What causes that 80s modem sound?

Ya it's my blue angel acting up again. I remember reading once what at causes that sound but can't remember now. It's the ticking, glitchy sound very much like an old modem. It's intermittent and sometimes quite loud. Happens even if I roll the volume all the way off, but goes away when I flick the standby switch... Rectifier?

Natman said:

Ya it's my blue angel acting up again. I remember reading once what at causes that sound but can't remember now. It's the ticking, glitchy sound very much like an old modem. It's intermittent and sometimes quite loud. Happens even if I roll the volume all the way off, but goes away when I flick the standby switch... Rectifier?

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Serious question: do you have your cell phone sitting on the amp? It can impact a lot of different powered speakers, including guitar amplifiers. Beyond that, what is the power like where you are playing? I've had the elevator in the building cause a ton of noise on my amp when it (the elevator) was in use.

Hmm, I didn't think of that. We were in a small basement and 10-12 people in the room each had a cell phone. Don't know about the wiring in that place but we had a bunch of crap plugged into 2 oulets using power bars (keyboard, a laptop, 2 guitar amps with pedals). I assumed it's my amp because it has been misbehaving, time for a tuneup...

Radio frequency picking up through a microphonic preamp valve maybe?

Definitely sounds like radio frequency from the description. Can you record it doing it, and post?

I'll try and see if it happens at home.
Funny I was going to record it last night but there was too much extraneous noise so I decided to pass.

My equipment has picked up interference from: cell phones, PS3, wifi, TV, lamp, power strip, computer, low FM band stations, and wiring in the wall. The input sensitivity on channels with multiple, high gain (capacitor bypassing the cathode), stages will really make any noise an issue compared to cleaner, less boosted channels.

The entire planet is covered by an electromagnetic field of its own and we have artificial fields of varying sizes around any device using electricity. When electricity travels down a wire, it creates and causes a change in the electromagnetic field around the wire. Guitar cables have a grounded sleeve to contain the field and stop incoming fields, but a damaged or poor cable, a coiled cable, running a cable parallel to a power source or power line, and placement of the amplifier, guitar, and equipment can affect interaction with other electromagnetic fields and sources.

If you have any wires carrying power that have to be crossed by a signal wire, a 90 degree angle and a bit of space between them will quiet the noise.

Coiled cables create a stronger EM field. If it interacts with an outside source, it will pick up more noise from that source than a relatively straight length of cable would.

(Sidebar)
DC is quiet as a power source. AC has to be converted to DC for electronics. While this conversion can result in low noise, the power filtering must be adequate. Many vintage pedals, some boutique pedals, and inexpensive, modern pedals don't have proper filtering when run from an AC adapter. Some daisy-chained AC adapters for pedals do not have a way of supplying clean power to multiple pedals and are also sensitive to the power inputs on the pedals themselves (One Spot for example).