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Tube amps have a noise floor ranging from nearly silent to noisy. I have a dB meter and decided to do a bit of an experiment.
All measurements are taken at 2 feet from the amp’s speaker’s center, guitar is plugged in, and volume knob of amp at ~11 o’clock. The number shown is what I am calling the Net Noise Floor, and the room in which measurements are taken is a practice space that is fairly quiet (much quieter than a gigging situation).
Net Noise Floor = Amp Noise - Ambient Room Noise
Net Noise Floor Measurements:
5 watt hand-wired champ clone - 4dB
12 watt Princeton - 1.5 dB
35 watt boutique vibrolux - 6.5 dB
The Princeton is super quiet, and the champ has a pleasing tube hum. I find that the vibrolux at 6.5 dB over ambient room noise is just too noisy for anything but mid to large room gigging, and is somewhat distracting in quiet environments.
So, just curious what other tube users experience, find acceptable, and think is just too much noise.
Cheers!
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01-05-2022 05:56 PM
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I have this 1949 Gibson GA-50 amp ... it has a good amount of white noise, of which - on this dear amp, does not disturb me from anything.
it is all quiet at home where I play, in combination with the 1947 ES-125 and its non-adjustable early P90 pick-up,
my gentle music sounds like a US car radio from the 1940's ... while driving around carefully, in the wet, meanwhile,
the white noise from the amp emulates the rain sounds perfectly.
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This interesting, I’ve never measured the white noise with a db meter.
im a tech, and the noise can be an issue for sure but I’ve just gone by the ‘annoying or not’ rule.
i’d be interested to find out what db level is most commonly the threshold for annoyance.
and one easy way to sort of equalize your observations would be to turn the volume off and see. You won’t hear the preamp noise but the noise of the rest of the amp at idle.
also swapping tubes can have a profound effect on noise levels. So can the speaker efficiency and bandwidth.
just some thoughts.
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Great imagery. Tube amps all have character
Originally Posted by Filmosound 621
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I’ll take some additional measurements and let you know the dB at idle.
I have swapped the first tube, and cleaned all relevant spots inside. The white noise is still there, but doesn’t get into the signal. It is also quieter than a good running original Vibroluxe.
The white noise is only apparent in a solo practice environment — so I would chalk it up to character like Filmosound describes.
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If it’s hiss, can be the condition or age of your preamp gain tubes. It could also possibly be a valve rectifier. Does hiss level change as amp heats up?
hum is more often than not power supply hum. Noise can be as simple as shielding and component placement. Interesting that the most commonly available amp in your collection was the quietest. Do you know if it is a pcb construction?
I find buzz intolerable, other radio stations amusing, and some background hiss part of the character. I seem to find the hiss is only noticeable when there is no music or talking occurring and ambient noise is almost nothing.
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The Princeton Reverb II does not make any noise that I can discern. Apart from the hand-wired goodness, its 22 Watt signal going into a 220 Watt speaker probably helps.
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Are all Princeton’s still hand wired? Wow I had no idea. I rarely see them on the shelves down here. In fact I can’t recall ever seeing one on the shelf to look at.
is the wattage to speaker pairing a contributing factor to the audible noise based on the speaker capacity being over spec’d?
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The Princeton Reverb II was the one of the II series amps introduced in the 1980s. These were the last hand-wired Fender amps, besides some limited runs.
I assume wattage and speaker matter, but I know nothing of these things. I cannot think of another reason for the eerie silence of my amp.
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Interesting - your method is valid if the room noise doesn't contain any power line hum. You need to tell us what is the absolute level of the room noise and also do a little further calculation on the results. Normally, the meter would have some sort of frequency weighting such as A weighting which attenuates the low frequency noise that we can't hear so well at low levels. Originally Posted by Campbell_jazz
The amp noise power and the room noise power add so that if, for example, the amp noise is equal to the room noise the combined level will be twice or +3dB. I have plotted a little graph that shows the actual amp noise relative to room noise as the combined level varies.
This makes the Champ 1.8dB above room noise, the Princeton 3.8 dB below room noise and the Vibrolux 5.4 dB above.
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I absolutely DETEST noise (too many years recording, I'm allergic to it). It's a dealbreaker on a clean amp.
My 2 useful cents, if you have/build a single ended amp, use a choke. It will knock that hum down by a lot.
