Strange Buzzing Noise from Tube Amp

[darkarn]

Ok, I think the open design and the 4 metal poles around it have something to do with the buzzing, I go see if removing them will solve it

 

[TeamStereo]

Hi, darkarn

Not sure if you have managed to locate the source of the buzzing sound, which, if I read correctly, is coming direct from the tube amplifier and not from the headphone or speaker.

With over 4 decades of experience in home repairs as an interest and backed by engineering education and experience, here are some pointers which may help in locating the source of the problem.

First I would say power supply source (13A points or power strips) is unlikely to be the cause. Loose vacuum tube may be possible. Verify by trying to move the component gently while taking the necessary precaution against heat and ht (high tension or voltage). The ht will take a long time to discharge even after the power supply is switched off.

I constructed a DIY tube amplifier 40 years ago but did not encountered such problem. My problem was humming noise from the speaker. It was caused by difficulty in bias adjustment.

Note that electrical and electronic parts using ac supply will generally vibrate and produce buzz or hum in varying degrees. Typical examples are coils, ballasts (as found in flourescent lights) and transformers.

Screws that have worked loose or not tightened properly can result in buzz or hum.

Some components may be touching each other causing the noise. Once I had buzzing sound from my old fashioned ding tong door bell. This was eventually traced to a transformer which I installed myself to replace the use of batteries. Because it was not securely fixed inside the door bell casing, it was touching the latter. A smart knock with a ruler (pun intended) on the case would stop the buzz for a period of time. In the end I used some pvc insulating tape as a cushion to separate the two parts to stop the buzz.

Uneven surface where the amplifier sits may be the cause. I once found this to be reason for the noise from one of my table fans.

Buzz can also be a sign of poor contacts. The sound comes from the sparks jumping across the very tiny gaps in the poor contacts. This may cause overheating or catch fire if allowed to run for a long time.

If your amplifier is still under warranty, return it for service. Otherwise you may have to open up the casing to do a thorough inspection. It is easier to locate the source of the vibration with the power supply on, but you have to be very sure of what you are doing. Use a insulated stick which can stand the high voltage to press against each suspicious part inside the casing to check if the buzz changes or stops altogether. Again I have to stress that unless you are a experienced DIY man like me, consider your safety carefully. It may be better to send it to a repair man.

Great you could chip in!

 

[mrsun18]

...
PS: I am using a second-hand Bravo Audio V2 tube amp and the buzzing will happen some times (i.e. not buzzing all the way)

My door bell didn't misbehave all the time too

Ok, I think the open design and the 4 metal poles around it have something to do with the buzzing, I go see if removing them will solve it

If this still doesn't solve it...from Amazon found pics of your tube amp...haha, with this I can really try to pin point the source.

Check for clearance between tube and top cover (glass or acrylic?), similarly between the big capacitor/cover. As mentioned before, the components should not be touching one another, including the small resistors - all must have sufficient clearance from one another.

Check no loose parts and tightness of screw connections at the heat sinks.

If all these fail, the next part involves risk taking and I will keep it in reserve for the time being.

 

[darkarn]

My door bell didn't misbehave all the time too

If this still doesn't solve it...from Amazon found pics of your tube amp...haha, with this I can really try to pin point the source.

Check for clearance between tube and top cover (glass or acrylic?), similarly between the big capacitor/cover. As mentioned before, the components should not be touching one another, including the small resistors - all must have sufficient clearance from one another.

Check no loose parts and tightness of screw connections at the heat sinks.

If all these fail, the next part involves risk taking and I will keep it in reserve for the time being.

The big capacitor is touching the acrylic cover, I am removing the cover to deal with that. None of the components are touching each other. I have also tightened all screws.

 

[mrsun18]

The big capacitor is touching the acrylic cover, I am removing the cover to deal with that. None of the components are touching each other. I have also tightened all screws.

Glad that I was able to help.

 

[darkarn]

Glad that I was able to help.

Thanks but I am still baffled at why would this still happen only when I reached home; the acrylic cover was already like that ever since I got it from seller

And I am still testing it out; haven't confirmed if this is the only cause (I think may have to remove the metal poles too; the buzzing noise will go away whenever I touch them)

 

[alamakazim]

grounding problem....can u just plug it directly to a wall plug and try

 

[darkarn]

grounding problem....can u just plug it directly to a wall plug and try

ha nor. ground loop problem.

unplug everything just the essential ones or just amp on power strip to test. now you have same ground potential on all equipment on the strip. if still got buzz means ground loop probably coming from AC line.

now remove the ground wire of the amp at the plug to test for a short while.. if still got buzz then not ground loop problem and confirm is equipment problem some where. if no more buzz then good luck can go happy looking for the item causing the ground loop on the AC line.

