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  • New tube amp noise...

    OK I just finished reading a comprehensive thread here on tube amp hum and there were tons of ideas/suggestions to fix it.

    So I will just cut right to the chase.

    I just spent Mega bucks on a custom built boutique amp.
    Received it a couple of days ago.
    Numero uno of my build requests was to make it as quiet as possible (no hums/hisses).

    While the overall sound of the amp is creamy smooth, as I wanted, it does have a hum and hiss that is
    noticeable in a quiet room, where I practice 99% of the time.

    I'm not sure what to do really?

    So I started comparing it with my two Fender amps (Princeton II and Vibroverb).
    I split both amps into head and speaker cab a couple of years ago.

    Both are much quieter.

    My new amp is also split into amp head and speaker cab.

    Where do you suggest I go from here?














    Last edited by Jazzer2020; 08-13-2017, 12:51 PM. Reason: Clarification on splitting into amp head/cab

  • #2
    I'll get some stupid questions out of the way first;

    Are you plugging all 3 amps into the same power source?


    Are you using the same guitar in all the amps?

    Have you tried switching guitar cables?

    As far as your "noisy" Princeton II Have you tried switching the speaker cable out from your "quiet" vibroverb?

    Comment


    • #3
      Originally posted by thatsbunk View Post
      I'll get some stupid questions out of the way first;

      Are you plugging all 3 amps into the same power source?


      Are you using the same guitar in all the amps?

      Have you tried switching guitar cables?

      As far as your "noisy" Princeton II Have you tried switching the speaker cable out from your "quiet" vibroverb?
      Thanks for helping out!
      Yes all 3 in the same power source, one at a time of course.

      Same guitar, yes. I've tried many guitars now in comparison but the hum is always there.

      This is not a cable issue. Strictly amp noise.
      The noise is there with no cables plugged in.

      Yes I did try switching speaker cables, but no difference.

      I've tried several different power outlets too. No change.

      Just now I discovered something interesting.
      I played with all the controls for the first time.

      The odd man out was the reverb knob.

      The hum is a 'B note' and can be broken down into two octaves.
      I noticed when I turn the reverb up from the 9 o'clock position it gets progressively louder in the
      lower B octave.

      Louder and louder until up to full at 5 o'clock position.

      I find this interesting, but having said that, even at 9 o'clock, where I had kept it until just now,
      the hum is annoying (in a quiet room). The hum just gets much much worse the more reverb is added.


      One more note that may or may not help.
      When the amp volume knob is increased, only the hiss increases, not any of the humming.






      Last edited by Jazzer2020; 04-23-2017, 10:30 PM. Reason: Clarity

      Comment


      • #4
        Does the hum go away when the reverb is at zero? Maybe a bad reverb tube? If amp is brand new it should be under warranty...

        Fwiw I have a PRRI & it is dead quiet (although when it's cranked there is a little hiss- but I would think that the case with most any amp).
        Last edited by thatsbunk; 04-24-2017, 05:39 AM.

        Comment


        • #5
          Since this is a new amp, the problem may be power tubes. As new tubes are burned in the bias cab drift a little and have increased hum. The kind of hum they produce is a low level background hum that doesn't change in volume. When tubes are matched and the bias perfectly balanced the hum is canceled. Tubes often need a couple of hundred hours to burn in and stop drifting in value. The brand and quality of tube plays an important role too. Some tubes can be dead on and drift little from the start and some can be wickedly bad drifting all the time.

          The cause of the low level hum can come from a number reasons. Number one is the filament voltages are likely AC. If the filament wiring isn't routed tightly against the chassis and that chassis is made of a low mu metal that doesn't shield well you can have higher levels of emf floating around in the chassis being amplified. Given this is a custom build you can have many other factors involving wire routing and component placement. If the power tubes are balanced this doesn't usually matter because the hum is canceled out. The problem could be insufficient DC filtering or over gained tubes too but I have no way of knowing at this point.