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IME, noticeable noise at idle in a tube amp is a sign of something being broken. I've had several tube amps, all of which have been noisy at some point, and then quiet upon being serviced. I don't service amps myself so can't comment much on the specifics, but my typical experience is I take it to a tech, explain/demonstrate the noise, and a week later I get an itemized bill that includes troubleshooting, replacement of a lot of components and stuff like resoldering connections.
l (and have) cleaned pots and replaced tubes myself, but that rarely does the trick. Caps and resistors are usually the culprits. I'll add that IME with vintage amps, the smaller cheaper single-ended ones that give great low-volume warmth and crunch also tend to be the most noise-prone. So reading that your Vibrolux is the noisiest of the bunch reinforces in my mind the idea that it probably needs some sorting out.
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Originally Posted by John A.
It's helpful to know that single ended amps (one power tube) typically have hum, but if you use a choke in the power supply, hum is reduced a great deal.
In 2+ power tube amps, hum is definitely a bad sign and you should see a tech before damage occurs.
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"Eerie silence" in any tube amp is a very good thing! Originally Posted by Litterick
Also, note that all of the amps named in this thread have tube rectifiers. The PRII has a solid state rectifier, a dead silent, long lasting component.
As long as your PRII is well maintained it should run very quietly. Over the years mine developed a hiss, but that was simply a dying pre-amp tube.
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Originally Posted by Filmosound 621
I have this 1949 Gibson GA-50 amp ... it has a good amount of white noise, of which - on this dear amp, does not disturb me from anything.
it is all quiet at home where I play, in combination with the 1947 ES-125 and its non-adjustable early P90 pick-up,
my gentle music sounds like a US car radio from the 1940's ... while driving around carefully, in the wet, meanwhile,
the white noise from the amp emulates the rain sounds perfectly.
Agreed, a very romantic type of post that made me wish all of my kit wasn't so new. Would work well with a bottle of Chateau Lafite Rothschild Originally Posted by Campbell_jazz
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Just because I love to see people get into working on and building their own amps, if anyone would like to try to reduce some noise in their amp here’s a few helpful/simple tips.
But first be sure you know how to drain the voltage and keep it drained while you’re in there.
Generally at about the 5 year point, all the metal contacts will need so be cleaned. Jacks, tube sockets, pots. Even if you don’t think it needs it and there isn’t any signs of crackling when you wiggle them, you’ll be amazed at how much better your amp will sound. And you might also kill some noise.
along with this the tube socket pins need to be made tight again (retentioned). Different tubes can have slightly different pin sizes and some will stretch out your socket spins a touch making things a little noisy if you then use smaller pinned tubes. So this is recommended as pat of your 5 or 10 year servicing.
resistors- carbon comp resistors are very noisy and in old amps just part of the deal for the old sound. But as they age and/or absorb moisture they generate noise. Plate resistors especially. But also can be resistors in series with the tube grids.
capacitors- if coupling capacitors are leaky they will leak dc juice to the tube grids. This can thrown the bias way off and depending on the design, often adds significantly to noise.
it’ll take a voltage meter to check this or the caps can just be changed on an old amp if you’re not concerned about preserving as many original parts as possible.
after these things, it can get slightly more complicated as you move into lead dress adjustments, reducing coupling between components, and power supply checks, adjustments.
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One way to get around the noise generated by a tube amp is to switch to an amp with a fan.
The fan makes so much noise that the hiss is effectively drowned out.
I'm talking about my old Boogie Mark III.
Of course, you can probably retrofit any tube amp with an inexpensive fan.
I think I'm joking.
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As a little more info, I measured the ambient dB at 39dB. Then the vibrolux with volume and reverb at 0, I measured at 49-50 dB.
I would describe the noise as light static or wind noise.
And for those who advise I get the amp checked out, I did. From the tech:
”The background hiss (what I describe as wind noise) is mostly tube shot noise, and comes from the preamp recovery stage. This is why most of the controls don’t change the sound (even with the input volume at minimum), because that stage is fixed gain and always enabled, even if the reverb is turned all the way down. This is also pretty typical of other AB763 Fender amps, and when I put yours right next to an original AB763 from a 1966 Deluxe yours is quieter.”