**Try at your own risk. if you no EE knowledge better don't touch it the plug. get a EEE guy to help you.

Hmm... Ok, what I am doing right now is the following:

1. Remove the 4 metal poles
2. Remove the top acrylic plate
3. Connected the amp directly to the wall socket (which means my laptop is now using the power strip)

I will then troubleshoot accordingly; hopefully it is nothing too serious.

 

[alamakazim]

Hmm... Ok, what I am doing right now is the following:

1. Remove the 4 metal poles
2. Remove the top acrylic plate
3. Connected the amp directly to the wall socket (which means my laptop is now using the power strip)

I will then troubleshoot accordingly; hopefully it is nothing too serious.

do the simplest stuff 1st... plug to socket..

 

[darkarn]

do the simplest stuff 1st... plug to socket..

I have done all three already actually I will go test then report back

 

[darkarn]

haha does the case or 4 poles touches any electrical trace or ground on the PCB? if not hard to believe it will have effect. in fact not possible la.

I thought that they are possible causes considering how the buzzing will die off the moment I touched them

 

[darkarn]

maybe there's some electrical continuity between the poles and the circuit. then that sounds like a ground loop issue.

I'm not a EEE. but imo the easiest way to test for ground loop is to remove the ground wire for that short while. meaning totally nothing on your amp. just standalone. then you can know straight away whether the buzz comes from external or internal before taking other steps.

I don't think there's a ground wire for my amp

 

[darkarn]

DC on a switch mode power supply? doesn't matter same steps if you want to test ground loop. and run your laptop on battery and remove from plug. so you only got 2 equipments in this whole audio chain.

the set up should be AC 230v ->laptop (battery) + Amp and dac (no ground)

i'm not EEE so engineers don't hoot me if i'm wrong. ahaha

It is using DC power. And so far, so good...

Wall Socket L: Power Strip => Laptop | Fiio Taishan
Wall Socket R: Bravo Audio V2 tube amp

 

[darkarn]

no more buzz? if that solve the problem for you then great! just leave it separated lor

Not yet; last night I got the buzz again. It stop buzzing when the Taishan is switched off though.

I am going to bring the amp to another room, hook it up to my Clip Zip and test; isolate the problem once and for all.

 

[mrsun18]

Not yet; last night I got the buzz again. It stop buzzing when the Taishan is switched off though.

I am going to bring the amp to another room, hook it up to my Clip Zip and test; isolate the problem once and for all.

Just to be very sure that there is no communication breakdown - you are not hearing the buzz through your headphone when the Bravo is in use - because you did not acknowledge my question earlier on.

I think you know that the tube amp and your Taisan are fed by separate dc supplies, so actually there is no conventional ground loop to talk about. Having said that, it must be recognised that the screen on the output of Taisan and the screen on the input side of Bravo may be at a different potential with respect to earth.

That may explain why there is no buzz when Taisan is switched off. Similarly, I think you won't hear the buzz with Clip Zip through Bravo.

The metal poles, even if there are isolated from the pcb, will have static built up gradually. When you touch them, the static is discharged through you. Test it with a test pen, if you have one. You may see a faint glow.

I believe you are game for experiment. Try to tie an earth wire round them and see what happens.

 

[darkarn]

Just to be very sure that there is no communication breakdown - you are not hearing the buzz through your headphone when the Bravo is in use - because you did not acknowledge my question earlier on.

I think you know that the tube amp and your Taisan are fed by separate dc supplies, so actually there is no conventional ground loop to talk about. Having said that, it must be recognised that the screen on the output of Taisan and the screen on the input side of Bravo may be at a different potential with respect to earth.

That may explain why there is no buzz when Taisan is switched off. Similarly, I think you won't hear the buzz with Clip Zip through Bravo.

The metal poles, even if there are isolated from the pcb, will have static built up gradually. When you touch them, the static is discharged through you. Test it with a test pen, if you have one. You may see a faint glow.

I believe you are game for experiment. Try to tie an earth wire round them and see what happens.

