Unfortunately, it looks like I'm having this same issue. It happened twice today using a b stock unit I received Friday. Initially I thought it might have been related to ESD, both times it happened as I returned to my desk and picked up the headphones and got a zap and then the loud buzz from the headphones. I was using a Hifiman HE400i 2020. Turned the amp off and tried again. Both amp and headphones seemed ok, but I've stopped using it and will contact Schiit.
I don't know how I missed this thread. I thought that I was the only person that had a problem with there Schiit Heresy burning up headphones. I will post my experience here.
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This happened to me six months ago on two headphones in December 2020. I was plugging various headphones between $100 headphone amps so that I could share online what were the best amp/headphone combinations. The headphones were brand new. The two headphones sent the Schiit Heresy into protection mode were OneOdio Pro-50 and a Fostex T-50RP I am certain that it was due to ESD as I was getting constant electric shocks from all of my equipment during the cold months here in the Las Vegas, NV desert.
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The OneOdio Pro-50 had one driver burn out on one side. The Fostex T-50RP survived. Since this burnup, I have not dared to switch headphones while the Schiit Heresy is powered on because I fear that it might destroy another headphone. I power off the amp and switch headphones then power up again. Mostly the amp has sat unused as I a get stressed out when using it instead of enjoying it.
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I contacted Schiit to see if they could take it back and let me buy a better amp. I would rather get a Jotunheim 2 or Lyr 3 so I don't have to worry about my headphones burning up. Schiit will not just let me upgrade because I purchased B-stock. It states on the Schiit B-stock page "There are no trade-ups. If you know what you want, that’s great." However, I was not aware when I purchased the amp that it destroyed and burned up headphones. So, they really should take it back. Schiit responded that they would "need to take a look at it in service first before we can look into any possible refund options."
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So, my options are to spend another $20 shipping to ship it to Schiit that I might not even get a $89 credit towards purchasing another product. Does that sound like a good deal to you?
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My advice to everyone is to stay away from the Schiit Heresy if you live in a climate where you get lost of Electrostatic discharge. My second piece of advice is to not purchase anything B-stock from Schiit even if you know it is the model you want. The $10 discount is not worth it in the end because it will cost more than that to ship it back even if it is a faulty product on the error of Schiit. Just buy Schiit's regular stock so that they will take it back and you will not have a stressful time dealing with them.