[skhan007]

Not for the Crack, there should not be contrasting opinions. Never leave phones in during power on or switch off.

I had always believed this too, but recently got a new tube amp (Woo Audio) and the builder states to ALWAYS have your headphones plugged in during powering up to avoid an “open circuit.” Weird that there’s such a divide on this topic. I read that with OTL amps like my BHC it’s not that important, but for OTC amps, Mr. Woo states that you should have your headphones plugged in.

 

[Beefy]

I had always believed this too, but recently got a new tube amp (Woo Audio) and the builder states to ALWAYS have your headphones plugged in during powering up to avoid an “open circuit.” Weird that there’s such a divide on this topic. I read that with OTL amps like my BHC it’s not that important, but for OTC amps, Mr. Woo states that you should have your headphones plugged in.

Completely different amps. The Crack has a bleeder resistor on the output. The Woo SHOULD have a bleeder resistor on the output.

 

[Cowwe]

Not ideal but have you reached out to Bottlehead regarding their repair service?

I haven't. Since I live in Italy, both the repair and the shipping costs are going to be very high compared to the price of the amplifier itself, and the idea of shipping the built amp in a box overseas does not fill me with confidence so I have been opting for locals instead. Plus, I don't know what I would do if after receiving it back from Bottlehead HQ I still had this problem (if it turns out the issue is somehow not within the amp itself).

 

[dstarr3]

I gotta ask, are all the devices in the audio chain plugged into the same outlet via power strip or some such? If you have different devices plugged into different outlets, you could be introducing a ground loop hum and maybe that's what you're hearing.

 

[Cowwe]

I gotta ask, are all the devices in the audio chain plugged into the same outlet via power strip or some such? If you have different devices plugged into different outlets, you could be introducing a ground loop hum and maybe that's what you're hearing.

It is something that I had thought about too, so I made sure to test the amplifier into many different outlets. Even when plugged with no electronic decides in its area the noise has always been there. The source doesn't even matter, as the noise appears even when no RCA's are connected.

 

[Hypops]

It is something that I had thought about too, so I made sure to test the amplifier into many different outlets. Even when plugged with no electronic decides in its area the noise has always been there. The source doesn't even matter, as the noise appears even when no RCA's are connected.

I might have missed this, but when you tested it without any other component connected, do you hear the hum at all volume levels equally or does the sound level of the hum rise and fall with the change in gain?

EDIT: Just read through your Bottlehead forum thread. Since the Crack was effectively noiseless at both of the repair shops, it sounds like you're dealing with a power or interference issue in your house/apt. It could be a really pesky ground loop. And if you share power with (or pick up interference from) any nearby neighbors, it could even be something not in your control. Since you seem to have done everything possible to the kit itself, you could unplug everything (that you can safely unplug) in your entire house, then try. Could be funky wiring that is making a random appliance in a bedroom screw with the power in another room entirely.

The fact that it only impacts one channel is vexing, though. That's not the way ground loops typically work. So it's also possible you have something wired incorrectly (or a bad wire, joint, or component) with your grounds for the problem channel. And, of course, it's also possible that the problem is not just one thing.

BUT... the first thing I'd try is taking the amp to a friend's place or somewhere else where you can power and listen to it. If it sounds noise free, then the problem is with your home wiring.

 

[Cowwe]

Just giving some brief positive news to close the topic: I finally managed to find the fault.
It was actually the 22k ohm resistance in the right channel, that for some reason was being noisy. Replacing it completely got rid of the issue.
I don't know why the issue wasn't appearing back at the repairmen's places, but I'm willing to say that it was either up to randomness in the issue's appearance or something else.
Either way, thank you everyone for giving advice and support, I appreciate you guys!

 

[Cowwe]

On another note, since during this time I was also suggested to make sure to keep the headphones unplugged while turning on and off the amp, I got to thinking about something else. I don't dig the idea of inserting and extracting the headphone jack at least twice a day (and I do like to switch headphones around), so I was looking for some kind of extension that would take the abuse instead of the amp's own jack input. A 6.3mm female in and 6.3mm male out, maybe curved by 90 degrees so it also stresses the cable a bit less (and doesn't get it to be too tall) .
Does anyone have something like this in mind? I have looked around a bit but didn't find much. Is it a dumb idea?

