Fix Tube Amp Hum, Buzz and Hiss

Beyond pouring sweet, sweet honey into your ears, even modern tube amps can make some unwanted noises, hums and buzzes. First thing to remember though is that this is often a problem of system matching and not the amp by itself. The good news though is that once you've solved the issue the resultant sound is in no way compromised, so you can keep your system.

So why a system issue? Usually it’s that the amp (often a tube amp as they're circuitry is kept as simple as possible (usually)) is highlighting a weak point in your system. Don’t despair though, more often than not the solution is easy - but it can be a process to identify where the fault lies. 

1. Ensure Good System Hygiene

Before troubleshooting it’s a good idea to get the system in the best state possible and start from there. That way 1) you’ve set yourself up for the best sound possible out of your system, and 2) troubleshooting, if still needed, will have to deal with less ambiguity. So no matter what’s system you have here’s how to give it the best chance for least hum, lowest line noise and highest signal.

Must Have

• Create an electrical island. Use one power board dedicated to your system. Have all items of the system on this single board while also removing anything unrelated off the board. Work backwards, so amp, pre, DAC, any reclocker or streamer. These are definitely on the board.
• Music server/laptop and network switches are incredibly noisy. These should ideally be off the board but:
  • If you have a network endpoint or streamer feeding your DAC then have the server and switch off the single board and just a single ethernet cable coming in (or wifi signal). This is still not ideal, see “Really Nice to Have” below.
  • If your laptop or music server is feeding your DAC directly then it should be on the same power board. Wifi is good at this point for a laptop but all the peripherals (monitor, disk drives, etc) are adding a lot of noise.
• Get a decent power board.
  • Make sure all power cables are 3-prong cables where possible. The one between the power board and the wall socket too.
  • On power boards and power conditioners, the common thought is that filtering the power of unwanted noise is the best solution. This can also reduce dynamics in your music though. Nordost’s ethos is to not hammer the power signal into submission but to work with it to get the best solution with what’s coming out of the wall.
• Get decent power cables. People who have never A/B’d power cables say “why bother as it’s the last meter in 4,000m from the power station”. This is false thinking as an electrical circuit draws power, it isn’t pushed into the system. So in reality the power cable between wall socket and component is the FIRST meter.
• Get decent interconnect cables. Many interconnects have poor grounding connections and/or shielding. They can attract massive amounts of RF noise.

Really Nice to Have

• A huge amount of noise can come into a system over the network ethernet cables. My preference is always for direct network connection so there’s the least chance of network bandwidth issues (especially true if sending DSD or upsampled music over your network). SO how to solve? Fibre Optic cabling is the solution! Full bandwidth and over long lengths with no RF noise creeping into the cable, and if the converters are designed properly then the noise already in the network is reduced or eliminated. This is where Sonore steps up to the plate. They specialise in just this. With ethernet to fibre optic converters they allow you to add a fibre optic moat into any system. Or for best results they have dedicated fibre optic endpoints that feed directly into your DAC (and are Roon and Spotify Connect enabled). Yes wi-fi will create a moat too but wi-fi has bandwidth and endpoint issues as well as big potential to introduce RF noise into the system.
• Audiophile grade network switches are a good addition to your system and can be put on the single system power board if convenient.
• On switch mode power supplies (SMPSs), many people swear by having no SMPS’s on their power board and removing all these to other power boards or replacing with audio grade liner power supplies.

The Cherry on Top

• Have an electrician install a dedicated power line from your switch box.

2. Break-In Components

This is needed on all components: digital, analogue, speakers and headphones, cables and tubes. Play music through the system/component for 48hrs at least before making any judgement call on quality or A/B’ing it. Components can sound shrill, fatiguing, undynamic and lifeless until broken in.

One special case is tubes. If your new tubes or tube amp has a high pitched, variable whining noise then the tubes may just need 20mins use in order to settle. 

3. Troubleshoot Any Zero Volume Hum

So you’ve just spent decent dollars on an endgame tube amp. You plug it in and turn it on but immediately there’s a strong hum/buzz even when the volume is set to zero. WTF? Don’t worry, seems there’s insufficient grounding of the system, follow these steps: 

4. Optimise Variable Volume Hum/Hiss

While the hum from point 3 is a fault to be fixed, a lower level hum/hiss that varies with the volume of the amp is more a part of the amp that can’t be removed, but it can be managed. This form of hum is either inherent to the amp (from the transformers) or from the tubes. Tube amps often have a higher noise floor than solid state amps but this is part of the more organic sound they produce also so you take the good with the bad. One reason to spend more on a tube amp though is that generally the more you spend, the blacker the background. This is very true of the Feliks Euforia, ampsandsound Bigger ben and Ovation and the Auris Nirvana and Headonia.  

This form of hum/hiss noise is much more of an issue for headphone rigs than speaker-based ones as the same intimacy headphones bring also carries with it the noise floor. Also it must be noted than noise floor affects some people more than others – if you can hear the inherent hum but it doesn’t affect your listening enjoyment then don’t stress and carry on. But if it doesn’t annoy or distract you then here are three things at play and what you can do to manage each.

• Impedance Matching. Make sure the amps impedance or impedance settings are matched to your headphones. For an amp with multiple impedance options, the high the setting of the output impedance, the more dynamic the music but also the higher the noise floor. Also some headphones (like Focal Utopia) are super sensitive so use adjust the amps output impedance as needed for best mix of dynamics and noise floor. It’s for this reason that generally tube amps are a bad match for IEMs which are very sensitive.
• Tube Noise Floor. Each type of tube has it’s own noise floor characteristics. On the Bigger Ben for example you can use either KT88 or EL34 tubes. KT88s are more dynamic and powerful but also have a higher noise floor. So if your cans are easy to drive then you may be needlessly using a tube that has higher noise. Whereas EL34s have less power but also a lower noise floor. So try each with your headphone to see what matches best. That said the tone of each type of tube is also different and likely that is the defining character you are chasing.
• Hum/Hiss Tied to Volume Level. Generally, the low level hum and hiss of a tube amp will increase as you increase the volume. This is often not an issue as the signal volume also increases and so the noise is never heard. If it is an issue though maybe your DAC or preamp is not outputting enough power and so you’re having to ride your amps volume pot pretty high. Try boosting the DAC/Pre output by going to line level output or increasing/maxing it’s volume pot and then dropping the volume on the amp. Generally higher source volume and lower amp volume is the way to go for best results all around.
  • A second part of this volume based variability to the hum/hiss is that some amps have a volume setting at which the hum is actually the lowest (e.g. 40% of max volume might be the lowest hum level. If this is the case then leaving the amps volume at that level permanently and adjusting listening volume with the DAC or preamp’s volume pot is the way to go.

So that’s about it. It’s not all rocket science but the nature of single box systems is such that a methodical approach and maybe some small purchases for grounding cables or alternate brand interconnects is all that’s needed.

Any questions though send an email and we’ll see how we can assist.

Cheers

Hugo