Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Nignoog on December 04, 2020, 05:52:57 AM
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Dear Bottlehead gurus,
It's been a while since I have visited your hallowed forums of eternal knowledge and problem solving. Here's the scoop:
I had a few issues with my Crack a few years ago. I sent it in to be repaired and it came back working perfectly. Over the last few months I noticed some interference in the left channel. It's a faint ringing that is sporadic, almost like Morse code. I can't hear it when sound is playing, but when there is silence it's very apparent and annoying.
Here's the part that is bizarre. When I move it away from my computer and plug it in somewhere else, it's dead silent. And I recently relocated my computer to a room that previously had no issues when the Crack was plugged in. So it must be my computer right? Well, when I shut it down and literally unplug everything, the interference is still present. I have tried the following to no avail:
1. Different electrical sockets
2. Creating a "shield" by holding a large jellyroll pan around the Crack
3. Tried "shielding" the tubes with tin foil and a large metal bowl
4. Tried moving the Crack around my desk to find a spot that doesn't pick up the interference
5. Tried tightening all the screws
A few observances that may help the diagnosis:
1. When I hold the Crack in my hands while it's on, if I press firmly on the chassis, I can feel it vibrating slightly, or rather, pulsing with energy. I am assuming that's normal, but I never noticed it before.
2. I have had multiple rectifier tubes, two 6080's and one 6AS7G, have their left channel break. They don't fail, but when I tap on those tubes with a pencil, I can hear ringing/vibrations in the left channel of my headphones. Not sure if the Crack is actively disrupting/breaking tubes. The current 6AS7G I have in is fine right now.
I am at a total loss. I have scoured the forums for answers and feel like I have exhausted all logical and possible solutions. Help me Bottlehead gurus, you're my only hope.
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The morse code type sound is typically from a cell phone or wifi router that's too close to the amp. Based on your description, I would be leaning toward your cell phone being the culprit. It's also possible that you have some other LTE enabled device nearby causing the problem.
Tapping on a tube and hearing noises doesn't indicate that anything is wrong with the tube. Those aren't broken tubes. That is a physical reaction inside the tube called microphony.
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Thanks for the quick reply Paul.
I have removed from the room all devices that emit or receive signals (including my phone, laptop, and watch) and the left channel interference still persists. I can't think of anything else in the room that could be transmitting an LTE signal. What else can I try to diagnose or ameliorate the interference?
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Try taking your amp to a different dwelling. It's somewhat possible that you may also have noise riding on your powerline, so it's good to eliminate that from the list of possibilities. Also be sure you aren't listening to the amp with nothing plugged in and the volume pot all the way up, as that is a recipe for picking up external noises and amplifying them.
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Have you done the diode mod on the power in socket? That will often clear up strange noises. It did for me.
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@Paul
I will take my amp into my office and give it a whirl. I have found that certain sockets, or at least the rooms in which the sockets lie, in my apartment do not produce any noise. Is it possible that the noise riding on powerlines can be in certain areas but not others? Additionally, if I pick my amp up and move it around, it can effect the noise levels. Wondering again if noise in powerlines can change based on proximity.
And good to know about listening without anything plugged in. How much needs to be plugged in though? Just RCA cables? A DAC too?
@Deluk
I saw that solution but want to exhaust other options first. I'd hate to perform surgery before ruling out it's just a "common cold."
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Just turn the volume pot all the way down when you do your tests. If the reception of this noise changes when you move the Crack around where you are now, that does not indicate pollution in the powerline, but rather a wireless device spewing out a lot of noise.
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Paul,
I took my Crack to work and plugged it into a surge protector and wall outlet. Dead silent. Based on your suggestions, it sounds like half of my apartment is polluted with wireless interference and the other half is not. Aside from relocating my amp, is there anything I can do to further diagnose or fix the issue?
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This would be my next step:
@Deluk
I saw that solution but want to exhaust other options first. I'd hate to perform surgery before ruling out it's just a "common cold."
It's barely surgery. It only involves removing about 1-2" of bare wire and replacing it with two reverse-paralleled diodes. All in, it's maybe 10 minutes of work, 9 of which is spent getting the soldering iron setup up and hot. Plus, the area involved is readily accessible - very low risk of accidentally melting something with the barrel of the soldering iron. ;D
cheers, Derek
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Based on the recommendations shared in this thread, I think it's time for me to add the diode modification to my Crack.