 

[JTbbb]

On another note, since during this time I was also suggested to make sure to keep the headphones unplugged while turning on and off the amp, I got to thinking about something else. I don't dig the idea of inserting and extracting the headphone jack at least twice a day (and I do like to switch headphones around), so I was looking for some kind of extension that would take the abuse instead of the amp's own jack input. A 6.3mm female in and 6.3mm male out, maybe curved by 90 degrees so it also stresses the cable a bit less (and doesn't get it to be too tall) .
Does anyone have something like this in mind? I have looked around a bit but didn't find much. Is it a dumb idea?

Always in place.

 

[Galapac]

On another note, since during this time I was also suggested to make sure to keep the headphones unplugged while turning on and off the amp, I got to thinking about something else. I don't dig the idea of inserting and extracting the headphone jack at least twice a day (and I do like to switch headphones around), so I was looking for some kind of extension that would take the abuse instead of the amp's own jack input. A 6.3mm female in and 6.3mm male out, maybe curved by 90 degrees so it also stresses the cable a bit less (and doesn't get it to be too tall) .
Does anyone have something like this in mind? I have looked around a bit but didn't find much. Is it a dumb idea?

The way that the jack is made it would take something very harsh for the jack to break down as there is a scissor-like blade that does the connection to the jack. I have never heard of it failing in my experience but there are adapters out there for this if you feel the need.

You would wear out the tube sockets first before the headphone jack IMO if you tube rolled frequently but there are also socket savers for those.

 

[michael2v]

Just giving some brief positive news to close the topic: I finally managed to find the fault.
It was actually the 22k ohm resistance in the right channel, that for some reason was being noisy. Replacing it completely got rid of the issue.
I don't know why the issue wasn't appearing back at the repairmen's places, but I'm willing to say that it was either up to randomness in the issue's appearance or something else.
Either way, thank you everyone for giving advice and support, I appreciate you guys!

How did you ever figure this out?

 

[Hypops]

On another note, since during this time I was also suggested to make sure to keep the headphones unplugged while turning on and off the amp, I got to thinking about something else. I don't dig the idea of inserting and extracting the headphone jack at least twice a day (and I do like to switch headphones around), so I was looking for some kind of extension that would take the abuse instead of the amp's own jack input. A 6.3mm female in and 6.3mm male out, maybe curved by 90 degrees so it also stresses the cable a bit less (and doesn't get it to be too tall) .
Does anyone have something like this in mind? I have looked around a bit but didn't find much. Is it a dumb idea?

Not a dumb idea. Depends on the quality of the jack. For a 6.3mm, I can't imagine it wearing out anytime soon, but who knows. You could go with a cable adapter (like what JTbbb posted above), or you could go even simpler--and avoid any potential cable quality issues--by just getting an adapter jack. Neutrik and other similar companies make 90 degree 1/4" to 1/4" plugs. They even sell self-muting plugs so you don't have to worry so much about the power up-down sequence (never used a self-muting plug myself, so I don't know if they affect sound quality).

 

[dstarr3]

Yeah, I don't think 1/4" jack wear is a concern. I've never heard about 1/4" jacks wearing out anywhere except, like, radio stations where they get plugged and unplugged a hundred times daily. Even then, it takes years. I'd be more concerned about introducing another electrical connection with an extender or adapter rather than wear and tear on a headphone jack.

 

[JTbbb]

The way that the jack is made it would take something very harsh for the jack to break down as there is a scissor-like blade that does the connection to the jack. I have never heard of it failing in my experience but there are adapters out there for this if you feel the need.

You would wear out the tube sockets first before the headphone jack IMO if you tube rolled frequently but there are also socket savers for those.

I had a Feliks Euforia AE where the female 1/4” jack became sloppy and fell apart inside. Cost me a pretty penny to get this repaired. Once bitten twice shy!

 

[Cowwe]

How did you ever figure this out?

The issue had to be most likely on the right channel, since it was the only one affected. Replacing the volume potentiometer, output caps and sockets didn't change anything, so it had to be something in between. Turns out it was that resistor.