          The reverb hum too is most likely the result of filament voltage. It can also be the shielded wire between the tank and circuit aren't the best wiring too. Filament hum can be reduced by using a spiral filament heater. The Sovtek LPS is supposed to be better at this. https://www.tubedepot.com/products/s...mp-vacuum-tube. Problem is they aren't the best choice for combos because they can become microphonic from the vibration. The reverb circuit adds extra gain stages and the tank contains elements at the ends of the springs that work similar to a speaker to make the string vibrate and a microphones to receive the signal. Any added hum from the tank circuit will be added to the signal chain. Shielding the bottom of the tank may be a way of reducing hum.

          All of these need to be tested by an expert and minimized. The problem may not be one single item but a combination of many smaller items.

          Hiss is common with all tube amps. Its caused by two main items. One can be carbon resistors which reduce electron flow. Electrons collide with the carbon inside which reduces current but it also adds noise to the signal. The other is the tubes themselves. A beam of electrons is created as the filaments heat the cathode. They pass through a grid trying to get to the anode. This grid is a physical screen like a screen door. The electrons either pass through the holes in a straight line or hit the wire mesh and ricochet around hitting other electrons.

          These electrons bouncing around cause hiss and there isn't a dam thing you can do about it besides minimize and mask the effect. Comparing one amp to another is pretty useless unless you compare the circuitry. Guitar amps in general have high gain staging so noise is going to be in your face. The difference in his between one amp and another may be the amount of gain staging and total wattage, its may be the tone stack that EQ's a certain amount of the hiss away. It can be the speaker itself. many speakers roll the treble off at a lower frequency then others and thereby masks the higher frequency hiss. The speaker SPL level may be high which can increase the noise floor making both the his and hum more audible.
          The circuit type can be a huge factor, Class A vs AB for example. The type of power tubes used and how hot they're biased play a huge role.

          What it all boils down to is, a trade off. If you want hot tube tone you're going to have to deal with a certain amount of hiss. You want a loud sound from a lower wattage amp a high SPL speaker with a wider frequency response will make that hiss more apparent. Vintage speakers had lower SPL levels which keep the noise floor low and they're limited frequency response rolled off the top end masking much of the his an amp normally causes.
          You can do certain things when building like using metallic resistors which have lower noise levels, using tubes that are quiet, and biasing the tubes to a lower level but you will loose gain and tone when you crank the amp up.

          For the hum I recommend running the amp for a month or two. If the hum persists, have the power tubes rebiased or replaced. If you can check the brands of tubes used I can make other suggestions. Some tubes like Electro Harmonic's are low noise high gain and can make a huge difference in noise levels. The speaker can be swapped to something else and mask a great deal of the problem too. Everything else would need to be gone over by an expert (not nessarily a builder either - it doesn't take a degree in electronics to build an amp but it does to minimize the issues with a poor build)

          Comment


          • #6
            Originally posted by Jazzer2020 View Post
            ...

            The odd man out was the reverb knob.

            The hum is a 'B note' and can be broken down into two octaves.
            I noticed when I turn the reverb up from the 9 o'clock position it gets progressively louder in the
            lower B octave.

            Louder and louder until up to full at 5 o'clock position.

            I find this interesting, but having said that, even at 9 o'clock, where I had kept it until just now,
            the hum is annoying (in a quiet room). The hum just gets much much worse the more reverb is added.

            The note 'B' is very close to 60Hz or a multiple. - it is possible part of the Reverb circuit is picking up some 60Hz radiation (which WRGKMC erroneously referred to as "emf" in the above post) from the amplifier circuit or floating around the room.

            It could be something as simple as a a poor ground connection on one of the wires connecting the reverb tank

            One more note that may or may not help.
            When the amp volume knob is increased, only the hiss increases, not any of the humming.
            If the problem is a filter capacitor in the power supply then that would indicate the filter for the power tube bias supply (if the amp has fixed bias).







            As a human being, you come with the whole range of inner possibilities
            from the deepest hell to the highest states.

            It is up to you which one you choose to explore
            .

            Comment


            • #7
              Originally posted by onelife View Post


              The note 'B' is very close to 60Hz or a multiple. - it is possible part of the Reverb circuit is picking up some 60Hz radiation (which WRGKMC erroneously referred to as "emf" in the above post) from the amplifier circuit or floating around the room.

