Old 04-03-2020, 02:18 PM   #1
Fergler
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Default Need help with electrical layout

I have some sort of USB and/or power ground loop or GVI that I'm having trouble ridding from my system, as well as some hashy GPU or power noise problem coming from the computer.

Here is a map of the layout:
https://i.imgur.com/eUVVJy1.jpg
Note that all power is running off one plug from one circuit, trying to reduce the possibility for a ground differential between parts.

I've confirmed a few things:

1. A 120hz hum in the guitar signal line. Turning down the guitar volume at the guitar increases the volume of the hum. Lifting ground on the guitar effects board or going through a DI box with ground lift on doesn't eliminate it. The guitar pickup is a "noiseless" single coil, custom made. I use quotes because when I switch to both pickups in humbucking configuration it gets rid of hum a lot more.

2. Unplugging the computer makes the hash go away, and stays away until the battery is recharged to 100%. In other words, that noise is only present when the laptop is plugged in and fully charged. It also removes the slight whine when moving or scrolling things on screen, as expected. No LED room lights or dimmers are on at this time, but there are LEDs present on the pedalboard (I can hear them whine when I switch patches. This sound is somewhere around 670hz)

https://clyp.it/pgvokzac
https://clyp.it/nvhjohyz

And confirmed a few things to have no effect:

1. Unplugged or turning off the speakers, connected by balanced TRS, or unplugging the TRS.
2. Disconnecting the FCB1010 or any of the USB devices besides the interface.
3. Lifting ground for the USB connections by covering Pin 4 with etape.
4. Unplugging both refrigerators in the apartment... though that did remove the room mode resonance xD. Hate this fridge... (always unplugged for acoustic guitar recording!) I recorded the noise while plugging them back in, only heard a slight fade in and out as the power in-rush occured then back to normal.

And one other interesting issue that seems related to the power supply. When I disconnect it I get a garbled sound and also ASIO seems to reset and become much more latent (~200ms delay) until I reset ASIO by opening and closing the Audio Device window. If I play audio through this it is mangled as much as the sound heard in the ASIO failure file below. This can sometimes happen without unplugging, but the sound is then more like an increasingly loud chirp at about 2.5x per second. Still leaves the audio latent afterwards. Interestingly, does not affect any recording...

https://clyp.it/k0itoucx

The solutions I've been looking at but am unsure of their actual effectiveness is:

A toroidal isolation transformer (about $200 CAD at least).
and/or a common and differential mode EMI line filter
USB power decoupling dongle (removes laptop from power connection to USB, replaces it with external 5v power supply). I already tried removing Pin 1 but apparently it is needed even for devices which don't need bus power. After this none of the powered devices showed up as available and windows didn't recognize them.
A typical power conditioner. From what I understand, these don't do much at all for ground issues.

Any thoughts from people who have chased these issues in pro studios or are electricians?

I'm especially concerned that I can't find a local dealer for an isolation transformer to try before I buy or return after if it doesn't work. It seems like the best way to clean up my noise issues.
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Last edited by Fergler; 04-03-2020 at 02:23 PM.
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Old 04-03-2020, 03:28 PM   #2
Allybye
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Wow.
I find it hard to understand your description(s) except you get 120Hz hum and higher fequency digital interference?

If that is correct then likely two different causes.

Hum pickup by guitars or mics or earthing loops etc. on those inputs/cables

Possible interference from switched mode power supplies or digital signals getting picked up by cables in the vicinity of the laptop. Keep analogue elements well clear.


Some initial basic advice.

1 never remove safety earth connections. They are there to protect personnel and without them you increase massively the risk of shock under fault conditions.

2 you seem to have an overly complex system. Try to simplify and start from there. Perhaps you can explain what you are trying to achieve? There seem to be connections all over the place.

Most hum is picked up on lower level signal circuits (e.g. mic level signals) and on higher level signals of high impedence such those interfaces to guitars that are unbalanced. Also guitar pickups can pick up stray magnetic fields (even humbucking ones) so they can often be improved by changing location (moving away frm power supplies) or even just rotating the guitar.

Try starting with a simple system, prove each input is clean and or move on to the next - individually connected. Forget the conditioning/complex fixes till the basics are sorted!

ps the quality of your pic could do with improvement to read your annotation to help understanding your system.

Last edited by Allybye; 04-03-2020 at 03:35 PM.
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Old 04-03-2020, 04:50 PM   #3
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Don't just buy stuff, hoping that it will cure the problem. Ground loops usually occur at balanced units, where signal ground is not properly connected to chasis ground. You solve it by disconnecting pin 0, usually on input to next unit. With unbalanced units using wallwart, you can use transformer isolators. If unbalanced unit is grounded via power plug, you can try to disconnect cold wire to break loop. Each unit must have only one connection to ground - imagine units as squares, each standing only on one leg on the ground. If square stands on two legs, you are inviting problems.
Chasing it is a bit tricky, but with such small system shouldn't be too hard, Just go disconnecting interconnecting cables, untill you get to the one that breaks loop. Then make custom cable with disconnected pin0/shield/ground wire.
Never disconnect safety/chasis power connection to lift ground! Always work on audio cables instead.

