Hi Everybody,
This is my first post on this fine forum. I end up here a lot by searching for solutions to tube amp problems. This forum seems to have the best combination of knowledgeable and helpful people. I'm wondering if you can help me with a problem that has been stumping me for a while. I have a very irritable noise that I've been trying to track down.
Take a listen to these videos and let me know if you have any idea of how to go about finding the cause and getting rid of it. I've done a ton of things but I'm kind of worn out and going around in circles. Although the amp is heavily attenuated, please let me assure you that it is notceable even at high volumes and without the attenuator (I use the attenuator to save my hearing and my marriage). Not as much, but it's really one of those things that you can't unhear. In searching for solutions I see some people say that this is normal but I really don't think it is.
I'm a technologist and I've been in the electronics industry for almost 25 years so you'd think I could have solved this by now. But tubes are a different beast, during the day I work on boring modern electronics. I have a scope, signal generator, etc, and I've been building amps and looking at tube amp waveforms for years, but admittedly I haven't dug in deep enough and I don't have the skills of some of the people here. Apologies in advance for the differences in volume between clips.
YouTube
YouTube
YouTube
The amp is a DIY build, essentially a 100W Marshall Major, with some extra gain in the preamp. Ultralinear power amp with 2 KT88's, cathodyne PI and driver, etc. Power supply is high 500's VDC, JTM45/100 PT.
If you notice in the 1st video, I have hardly any speaker volume and the noise is easily heard. I put my ear over the OT and I can hear it plain as day. So I unscrewed it from the chassis, took the end bells off, and tried to move/squeeze the windings and laminates but I couldn't make it stop. I've already swapped all tubes (I thought it was power tubes first but the noise is definitely in the OT). I've tried other cables, guitars, speaker cabs, etc - it's definitely in the head.
Thanks in advance for any responses, any help at all is greatly appreciated,
Darrin
This is my first post on this fine forum. I end up here a lot by searching for solutions to tube amp problems. This forum seems to have the best combination of knowledgeable and helpful people. I'm wondering if you can help me with a problem that has been stumping me for a while. I have a very irritable noise that I've been trying to track down.
Take a listen to these videos and let me know if you have any idea of how to go about finding the cause and getting rid of it. I've done a ton of things but I'm kind of worn out and going around in circles. Although the amp is heavily attenuated, please let me assure you that it is notceable even at high volumes and without the attenuator (I use the attenuator to save my hearing and my marriage). Not as much, but it's really one of those things that you can't unhear. In searching for solutions I see some people say that this is normal but I really don't think it is.
I'm a technologist and I've been in the electronics industry for almost 25 years so you'd think I could have solved this by now. But tubes are a different beast, during the day I work on boring modern electronics. I have a scope, signal generator, etc, and I've been building amps and looking at tube amp waveforms for years, but admittedly I haven't dug in deep enough and I don't have the skills of some of the people here. Apologies in advance for the differences in volume between clips.
YouTube
YouTube
YouTube
The amp is a DIY build, essentially a 100W Marshall Major, with some extra gain in the preamp. Ultralinear power amp with 2 KT88's, cathodyne PI and driver, etc. Power supply is high 500's VDC, JTM45/100 PT.
If you notice in the 1st video, I have hardly any speaker volume and the noise is easily heard. I put my ear over the OT and I can hear it plain as day. So I unscrewed it from the chassis, took the end bells off, and tried to move/squeeze the windings and laminates but I couldn't make it stop. I've already swapped all tubes (I thought it was power tubes first but the noise is definitely in the OT). I've tried other cables, guitars, speaker cabs, etc - it's definitely in the head.
Thanks in advance for any responses, any help at all is greatly appreciated,
Darrin
Check the idle current of the output tubes, the DC current may be off to much for the output transformer.
