Mesa D800 Noise

[cgg199]

My Mesa D800 has recently started making a lot of noise when using it and after tying to troubleshoot, I'm in need of some advice.

 

With nothing plugged into the input the amp is fine. From there I've plugged in a few different basses to see how I reacted and things went as follows:

 

Dual humbucker bass - no noise when using humbuckers, lots of buzzing when coil split, more than would be expected of single coils.

 

Passive Jazz bass V with Nordstrand Hum cancelling pickups - no noise when pickups blended at 50/50, loud buzzing when blended anywhere other than dead centre.

 

Shuker PJ5 - Some noise when P pickup isolated, lots of buzzing when introducing any bridge pickup at all. Aguilar hum cancelling bridge pickup, and is the same in both active and passive settings.

 

The same noise has happened on a few gigs now and at home so I've ruled the power source. It seems what I'd expect of 60hz hum, but no idea why it's happening on my basses with him cancelling pickups. It's also a new thing that hasn't been present in the past. I've attached a shirt video of the sound.

 

Any ideas as to what could be causing it, or anything I can do to reduce the noise as currently it's not workable on a gig? Any help is much appreciated!

 

 

[Merton]

Paging @agedhorse

[agedhorse]

If the amp is quiet with nothing plugged into the input, this means that the interference signal is entering from the bass or wiring.

 

Now, when it's quiet using humbuckers but noisy using single coil (or split coil), this confirms that the noise is environmental and is entering the bass through the pickups. In humbucking mode, this cancels common mode environmental noise, which is working as it should. The same thing applies to the Nordstrand pickups, which allow you to sweep between single coil and hum bucking, and the noise nulls out when fully humbucking.  Also, the noise profile is mostly 50 (or 60Hz) with very little second or third harmonics which also indicates that the noise is radiated from the power source and is unrelated to the amp's power supply. I bet the noise changes with your position in the room, or just turning it around a bit?

 

Things that cause this include an amp with a noisy line frequency (lead sled) transformer that has a loose radiated electro-magentic field, large motors, some lighting, and some old school fans. There is a slight possibility that the noise is due to circulating currents in your power ground/earthing system, but unlikely since the amp would usually have some noise with nothing plugged into it.

[cgg199]

Thanks very much go the reply!

 

Just to clarify a few more things, the Nordstrand and Aguilar jazz bass pickups are all dual coil so when a single pickup is selected shouldn't they also be acting as humbuckers, therefore not creating so much noise? 

 

The noise does change slightly when moving the basses around the room but not massively.

 

The work around on gigs has been to take a DI straight from my pedalboard as this has been a much cleaner signal. Once the amp is introduced the buzzing is present. If the issue was the bass wouldn't the noise be similar coming from my pedalboard?

 

I've had a further play around and going direct through a powered PA speaker and a Fender Rumble 15 there is no buzzing, and everything is working as expected. Also I do a lot of practice through an interface and through headphones and again the buzzing isn't present. Obviously things will never be silent but with the Mesa things are currently unusable. As mentioned above the issue is new as well and hasn't been a problem ever before. I've had the amp maybe 6 or 7 years now and have gigged through all of that time. 

 

 

 

 

[agedhorse]

Is the amp quiet without the pedalboard, bass straight into the amp?

 

Where are you located? What is your power source?

 

there is also a possibility that there is a ground loop between the amp and pedalboard, or even a single pedal on the board. 

[Stub Mandrel]

I have found that some LED lighting can introduce various unexpected hum behaviours.

[Steve1250]

My D800 was having a similar issue some time ago, I found a screw missing from the bottom of the casing, replacing that cured the problem, might be worth a quick look 

[agedhorse]

3 hours ago, Stub Mandrel said:

I have found that some LED lighting can introduce various unexpected hum behaviours.

 

2 hours ago, Steve1250 said:

My D800 was having a similar issue some time ago, I found a screw missing from the bottom of the casing, replacing that cured the problem, might be worth a quick look 

Both of these are possibilities, not terribly common but possible.