Check this: https://www.ranecommercial.com/kb_ar...p?article=2107

Last edited by sonicowl; 04-03-2020 at 04:59 PM.
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Old 04-03-2020, 05:18 PM   #4
karbomusic
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The way those devices all interconnect (which has to be that way), if it's a ground (either loop or parasitic on the ground plane) it's there and not the actual AC plug.

Does this occur if you unplug the guitar cable from the device it's plugged into (so neither the guitar or cable is plugged in)? If a ground loop, the guitar should be irrelevant, if EMI going into pickups that's a different issue but that also usually has a 120 Hz component. Guitars are great for finding where wires are in your wall (no kidding).

Hum cancellers... I promise it is well worth your time and lack of frustration to have various types lying around and a couple extras - one of those AC types + a couple like the two-channel one like an ART DTI - these are LIFESAVERS in multiple situations - they have saved my ass multiple times - power conditioners not so much other than keeping any existing noise riding in on the AC line and voltage regulation.
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Last edited by karbomusic; 04-03-2020 at 05:26 PM.
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Old 04-04-2020, 05:15 AM   #5
Allybye
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Ah, apologies are due!
Was looking at your image in a browser, using IMGUR app all is clear.

I was intrigued enough to fead the link you posted @Sonic to the Rane description of interconnects.
I write as an engineer rather tban musician experienced in designing and using audio equipment and other equipment that is much more critical of Electromagnetic Interference (EMI) as regards safety not just something annoying and unwanted. It makes interesting reading but confusing at times!!
Such comments as " The method specified by AES48 is to use balanced lines and tie the cable shield to the metal chassis (right where it enters the chassis) at both ends of the cable. " seems to be contradicted later in the doc by "suggested cable assemblies" type 1 with the shield disconnected: and writing that one method can be guaranteed to get rid of hum after writing " Balanced interconnect was developed to be immune to these noise currents, which can never be entirely eliminated. "...and as a consequence of that latter statement induced hum and noise can never be entirely eliminated but can be reduced to more than acceptable levels.

Further feeding a balanced circuit signal into an unbalance input does not necessarily fesult in a 6dB loss.
Balanced really describes the impedence balance to earth. That combined with the screen and wire twist (reduction of low and high frequency EMI) feeding into differential inputs (largely cancelling what interference is induced) provides very low induced noise levels.

They do not get rid of all noise - and hence the reason I mention it.

As was posted above by the respondents guitar pickups can be very prone to induced hum. Rectified mains (50Hz or 60Hz) hum will give large amounts of harmonics at 100 or 120Hz;coupled with the need to be part of a high impedence circuit they are areas to concentrate on despite their high signal levels or humbucking coils (another balancing attempt!). From what you write they seem to be possibly picking up hum via the coils but there can be another cause in addition. As writ above disconnect them. Simplify- work in stages!

Mic signal are quite low level and thus benefit greatly from impedence balancing. Still worth looking into in case of faults in wiring, or indeed many mics (particularly dynamics) near sources of interference.

These comments are not to detract from the probable issue of ground loops and the good advice already posted and the idea of building up your system in small sections is a great way forward to find the issue(s).

Keep your digital bits i.e. laptop and it associated power supplies, leads and Asio cables away from analogue cables and devices -especially tbe unbalanced ones. Likewise their power supplies/cable away from analogue. If the various analogue and digital (or power) cables must be close together do not run parallel and cross at right angles.

After all that then consider ground loops and the suggestions in the Rane document for interconnect terminations.


And do then post back!

Last edited by Allybye; 04-04-2020 at 07:57 AM. Reason: hopefully adding some useful info
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Old 04-04-2020, 04:57 PM   #6
Fergler
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Hey guys thanks for all the feedback.

The guitar and it's cable were disconnected as part of testing many times, still had humming from the pedalboard with nothing attached. I tried all gear in isolation.

It turned out to be due to the power bar I was using. I switched it out with another one and the hum problem is gone.

There is still some lower level hum which I will still try a ground lift on the power bar to check if that will remove it, and I still hear the GPU/full battery noises but I'm pretty confident the USB decoupler will fix this as I've watched several demonstrations with the same noise.

The mains power could still do with some filtering anyway but it's far less an issue. That's more related to the buzz from my monitors.

As for how complex this set up is, it's really not. It's just 3 analog inputs and 3 midi inputs in a home studio. I just intend to use them all in fast succession so there's no unplugging of anything. Thats when the problem sound started stacking to unbearable levels.
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Old 04-04-2020, 05:58 PM   #7
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Quote:
Originally Posted by Fergler View Post
Hey guys thanks for all the feedback.

The guitar and it's cable were disconnected as part of testing many times, still had humming from the pedalboard with nothing attached. I tried all gear in isolation.
Ah, cool, glad you did that and also that you got it fixed.
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Old 04-05-2020, 01:56 AM   #8
Allybye
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Yes good to read of progress.....
....but please do not lift and mains safety earths/grounding, we might not hear from you again!!!!
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Old 04-09-2020, 04:55 PM   #9
Fergler
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Quote:
Originally Posted by Allybye View Post
Yes good to read of progress.....
....but please do not lift and mains safety earths/grounding, we might not hear from you again!!!!
Believe me I know I worked in construction and work currently in live audio. I know about ground pins
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