              It could be something as simple as a a poor ground connection on one of the wires connecting the reverb tank



              If the problem is a filter capacitor in the power supply then that would indicate the filter for the power tube bias supply (if the amp has fixed bias).
              Thanks WRG and onelife.

              I forgot to mention one thing. Like my Fender Princeton II and Vibroverb, my custom amp consists of separate head and speaker cab.

              I did a little more testing today. Using the Fender Princeton II head + custom speaker cab and comparing it to the custom head + custom speaker cab.

              The overall sound was very close. A little brighter with the FPII. The noise level was close between the two amps, just slightly different characteristics. More highs (noise) with the FPII, more lows with the custom amp.

              More twiddling with the volume knob today (custom head) revealed that the hum does in fact increase as you increase the volume.
              I may have set the Treble and Bass knobs to 0 yesterday when I said I could only hear the hiss increase on the volume knob.
              Because today when I started playing the amp, the Treble and Bass were at 0. I didn't even notice for a while.

              I said to myself, "Wow my FPII sounds much better than this new custom build!"
              When I set the Treble and Bass properly they were very similar in sound.

              I'm not technically inclined like you guys are with amps.
              But I do possess extremely sensitive hearing and can hear sounds/noises that many people can't.

              Having said that, when I read others here saying their 'X' tube amp is dead quiet, I say to myself
              shouldn't my Mega$ custom built amp also be dead quiet?

              I mentioned that my Fender Princeton II was pretty dead quiet before I separated head and speaker cab.
              That is the noise level I am expecting (pre-split).





              Comment


              • #8
                Not to make things too complicated, but all tube amps will emit some sort of hum/hissing, that’s why guitar tube amplifiers sound so good.

                Some obvious things to stay away from with a guitar tube amp. CRT old style TVs will cause a 60Hz hum if present in the same room, so if you have one on in the room, get a LCD or LED to replace it. Also, make sure that your guitar pickups are far enough away from the transformer(s) in the guitar tube amp - instant 60Hz hum. You may want to get some Deoxit (deoxidizing solution) and clean your preamp tubes. Owning a guitar tube amp you should always clean your pre/power amp tubes when replacing them even if they are new they still build up a corrosive barrier that can cause a hum, hissing and/or scratchy type of irritating nuisance.

                Good luck.

                Comment


                • #9
                  Originally posted by onelife View Post
                  The note 'B' is very close to 60Hz or a multiple. - it is possible part of the Reverb circuit is picking up some 60Hz radiation (which WRGKMC erroneously referred to as "emf" in the above post) from the amplifier circuit or floating around the room.
                  It could be something as simple as a a poor ground connection on one of the wires connecting the reverb tank If the problem is a filter capacitor in the power supply then that would indicate the filter for the power tube bias supply (if the amp has fixed bias).
                  Erroneous??? You really need to brush up on your abbreviations. I realize some countries use different terminologies in electronics, but this one permeates the internet so I cant see how you can possibly get this one wrong.

                  EMF has two definitions.

                  One is Electromagnetic Force = Electromagnetic force is the force present between electrically charged particles such as electrons and protons. It has the ability to repel and attract charges. The electromagnetic force is attractive for unlike charges( electron and proton) and repulsive for like charges (two electrons or protons). Electromagnetic force is responsible for the binding of atoms.
                  http://www.physics-and-radio-electro...tic-force.html

                  The second definition - the one I was obviously referring to -

                  Electromagnetic Field = An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction. It is one of the four fundamental forces of nature (the others are gravitation, weak interaction and strong interaction).
                  https://en.wikipedia.org/wiki/Electromagnetic_field

                  Everyone is exposed to electromagnetic fields (EMF) of different frequencies that permeate our environment. Exposures to many EMF frequencies are increasing significantly as technology advances unabated and new applications are found. While the enormous benefits of using electricity in everyday life and health care are unquestioned, during the past 20 years the general public has become increasingly concerned about potential adverse health effects of exposure to electric and magnetic fields at extremely low frequencies (ELF). Such exposures arise mainly from the transmission and use of electrical energy at the power frequencies of 50/60 Hz.

