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8k noise from heater unit Saturation Plugins
Old 14th February 2019
  #1
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8k noise from heater unit

Hello!

I'm working with a Mr. Cool ductless heating unit, DIY-18-HP-230a, and its causing an 8k tone in the recording studio. Specially, the heater noise is showing up on microphone lines and guitar amps in the live room.

Attached is a sample of the frequency that occurs when the heater is turned on. The heater is turned off after a few seconds to show the noise floor.

SOME BACKGROUND:

- there are two legs of electricity coming from the main house to the studio. All of the audio gear is on one leg and the lights, Etc. are on the other.
- the unit requires both legs to opperate.
- the noise shows up on mic lines and guitar amps.


THE PLAN:

- My first instinct is to simply move the cable around and see if there is a place where the frequency is less/disappears.
- Otherwise, I'm looking into the grounding schematic of the studio.

Has anyone seen and/or dealt with a problem such as this?

Thank you!
Attached Files

Victors noise_0210.wav (2.18 MB, 233 views)

Old 15th February 2019
  #2
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Starlight's Avatar
The manufacturer states that this unit produces from 29 to 45dBA which is too loud for a studio. Better would be something like a Mitsubishi or Dakin which produce in the high teens to low 20s.
Old 15th February 2019
  #3
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I understand that it’s not the most ideal unit for a studio space. However the problem is still perplexing.

The unit is causing an 8k frequency to show up on mic lines that are positioned in the live room. (The unit is in the control room)

What’s the work around for this scenario?

Thank you for the quick responses
Old 15th February 2019
  #4
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well, such problems are not easily fixed. You have to find out, which way the noise finds it's path into your audio signals. Could be galvanically through the power lines, or through a magnetic or electric field.
The fact, thats it's on low level lines like microphones and guitars indicates the latter. So moving cables could give you some hints.

greetings

fabian
Old 4 weeks ago
  #5
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It’s an issue that definitely isn’t common! I’ll make some adjustments and see if that resolved the issue. Thanks!
Old 4 weeks ago
  #6
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8k noise from heater

After checking in on the studio the other day, I did some trouble shooting with the 8k heater issue and wanted to expound on some things.

When the heater is on and a Wurlitzer is plugged into either leg of electricity coming from the main house, (one is used for audio, the other for lights, etc.) there is this 8k ringing coming from the speakers. The problem also pops up on tube microphones that have their own power supply.

I traced the cables and the 240V cable that runs to the heater was in close proximity to some of the lighting cables. After moving them, there wasn't much change. That being said, there is one point when both the 240V and the lighting cables meet at the junction box and are both squeezed through a hole in the box, essentially right next to one another.

Funny enough, the noise doesn't show up when using the channel strips on the board (Sony MXP-3000) which is plugged into the same leg as the other audio equipment.

Now I understand this isn't the most ideal heating unit for studios, however it's what I'm working with and I'm curious if anyone has dealt with something like this before?

After some research, electrical snubbers have come up, zener diodes, etc. Anyone have any experience with these tools?

Thank you!
Old 4 weeks ago
  #7
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Quote:
Funny enough, the noise doesn't show up when using the channel strips on the board (Sony MXP-3000) which is plugged into the same leg as the other audio equipment.
can you clarify that?

maybe you can upload a little scetch of how the cables are routed?
Old 4 weeks ago
  #8
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M.Retra's Avatar
Does the frequency of the tone change if the blower speed is adjusted? The 8kHz tone "sounds" like it may have something to do with a variable speed drive for the motor. And I assume you're in heating mode right now?
Old 4 weeks ago
  #9
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Quote:
Does the frequency of the tone change if the blower speed is adjusted? The 8kHz tone "sounds" like it may have something to do with a variable speed drive for the motor. And I assume you're in heating mode right now?
It has certainly, but it is the switching frequency of the pwm control which is fixed and doesn't change with the motor speed.
Old 4 weeks ago
  #10
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M.Retra's Avatar
Quote:
Originally Posted by fabelle View Post
It has certainly, but it is the switching frequency of the pwm control which is fixed and doesn't change with the motor speed.
.

Right, and I agree. Fixed frequency yet the pulse width changes. However, the switching of the signal may be pretty harsh, with no filtering, to save costs.