Paiseh, I thought the first part last post was not a question. That's right, I just tested the amp by just using it and my Clip Zip with both my IEMs and headphones. I can confirm that the buzzing is indeed coming from the tube amp only since I don't have such problems when using my IEMs/headphone with my Clip Zip alone. I have tried my IEM and headphones on my PC's soundcard and also confirmed that they are not the source of the buzzing.

I am not sure what you meant by "screen" though but yes, both the Taishan and the tube amp have their own DC power sources.

I have also noticed the static buildup of the metal poles too; when I touch them (particularly the one nearest to the Line In ports), the buzzing noise will go away (I don't have a test pen though). I have also noticed that the same effect can be achieved if I touched the metal part of the big capacitor behind the tube.

So, I am going to try some of your ideas out: I will attempt to wrap the top of the capacitors and the metal pole nearest to the Line In ports with some black tape (should be insulating enough right? ) and for the big capacitor, I will stick a wire to it to act as a ground wire too (since I am not sure what you meant by tying it around the 4 poles...).

 

[mrsun18]

Paiseh, I thought the first part last post was not a question. That's right, I just tested the amp by just using it and my Clip Zip with both my IEMs and headphones. I can confirm that the buzzing is indeed coming from the tube amp only since I don't have such problems when using my IEMs/headphone with my Clip Zip alone. I have tried my IEM and headphones on my PC's soundcard and also confirmed that they are not the source of the buzzing.

Paiseh too. After reading your reply a few times, I have a feeling that you are hearing the buzz of your Bravo through headphone. This is because you emphasised that there was nothing wrong with your headphone/iems.

My previous diagnostics was based on the understanding that it was the vibration from the tube amp.

So pardon me if I asked again by another way (like a lawyer ): Do you hear the vibration/buzz from the tube amp without wearing/using the headphone?

I am not sure what you meant by "screen" though but yes, both the Taishan and the tube amp have their own DC power sources.

Screen means the outer part of the RCA sockets and the screen wire of the coaxial cable connecting the output of the Taishan to the input of the tube amp. This is usually connected to ground of pcb.

I have also noticed the static buildup of the metal poles too; when I touch them (particularly the one nearest to the Line In ports), the buzzing noise will go away (I don't have a test pen though). I have also noticed that the same effect can be achieved if I touched the metal part of the big capacitor behind the tube.

So, I am going to try some of your ideas out: I will attempt to wrap the top of the capacitors and the metal pole nearest to the Line In ports with some black tape (should be insulating enough right? ) and for the big capacitor, I will stick a wire to it to act as a ground wire too (since I am not sure what you meant by tying it around the 4 poles...).

No harm trying though the static build up may be caused by capacitive coupling, meaning ac still can conduct through air or insulating medium (that's how capacitor works).

Tying the poles with earth wire means ground them with earth wire.

I had another look at the big capacitor at Amazon and noticed that it is rated at 25v. The capacitor is meant to stabilise the dc supply to anode of the tube. So essentially it means that the voltage is much lower than I expected. That explains why the amplifier adopted an open design since only low voltgae was used. A schematic diagram seen here:
Bravo 12AU7 Mods and Appreciation thread | Rock Grotto
confirms that the voltage employed is 24v - a safe voltage to play with.

And from the pic showing the bottom side of the pcb, the metal posts are supposed to be grounded too.

Previously I have not considered th possibility of a failing capacitor (there may not be visible sign of bulging, crack or burnt mark). Take note of this and look at the grounding issue too.

Any possibility of Taishan's fault?

One more thing you can try. Your Taishan and Bravo are fed by two separate dc supplies. Reverse the polarity of one of the ac plug for the adaptor, say for the Bravo, and see the buzz will go away. There are two pins on the ac side of the adaptor. Say pin A is inserted to live terminal and pin B to neutral of 13A socket. Change pin A to connect to neutral and pin B to live.

 

[darkarn]

Paiseh too. After reading your reply a few times, I have a feeling that you are hearing the buzz of your Bravo through headphone. This is because you emphasised that there was nothing wrong with your headphone/iems.

My previous diagnostics was based on the understanding that it was the vibration from the tube amp.

So pardon me if I asked again by another way (like a lawyer ): Do you hear the vibration/buzz from the tube amp without wearing/using the headphone?

Orh, so that was what you were asking all along! Paiseh, I thought you meant whether I was hearing that when I am using the tube amp in any manner I don't hear any buzzing or vibration when I just left the tube amp on without listening to any form of music.

Screen means the outer part of the RCA sockets and the screen wire of the coaxial cable connecting the output of the Taishan to the input of the tube amp. This is usually connected to ground of pcb.

