimes the sound actually switches, spontaneously, from the multibit DAC to the built in Realtek sound card and then switches back to Lyr (Lyr is driving different speakers than the Realtek card). If the Realtek sound card is disabled then the sound cuts out completely and Fubar ends with an error message. I tried two different USB outlets on the computer, no difference.
Moved the Lyr to Computer 2, still using USB cable 1 to the multibit input, also tried two different USB ports:
Again the sound cuts out for 1 to several seconds. Sometimes the sound actually switches to the built in Realtek sound card and then switches back to Lyr (Lyr is driving different speakers). If the Realtek is disabled then the sound cuts out completely and Fubar ends with an error message. Tube becomes microphonic and there is some audible feedback when Lyr gets fully warmed up (mild “howl” comes and goes, touch or tap the Lyr and the “tap” is audible in the speakers. Tapping increases the feedback howl.) This also occurs with Windows Media Player and YouTube as the source.
Switch to “USB A-B cable 2”: Feedback and microphonics seem worse. Start Fubar, feedback slowly builds, stop Fubar and the feedback remains! This seems like it could hurt something, if only my relationship with my wife.
Switch back to USB cable 1. I get cutouts hot or cold, microphonics only when tube (a vintage Crosley) is hot.
Confession time. I am a cable denier. I work in aerospace, I am a mechanical engineer but work closely with electrical engineers who design wires for great reliability and resistance to stray currents. I’ve been in charge of cable test programs. All of the angst about wires in aerospace seems centered around grounds and connectors, especially the connectors for grounds. Of all the cables that I am convinced “cannot matter!” a USB cable is number one on the list. Further confession: These two USB A to B cables were each included free with a printer, back when printer cables were included free. They are old. They work great with printers.
Bought a new, non-audio, USB A to B cable at Microcenter for $21.99. It was a cheaper, USB 2.0 cable. USB 3 cables were more expensive.
Installed the new cable, let us call it Cable 3, Lyr is still on PC 2. The cutouts have not reoccurred. Microphonics remain, tap the Lyr anywhere when the tube is hot and the sound is horrible, drag your fingernail across the case of the Lyr and you can hear it in the speakers. Swapped the vintage Crosley tube for a vintage GE tube, microphonics are gone! No cutouts, I am in hour 3 or so with Cable 3. We will continue.
Day 2 – still no sound cutouts, probably 3 hours of listening. I am starting to think the problem is solved. This computer does not have great speakers for A/B comparison of a Modi to the Multibit DAC. I’m just happy that the multibit DAC/Lyr are playing sound. I will need to revamp some system, probably my best one, to A/B the Modi versus the multibit module.
Note that I have no idea how the sound quality compares between the old and new cables, the sound cutouts were too annoying for serious comparison and as we speak I have yet to hear the multibit DAC driving good speakers without that problem. I am just happy that with the new cable everything seems to work.