Is there an “acceptable” noise floor for a Single Ended Tube Amp?

James Knox

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After applying careful attention to lead dress, grounding, component placement, etc., if one were to hear the faint whisper of something coming from the speaker of a new build, at what point would one start tearing into the build? At what level does one walk away and say, “turn it up and Rock and Roll!”

I’ve read and heard opinions all the way from, “all single ended tube amps have SOME noise”, to “if a guy can’t build a DEAD SILENT Single Ended Tube Amp, he doesn’t know what he is doing”, to “if you can’t hear it while you are playing, it is fine”.

I realized recently I have become paranoid of noise :eek:

If I put my ear 6-12” in front of the speaker and hear an almost imperceptible hum, I feel sad :(

So, what is the Shock Bro Line of what is acceptable and what is not?
 

corliss1

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I think this will be hard to describe and is dependent on each person.

There's "noise" and "hum" which are very different things. Hum to me, that's very very low level, and doesn't increase with volume, is acceptable. Noise is something created by lots of gain or resistors/tubes/parts that are just noisy by default. Both can be reduced, but there's always gonna be some level of hum in a single-ended amp, simply because the output stage doesn't have the hum rejection that push pull does.

I'm pretty obsessive over noise and I'll trace through things and try and isolate noisy parts as best I can. I've had some where I thought it was noisier than I wanted, and the customer said "man, this thing is way more quiet than before" just it's just very subjective.

Examples? A Deluxe Reverb should be pretty darn quiet. No noise, no hiss. A Peavey 6550 is gonna have noise because of all the gain stages no matter what you do. So.....depends.
 

boxocrap

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After applying careful attention to lead dress, grounding, component placement, etc., if one were to hear the faint whisper of something coming from the speaker of a new build, at what point would one start tearing into the build? At what level does one walk away and say, “turn it up and Rock and Roll!”

I’ve read and heard opinions all the way from, “all single ended tube amps have SOME noise”, to “if a guy can’t build a DEAD SILENT Single Ended Tube Amp, he doesn’t know what he is doing”, to “if you can’t hear it while you are playing, it is fine”.

I realized recently I have become paranoid of noise :eek:

If I put my ear 6-12” in front of the speaker and hear an almost imperceptible hum, I feel sad :(

So, what is the Shock Bro Line of what is acceptable and what is not?
it kinda like getting a little over sensitive with a guitar and hearing that 64th of a tone out of tune..place your head between two powerful speakers and turn the volume way up on a heavy song...say some led zep...i doubt you will be quite so sensitive to a little slight hum from your amp..or check the cables and ground..could be that
 

tubedude

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Most singleended amps need more filtration to achieve the hum level expected listening to a push-pull amp of roughly the same power consumption.
If you are 12" from a grill cloth and imagine noise you have an outstandingly well filtered SE amp.
And what Corliss1 said.
 

James Knox

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There's "noise" and "hum" which are very different things. Hum to me, that's very very low level, and doesn't increase with volume, is acceptable.

Thank you! Yes, I’m referring to extremely low level hum with no guitar plugged in and no change by turning vol, tone, NFB switches of pot, etc.

I'm pretty obsessive over noise and I'll trace through things and try and isolate noisy parts as best I can.

I feel ya Bro. I bought an Oscilloscope with a built in Freq Generator for tracing and isolating noise, but I haven’t learned to use it yet. Are you using a Scope?
 

James Knox

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If you are 12" from a grill cloth and imagine noise you have an outstandingly well filtered SE amp.

I’m using 40/20/8 filters with a Full Wave Rectifier. I *think what I’m hearing is real, but very faint. I’m trying to come up with a metric that I’m comfortable with “walking away”.

Is DEAD SILENT actually possible?
 

corliss1

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No, a scope likely isn't going to help with such low level issues like this. If the issue was obvious enough to be a problem, then you could be in scope land.
 

echuta13

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Is DEAD SILENT actually possible?

If it was... would you chase that? I would chase it to a degree perhaps, but we all have to work within certain constraints.
I use an extra power node in my SE amps for example. I use metal film resistors in the signal chain. I add DC (via a 6.3v center tap) to the filaments.
Good component layout & lead dress are a big part in killing noise before it's an issue. Not always practical, or realistic, but something to shoot for!
 

