Electronics Wizzes - Help with Tracking down a buzzing in my headphones

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networkn

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#147293 15-Jun-2014 11:28

Hi There!

So I bought a Crack Amp Kit, which is a Tube based Headphone Amplifier. I have built it, all the resistance and voltage checks are good, but when I plug in a DAC to the Crack Amp, I have buzzing in my ear, which doesn't affect the quality of the music itself, just the buzz is present.

So the Gear I have is:

PC
Odac (USB Based DAC)
O2 Amp (AC Powered)
Crack Amp (Ac Powered 3 Pin)
Schiit BiFrost DAC (AC Powered 3 Pin)
T1 Beyerdynamic Headphones, HD650 Headphones, HE400 Headphones - Noise is present in all of them.

Troubleshooting has led me to the following list of things:

1) Amp with nothing connected - No unusual noise
2) ODAC connected to Crack, but no USB Connected - No unusual noise
3) ODAC connected to USB on Desktop Computer, connected to Crack - Noisy
4) Bifrost connected to USB on Desktop, Connected to Crack - Noisy
5) ODAC/BiFrost Connected to Laptop via USB - No Noise
6) ODAC to Headphones directly, connected to PC or Laptop via USB - no Noise
7) BiFrost Connected via Optical SPDIF to Crack - Slight noise - Not as bad as via USB
8) ODAC connected to PC via USB then Connected to O2 AMP - No Noise
9) ODAC Connected to Laptop via USB then Connected to O2 Amp - No Noise
10) Noise from 3 doesn't seem to change as I adjust the volume knob on the crack
11) Noise from 3 doesn't seem to change if I remove one of the RCA's or the other, or if I swap them around
12) Noise from 3 not affected by type of music playing, or sample rate etc.
13) Noise from 3 can be drowned out if the volume is loud enough (Music
14) The Music coming from the crack in 3 sounds Excellent, just the buzz in the background
15) Noise from 3 moves from right hand to left hand depending on how far the headphone is inserted into the jack.
16) BiFrost connected via Toslink - Noise.
17) I have removed all peripherals from my PC except power, and the cable connecting me to the DAC - Noise.

I am at my wits end, the buzzing isn't something I can live with.

I am told it's likely a grounding issue, probably a ground loop, but that if this is the case then Toslink connection between my PC and BiFrost shouldn't have a problem, which it does.

What can I do to further troubleshoot the problem ?

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#1065992 15-Jun-2014 14:07

You got an Isolating transformer ?

If not, borrow one and then plug ONLY your PC into it, then test it with ONE item at a time (plugged into the ordinary mains).

If its an earth loop the transformer will break it.

If you have multiple items connected then the earthlink can be between any two of them.

If you have an earth look change which item is using the isolating transformer.

Just remember, you are amplifying signals, so the earth loop does not need to be much of a problem, because the problem gets amplified along with everything else.

Check that the earths on everything are connected (properly), one dodgy earth connector will be enough.

Is everything plugged into the same circuit, use a multi-box, the earth loop may between power sockets if they are on different fuses/breakers.

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networkn

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#1066000 15-Jun-2014 14:20

sir1963: You got an Isolating transformer ?

If not, borrow one and then plug ONLY your PC into it, then test it with ONE item at a time (plugged into the ordinary mains).

If its an earth loop the transformer will break it.

If you have multiple items connected then the earthlink can be between any two of them.

If you have an earth look change which item is using the isolating transformer.

Just remember, you are amplifying signals, so the earth loop does not need to be much of a problem, because the problem gets amplified along with everything else.

Check that the earths on everything are connected (properly), one dodgy earth connector will be enough.

Is everything plugged into the same circuit, use a multi-box, the earth loop may between power sockets if they are on different fuses/breakers.

Not sure if this helps, however I did have everything plugged into 1 Zap catcher and the problem still existed. Can you give me an example of a suitable isolating transformer? Would a UPS do it ?

I presume if the Crack Amp earth wasn't connected I'd be having much bigger problems (it has a fuse) or I'd hear noise just connecting HP's to the amp and nothing else (I only hear a slight noise when the crack amp is turned up past 80%

Comments in other places indicated if I connected the DAC to the PC via Toslink the Ground shouldn't be a problem, but same thing happens. Unsure if that helps.

Niel

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#1066049 15-Jun-2014 16:08

Switch mode power supplies have a low impedance to earth/neutral. This is where your earth loop (buzz) comes from. Can you change one of the power supplies to an old linear "brick" supply? Else try http://www.trademe.co.nz/music-instruments/pa-pro-audio-dj-equipment/cables/auction-740393126.htm

You can never have enough Volvos!

sir1963

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#1066059 15-Jun-2014 16:25

networkn:
sir1963: You got an Isolating transformer ?

If not, borrow one and then plug ONLY your PC into it, then test it with ONE item at a time (plugged into the ordinary mains).

If its an earth loop the transformer will break it.