Based on what I read in the thread about the modification, I searched Amazon for diodes that will work. Before I order, can someone please confirm this will be adequate:
https://www.amazon.com/FAIRCHILD-SEMICONDUCTOR-1N4001-STANDARD-pieces/dp/B00LQPV2KA/ref=sr_1_4?dchild=1&keywords=1N4001+diode&qid=1607459465&s=industrial&sr=1-4
And if there a better diode, for ease of installation or better performance, would you let me know or post a link please so I can get those instead.
And thank you to everyone who has helped me and commented on this thread!
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Yes, you can use those diodes.
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I have ordered the diodes and a solder wick. Based on the picture and what I can glean from the thread on this modification, is it simply a matter of removing the buss wire from the chassis ground and the 3-prong electrical ground and then soldering in two, twisted diodes between the two grounds? And the other half of the buss wire remains connected between the chassis ground and the connection labeled as #13, right?
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Yes, that is correct.
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And remember to "reverse parallel" the diodes - i.e., have the marked bands of the diodes at opposite ends before twisting the leads together.
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Thank you for the tip! I see that in the picture now. I would not have done it had you not mentioned. You saved me a serious headache!
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Bad news, I added the two diodes as directed but the sound still persists. As far as I can tell, the modification made no discernable difference. I reflowed the joints twice after the initial installation to make sure it wasn't a cold/flaky joint. I am attaching pictures for reference. Assuming the pictures look good, any other ideas?
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When you took the Crack to work, did anything change in the signal chain from source to amp to headphones to your ears? I.e., was it identical to the setup that gives you interference in your room at home?
Do you have LED lights near the Crack? Perhaps a desk lamp? They can have weird effects on nearby electronics.
cheers, Derek
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I forgot to ask if this noise is attenuated by turning down the volume control to 0.
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The black brick switching type power supplies can produce strong electronic noise into their local area. Make sure there are none of those plugged in near the Crack. They can be supplying power to all sorts of devices and it's easy to forget about them if they are plugged into a power strip behind a desk for example. The power to your crack might be coming from the same power strip.
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@Deke609 Sort of. I just brought the amp in with the my HD650s so I didn't plug it into a DAC. However, I have tested the amp like that at my apartment as well, so in regards to the test being the same, it was. There are no LEDs or lamps nearby, I have tried turning off all electronics in surrounding area to no avail.
@Paul The noise is completely unaffected by the volume.
@Deluk I have tried unplugging literally everything in my room and in addition, turned off the the Wi-Fi router and HVAC, even though they are in another room; no dice.
In contrast to what I said on the 10th, the diodes now do seem to make a slight difference (which makes me think burning in might have done something), but the interference is still present. Any other ideas or thoughts? I have 3 extra diodes available, is it worth it to slap another one or two on? I am assuming that's a no go though...
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Maybe post some pics, including one of the entire underside.
cheers, Derek
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I am wondering how helpful pics will be for two reasons:
1. I sent my Crack in to be repaired a few years ago and I haven't touched it since.
2. If the interference goes away when I relocate the amp, shouldn't that imply that the issue lies outside of the amp, not within?
I am happy to post some pictures if you and others think it might help, I am just weary about the prospect of having to do an soldering.
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Dunno. But what's the harm in posting some pics?
I'm curious as to why the interference only shows up in the left channel. That suggests to me that there is something about the wiring of that channel that makes it more susceptible to picking up noise. Maybe that's something worth exploring. Pics might help with that.
cheers, Derek
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2. If the interference goes away when I relocate the amp, shouldn't that imply that the issue lies outside of the amp, not within?
Yes, this is quite true. It's somewhat possible that picking up a cheap pair of used tubes on eBay might mitigate this issue a little bit. It's certainly an inexpensive experiment to try!
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I have a few other tubes here already that I will try.
In the meantime, I am wondering if the picture I am attaching shows what is negatively impact the Crack's performance. I noticed that the building across from mine has a lot of satellite dishes and antennas on the building. And the area in my apartment where there is no interference is in the opposite direction. If you think the antennas are the culprit, is there anything I can do short of relocating the amp?
https://imgur.com/a/2qwDmmi
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Yeah, that would do it! It's probably particularly bad because you are up above the ground and those are aiming right at you.
One thing you could try is to buy a 0.1uF Z5U capacitor (voltage doesn't matter) and solder one end to the right RCA jack shell and the other end to terminal 22 (be sure terminal 22 has continuity to the chassis plate). That may give the noise an alternate path to travel that isn't through the circuit itself.