Opa Alice build noise floor

[wamosjk]

I just did my first build with an OPA Alice circuit with the hex board from JLI Electronics. It has the TSC1 capsule and the body is just one of those cheap u87 knockoffs from aliexpress. So my question is what is a typical noise floor for this build. I really dont have a frame of reference because all of my other mics are dynamics and I heard the OPA Alice circuit is supposed to be extremely quiet. Right now the self noise is faint but it is there and since this is my first build I just wanted to make sure that I don't have an issue somewhere that needs to be addressed. Here is a raw recording demonstrating the noise floor. I will link to the .wav files and also attach them to this post.


View attachment opa-alice-noise-floor.wav

As you can tell from the recording the noise floor is really faint but is there if you turn up the recording. Everything seems to be clean on the board as I cleaned it several times with 99% alcohol and a microfiber cloth. I also saw in the troubleshooting the following:

Scenario two: Noise. Our probable faulty functions for this one are wiring or a short of some kind to the shell. IfXLR_2 or XLR_3 is shorted to ground, you can have noise.This is caused by not enough supply current and running the operational amplifier below rated voltage. You canhear what this sounds like if you have the mic connected, and then turn phantom power off. As voltage drops, atsome point noise kicks in, then falls off as voltage completely goes away.

So I made a recording of me turning off the 48v power.

View attachment opa-alice-circuit-turning-48v-off.wav

This seem like it might be the issue but I'm not sure. So I just wanted to post on here to see if anyone has had any experiences and could point me in the right direction. Am I just being paranoid and the self noise is totally normal for this build or do I have an issue that needs to be addressed either in the circuit or the cheap shell its currently in? If you need more info let me know. Here are some images as well.

Edit: here is a recording of the sm58 with a mic booster at the same gain level.

View attachment sm58-noise-floor.wav

 

[mrgrooves666]

Well, you need to share more "in wich context" details, like how much gain do you have at the preamp. The circuit is pretty low noise yes, but depending on how much gain are you using at the preamp, that noise will come up nevertheless. But in what context...meaning is the level at the preamp actual real scenario, or practical level, or are you testing @ 58+ db gain? if its the latter, then yeah, it might be normal....links to files don't work btw...

 

[wamosjk]

Well, you need to share more "in wich context" details, like how much gain do you have at the preamp. The circuit is pretty low noise yes, but depending on how much gain are you using at the preamp, that noise will come up nevertheless. But in what context...meaning is the level at the preamp actual real scenario, or practical level, or are you testing @ 58+ db gain? if its the latter, then yeah, it might be normal....links to files don't work btw...

Im running through the tascam 1x2 hr interface and the knob is at 75%. The max gain on the interface is 58db. But if i plug in a shure sm58 i dont really hear the noise floor but its also a dynamic so it doesnt have a self noise. It should be noted that im on linux and on windows i can use less gain but my main computer that has dual boot to windows has like 9 fans so the fans make more noise than the noise floor of the mic. As far as the links they seem to be working fine for me. They are on google drive and i have it set so anyone can view them. I also attached the same files to the post as well so you can just view them that way.

 

[ccaudle]

Probably reasonable noise level. I assume you were not speaking very loudly, the timbre of your voice sounded like normal level for a close conversation. I have trouble guessing what that would translate to in SPL, but the noise floor was just audible at that gain setting.
Did you record the audio so you can get an idea of the SNR at that level?

if i plug in a shure sm58 i dont really hear the noise floor

How does the signal level from the SM58 compare to the condenser mic at the same gain level? Difference between signal level and noise floor is what you typically care about.

im on linux and on windows i can use less gain

That doesn't really make sense unless there is software gain on the windows system or software attenuation on the linux system. If there is software gain on the Windows system the end result probably isn't very different, because that gain would bring up the level of the signal and the noise floor. If there is attenuation happening on your Linux system then that would be a disadvantage because increasing the preamp gain to make up for it would increase the preamp noise floor as well.
Understanding how to optimize your software settings is a side topic from the original question, so to answer that, the noise floor does not sound unexpectedly high to me. To get objective numbers would require a much more rigorous measurement setup, either an acoustic noise source of a known SPL, or a preamp with accurate gain settings and a way to measure the electrical noise level.

 

[wamosjk]

That doesn't really make sense unless there is software gain on the windows system or software attenuation on the linux system. If there is software gain on the Windows system the end result probably isn't very different, because that gain would bring up the level of the signal and the noise floor. If there is attenuation happening on your Linux system then that would be a disadvantage because increasing the preamp gain to make up for it would increase the preamp noise floor as well.

Ya for some reason linux just doesn't like this Tascam 1x2hr audio interface. I had a different intgerface and didn't have that problem with but that interface really sucked. I like this interface I just have to turn it up a little more on linux. It really never presented an issue (until now). The Tascam 1x2hr does have proprietary windows drivers but no linux drivers so there may be something they're doing there to boost the signal in windows.

How does the signal level from the SM58 compare to the condenser mic at the same gain level? Difference between signal level and noise floor is what you typically care about.

So I made a recording with the noise floor of the sm58. I attached it to the original post. I also removed the links from the post and inserted the audio into the post (My first posts here and didn't see the insert button the file attachment). I won't attach it here too just to save the site from duplicate uploads At first I just used the sm58 but since its a dynamic it was much quieter so I decided to just hook up my mic booster and when I do that the signals are relatively the same and the mic booster should introduce clean gain and not introduce any added noise. So there does seem to be some noise you can see the noise seems quite a bit less. Not sure if this seems normal or not because like I said all of my frame of referece is with dynamic mics so I never really had to deal with condenser self noise. I really just wanted to make sure I built the mic correctly and didn't have any issues that I need to address and everywhere says the OPA Alice circuit is really quiet (around 6db). So if I am getting any extra noise I would like to fix it. I was a bit concerned about the noise turning off the 48v power because in the troubleshooting it states.

Scenario two: Noise. Our probable faulty functions for this one are wiring or a short of some kind to the shell. IfXLR_2 or XLR_3 is shorted to ground, you can have noise.This is caused by not enough supply current and running the operational amplifier below rated voltage. You canhear what this sounds like if you have the mic connected, and then turn phantom power off. As voltage drops, atsome point noise kicks in, then falls off as voltage completely goes away.

So I'm not sure if that noise I posted is the noise they are talking about here. If so I may need to get a different body for it.