Off the top of my head, I think the only way to correct for this is to get an isolation transformer to supply the "sensitive" old school equipment. Or just turn it off when this equipment is used. Other checks/corrections would be: 1) checking length of power, neutral, and ground runs from the source to your studio and increasing size (could be an impedance issue?), 2) checking the incoming sine on a scope to see just how bad it is, 3) contacting the manufacturer to ask WTF?

The Sony console perhaps utilizes a switching power supply and/or it has huge filtering capacitors on the rails.
Old 4 weeks ago
  #11
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Quote:
Off the top of my head, I think the only way to correct for this is to get an isolation transformer to supply the "sensitive" old school equipment
not as long as its not clear, which path the noise takes. your solutions only work if its galvanically induced. But could also be capacitive or inductive, i.e. through magnetic or electrical field.
Old 4 weeks ago
  #12
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M.Retra's Avatar
Quote:
Originally Posted by fabelle View Post
not as long as its not clear, which path the noise takes. your solutions only work if its galvanically induced. But could also be capacitive or inductive, i.e. through magnetic or electrical field.
Inductive is magnetic. Galvanic, as far as I have known, is current flow between dissimilar metals. I just think the incoming sine wave is being chopped up with harsh, nasty spikes (with perhaps a DC component).
Old 4 weeks ago
  #13
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Quote:
Inductive is magnetic.
yes, thats what I was trying to say, inductive coupling works through a magnetic field, capacitive coupling through electrical field.

Quote:
Galvanic, as far as I have known, is current flow between dissimilar metals.
In terms of electromagnetic compatibility galvanic coupling means the interference is coupled through a metallic path.

Quote:
I just think the incoming sine wave is being chopped up with harsh, nasty spikes (with perhaps a DC component).
yes, thats what a motor controller does. It generates a fast series (8kHz in this case) of pulses with varying width. So the source of the noise is quite clear, but it's not clear, which route the noise takes.
OP said that it's being picked up by guitar pickups and microphones, which may suggest, thats it through electrical or magnetic field.
Old 4 weeks ago
  #14
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Quote:
Originally Posted by fabelle View Post
yes, thats what a motor controller does. It generates a fast series (8kHz in this case) of pulses with varying width. So the source of the noise is quite clear, but it's not clear, which route the noise takes.
I was unclear in my original reply, my fault, but what I meant to say is that the incoming power to the motor driver was being "dirtied" by the driver's circuitry itself. Therefore, when the HVAC unit is running, the incoming AC lines to the studio now have a bunch of this noise on them, which in turn gets supplied into other devices and equipment. Furthermore, the way I interpreted "noise in mics and guitar pickups" is not within these devices themselves, but in the amplifiers they're connected to. Anyway, that's my take on the matter...

Indeed, the OP has a journey ahead of him. I'd start by checking the incoming power while HVAC is off/on with an oscilloscope, if he has one.
Old 3 weeks ago
  #15
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Quote:
Originally Posted by fabelle View Post
can you clarify that?

maybe you can upload a little scetch of how the cables are routed?
To explain what I meant, the noise doesn't show up when a previously recorded track is brought up on a fader, or a song from the internet is played in the studio. It only shows up on other audio equipment, IE a guitar amp, the Wurlitzer, or a tube microphone with its own power supply. Is that clear?

The board is plugged into the same power as the other equipment, I think @M.Retra is correct, being that the board has filtering caps.
Old 3 weeks ago
  #16
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okay, seems to be galvanically coupled then. The thing is, that when that older gear was developed no such thing as switched power supplies or pwm controllers existed, so good filtering circuits were not really needed.
You can try and add such a device (schaffner builds them in various forms) at the input of the heater. But maybe buying another heater which doesn't regulate fan speed would be simpler and should work the best.
Old 3 weeks ago
  #17
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I'm just going to come out and say it: unless we're talking about pipes, corrosion, boats, or dissimilar metals, the term "galvanic" should stop being used in this particular scenario.

Old 3 weeks ago
  #18
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Quote:
I'm just going to come out and say it: unless we're talking about pipes, corrosion, boats, or dissimilar metals, the term "galvanic" should stop being used in this particular scenario.
Agree, my bad. In german the term is also used the way I did. The correct english term would be conductive coupling.
thanks for pointing it out, again.
Wikipedia on Electromagnetic Compatibility
Old 3 weeks ago
  #19
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Thank you for the replies!

This situation definitely has my head turning. I'll keep the page up to date as I progress.... thanks again!
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