Studio noise, please help!!

[mrtnasty]

This noise is driving me crazy and I can't figure out what is causing it. My signal chain is microphone into RCA Ba2, int RCA Ba6a, into Focusrite Clarett+ 4pre. This was recorded with the Ba2 gain all the way down and the Ba6a gain all the way up. Also I wired up the inputs and outupts for the Ba2 and Ba6a myself according to the manual, but connected input and output xlr pin1 to the chassis along with the ground of the power cord. Disconnecting ba6a input pin 1 did not help. Unplugging my wireless router did not help. If I cup the Ba2 preamp tubes with my hands, the noise is reduced. If I pick up the ba2 and rotate its orientation, the noise is reduced in some positions. This noise happens in my living room but is greatly reduced in my (unfinished) basement. Please help and thank you!
View attachment Output 1-2.mp3

 

[scott2000]

I think you're not alone in this fight. Before everyone jumps in with the usb,computer grounds..., unbalanced connections,etc.....,

.....there's not a wireless router in the room is there?

 

[Ike Zimbel]

Where is your cell phone when this is happening? And, do you live in an urban area where there may have been recent changes to the cellular infrastructure...as in a new antenna installation nearby?

 

[dmp]

You need to methodically evaluate - use the process of elimination to identify the problem.
Get another microphone, another preamp, narrow down exactly what piece of gear is allowing the noise pollution.
If you are using a known 'good' preamp & mic, is there still a noise problem?
Create a 'dummy' microphone plug with a 150 ohm resistor on a female XLR and plug that into the preamp. Problem still there?
Does rotating the microphone reduce or change the noise?
Do you have all the lights off, particularly anything on a dimmer switch?
You probably have two issues, some EMF noise pollution in the environment and a part of your signal chain that has a shielding weakness.

If I pick up the ba2 and rotate its orientation, the noise is reduced in some positions.

Sounds like this piece of gear may have a problem with ground layout or shielding. It could be that you used a input transformer that is not sufficiently shielded. It could be the ground layout is poor. Lots written here on grounding. The hardest part of making a high level piece of DIY gear is getting the ground scheme right. It could be a bad tube.
Once you've narrowed down the problem to a piece of gear, continue the methodical evaluation. Swap parts, ground scheme, shielding etc...

 

[mrtnasty]

You need to methodically evaluate - use the process of elimination to identify the problem.
Get another microphone, another preamp, narrow down exactly what piece of gear is allowing the noise pollution.
If you are using a known 'good' preamp & mic, is there still a noise problem?
Create a 'dummy' microphone plug with a 150 ohm resistor on a female XLR and plug that into the preamp. Problem still there?
Does rotating the microphone reduce or change the noise?
Do you have all the lights off, particularly anything on a dimmer switch?
You probably have two issues, some EMF noise pollution in the environment and a part of your signal chain that has a shielding weakness.

Sounds like this piece of gear may have a problem with ground layout or shielding. It could be that you used a input transformer that is not sufficiently shielded. It could be the ground layout is poor. Lots written here on grounding. The hardest part of making a high level piece of DIY gear is getting the ground scheme right. It could be a bad tube.
Once you've narrowed down the problem to a piece of gear, continue the methodical evaluation. Swap parts, ground scheme, shielding etc...

Thanks! It's a real Ba2 (with replaced caps) but I wired the jones connector and grounded both input and output xlr pin1 and power cord ground.

 

[mrtnasty]

I think you're not alone in this fight. Before everyone jumps in with the usb,computer grounds..., unbalanced connections,etc.....,

.....there's not a wireless router in the room is there?

There is a wireless router, but I unplugged it and the noise was still there

 

[mrtnasty]

Where is your cell phone when this is happening? And, do you live in an urban area where there may have been recent changes to the cellular infrastructure...as in a new antenna installation nearby?

I put my cell phone on airplane mode, I don't live in the downtown of a big city, but I'm not sure about new antennas in my area.

 

[scott2000]

Maybe others can chime in with how they terminate cables in a noisy environment if that is the case of where the noise is coming from......Cap at the end with no shield etc?

Thor started getting into a bit of thinking on the subject here as well
https://groupdiy.com/threads/are-th...wireless-routers-and-such.84986/#post-1106251

good luck!
Don't leave us hanging if you find some success

 

[mrtnasty]

Update: seems like the noise is coming from the Ba2. When I connect the Ba2 straight to the interface, the noise is there. I moved everything into my basement and the noise is considerably reduced. Also the shields that cover the anode of the 1620 seem to be pretty important for reducing noise. Worth mentioning also, Im using a ribbon mic, and I noticed that the orientation of the mic is important for reducing noise, there is one direction in which there is no buzz, and if I move it out of this position, the buzz increases, sort of like single coil pickups on a guitar. Wish I had a better solution but I'm happy to have reduced noise to a useable level. Will continue to update if I figure out any better grounding or shielding techniques.

 

[Matt Syson]

Ribbon mics need quite a bit of gain AND nearer the correct input impedance (higher transformer step up ratio) AND you probably need metal outside casing for the preamp because you are inviting HF noise to enter. Ribbon mic sensitive to direction, you need to find the HUM source (mains wiring or power transformers) this is on top of your MF noise.