Maguchi

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After applying careful attention to lead dress, grounding, component placement, etc., if one were to hear the faint whisper of something coming from the speaker of a new build, at what point would one start tearing into the build? At what level does one walk away and say, “turn it up and Rock and Roll!”

I’ve read and heard opinions all the way from, “all single ended tube amps have SOME noise”, to “if a guy can’t build a DEAD SILENT Single Ended Tube Amp, he doesn’t know what he is doing”, to “if you can’t hear it while you are playing, it is fine”.

I realized recently I have become paranoid of noise :eek:

If I put my ear 6-12” in front of the speaker and hear an almost imperceptible hum, I feel sad :(

So, what is the Shock Bro Line of what is acceptable and what is not?
A "little" noise is typical on single ended tube amps. If it is more than a "little", there may be something wrong with that specific amp and a tech should be able to fix that. For live performance the amount of noise on a well functioning single ended amp is not enough that it is perceptible by the audience. For recording, you can "ride the fader" for silent passages either during tracking or mixdown. If you try and alter an amp too much to get rid of noise, you may alter what makes that amp sound so good in the first place. Boogie on!
 

2L man

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I have tried to reduce hum improving filtering installing a choke and more RC stages. Quietestso far is where I also did install resistors to negative (ground current return) leg before B+1 filter. But there I have five RCR stages so I can't say does the resistors on return leg effect or the capacitance what five capacitors bring.

To me it looks clear that when cost is considered adding filters has much better effect than adding a Choke when solid state rectifier is used. Naturally some circuits the tube rectifier require a Choke.

I have read somewhere that the Choke can radiate electromagnetic field which then OT can absorb?

I have seen circuits where another Choke being used also on negative ground return so that I could test because I already have few more Chokes.

I think nowadays building Mosfet circuit is best and cheapest method to improve PS output regulation. Also adding soft start to same circuit require a resistor and capacitor. If bringing Mosfet to tube amps interest for start searching "Mosfet follies" is good page.
 

James Knox

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You have built several SE amps. What is the quietest one you have built?

Good question! I posted this question because I had some trouble on a recent build (but you knew that, lol)and after fixing the “noise” problem I reported that the amp was “dead silent”. While getting the amp ready to ship to its new owner, I usually perform a final test with the brand new tubes installed, just to make sure everything is tip top. I record voltages, listen for hum, crackle or noise of any kind, etc. In doing so, I become aware of a very faint Hum when I get close to the speaker. I turn the amp off and on, just to make sure. Yep, something there. Oh great, now I have LIED to my Brothers... OK, lesson learned. I guess I’m repenting by asking if DEAD SILENT is really possible?

Sorry LLC, for the long answer. The short answer to your question would be “super quiet”. In fact, I’m gonna go back and correct that earlier post...
 

James Knox

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If it was... would you chase that? I would chase it to a degree perhaps, but we all have to work within certain constraints.
I use an extra power node in my SE amps for example. I use metal film resistors in the signal chain. I add DC (via a 6.3v center tap) to the filaments.
Good component layout & lead dress are a big part in killing noise before it's an issue. Not always practical, or realistic, but something to shoot for!

I guess I have been chasing it, but now I’m re-evaluating! I just heard about using DC for the filaments - I need to look into that.
 

James Knox

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Quietestso far is where I also did install resistors to negative (ground current return) leg before B+1 filter.

Is that the “balanced filter” that Merlin talks about? I read about that but didn’t quite understand how to implement it. Does it work by using a 5 watt resistor on either side of the first Filter cap rather than a 10 watt dropping resistor on the B+? Or, do you use two 10 watt resistors, one on either side of the Cap?

To me it looks clear that when cost is considered adding filters has much better effect than adding a Choke when solid state rectifier is used.

Yes, agreed! How do you determine how high to go? I am currently building with 40uf with a Full wave rectifier.

If bringing Mosfet to tube amps interest for start searching "Mosfet follies"

Wow! Just read that.... man, I love RG Keen. Haha, now ANOTHER rabbit hole to go down. Side note: I had dinner with my Boss at the time with RG at a NAMM show. I had no idea who he was at the time...
 




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