If you have multiple items connected then the earthlink can be between any two of them.

If you have an earth look change which item is using the isolating transformer.

Just remember, you are amplifying signals, so the earth loop does not need to be much of a problem, because the problem gets amplified along with everything else.

Check that the earths on everything are connected (properly), one dodgy earth connector will be enough.

Is everything plugged into the same circuit, use a multi-box, the earth loop may between power sockets if they are on different fuses/breakers.

Not sure if this helps, however I did have everything plugged into 1 Zap catcher and the problem still existed. Can you give me an example of a suitable isolating transformer? Would a UPS do it ?

I presume if the Crack Amp earth wasn't connected I'd be having much bigger problems (it has a fuse) or I'd hear noise just connecting HP's to the amp and nothing else (I only hear a slight noise when the crack amp is turned up past 80%

Comments in other places indicated if I connected the DAC to the PC via Toslink the Ground shouldn't be a problem, but same thing happens. Unsure if that helps.

The isolating transformer means that the secondary of the transformer is "isolated" from the primary, i.e. there is no longer any earth reference
there is no longer any "neutral" as such.

idle

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#1066074 15-Jun-2014 16:51

I get buzzing in both ears, rather like one hundred crickets. But I do not have headphones, let alone a headphone Amplifier! I am not being entirely facetious, but I have tinnitus, which can result from excessive noise, particularly in the higher frequencies. Tinnitus is a medical condition which may be present during noise in certain frequency ranges and not in others, but, if severe, may be permanent, and be associated with loss of hearing in high frequency ranges. I suppose what I am saying is check your system in various frequencies to make sure you have a technical problem rather than a medical condition.

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#1066115 15-Jun-2014 18:18

idle: I get buzzing in both ears, rather like one hundred crickets. But I do not have headphones, let alone a headphone Amplifier! I am not being entirely facetious, but I have tinnitus, which can result from excessive noise, particularly in the higher frequencies. Tinnitus is a medical condition which may be present during noise in certain frequency ranges and not in others, but, if severe, may be permanent, and be associated with loss of hearing in high frequency ranges. I suppose what I am saying is check your system in various frequencies to make sure you have a technical problem rather than a medical condition.

Confident it's not my ears.

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#1066117 15-Jun-2014 18:19

sir1963:
networkn:
sir1963: You got an Isolating transformer ?

If not, borrow one and then plug ONLY your PC into it, then test it with ONE item at a time (plugged into the ordinary mains).

If its an earth loop the transformer will break it.

If you have multiple items connected then the earthlink can be between any two of them.

If you have an earth look change which item is using the isolating transformer.

Just remember, you are amplifying signals, so the earth loop does not need to be much of a problem, because the problem gets amplified along with everything else.

Check that the earths on everything are connected (properly), one dodgy earth connector will be enough.

Is everything plugged into the same circuit, use a multi-box, the earth loop may between power sockets if they are on different fuses/breakers.

Not sure if this helps, however I did have everything plugged into 1 Zap catcher and the problem still existed. Can you give me an example of a suitable isolating transformer? Would a UPS do it ?

I presume if the Crack Amp earth wasn't connected I'd be having much bigger problems (it has a fuse) or I'd hear noise just connecting HP's to the amp and nothing else (I only hear a slight noise when the crack amp is turned up past 80%

Comments in other places indicated if I connected the DAC to the PC via Toslink the Ground shouldn't be a problem, but same thing happens. Unsure if that helps.

The isolating transformer means that the secondary of the transformer is "isolated" from the primary, i.e. there is no longer any earth reference
there is no longer any "neutral" as such.

Sorry but I am no clearer as to what I am supposed to do ?

networkn

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#1066118 15-Jun-2014 18:21

Niel: Switch mode power supplies have a low impedance to earth/neutral. This is where your earth loop (buzz) comes from. Can you change one of the power supplies to an old linear "brick" supply? Else try http://www.trademe.co.nz/music-instruments/pa-pro-audio-dj-equipment/cables/auction-740393126.htm

Hi,

thanks for the reply. I bought one of the linked trademe items, I'll have it tomorrow and get back to you.

The PSU I have is :

http://www.seasonicusa.com/Platinum_Series_XP2.htm

660W model. Unsure if this is relevant, but it's one of the most highly rated Power Supplies Available.

Will the linked trademe item, likely cause the sound quality to drop? I hope not.

Niel

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#1066128 15-Jun-2014 18:37

Given that you have a tube amp, nothing will drop the sound quality (relatively).

That is a switched mode power supply. Essentially you cannot buy a linear power supply any more, not that it is illegal but just that the minimum efficiency requirement for NZ is level IV and there is no way a linear power supply can reach that so it is nearly impossible to find a (new) linear power supply retail these days.

I would not use an isolation transformer, although it will likely work. The reason being that you loose your neutral reference so your gear is essentially floating and the RCD in your switchboard will not work (assuming you have one). Isolation transformers are intended for improving safety in some specific situations (for example accidentally drilling into live wires), not for fixing audio earth loops.

