Do I have a ground problem? (and how the F do I fix this?)

[2dor]

So I was running some sweeps into the FX return of my Ceriatone Chupacabra 50 to gauge how the loads and cabs I have stack against each other & I saw something that has me worried a bit (gave me a sleepless night).

I usually run a sweep into the FX return of the amp (with a load or a cab attached) then do a "Tone Match" in the React:IR tone matching application.

What I saw first in the Chupacabra's plots was a huge spike at 50Hz (our outlets are 230V 50Hz) and then what looks like harmonics at 100, 150, 200 etc.
I measure with the amp at 4 ohms (two 8 ohm loadboxes connected) and at 8 ohm with each loadbox connected separately.

I tried another wall socket on another breaker and the measurements look very similar:

...given that I know Nik from Ceriatone had an extra cap. fitted into my Chupacabra between the cathode and PI that I recently got to trim down some hum he couldn't get rid off when the amp was built, I took out my King Kong 100 and ran the same sweep through its effects loop to gauge the frequency response and see if the same thing happens to that amp.

Much to my surprise, I see the same thing albeit it looks like it's not as bad at 50 HZ in the King Kong as it is in the Chupacabra 50:

I moved the King Kong 100 to the other wall socket and re-ran the sweeps and - yeah - still similar.

Looking at all of this, and those harmonics, how do I go about fixing this stuff? Guess I need some sort of voltage regulator - any suggestions please?
I ran sweeps in the past weeks etc and I did see a slight bump at 50Hz but nothing of this magnitude

 

[SKU]

Remove all DC adapters from the power line that you use for your amp. Preferably remove anything other than the amp and the loadbox and see if it still happens. You also want to make sure that the wall plug you use for your amp is separated and not shared ( parallel line ) with the wall plug where you plug your computer for example ..

 

[2dor]

Remove all DC adapters from the power line that you use for your amp. Preferably remove anything other than the amp and the loadbox and see if it still happens. You also want to make sure that the wall plug you use for your amp is separated and not shared ( parallel line ) with the wall plug where you plug your computer for example ..

Thanks! That was what I was trying to root out by going to another socket with the amp but I'm not 100% convinced those wall sockets aren't joined together somewhere since they're int he same room; gonna grab an extension cord and tap one of the other sockets in the other rooms and see what's what.

 

[headcrash]

Maybe you can give us a more detailed overview of your measuring signal chain.
Often you will get ground loops when connecting two AC powered devices via signal cable. Often the ground loop is worse or even occurs not until the devices are connected to different power outlets, that are far away from each other. Using the same outlet often reduces the risk of building a ground loop.
Also, you might want to check in your power distribution (if you have access to it), which the sockets in your room are tied to one circuit.

Can you actually hear the hum or its harmonics? With a noise level that high above the actual signal level, you should be well able to hear this. So if you cannot hear it, chances are high, that the hum occurs only if your measuring equipment is connected.

 

[James Freeman]

That's normal for tube amps, AC heaters, ripple, 60's grounding scheme, etc.
What's more important is the Signal-To-Noise Ratio of these noises.

Example clip;
JCM800, Tones on 5, Master 1, Gain 7.
First 10 seconds with guitar volume off, then playing.
That's after I elevated the heaters to 80vDC and did the Larry/Psionic grounding scheme.


Line 6 even emulates these power supply noises (Hum, Ripple).
I don't think you can get ruler flat noise floor with tube amps, that's the nature of the beast.

Amp Off:

Amp On:

 

[2dor]

Maybe you can give us a more detailed overview of your measuring signal chain.
Often you will get ground loops when connecting two AC powered devices via signal cable. Often the ground loop is worse or even occurs not until the devices are connected to different power outlets, that are far away from each other. Using the same outlet often reduces the risk of building a ground loop.
Also, you might want to check in your power distribution (if you have access to it), which the sockets in your room are tied to one circuit.