Ah, I see...

No harm trying though the static build up may be caused by capacitive coupling, meaning ac still can conduct through air or insulating medium (that's how capacitor works).

Tying the poles with earth wire means ground them with earth wire.

Err I am not sure if using any copper/silver wire will work (I am just sticking a random copper wire I found onto the top of the capacitor, with the other end onto the bottom right metal pole), and how to do the tying exactly (i.e. one wire per pole or one wire for all four | the other end go to where)

I had another look at the big capacitor at Amazon and noticed that it is rated at 25v. The capacitor is meant to stabilise the dc supply to anode of the tube. So essentially it means that the voltage is much lower than I expected. That explains why the amplifier adopted an open design since only low voltgae was used. A schematic diagram seen here:
Bravo 12AU7 Mods and Appreciation thread | Rock Grotto
confirms that the voltage employed is 24v - a safe voltage to play with.

And from the pic showing the bottom side of the pcb, the metal posts are supposed to be grounded too.

How do I check whether the metal poles are grounded or not? And thanks for the link, I wonder why did I miss that out during my search...

Previously I have not considered th possibility of a failing capacitor (there may not be visible sign of bulging, crack or burnt mark). Take note of this and look at the grounding issue too.

I checked for that already, no sign of damaged capacitors . I am not sure how to check for the grounding issue though

Any possibility of Taishan's fault?

Nope, the buzzing still occurred when I was testing with only the tube amp last night.

One more thing you can try. Your Taishan and Bravo are fed by two separate dc supplies. Reverse the polarity of one of the ac plug for the adaptor, say for the Bravo, and see the buzz will go away. There are two pins on the ac side of the adaptor. Say pin A is inserted to live terminal and pin B to neutral of 13A socket. Change pin A to connect to neutral and pin B to live.

I cannot open up the plugs for both devices to carry out this mod

 

[mrsun18]

Orh, so that was what you were asking all along! Paiseh, I thought you meant whether I was hearing that when I am using the tube amp in any manner I don't hear any buzzing or vibration when I just left the tube amp on without listening to any form of music.

Ok. Hum is usually used to describe lower frequency noise coming through speakers or headphone, whereas buzz is a higher frequency noise, more like vibration coming through the air. Anyway, never mind.

Err I am not sure if using any copper/silver wire will work (I am just sticking a random copper wire I found onto the top of the capacitor, with the other end onto the bottom right metal pole), and how to do the tying exactly (i.e. one wire per pole or one wire for all four | the other end go to where)

Don't bother, I think it won't work. See below also...

How do I check whether the metal poles are grounded or not? And thanks for the link, I wonder why did I miss that out during my search...

You will need a multimeter. Anyway, the metal poles should be grounded to the pcb ground already, if the screws are properly tightened, unless the pcb cracked. When you touched the pole and the hum went away, there was some kind of high impedance connection between the floating ground of the tube amp and the earth. If you connect a wire from the floating ground (using the screw of one of the poles) to the earth terminal of a 13A socket outlet, it may or may not eliminate the hum. From what I found out, even microphone or guitar amp manufacturers have to produce many prototypes (of the same schematic circuit) with different wiring methods for grounding to produce a hum-free product.

Google search very often turn out millions of hits, also depends on the search term used. I searched 'bravo v2 tube amplifier schematic diagram' and clicked on a link which shows how to adjust the dc bias because it may help in reducing hum. But that discussion thread didn't show the anode voltage which I was interested in. Anyway I found a link within the thread which led me to another thread. This was the one I gave you the link.

This link below shows how to adjust the bias voltage which may help to reduce the hum. But you will need a multimeter to do it. A cheap one is about $20. It was sold by NTUC but not sure if they are still selling. I have a Sanwa YX360TRF bought for $42 nine years ago.
How to adjust the bias Bravo / Indeed amps | Rock Grotto

I checked for that already, no sign of damaged capacitors . I am not sure how to check for the grounding issue though

Failing capacitors or other components in early stage of failure may not show physical sign of damage, but because they are starting to fail, the physical attributes, such as resistance, insulation, capacitance or inductance may change and affect the performance or give rise to problem such as this effect of hum.

Check for grounding issues was just a general reminder.

Nope, the buzzing still occurred when I was testing with only the tube amp last night.

Even when Taishan or other music sources not physically connected to tube amp? I want to rule out Taishan completely and the possible effect of two floating ground from two different devices.

