General question about electrical interference

[Nignoog]

Hello friends,

I recently completed my crack build last week. It is an auditory revelation. I’m so pleased with it. I do notice a few anomalies with it and I would like to learn more. Here are my observations and questions:

1. If i mute my computer volume and turn the potentiometer all the way up, I can hear faint, fuzzy music in the background. Is this a radio station? If not, what is it? If so, how does the crack receive and play FM frequencies?

2. Will the proximity of my cellphone affect the amp? Today I was on a call with my brother on speaker and I had my headphones on. When I moved the charging iphone closer to the amp I felt like I could hear some feedback or rhythmic fuzz. When I unplugged the phone, I think it went away. I guess, generally speaking, what and how is this amp capable of picking up and playing other electrical signals. Is it unique to tube amps?

N.b. I have little to no background in this so if anyone who attmepts to tackle these questions could explain it like you would to a toddler, I would be much obliged. Thanks friends.

[Paul Birkeland]

1. If i mute my computer volume and turn the potentiometer all the way up, I can hear faint, fuzzy music in the background. Is this a radio station? If not, what is it? If so, how does the crack receive and play FM frequencies?

It could be an op-amp in your computer picking up AM radio.  I would guess that if you unplug the Crack from your computer, this goes away?

2. Will the proximity of my cellphone affect the amp? Today I was on a call with my brother on speaker and I had my headphones on. When I moved the charging iphone closer to the amp I felt like I could hear some feedback or rhythmic fuzz. When I unplugged the phone, I think it went away. I guess, generally speaking, what and how is this amp capable of picking up and playing other electrical signals. Is it unique to tube amps?

Oh yeah, certain phones and certain tubes will talk to each other a little bit.  Doc B. had an early smart phone about 12 years ago that was particularly noisy around our gear, but the seem to have gotten better since.  Solid state headphone amps generally have severe bandwidth limits to maintain stability, while some tube circuits (like the Crack) do not, so you can hear some modulations as a cell phone tries to talk to its nearest tower.