So then the “noise” is typical background noise from an amp of this vintage? Is that what other delux, twin, and vibrolux users experience? And if so, like it or move on?
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I added a fan to my Vibrolux Reverb. I had an extra fan from an old computer enclosure, and I screwed it to the crosspiece in the back. Being a standard 12VDC, I used an older spare 12V wall wart, clipped the end connector, and soldered the wires to the fan. I plug it into the spare AC outlet on the back. It works very well, not very loud, and it keeps the chassis cool. Without the fan, the chassis exterior is uncomfortable to the touch, with it the chassis is cool to the touch, below body temp. I like to think that keeping it cool helps extend component life, especially tubes.
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Originally Posted by Gitfiddler
"Eerie silence" in any tube amp is a very good thing!
Also, note that all of the amps named in this thread have tube rectifiers. The PRII has a solid state rectifier, a dead silent, long lasting component.
As long as your PRII is well maintained it should run very quietly. Over the years mine developed a hiss, but that was simply a dying pre-amp tube.
Of course, the rectifier; I should have thought of that.
I play eerie music, so it is satisfying to have the right kind of silence.
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Originally Posted by Litterick
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I have an amp I built based on the deluxe reverb on my bench now, where I'm trying to reduce the hiss (sounds much like white noise).
(I've considered a large variety of causes and solutions, like swapping tubes, leaky caps, shielding, inspected solder joints, wire dressing, use metal film resistors etc.)
I had both hiss with the volume knob at zero as well as hiss that increases with the volume knob (and gets shaped by the tone stack).
I managed to get the hiss, with the volume knob at zero, down to being inaudible by scaling down the resistors I've circled red by a factor of ~5.
(I could also scale the caps up by a factor ~5, to follow the theory of component scaling correctly, but I do think the amp sounds really great with the caps unchanged, but I will try that as well too to see what I like best).
The hiss, which changes with the volume knob, got noticeably lower by changing the grid stopper to the first tridoe (V2a) to 10k.
(technically you can add an appropriately sized cap to ground to get the get same cut off (ultrasonic) frequency as you would otherwise get with the miller capacitance and the grid stopper, but I didn't bother with it, it is not that much of a difference).
Valves operate with low currents and high voltages. Valve stages have high input impedances which can make them more prone to noise than transistors which operate on lower voltages and higher currents (in general).
The resistor values that I scaled are part of a voltage divider, which reduce the voltage (signal level) that goes into the third triode (it also mixes the dry signal and the reverb signal), so I personally don't see any disadvantage of getting more or less the same signal level with different component values, which are less prone to noise. According to my ears, this is a really great mod.
In general I think using a smaller grid leak resistor, to reduce the input impedance to the gain stage, can be an option worth considering to reduce hiss. In somecases you can choose to sacrifice some gain to achieve it if you want to.
Make sure to understand the circuit and scale other components accordingly as well. For instance the grid leak and the coupling cap from the previous stage form a low pass fliter and you need to scale the coupling cap (in the inverse proportion) too to get the same frequency response.
In order to test if changing a grid leak will have any impact, on some suspect common cathode stage*, you can disconnect every thing from the grid apart from the grid leak and grid stopper (if there is one), turn the amp on and listen if you hear hiss. Then you can ground the grid to listen for if the hiss gets reduced (you can ground both sides of the grid stopper too). You can also try to connect lower resistor values in paralell with the grid leak, to listen to the amount of reduciton.
(don't try this without knowing the approprate safety measures of working on valve amps)
(* before disconnecting components you can pull preamp tubes one at the time to listen to which have impact on the hiss level )
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So has anyone measured the idle “noise” that their tube amp makes?
My baseline room noise is 38-39.5 dB.
My quietest amp adds about 1-2 dB of idle hum.
my loudest amp adds about 11-13 dB wind type noise.
Just curious what others are measuring?
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so you are comparing the measured noise of different amps when their volume knobs point to the same direction? Originally Posted by Campbell_jazz
(I assume the plugged in guitar has its volume pot on 0)
That does indeed sound pseudoscientific
I would guess the signal output level of the different amps differ significantly at this setting too?
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I am not sure how to normalize this, so I did measurements as if I were playing — guitar and amp at the usual settings, and then measuring noise level above ambient noise. Originally Posted by orri
The measurements hold (mostly) if I unplug the guitar and turn volume to zero.
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