ThePhoenix

Sounds reasonably easy, thank you for your help!

Thank you; I didn't know about needing to turn it all of the way down (good thing I haven't tried anything yet). Do you have any idea what I might be looking for to actually do the adjustment?

The amp has been back in my hands for a couple of weeks now and sounds great; there was a scare the static was returning one evening, but I think that was something else as I haven't heard it since (knock on wood). That said, it was recommended to me by the forum member who worked on it to swap out the generic transistors they used with a pair of THAT340s once I could get my hands on a pair and, once I had them, to make sure I check the DC Offset and adjust as necessary. I'm assuming I measure off of the volume pot like I did when we first started troubleshooting; what is it, exactly, that I should be doing to adjust it?

I've heard back from the awesome forum member who's checking out the amp. They found that three of the four MAT BJTs were bad, which is why I didn't notice a difference when I swapped them around. They've replaced them, adjusted the output, and have the unit on its way back to me as I type this out. So, thanks again to them and everyone else here! I can't wait to have it back and look forward to hearing it without concern of that awful static.

So, a small update. A very kind forum member offered to take a look at the amp and see if they can find the issue and rectify it. I'm very thankful to them and everyone else who's offered their advice and hope the problem can be eradicated. I will update this thread with anything they find. Thanks again!

That's a good idea on taking it out of the enclosure. I'll look at it and do some soul-searching. I love the darned thing when it's quiet and performing correctly, but it sure is annoying to know something's not right and, of course, have one's music interrupted with a bunch of static. That said, maybe this is the universe's sign that now isn't the time to upgrade and I should just sell it, cut my losses, and move on. Thanks again, everyone, with your suggestions and contributions! I'll report back what I decide to do and, later, if I get any resolution on the matter.

Okay, so I can report back with static updates (yay, what fun this is - not). After doing some listening, I'm not wholly convinced the imbalance is outside of the norm or that it isn't something wrong with me physically. It seems to come and go, but that could also be the music, so I'm going to ignore this for the time being and focus on the static. Anyways, while testing the above, I finally got some static. I quickly shut the amp off, swapped the L/R channels on the left side of the pot (that go to the circuit board), and turned the amp back on. The static remained with the left channel. [I think I've noted it before, but if I swap my headphone connections from L to R, the static does follow.) With that discovery, I think it is safe to say that the issue is somewhere in the left channel circuitry (or even the XLR out). Is there anything else I can measure/test, or should I start packing it up to ship to an expert? [I also have half a mind to sell it to an intrepid DIY'er who wants to deal with it. We'll see what happens.]

That sounds like it's above my abilities. Hmm.... Well, I need to determine if the initial issue is resolved/gone or not and go from there. I'm switching the wires back this morning and do some A/B-ing between the BiPolar and my old amp to see if I am hearing a channel imbalance or not (I was very sure of it the other day, less sure yesterday). Obviously, if the static returns we know I just got absurdly unlucky last night (the story of my life with nice things). Also, I know I've said it already, but thank you so much for sticking with me on this. I really appreciate it.

Well, for the two hours I tried, I got no static. Which is either insanely "lucky" OR the part finally failed OR the static was caused by a dodgy connection to the volume pot. So, I'm going to switch everything back to how it should be tomorrow morning and I guess keep waiting to see if any static comes across. With the potential of it being a problem (if not THE problem) and there being the believed channel imbalance, I'm considering replacing the volume pot just to be safe. I know these vary wildly in price from "reasonable" to "are you kidding". Right now it looks like there's an Alpha brand pot in there; I know Alps and TKD are the names thrown around here most often; is there one I should look at/consider if I go this route for peace of mind?

Okay, so I've played around with the wiring a bit. Naturally, the problem didn't immediately hold its hand up and reveal itself. First, I swapped the L/R wires leading from the pot to the circuit board. The "pop"/static with the volume pot stayed with the left channel. The channels were definitely swapped, so not sure why that didn't change. After playing around with it for a few minutes, I shut the amp back off and switched those first wires back around. Then, I swapped the wires coming in from the XLR inputs. Still no change as far as the turn-on noise (which isn't a big deal) and volume pot static go. Again, the L/R audio is definitely swapped. I didn't notice any of the static I've been having in the few minutes I tested, so once I'm done writing this post, I'm going to just listen to silence and wait/see if that issue has swapped channels or not. I would guess from the results of the testing above, that it will not, but I'll report when I get some (damn these intermittent issues!). I believe the channel imbalance remained on the left side. That said, I'm second-guessing everything I hear and I can't measure it, so maybe I'm just nuts (very possible). I've been listening to an old amp to compare/try and placate myself that I haven't damaged my headphones, and I do think there is an imbalance of some kind.

Awesome, thank you. I'll try it out when I have a chance and report back (crossing my fingers this is the whole issue!).

I did not attempt to separate the BJT sockets, but I'll fiddle with them to make sure they didn't separate. For the volume control, are you saying I should switch the two L wires with the two R wires on the left of the pot? Or, that I should swap all of the wires from the left side (going to the circuit boards) to the right (from the XLR inputs)?

In the central bit of Missouri, USA (specifically, around the Lake of the Ozarks). I knew asking for help with this particular issue and getting it resolved would be a long shot; I'm so thankful Spritzer and the rest of you have offered advice already.

