Bottlehead Forum
Bottlehead Kits => Mainline => Topic started by: SmashBruh on September 19, 2019, 11:46:57 PM
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Hello everyone, I'm having a couple of very small issues with my mainline. For a while now when I plug headphones into the amp if it's already on it'll make a metallic "ting"/sizzle come out of the headphones. It goes away after a second or two (almost "fading) but the same will happen sometimes when changing the coarse attenuator. Recently I've also noticed that every once in a while when changing the volume pot while listening to music I'll hear a small crackle of sorts. It only lasts for a second but it's not consistent. I'm not sure if this is the tubes aging or what but I've also noticed lately that if I change my headphone's impedence from "high" to "low" and vice-versa there'll be a sound similar to that ting/sizzle that will last a few seconds and then go away. Same happens when I turn the amp off. I'm wondering if these are all normal things that are just par and parcel with manipulating current and tubes? Or is this abnormal? Is it dangerous/concerning? I really don't want to disassemble this thing as I'm not particularly great at desoldering things... But I also want to make sure the amp is performing to it's full potential, even if it sounds great when just left alone...
EDIT: Adding a photo just in case you guys see something clearly wrong that I missed
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That is microphonic behavior that's very common to the 6C45PI, as well as certain other tubes. It's nothing to be worried about or to chase down.
The crackle would be less normal, but could be a tube that needs some burn in time, or it could be that there's a solder joint in the amp that isn't quite solid.
-PB
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I had a crackle/pop issue with the course Mourguiet attentuator in a Stereomour. It turned out to be an unsoldered connection between a resistor and the attenuator. The resistor lead was well crimped, so worked fine without noise when the course attenuator was set, but would briefly crackle/pop when switching to or from the affected attentuation setting (I think it was the -18dB position).
If in your case the crackle is particularly bad when switching to or from a certain position, then I'd focus your investigative efforts there. If it's not associated with a particular position on the attenuator, then I'd look for a loose connection somewhere close to the course attenuator that might be jostled by clicking from one position to another. The mechanical resistance of those attenuators is pretty strong and sets off a pretty big vibration in the chassis. The fact that you are now hearing the same thing when switching impedances is consistent with a loose connection -- one that is getting looser and is now affected by lesser vibrations.
You could also try to rule out the input wiring as the culprit by changing the inputs used to see if if only one is affected. Ditto for the outputs.
cheers and good luck, Derek
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That is microphonic behavior that's very common to the 6C45PI, as well as certain other tubes. It's nothing to be worried about or to chase down.
The crackle would be less normal, but could be a tube that needs some burn in time, or it could be that there's a solder joint in the amp that isn't quite solid.
-PB
Oh you're absolutely right! Based on your comment I moved everything more slowly and precisely easing it into it's final position and noticed the noise was completely gone! The crackle in my fine attenuator persists though.
I had a crackle/pop issue with the course Mourguiet attentuator in a Stereomour. It turned out to be an unsoldered connection between a resistor and the attenuator. The resistor lead was well crimped, so worked fine without noise when the course attenuator was set, but would briefly crackle/pop when switching to or from the affected attentuation setting (I think it was the -18dB position).
If in your case the crackle is particularly bad when switching to or from a certain position, then I'd focus your investigative efforts there. If it's not associated with a particular position on the attenuator, then I'd look for a loose connection somewhere close to the course attenuator that might be jostled by clicking from one position to another. The mechanical resistance of those attenuators is pretty strong and sets off a pretty big vibration in the chassis. The fact that you are now hearing the same thing when switching impedances is consistent with a loose connection -- one that is getting looser and is now affected by lesser vibrations.
You could also try to rule out the input wiring as the culprit by changing the inputs used to see if if only one is affected. Ditto for the outputs.
cheers and good luck, Derek
Yeah, my crackle is on my fine attenuator and is definitely a different noise than what I was hearing everywhere else. Everything else seems to be microphonics related like what Paul mentioned. The noise on the fine attenuator seems to mostly come from setting it to -7.5 db though. I took a quick look at the connection (didn't flip it over, just lifted it up and shined a flashlight) and it seems to be pretty sell soldered. I've noticed a bit of oxidation on the attenuator though. I've heard spritzing them with deox-it can help. Is this something you guys would recommend?? If I do this are there any precautions I should take? (Something about spraying anything directly onto electronics without being able to wipe it off immediately doesn't feel right lol)
EDIT:
Decided to look under the hood to see if any connections seemed suspect. Does this one seem okay to you guys? Or does this look cold to you?
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You can definitely spritz the switch.
Do you get that noise in both channels around the -7.5dB switch position?
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You can definitely spritz the switch.
Do you get that noise in both channels around the -7.5dB switch position?
I do believe I did get some noise in both channels but if memory serves it was stronger on the right channel. That said, ever since spritzing the switches this morning it seems to be completely silent when switching volumes no matter where I go!
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Update: So I'm still getting the popping when I switch volumes... Testing it with a continuous tone (https://www.youtube.com/watch?v=CZaCN3hAVHI) has revealed that both the course and fine attenuators are affected equally and it's always a small "pop" that happens when I switch volumes while there's something playing. Again, it's very very small but if it's not normal I want to resolve it y'know? :(
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A small pop on a stepped attenuator isn't particularly abnormal. If all steps of the fine attenuator are giving you the same pop, then there's definitely nothing to worry about. (I say this mostly because the -0dB step on the fine control has nothing connected to that particular position).
-PB