                  Low Frequency Radiation/Power Lines (ELF fields) are defined as those having frequencies up to 300 Hz and can produce electromagnetic interference (EMI). At frequencies this low, the wavelengths in air are very long (6,000 km at 50 Hz and 5,000 km at 60 Hz) Magnetic fields come from the motion of electric current. Their strength is measured in units of tesla (T) In some countries another unit, called the gauss (G), is commonly used for measuring magnetic induction. Any device connected to an electrical outlet, when the device is switched on and a current is flowing, will have an associated magnetic field, the strength of which is directly related to the current drawn from the source. Magnetic fields are strongest close to the device and get lower with distance. Most common materials do not shield them.

                  http://hps.org/hpspublications/artic...infosheet.html

                  Comment


                  • #10
                    Originally posted by WRGKMC View Post

                    Erroneous??? You really need to brush up on your abbreviations.
                    Another one I keep in my handy tube amp tool bag - Light Amplification Stimulated Electromagnetic Radiation.

                    Comment


                    • #11
                      Originally posted by WRGKMC View Post

                      Erroneous??? You really need to brush up on your abbreviations. I realize some countries use different terminologies in electronics, but this one permeates the internet so I cant see how you can possibly get this one wrong.

                      EMF has two definitions.

                      The second definition - the one I was obviously referring to -

                      In your own words...

                      Originally posted by WRGKMC View Post
                      I always get a laugh when people blame hum on AC. What do you think an outlet is supposed to provide DC?

                      AC Alternates in current and as it does it generates and external magnetic field around all wires. This electromagnetic force (EMF) is the same as any other radio wave except its 60 cycles falls within the same frequency range as the audio spectrum or 20~20Khz.

                      Although electromagnetic field is sometimes abbreviated as EMF it is more commonly referred to using EM field to avoid confusion.
                      As a human being, you come with the whole range of inner possibilities
                      from the deepest hell to the highest states.

                      It is up to you which one you choose to explore
                      .

                      Comment


                      • WRGKMC
                        WRGKMC commented
                        Editing a comment
                        All right then, the force produces a field. My mistake, and No, EM is not used more then EMF to reduce confusion. EM is normally associated with a nuclear blast producing an EM pulse. It's still a magnetic field but its not used more in technical discussions, at least not here in the US.

                    • #12
                      Originally posted by onelife View Post


                      In your own words...




                      Although electromagnetic field is sometimes abbreviated as EMF it is more commonly referred to using EM field to avoid confusion.
                      What about "Chocolate Fudge Sundae"?

                      Comment


                      • #13
                        My amp builder will be contacting me shortly to advise on next steps.

                        In the meantime I have a question for you guys.
                        What is your opinion on the tremolo circuit? In the initial discussion for the amp build I asked if omitting the tremolo
                        would make the amp quieter (I never use it). He said it wouldn't so I decided to leave it in.
                        Your thoughts on it?



                        Comment


                        • #14
                          Originally posted by Jazzer2020 View Post
                          My amp builder will be contacting me shortly to advise on next steps.

                          In the meantime I have a question for you guys.
                          What is your opinion on the tremolo circuit? In the initial discussion for the amp build I asked if omitting the tremolo
                          would make the amp quieter (I never use it). He said it wouldn't so I decided to leave it in.
                          Your thoughts on it?


                          In engineering, we have a very applicable phrase we abide by: "If it ain't broke, don't fix it".

                          Comment


                          • #15
                            Originally posted by Cyborg View Post

                            In engineering, we have a very applicable phrase we abide by: "If it ain't broke, don't fix it".

                            I understand that in principle and in general use. And also agree with it.

                            I don't have electronic expertise at all. Just know the very basics.
                            I just assumed that the fewer parts introduced into a circuit, the less potential
                            noise is created. Maybe that's not true?

                            Now if the case is that this builder likes to go by a stock wiring diagram/schematic
                            for convenience sake, and making alterations that may help lessen noise
                            is not recommended by them (because of the additional work involved ),
                            then I'd like to know about it.


                            Comment













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