 

[Ike Zimbel]

Update: seems like the noise is coming from the Ba2. When I connect the Ba2 straight to the interface, the noise is there. I moved everything into my basement and the noise is considerably reduced. Also the shields that cover the anode of the 1620 seem to be pretty important for reducing noise. Worth mentioning also, Im using a ribbon mic, and I noticed that the orientation of the mic is important for reducing noise, there is one direction in which there is no buzz, and if I move it out of this position, the buzz increases, sort of like single coil pickups on a guitar. Wish I had a better solution but I'm happy to have reduced noise to a useable level. Will continue to update if I figure out any better grounding or shielding techniques.

Do the individual tubes have shields on them? That could help. Does the device have a complete case, or do the tubes and other components project out of the chassis? I'm not familiar with your kit, but if these things are modules that were meant to go in an overall frame/rack that might have shielded them in metal, and they're not in that situation, all bets are off for RF/EMF immunity.

 

[ccaudle]

I noticed that the orientation of the mic is important for reducing noise

Did you try the earlier suggestions?

Create a 'dummy' microphone plug with a 150 ohm resistor on a female XLR and plug that into the preamp.

Note that the recommendation for the XLR connector was reversed, microphones have pin connectors (male), not socket.

connected input and output xlr pin1 to the chassis along with the ground of the power cord.

That generally is the correct approach, but if this is RFI then the specifics of how long those connections are matter. Long shield connections have high impedance and can sometimes even re-radiate RF noise into nearby circuitry. Pictures of the exact physical construction might be useful.

This older thread describes in the first post a BA2 build which was a little noisy at first, and what changes were made to get it quiet:
BA2 build from 2012

 

[Cqwet Dbdfte]

This noise is driving me crazy and I can't figure out what is causing it. My signal chain is microphone into RCA Ba2, int RCA Ba6a, into Focusrite Clarett+ 4pre. This was recorded with the Ba2 gain all the way down and the Ba6a gain all the way up. Also I wired up the inputs and outupts for the Ba2 and Ba6a myself according to the manual, but connected input and output xlr pin1 to the chassis along with the ground of the power cord. Disconnecting ba6a input pin 1 did not help. Unplugging my wireless router did not help. If I cup the Ba2 preamp tubes with my hands, the noise is reduced. If I pick up the ba2 and rotate its orientation, the noise is reduced in some positions. This noise happens in my living room but is greatly reduced in my (unfinished) basement. Please help and thank you!
View attachment 122866

Have you found the source yet?

The noise has at least two components, a crackling noise and a single steady tone.
It does not sound like a 120Hz rectifier buzz, or a rectified AM station. Could be a beat tone between two SMPS'. Cellphones has a periodic characteristic noise when regularly connecting to the tower, just sitting around, and this is not it.
The cracking could be from a poor connection, anywhere in the signal chain, tube socket, cold solder joint, bad capacitor, bad tube, etc. I have some bad tubes that work like tone generators if you need them.
General advice:
Divide and conquer. Test each part of the system separately. Terminate each input and measure noise.
A bad solder joint in a cable or a broken conductor may be at fault.
Jiggling a cable a little should not increase noise.
Make a signal-chain diagram with every component and interconnect, note the gain from each stage, use this diagram for noting results.
Use an oscilloscope to measure noise, and out of band signals, in power supplies, and signal outputs with inputs terminated.

All and every modern piece of electronics have switching power supplies. Legal EMI specs are pretty soft.

 

[Big Valley Audio]

It sounds like cell phone interference.
The first thing I do when a client has noise issues that sound like that is use a cell phone tower locator app on my phone to see how close a cell phone tower is to me.
I’m in Canada and there are at least four free apps on the App Store (I use iPhone) for Canadian cell tower locations so I imagine there would be something for where you live.
If you are within a kilometer of one then it’s a very good chance that’s the issue.
Let me know if that’s the case and I can tell you some steps to reduce the noise.
Orientation of the offending gear to get the minimum noise is the first thing to do (which you have already done)

 

[cyrano]

Sound like RTTY. But it's too short to really tell. Any HAMs in the area? They could help you to identify the source.

 

[Cqwet Dbdfte]

Cell towers are unlikely to generate interference, cell phones in close proximity, yes.
If you live across the street form a tower you may get -40dBm at 700+MHz that needs to survive massive losses inside audio equipment, then be rectified at a level that will have some effect.
In the sound sample 4KHz, 10KHz, and 18KHz dominate at almost the same level, 1KHz and its harmonics are present.
I would be looking for SMPS', dimmers, monitors, etc.
There is 60/120Hz in there too, so missing ground/shield connections?

 

[Big Valley Audio]

Cell towers are unlikely to generate interference, cell phones in close proximity, yes.
If you live across the street form a tower you may get -40dBm at 700+MHz that needs to survive massive losses inside audio equipment, then be rectified at a level that will have some effect.
In the sound sample 4KHz, 10KHz, and 18KHz dominate at almost the same level, 1KHz and its harmonics are present.
I would be looking for SMPS', dimmers, monitors, etc.
There is 60/120Hz in there too, so missing ground/shield connections?

It wasn’t a huge problem until cell companies started using 5G in the 600 and 700 MHz bands here in Canada. Those low cell bands have surprising penetration into buildings. Past 2000Mhz the issues aren’t as much of an issue. Mostly I see it as interference in condenser mics but have also heard it in powered speakers and mic preamps.
Once you boost your mic pre up 35-40 dB then any noise that gets into the mics can get very objectionable