Who wound the transformer? When you took the covers off, did it look like it had been well varnished? I would contact the manufacturer and explain that something internal in the transformer rattles and you'd like to request an exchange.
pwgtang, I read about this and have considered it. I have 43mA on one tube and 37mA on the other. When I heard about tubes drifting away from being matched I assumed it would cause more hum, not that ugly noise. Would that really be enough to cause it? I thought about converting to dual bias.
audiowize, a very reputable winder that I don't want to name because this may not (and probably is not) be the problem, and I don't think it would be fair to name him.
I sent him an email asking his advice as to what the issue might be. I have a friend who can vacuum impregnate it, but I've read that this might affect the sound due to the dielectric of the potting material. It's kind of irrelevant as after I emailed the builder I took off the end bells and the windings are covered in some kind of wax type paper, so I can't even spray it (my friend also has some Dolph's spray) without tearing the OT half apart. The build looks great to me, and I don't feel any vibrations.
I sent him an email asking his advice as to what the issue might be. I have a friend who can vacuum impregnate it, but I've read that this might affect the sound due to the dielectric of the potting material. It's kind of irrelevant as after I emailed the builder I took off the end bells and the windings are covered in some kind of wax type paper, so I can't even spray it (my friend also has some Dolph's spray) without tearing the OT half apart. The build looks great to me, and I don't feel any vibrations.
I read today that current production KT88's don't react well to voltages above 500VDC and make rude noises. I previously had a plexi style PT in this amp at about 480VDC and I don't remember having this noise but I was running the amp unattenuated and so loud that my head was spinning. I've thought about putting it back in, as big a pain in the b*tt as it would be.
The problem that I have when I start thinking about making changes is that I have a friend with the exact same build as mine and his amp sounds awesome.
The problem that I have when I start thinking about making changes is that I have a friend with the exact same build as mine and his amp sounds awesome.
Every tube speaker amp I have ever run on dummy load "sang" when driven reasonably loud. Both output transformer and sometimes capacitors. Usually peaking at a few KHz.
This is normal. LARGE power transformers "sing" 60Hz despite effort to minimize it; there's suggested practical limits for (large utility) customers to write into contracts.
It is not impossible that a tube would sing. Actually makes sense, though I have never heard it (above other singing parts). It would work like an unbiased electrostatic speaker (on the 2nd harmonic). Except relatively small electrodes and very huge spacing relative to a practical speaker. And in vacuum, so sound would have to go down the base leads and shake the chassis through the socket.
Be a real player. Take the attenuator off, use an efficient speaker, you never hear the amp sing.
If you truly can't be jolly without over-worked KT88s padded down to 0.010 Watts, then put the amp in the other room and run a wire back, shut the door.
This is normal. LARGE power transformers "sing" 60Hz despite effort to minimize it; there's suggested practical limits for (large utility) customers to write into contracts.
It is not impossible that a tube would sing. Actually makes sense, though I have never heard it (above other singing parts). It would work like an unbiased electrostatic speaker (on the 2nd harmonic). Except relatively small electrodes and very huge spacing relative to a practical speaker. And in vacuum, so sound would have to go down the base leads and shake the chassis through the socket.
Be a real player. Take the attenuator off, use an efficient speaker, you never hear the amp sing.
If you truly can't be jolly without over-worked KT88s padded down to 0.010 Watts, then put the amp in the other room and run a wire back, shut the door.
PRR, I only attenuated the amp so heavily to clearly illustrate the noise. If I were to try to record it at full volume with an Iphone it would have been the worst clip ever made unless I stood a mile away, and I would have gotten grief for that. Maybe I undermined what I'm trying to achieve but I don't have access to recording gear. I figured these types of comments would come if I used the attenuator, but I did it anyway, as I figured it was the lesser of two evils. I actually will run the amp unattenuated on full and use a baffle, that works quite well. The tone I am getting is absolutely perfect for what I need to do (I just joined a Deep Purple tribute band, yes I am a dinosaur, sorry) except for that noise, and if I could get the same tone any other way, I would. Watch someone to tell me to get an AxeFX or a Kemper, I probably deserve it.
