Headphone amp mystery

I've got a weird situation. My Schiit Valhalla momentarilly cuts the signal in one channel or the other on occasion (though more often right channel) when playing records with my Sennheiser HD 580's, but it doesn't do this with any other source (no problems with digital or reel to reel input). I swapped the headphone cables, tried different headphones, reseated the tubes in the Valhalla, all to no avail. Only does it with the Senns on phono source...

To describe the phenomenon, it's like a loose connection or loose tube or something. Just a momentary erosion of the signal before it comes back. Drives me nuts. Doesn't happen with anything but phono, wth...

Seems to happen either immediately or within a few minutes of setting the arm down on the record, after that the signal stabilizes and I don't have any further problems near the end of the side.

The phono signal is fine through speakers and other headphones. I should also mention the interconnects are fine and the Senns don't do this using the headphone jack on my Rotel.

I never had this problem with my previous cartridge and phono preamp. Is it possible there is some sort of synergistic problem between the Valhalla and the Moon and/or the Hana? So confused!

 

That is weird. My first suspicion is that you're experiencing the infamous Sennheiser HD580 intermittent cable plug connection problem. Where the plugs and jacks at the headphone cups get an intermittent connection that can cut in and out or sound scratchy.

The weird part is that you only experience that with the phono input and not other inputs. The intermittent connection can happen when moving your head around causing more tension on the cable and for other similar reasons while moving your head or moving around. Perhaps you sit in a different spot or move around differently while listening to records compared to digital and other sources? When listening to records you do tend to need to get up to flip the record. Perhaps that's the cause?

An potential fix for the intermittent connection problem is to get the stock Sennheiser HD650 cable. The HD650 cable has a larger plug and slightly larger pins where it plugs into the ear cups. So it fits more snugly and doesn't wiggle as much and the bigger pins get better contact. You can order the stock HD650 cable from Amazon and B&H Photo and other places.

For background on the intermittent connection problem and fixes see these articles:
The Very Important Sennheiser HD 580, HD 600, and HD 650 Page 2
580_intermittency_repairs by jeepy206
How to Fix an Intermittent Connection in Sennheiser 580

 

Thanks @Ham Sandwich ! I hadn't considered the idea that I probably do move around the room more frequently when playing records versus digital. I'll try replicating the problem by dancing around and wiggling a little to something upbeat. I probably move around less as the record nears the end of a playing side (depending on how interesting the record is, I may be more attentive to my cocktail by that point).

The frustrating part is that the problem is so intermittent that it's made the troubleshooting process a time intensive process. I wish electronics would either work or fail, without any gray area in between, heh.

 

Do the headphones that do not have this problem have the same impedance as the Sennheisers?

 

No, I tried the AudioQuest Carbons. Way easier to drive than the Senns.

 

I discovered the Sennheiser intermittent connection problem back in the early 2000s. Both my HD580 and HD600 were affected. I ended up wedging little pieces of cardboard between the headphone cup jack and the two prong Senn headphone cable jack. The cardboard was cut from cereal boxes. That cardboard seemed to be the right thickness. The goal is to prevent the plug from willing in the jack.

Then sometime after 2010 I switched to using the stock HD650 cable. By that time Sennheiser had redesigned the jacks and plugs to make them fit more snuggly and not wiggle and made the springs inside the ear cups a bit larger. The redesigned HD650 cable didn't need the cereal box cardboard to keep them from wiggling. I haven't had an intermittent connection problem with my Senns since.

 

For anyone curious, I've finally tracked down the problem. It's gotten worse over the past few months; the distortion can now be heard with other sources (digital, CD, reel-to-reel), and when using other headphones with the Valhalla. Turns out it's not my Sennheisers at all, and it's not the Schiit headphone amp, either. It's the recording output selector knob on my Rotel preamp (I use the Tape 2 output to feed a pure line-level signal from my Rotel to the Schiit Valhalla for my headphones). Anyway, the Rotel is about 14 years old now, and the knob must be getting some buildup. Annoying that it took me this long to figure out what the problem is, but I have closure.

Since the problem was localized to one knob only (recording output), that is why I couldn't hear any dropouts using the same headphones with the built-in Rotel headphone amp, or through my main speakers. As for why I could only notice the problem with records at first, it might be that the buildup started in that area of the knob selector. As for why I could only notice with the Sennheisers? Assuming they are far more sensitive to noise and distortion than my other headphones.