I cannot open up the plugs for both devices to carry out this mod

If the Taishan is ruled out, then you only need to do the reverse polarity for the adaptor for tube amp. This is how you can do it: On one side of the adaptor, you have the dc supply cable for the tube amp. On the other side, based on Amazon pic, I assume you have a detachable ac supply cord to plug in to the two pins in the adaptor body. Detach the supply cord from the adaptor, turn the plug 180 degress and plug in to the adaptor again. That means one of the pins which was electrically connected to live previously is now connected to neutral of the ac supply, and vice versa. If the adaptor comes with a non-detachable ac supply cord, but comes with a 2 pin plug, then pull it out from the 13A socket, turn the 2 pin plug 180 degree and insert it into the 13A socket.

If the hum still won't go away, then I think you may have a tube that needs to be changed. Have you ever changed it before? Alternative, one or more parts (particularly the smaller capacitors) may have failed. I am not sure if bias adjustment for the heaters will help.

If you want to find out more about hum, google "floating ground hum"

 

[darkarn]

Ok. Hum is usually used to describe lower frequency noise coming through speakers or headphone, whereas buzz is a higher frequency noise, more like vibration coming through the air. Anyway, never mind.

Ah, I see. I thought these two terms are interchangeable

Don't bother, I think it won't work. See below also...
You will need a multimeter. Anyway, the metal poles should be grounded to the pcb ground already, if the screws are properly tightened, unless the pcb cracked. When you touched the pole and the hum went away, there was some kind of high impedance connection between the floating ground of the tube amp and the earth. If you connect a wire from the floating ground (using the screw of one of the poles) to the earth terminal of a 13A socket outlet, it may or may not eliminate the hum. From what I found out, even microphone or guitar amp manufacturers have to produce many prototypes (of the same schematic circuit) with different wiring methods for grounding to produce a hum-free product.

Strangely, it worked *somewhat*; if there is any hum left, it is significantly lower. I have a multimeter; do I stick one end to the top of the pole and another to its bottom and see if there is a current?

And I noticed that on the PCB, some metal bits that is supposed to be "covered" by the screws of the poles are missing/faded.

Google search very often turn out millions of hits, also depends on the search term used. I searched 'bravo v2 tube amplifier schematic diagram' and clicked on a link which shows how to adjust the dc bias because it may help in reducing hum. But that discussion thread didn't show the anode voltage which I was interested in. Anyway I found a link within the thread which led me to another thread. This was the one I gave you the link.

This link below shows how to adjust the bias voltage which may help to reduce the hum. But you will need a multimeter to do it. A cheap one is about $20. It was sold by NTUC but not sure if they are still selling. I have a Sanwa YX360TRF bought for $42 nine years ago.
How to adjust the bias Bravo / Indeed amps | Rock Grotto

Ah, I used the term "bravo audio v2 humming" and "bravo audio v2 buzzing". That mod will not work as I am using the 12AU7 version of the tube amp :S

Failing capacitors or other components in early stage of failure may not show physical sign of damage, but because they are starting to fail, the physical attributes, such as resistance, insulation, capacitance or inductance may change and affect the performance or give rise to problem such as this effect of hum.

Check for grounding issues was just a general reminder.

I see... Nothing much I can do about that eh... (Unless I go change them or something)

Even when Taishan or other music sources not physically connected to tube amp? I want to rule out Taishan completely and the possible effect of two floating ground from two different devices.

Yep, no buzzing noise from the Taishan alone... I hope.

If the Taishan is ruled out, then you only need to do the reverse polarity for the adaptor for tube amp. This is how you can do it: On one side of the adaptor, you have the dc supply cable for the tube amp. On the other side, based on Amazon pic, I assume you have a detachable ac supply cord to plug in to the two pins in the adaptor body. Detach the supply cord from the adaptor, turn the plug 180 degress and plug in to the adaptor again. That means one of the pins which was electrically connected to live previously is now connected to neutral of the ac supply, and vice versa. If the adaptor comes with a non-detachable ac supply cord, but comes with a 2 pin plug, then pull it out from the 13A socket, turn the 2 pin plug 180 degree and insert it into the 13A socket.

Thanks, I just did that, let's see how it goes...

If the hum still won't go away, then I think you may have a tube that needs to be changed. Have you ever changed it before? Alternative, one or more parts (particularly the smaller capacitors) may have failed. I am not sure if bias adjustment for the heaters will help.

If you want to find out more about hum, google "floating ground hum"

Changing of tubes does not help