In less time than it takes to read this thread, let alone try out all the many ideas, you could stick a few pieces of fO.q tape on your tone arm and have a sonic improvement you can actually hear.
Just sayin.
Just sayin.
Living with unsolvable hum - Any audio detectives out there?
No arguments with the specs and not operating at low frequencies (60 to 120 specifically); but at the same time THESE reduced man made noise in my stereo amp music environment. YMMV regardless of the Fair rite specs. More investigation on why, in my environment, noise reduction with mix 31....TBD..and curious to find out why. I have 6 Nest powered cameras, whole house alarm with some walwarts, 6 Orbi Wifi mesh satellites, 15 SunPower panels (that each have its own micro inverter per panel, an EV transformer (adjacent the the music room and mounted in the garage, a big screen TV in the music room, a dimmer powering 6 recessed lights (house was built in 2015), 2 mac workstations in the music room. Fast and easy calculus... I wanted to test and hear if the toroid would solve my noise issue to get a North Star solution. I am not including the other 50 plus workstations, servers, ham gear, etc. that I would have to test in my environment. We can say with high certainty: I have a 60 cycle transmission emitting in my house and that is received and amplified through the D100A and NOT the MFA amps or the WaveStream preamps. Bottom line...my donut reduced 60 cycle noise for the D100A when no source music played, similar to Montaldo’s situation. Did it go away completely. No. Do I need to experiment more? Yes. I had these Fair rites on hand, so I used what I had. Was it cheap and easy? Yes. If I just used the Fair-rite specs, I would agree with you....but because I had these readily available and tested it...the donuts are staying put until I can hunt and kill the other noise sources in my house. Maybe my house is the exception with all the gear I am running despite the house being newly built in 2015. Jim Brown did a very extensive writeup on RF and discusses Fair-rite’s Mix 31 for 1500 cycles to 30 megahertz. http://k9yc.com/RFI-Ham.pdf Pages 21 on provide very insights and how you could modify the chokes. He also provides cook book recipes for transformer, cap, and toroid filtering solutions in this doc. |
stuogawa22 posts01-03-2021 3:39pm This one is easy @stuogawa. If you look at things like dimmers, linear amplifiers, and linear power supplies, most USB chargers, etc. they draw power in bursts at 2x the line frequency, i.e. 120Hz or 100Hz. When they make that current draw, it is a burst of high frequencies. The noise spectra ends up being 120Hz mixed with high frequencies, and harmonics of both. When those high frequencies that are harmonics of the high frequency mixed with 120Hz enter your equipment, it modulates back down to 120Hz in your audio equipment. The ferrite will take out the high frequency harmonics so that they cannot modulate back down to 120Hz. It cannot remove common mode noise at 120/60Hz that is transferring from the pre-amp to the power amp if that is what is the cause. |
BIF suggested: "I reiterate my suggestions that you should send your preamp back to the factory for a thorough check-up. For all you know, a cap used to filter out low frequencies might be leaking." No push back on this idea..and expanding on your approach.... Montaldo should just take his preamp to a friends house and test it. No shipping charges. Safer. No minimum bench cost to open up the preamp. If preamp has noise at friend's house, then send preamp for sure. No use spending money if you can do a quick and easy test at friend's house. If preamp has no noise, then Montaldo has to hunt and kill the noise source....or suppress the noise. |
You're looking under the wrong rock:It is not an electrical hum problem, it is mechanical and coming from your preamp power supply. The S:N test of your preamp found no problem. You hear it next to your rack. Use an old mechanic's (weight doesn't matter) trick to imitate a stethiscope. Take a screwdriver. Place the plastic handle at your ear and touch the chassis of your preamp power supply to see if you hear the hum. If so, then the problem is there; probably due to a poor orientation of a toroidal transformer, or possibly bad rectifier tubes. |