All right; I took a number of photos (yay, 30s exposures!) from different angles in an attempt to be as helpful as possible. I've posted them all to an Imgur folder; please let me know if a Google Drive or something similar would be easier for you to use. I think everything is pretty logically organised, but let me know if you have any questions. I don't have a macro lens, so I did what I could with what I had readily available. Imgur LINK (it's private, only those with the link should be able to view it). I will reiterate that everything is exactly as it's been since I got it a couple of weeks ago (other than the swapping of the BJTs); I only mention it in case you see anything and go, WTF.

Doing some more listening; I'm more and more convinced there's a channel imbalance between the L/R channels (L being weaker). I'm not sure if I just simply didn't notice or if it's gotten worse over time, but I just swapped back to my previous amp to see if I was going crazy (or possibly damaged my headphones) and I'm confident it's there. While I'd love to believe it's all due to the potentiometer, would it also be possible for whatever resistor/transistor (not sure how many transistors there are or if it's just the BJTs) causing the issue to have failed completely and is now not amplifying the channel fully? [Also, I'm working on those photos. I'll have them up in a bit - sorry for the wait!]

All right, so I swapped the two MAT03 BJTs to no change (I heard static right away). I then swapped the two MAT02s; no change. So, it appears it isn't linked to them (unfortunately?) However, two things I noticed trying to test to see if anything else seems unusual or possibly wrong: I'm guessing this is normal, but there is an audible noise when you power the amp on only in the left channel. I don't know how to describe the sound, it's not really a pop, maybe a "plump"? When adjusting the volume, there's a noticeable sound very similar to the intermittent static (perhaps not quite as rough-sounding, but still there), also confined to the left channel. I remember thinking I heard something with the volume control when I got the amp, but I haven't really noticed it while listening to music and I put it out of my mind (sorry). Also, it seems stronger now than it did; it's clearly audible over medium/low-volume music.

Okay; will do! I'll need to charge a battery or two, but I'll get those when I can. Also, good idea - I'll try swapping them and report back. Affirmative - I have tried two sets of headphones (my balanced cables for the HD800 finally came in) and the issue persists between the two of them. Both headphones are known good off of different amps.

Since I can't test them, would replacing the BJTs be a worthwhile investment so we can cross them off the list of potentials? If I'm reading them correctly, it looks like each board has a MAT02 and a MAT03. [Also, it might just be me, but the issue seems to be getting worse/more consistent. I'm hoping that will help narrow stuff down.]

Ah, okay, so no testing, then. I looked up a THAT340 and I don't see anything like that as far as I can tell. Would a photograph of the boards in my particular amp be of any use to you?

Intermittent problems are, certainly, the worst. I just got done trying your suggestion; unfortunately, no change. I simply pulled them up and stuck them back in; should I have tried cleaning the contacts or anything? Also, since they're transistors, is there a way for me to test them for leakage or something (not sure if that's a thing with these)?

Okay, so I removed my headphones from the output, took off the top panel, turned the unit on (with no input), and placed the black probe on the screw for the Ground by the volume pot and the red one on the output using the handy little L & R circles (I'm hoping/assuming that's what they're there for). [For reference, the Multimeter is a Fluke 117; so, nothing super special, but I think it should be accurate enough for our needs.] On R, which I've never noticed any static on, reads 1 mV pretty consistently and only hopped around between -1 and +2 mV for the thirty seconds or so I watched it. On L, where the issue should lie, was much more jumpy; I saw everything between -7 and +9 mV. I thought it might be more helpful if I knew what it was reading during a static-y period, so I plugged my headphones in again (after shutting the unit off, which I assume is recommended), and got the following values: R: about the same, between -1 and +2 mV for the most part. L: I didn't actually see as large of a swing when I got confirmed static; only around +-3 mV. I'm guessing I was getting more before, but am obviously not sure. (naturally, I didn't get static for a long while when I was trying to measure for it. This after putting up with it for an hour earlier in the day.) Thank you so much for your help; I really appreciate it!

Okay, I would think I can do that. Though, dumb question, where should I be measuring that from and what values am I looking for? I know how to use a multimeter, but my knowledge of electronics is not very significant.

Thank you for your reply! I don't have an oscilloscope, but I'll look into getting one. I'm trying to avoid shipping it back to Iceland, but if that's the only solution, it is what it is.

Yep; that was a bust. Static started a few minutes in; I thought it seemed quieter than usual (perhaps indicating the condition was doing SOMETHING), but that was shortly proven incorrect and no change seems to have been made. So, I guess that's back to the drawing board and, more likely than not, shipping this back to the seller so I can try something else. Does anyone have any ideas on things to try? I still don't see how it could be an amp issue given it doesn't seem to be that old; that said, is there something I can look for to try and determine if there's an issue? I don't know how to solder myself, but I do have a multimeter I can use to test things if that would be of any help. I did think to ask the store I bought it from if the previous owner had mentioned any issues; they said, "no", but who knows if the previous owner even told them correctly. @spritzer; sorry to tag you in one this, but I'm starting to lose my mind over this. Have you ever heard of a Pure BiPolar having intermittent static in just one channel? Does it seem more likely to you for it to be a power issue or an amp issue?

Coming back to this for posterity; basically, despite thinking it was a poor cable, I was quickly proven incorrect (as stated previously). After more trail/error, I found that there seemed to be a correlation with my mini-split A/C & heat-pump running with the static (we had a few days of cool enough weather to shut it off completely; I didn't hear any static at all those two days - could've been luck, but I'm willing to bet there's correlation). Anyways, I bought myself a Furman Elite15i power conditioner in hopes it can catch/resolve whatever is going on with the power and let me listen in peace. I just plugged it in, so I'll report back in a few days (or minutes, depending on whether or not I have any more issues) with whatever findings I have.