Strange distortion in bass with 1 DAC only!?

[Loquah]

Hi all,

I've discovered a strange issue recently. I'll explain my system first:

PC --> Schiit Gumby (Gen 5 USB) --> Drop THX AAA 789 amp (XLR & RCA) + Mainline (RCA) --> AudioQuest NightOwls & Focal Clears

With the setup above, I hear bad bass distortion from the Mainline, but not from the 789 amp. If I use a different DAC (e.g. Topping D50s) I have no troubles with the exact same track and the volume seems to be identical (i.e. I don't think the Gumby output is too hot).

I've tried:

• Different RCA cables
• Changing which RCA input sockets I use on the Mainline
• Disconnecting the second set of RCAs from the Gumby so only 1 SE output is used

At this point I'm stumped. With the D50s, the Mainline sounds as pure as ever, but with the Gumby it's sounding like tripe  Any suggestions?

[Paul Birkeland]

You could try XLR to RCA adapters in the DAC and use the balanced output to the Mainline.  If this is something that works, you could certainly add a pair of 10K:10K input transformers to your Mainline and swap out one pair of the RCA jacks for XLR jacks.

The Gungnir specs an output impedance of 75 ohms, which is plenty sufficient to drive the input of the Mainline, but there isn't any info on the current available from the unbalanced outputs.

[Loquah]

Thanks Paul. I gather there are no risks to a DAC running XLR to RCA adapters?

[Paul Birkeland]

You could ask the manufacturer to be sure.

[Loquah]

Frustration got the better of me and I hooked it up. This required moving the DAC because I only have short balanced cables.

With the balanced connections, everything seemed to sound perfect so I hooked up RCAs to compare and low-and-behold the SE connection sounds fine now. Not sure what happened in the changeover, but I'm using a different power cord and different USB cable so I guess I have some troubleshooting to do. Any hints on what I might be looking for?

[Paul Birkeland]

Cables!

[Loquah]

Well that's a given at this point 

I'm using this as a learning opportunity - what cable-related factor would cause the bass only to distort? My totally uneducated guess is that power is the likely culprit, but I'd love to have a little bit of theory to back that up. Does power draw increase with stronger bass output and could this show up a power cable issue?

[Loquah]

Just to confirm. I've 're-installed' the DAC with a new power cable and all is well. Would still love to know what you think was going on with the power and the bass distortion if you have a moment, Paul.

[Paul Birkeland]

I would expect damaged cables to do that.  I have no idea why it is more obvious with low frequency content. 

[Loquah]

Thanks Paul. Appreciate the input. I made the cable myself so I'll pull it apart and look for damaged insulation (I won't reuse it)

[Love Rhino]

Sorry to pull up a thread from last year, but I wanted to share that I am currently having the exact same issue.  I'm running a gungnir with eitr into a thx 789 (balanced) and mainline (rca).  Haven't had an issue until tonight, then all of a sudden when listening with t5p on the mainline I'm getting very bad bass distortion.  Using the thx everthing is working like normal.  This might change the idea that its a cable issue. 

[Loquah]

Mine was 100% solved by changing the power cable, but I remember having an issue once with one of the ground connections in my amp being a bit dodgy and that caused distortion too. Might be worth checking your various earthing solder joints in the shop l amp.