It's very unlikely that voltage fluctuations in the phantom power (PP) could cause hiss. You haven't mentioned what models of condenser microphones you are using that show the problem, but, in general, it's only out-of-spec low voltages on the PP that would increase the hiss level.

However, you mention that the hiss only started when you got a Tascam US-1800. You also implied that it was the same problem as before (mains troubles), but that "it popped up again in the form of hiss". I have my suspicions that it's not the same problem, and what you are hearing is the noise level in the Tascam US-1800 pre-amps. This is known to be below standard, although you say that dynamic mics do not show the problem.

Please explain the conditions "When I have the mic doing nothing". What level is the gain trim set at? Does the position of the gain trim govern the level of hiss in that channel?

Hi Boswell,
Thanks a lot for the reply. Something really crazy just happened and I feel blessed. I was doing tests yesterday with turning everything off in the house and recording the noise and testing different approaches and comparing them and before I went to bed I decided to turn off the central heating of the water. I had done this before momentaneously and recorded to no avail, but it seems that turning it off and leaving it off for a few hours did the trick. I recorded a little something just now as a test and it's clean as a whistle! Thanks a lot for all the help you guys have given me over the years. Hopefully someone with a similar problem will stumble on to this thread.
Thanks again,
João

Boswell, post: 456652, member: 29034 wrote: It's very unlikely that voltage fluctuations in the phantom power (PP) could cause hiss. You haven't mentioned what models of condenser microphones you are using that show the problem, but, in general, it's only out-of-spec low voltages on the PP that would increase the hiss level.

However, you mention that the hiss only started when you got a Tascam US-1800. You also implied that it was the same problem as before (mains troubles), but that "it popped up again in the form of hiss". I have my suspicions that it's not the same problem, and what you are hearing is the noise level in the Tascam US-1800 pre-amps. This is known to be below standard, although you say that dynamic mics do not show the problem.

Please explain the conditions "When I have the mic doing nothing". What level is the gain trim set at? Does the position of the gain trim govern the level of hiss in that channel?

Hi Boswell,
Thanks for replying. What I meant by "the mic doing nothing" is me doing nothing and recording the silence within the room (along with the noise). I made a sample of me singing a part from a song into an sm58 and then into an at2020. In the dynamic example the preamp is actually turned up in relation the condenser one. At the volume that I'm listening to it on my monitors I don't even know that there is sound until the vocals come in. Very different situation with the condenser. I would rule out the preamps on the interface being noisy, at least for my standards. Here are the samples.
Thanks again,
João

[MEDIA=audio]https://recording.o…

[MEDIA=audio]https://recording.o…

Attached files sample at2020.mp3 (783.7 KB)  sample sm58.mp3 (783.7 KB) 

As a former Tascam interface/preamp user, I can say that their interfaces are inherently noisy, and pretty low in gain as well...now, I wasn't using the 1800, it was the model before that, (1640 maybe?)
and it used to give me fits... I had very nice mics, clean power in my studio, but the Tascam almost always gave me problems; noise being the most common, especially on tracks that were meant to be "forward" in the mix, like vocals.
How old is the AT2020 you're using? Did you get it new, or used? I'm suggesting the possibility that your issues might be a combination of things, which could possibly include both the mic and the interface .
Do you have access to another pre/interface that you could try? Or, another mic, even a 57/58 would be fne to narrow down the problem(s) By process of elimination...
But, and I stress this - in all things, default to Boswell. ( Boswell ) He's our resident electronics guru around here. ;)
--d.

Also...you may want to check to be sure that you are up to date with drivers (and firmware, if applicable) for the Tascam.
General order of diagnosis for an issue like this would be:
Cables
Mic
Interface
Drivers/Firmware
Plugging the device into another USB port
Plugging the device into another power source that's not on the same circuit.

Just a few suggestions. ;)

JoaoSpin, post: 456654, member: 41554 wrote: Hi Boswell, Thanks a lot for the reply. Something really crazy just happened and I feel blessed. I was doing tests yesterday with turning everything off in the house and recording the noise and testing different approaches and comparing them and before I went to bed I decided to turn off the central heating of the water. I had done this before momentaneously and recorded to no avail, but it seems that turning it off and leaving it off for a few hours did the trick. I recorded a little something just now as a test and it's clean as a whistle! Thanks a lot for all the help you guys have given me over the years. Hopefully someone with a similar problem will stumble on to this thread.
Thanks again, João

Very curious...Noises and posts coming and going like that.

The AT clip sounds a bit noisy, but it also sounds more distant, and then maybe the extra gain you had to use didn't help? What I do know is that my AT 2020 and a Shure Beta 86 both get noisier when the phantom voltage drops? Have you tried another condenser to see if they are affected by the problem?

JoaoSpin said: " I was doing tests yesterday with turning everything off in the house and recording the noise and testing different approaches and comparing them and before I went to bed I decided to turn off the central heating of the water. I had done this before momentaneously and recorded to no avail, but it seems that turning it off and leaving it off for a few hours did the trick. I recorded a little something just now as a test and it's clean as a whistle!"

I'm glad you're finding some "solutions", but there is no part of that which would help me sleep at night. I'd want to have a good electrician come in and test everything from my outside meter to the last receptacle. To my way of thinking these are symptoms indicating something is loose, something is leaking voltage into the ground, or something isn't making contact consistently. None of that sounds like normal behavior. Shorts in audio cables are certainly annoying, but shorts in high-voltage structural wiring can be quite dangerous.

Metals expand and contract with temperature changes. The lugs in a breaker panel (or fuse box) should be retightened periodically. The lugs on wall receptacles can get loose over time. Cable insulation gets dry and cracked leaving tiny gaps where AC can cause tiny arcs in statically charged air. Wiring around heating and cooling devices can be especially vulnerable.

One of the newest things here in the US in new home construction is the use of AFCI (Arc-Fault Circuit-Interrupter) breakers. I will spare you my clumsy description and link you to wikipedia if you'd like to learn more about what they do, and why it might be relevant to your problem.

You proceed as you see fit, but this would keep me up at night until I was sure there weren't sparks being generated somewhere within the building. It could be something as simple as a light socket making poor contact with the bulb when things start vibrating.

Good luck!

This is a fairly common problem that I have also encountered in the past. Thank you for this topic!