Can you actually hear the hum or its harmonics? With a noise level that high above the actual signal level, you should be well able to hear this. So if you cannot hear it, chances are high, that the hum occurs only if your measuring equipment is connected.

All good points.

The first set of measurements were with the amp plugged into a cable extender where I have my home PC, monitor and work notebook.

I suspected just by the spikes I was seeing at 50Hz and multiples of that this was possibly a ground loop and / or harmonics from the power grid.

When I did the first round of measurements I had this stuff plugged in. The 2nd round of measurements were done with the amps plugged into another wall socket (nothing else plugged into it aside from the amp) but - yeah - in the same room.

The signal chain I used for running my sweeps is as follows:

Motu M4 -> [TRS line out] -> Signal Art -> [GND lift up] -> FX Return of amp -> loadbox (or both 8 ohm loads with the amp's out flipped to 4 ohm for) -> XLR balanced out from the loads into the MOTU interface's inputs.

I see those spikes in the measurements but I don't hear any noticeable noise when I reamp a guitar DI using the same chain but going into the amp's input (not the FX loop). I seem to get pretty good SNR gauging the levels coming from the Suhr Reactive Load XLR which is what's puzzling me about those spikes:

- amp idles at about -61.5 dB with the Master volume at noon (no clipping engaged or anything so pretty damn loud)
- the entire guitar DI is reamped, peaks at -10.7 dB

 

[2dor]

That's normal for tube amps, AC heaters, ripple, 60's grounding scheme, etc.
What's more important is the Signal-To-Noise Ratio of these noises.

Example clip;
JCM800, Tones on 5, Master 1, Gain 7.
First 10 seconds with guitar volume off, then playing.
That's after I elevated the heaters to 80vDC and did the Larry/Psionic grounding scheme.


Line 6 even emulates these power supply noises (Hum, Ripple).
I don't think you can get ruler flat noise floor with tube amps, that's the nature of the beast.

Amp Off:
View attachment 19250

Amp On:
View attachment 19249

Awesome - I've noticed it's not that bad all the time though which leaves me even more scratching my head.
Would a voltage / power conditioner help with these? Guess the only thing I'm worried about is not having an amp blow out lol (I know they have fuses etc.) - paranoia's setting in the older I get lol

 

[James Freeman]

From what I can see in the Chupacabra 50 layout on their website, it has 6vDC heaters for V1 and V2.
If you don't hear buzz, all's good.

Yes, cranking a tube is not very healthy for the transformers, even with a load box I am at the lower range of the Master volume.

 

[2dor]

Looks like I had way too much attenuation on the sweep signal going into the FX Return of the amp so it made those harmonics even more visible.

 

[headcrash]

Looks like I had way too much attenuation on the sweep signal going into the FX Return of the amp so it made those harmonics even more visible.

So you basically had a weak S/N ratio into that FX return? That would explain things a little.
Also you might want to put an isolating transformer between Signal Art an FX return, something like the Palmer Wupper (funny, Palmer gave those new River-series products German river names...). Thsi would definately brek up the physical connection there.

Btw. what is Signal Art?

With guitar volume off, I don't experience any noteworthy hum in my amps (aurally!). So James' measurement seems reasonable to me.

 

[2dor]

So you basically had a weak S/N ratio into that FX return? That would explain things a little.
Also you might want to put an isolating transformer between Signal Art an FX return, something like the Palmer Wupper (funny, Palmer gave those new River-series products German river names...). Thsi would definately brek up the physical connection there.

Btw. what is Signal Art?

With guitar volume off, I don't experience any noteworthy hum in my amps (aurally!). So James' measurement seems reasonable to me.

Signal Art is a reamp box - it has an iso transformer in it.

I re-ran tests / sweeps last night and everything looks great. Just a "dummy user" case here.

 

[headcrash]

Ok !
...oh and while reading "transformer"....of course isolating transformers can pick up hum, of course. So it depends on the transformer box itself, abut also where and in which orientation it is placed in relation to a potential noise field.