I guess I'm a bit all over the place describing what I'm trying to achieve, and I didn't give all of the information because I didn't want to have a 10,000 word first post to the forum in fear that nobody would read it. I should have been been more clear in my opening post and asked, what should I look for, to prove that this is typical transformer noise and not some other issue? I blew the speakers in my cab when I first built and played the amp. I have a Marshall 1960BHW 4x12 that had reissue speakers in it. It was a used cab so I can't say 100% that it was the amp but I'm concerned that I have some other issue that is not OT noise. So yes, I'm kind of worried to crank the amp right now. I don't see anything crazy on the speaker jack signal but I'm no expert, that's why I'm here. I'll attach pics of the signals at the output of the PI, clean and with the amount of gain that I need to achieve the desired tone. If I remember clearly, I think it was a 400Hz square wave at about 70mV into the input jack of the amp. Does aybody see a problem with it? It looks like a sawtooth to me and that notch is funky. Like I said, maybe this is clear as day to somebody or everybody here, that's why I'm here.
Do you really think that noise is normal? I've heard hums and buzzes from transformers, but that sounds absolutely nasty to me. And even with the amp at full, I can still hear it on the notes. Obviously not as much as when it's attenuated, but once you hear it, you can't unhear it. I'm no Eric Johnson, but I don't think I'm trying to tell the difference between battery brands here. My ear is good enough to know that this is not normal, even at full volume. And as mentioned before, my friend has the same build and does not have this noise. So why should I accept it? I know there are a lot of guys here that know their stuff and I appreciate whatever help I can get, but I'm going to politely ignore any other comments like these, probably to my detriment because you were the one guy I was hoping would show up and point me in the right direction.
I'm just hoping that someone will give me a few tips on what to look for to make sure that I don't blow the nice and expensive replacement speakers that I have in the cab now, and so I can enjoy the underlying tone that I've been searching for since I was about 13 years old.
I guess I'm a bit all over the place describing what I'm trying to achieve, and I didn't give all of the information because I didn't want to have a 10,000 word first post to the forum in fear that nobody would read it. I should have been been more clear in my opening post and asked, what should I look for, to prove that this is typical transformer noise and not some other issue? I blew the speakers in my cab when I first built and played the amp. I have a Marshall 1960BHW 4x12 that had reissue speakers in it. It was a used cab so I can't say 100% that it was the amp but I'm concerned that I have some other issue that is not OT noise. So yes, I'm kind of worried to crank the amp right now. I don't see anything crazy on the speaker jack signal but I'm no expert, that's why I'm here. I'll attach pics of the signals at the output of the PI, clean and with the amount of gain that I need to achieve the desired tone. If I remember clearly, I think it was a 400Hz square wave at about 70mV into the input jack of the amp. Does aybody see a problem with it? It looks like a sawtooth to me and that notch is funky. Like I said, maybe this is clear as day to somebody or everybody here, that's why I'm here.
Do you really think that noise is normal? I've heard hums and buzzes from transformers, but that sounds absolutely nasty to me. And even with the amp at full, I can still hear it on the notes. Obviously not as much as when it's attenuated, but once you hear it, you can't unhear it. I'm no Eric Johnson, but I don't think I'm trying to tell the difference between battery brands here. My ear is good enough to know that this is not normal, even at full volume. And as mentioned before, my friend has the same build and does not have this noise. So why should I accept it? I know there are a lot of guys here that know their stuff and I appreciate whatever help I can get, but I'm going to politely ignore any other comments like these, probably to my detriment because you were the one guy I was hoping would show up and point me in the right direction.
I'm just hoping that someone will give me a few tips on what to look for to make sure that I don't blow the nice and expensive replacement speakers that I have in the cab now, and so I can enjoy the underlying tone that I've been searching for since I was about 13 years old.