You can never have enough Volvos!

Niel

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#1066132 15-Jun-2014 18:42

A linear transformer has the same effect as a mains isolation transformer, except that the output is a safe/separated extra low voltage (SELV) instead of mains. So if you know how a linear transformer works, then think of an isolation transformer as the same but 240V AC out.

You can never have enough Volvos!

networkn

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#1066133 15-Jun-2014 18:44

Ok well I think I'd rather avoid replacing the power supply in my PC, it's a performance beast and the cable layout would be difficult to replicate. I'll skip the isolating transformer as well on your recommendation. I am praying this item you linked to fixes it, or I am out of ideas.

Why would my O2 Amp have no issues but my Crack Amp does?

sir1963

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#1066150 15-Jun-2014 19:36

Niel: Given that you have a tube amp, nothing will drop the sound quality (relatively).

That is a switched mode power supply. Essentially you cannot buy a linear power supply any more, not that it is illegal but just that the minimum efficiency requirement for NZ is level IV and there is no way a linear power supply can reach that so it is nearly impossible to find a (new) linear power supply retail these days.

I would not use an isolation transformer, although it will likely work. The reason being that you loose your neutral reference so your gear is essentially floating and the RCD in your switchboard will not work (assuming you have one). Isolation transformers are intended for improving safety in some specific situations (for example accidentally drilling into live wires), not for fixing audio earth loops.

The isolation transformer will help prove / help isolate where the earth loop is occurring. It is not intended as a permanent fix.
The fact that the other parts of the system are earthed/ground reference will mean that the PC is not floating a such, it will be actually be earthed
through the earths from the other items, however because the PC no longer has an earth connection from its own mails cable there can no longer be a "loop"

Therefore if there is any hum , it must be some where else .

networkn

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#1066179 15-Jun-2014 20:22

sir1963:
Niel: Given that you have a tube amp, nothing will drop the sound quality (relatively).

That is a switched mode power supply. Essentially you cannot buy a linear power supply any more, not that it is illegal but just that the minimum efficiency requirement for NZ is level IV and there is no way a linear power supply can reach that so it is nearly impossible to find a (new) linear power supply retail these days.

I would not use an isolation transformer, although it will likely work. The reason being that you loose your neutral reference so your gear is essentially floating and the RCD in your switchboard will not work (assuming you have one). Isolation transformers are intended for improving safety in some specific situations (for example accidentally drilling into live wires), not for fixing audio earth loops.

The isolation transformer will help prove / help isolate where the earth loop is occurring. It is not intended as a permanent fix.
The fact that the other parts of the system are earthed/ground reference will mean that the PC is not floating a such, it will be actually be earthed
through the earths from the other items, however because the PC no longer has an earth connection from its own mails cable there can no longer be a "loop"

Therefore if there is any hum , it must be some where else .

I clearly don't understand what's occuring because the PC is grounded (3 pin AC Power) and the AMP has 3 pin AC Power, AND the DAC also now have 3 pin power, where can a ground loop occur. Laptop to DAC to AMP works fine, and PC to DAC to OTHER AMP works fine.

Could the PSU on my Crack amp be incorrect? Presumably though voltage checks and resistance checks would have failed?

networkn

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#1066181 15-Jun-2014 20:24

Picture of the Crack AMP PSU Area:

https://www.dropbox.com/s/xeehllzo0j18x0w/20140615_202252.jpg

Aredwood

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#1066232 15-Jun-2014 21:48

The audio ground and the mains ground will be connected together inside the crack amp. And inside your PC. this means you have a loop that starts at the multi box or your houses earth wiring, runs to the case of your PC, through the ground wire in your audio cable to the crack amp. Out the crack amps power cable back to the multi box / house wiring. Using the laptop breaks the loop because Laptop power supplies even if they are 3 pin normally don't carry the ground connection through to the laptops chassis connection.

Try the ground loop isolator from trademe to verify that it is a ground loop problem. If you don't want to use it permanently. The best way (I think) is to modify the crack amp. What you need to do is have separate audio ground and mains ground. Connect the metal panels, Transformer case ect to the earth pin On the crack amp. Insulate the ground of the RCA connections and the headphone connections from the case if not done already. Make sure that no other audio grounds are connected to the case. Get a high current bridge rectifier such as http://jaycar.co.nz/productView.asp?ID=ZR1324&w=bridge+rectifier&form=KEYWORD Connect the +and - terminals together. And the 2 AC terminals together. Then connect 1 side to your audio ground. And the other side to the mains ground. This will block any small circulating currents because the diodes in the bridge rectifier will only start conducting if there is more than 0.5V difference. But if mains power somehow livens the audio ground, The diodes which can handle 70A (2X35A in parallel) will easily conduct it to ground so the circuit breaker / fuse will still cut the power as normal.

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