Amp hum increases and decreases

[rlw3]

My lp 275s hum more at some times than at others. I am referring to the amps humming not humming heard thru the speakers. Is this caused by ac quality going up and down during the summer months? Is this caused by having the amp on all day on a saturday?:scratch2:

[Still-One]

Sounds like a bit of DC might be getting to your amps. Depending on what is on in your home at any given time the humming could be fluctuate a bit.

[rlw3]

Jim
Does DC get into the AC due to AC quality problems (summertime sag)? It happens without me turning on anything different, and the amp is on its own 20 amp circuit.

[ronenash]

Ray,
Its hard to tell what causes Changes in the quality of your ac line. A dedicated 20A line only means your amp have more available current. It has nothing to do with the quality of the ac line.
The only way to get good Clean power is a power conditioner that isolates your system from the electric company grid.

[Coppy]

My lp 275s hum more at some times than at others. I am referring to the amps humming not humming heard thru the speakers. Is this caused by ac quality going up and down during the summer months? Is this caused by having the amp on all day on a saturday?:scratch2:

Not to state the obvious, but the hum is generated by the power transformers. c-j listens to all their big amps before the pretty stuff goes on to be sure they sound okay but also to check for noisy transformers as well. There is apparently no way to check for this until they are under load in the amp. They end up changing out more transformers than you might expect. That said, don't know what might cause the transformer vibration to vary... maybe a variations in the frequency of the AC coming in.

At least it's not coming from the speakers.

Bob

[rlw3]

thanks to all.
What surprises me is how at different times the level of hum noise varies. it is usually higher later in the day. I was beginning to worry it was a problem related to the amp being on for too long that day. Hopefully after air conditioner season is over the AC will be cleaner and the hum greatly diminished.

[pstrisik]

Not to state the obvious, but the hum is generated by the power transformers. c-j listens to all their big amps before the pretty stuff goes on to be sure they sound okay but also to check for noisy transformers as well. There is apparently no way to check for this until they are under load in the amp. They end up changing out more transformers than you might expect. That said, don't know what might cause the transformer vibration to vary... maybe a variations in the frequency of the AC coming in.

At least it's not coming from the speakers.

Bob

I've got some soft hum coming out of both speakers (Pr11A) that started recently. :sigh: It was worse when I had usb fans plugged into a switched outlet in the power conditioner (using an iPhone USB/AC adaptor), but still there without. I should have my LP125M back by the weekend, so I'm kinda waiting to see if it is there with them to help isolate the problem. The conditioner is an older Monster unit and I just received a current model Panamax, so I'll see if that makes a difference as well when I swap that in. The hum is still there when plugged directly into an outlet. There whether I have the preamp in the chain or take it out and send signal through my AV pre/pro.

(I don't mean to hijack, but hopefully there is room for both issues in discussion. I'll move to a new thread if you wish Ray.)

[rlw3]

your comments are always welcome Peter. please come back to this thread and report on the results of the changes you made.
I also want to note that the lp 275 seems to vary more in how loud the tranny hum gets than 2 music reference amps and 2 cj amps i owned. the premier 12 was also a lot more quiet not only with tranny noise but also speaker noise. I wonder if the 6922s(input and driver tubes) only virtue are their availability. I wish i could hear a lp275 modified to use the 5751s and 6fq7s instead of 6922s. if wishes were fast trains i would ride and ride.....

[pstrisik]

Thanks Ray.

Are you suggesting that 6922's may be inherently noisy?

I'm waiting to hear from Mel about my LP125M return shipment. It was supposed to be shipped Monday but I didn't get any tracking info. I called a half hour ago and am waiting for her email that receptionist said she was sending right away. I guess they are trying!

[rlw3]

Peter,
In my experience since the early 80s,the sparkle, magic and quietness of the 12ax7/5751 family has greatly exceeded 6922s. Currently my lp 275s sound better than my premier 12s in the areas that more power benefits. However the 275s have a a lack of sparkle which i hope will go away when i get up to 800 hours. I am now at 400 hours and if it does not improve the 6922s will be suspect.
Previously when my 6922s did sound great it was for a short time only. Roger Majeski of music reference,who I deeply respect, told me that tubes do not have an enherent quality and the sound of the tube was dependent on the circuit that it was in. I seem to be very sensitive to tube deterioration and 6922s never seem to have a long honeymoon period before the sparkle is gone and the noise picks up. If I had the $ I would probably not go for a cj gat which is 6922 based. The tubes in my act 2 series 2 are a more robust varient with the same lack of sparkle but at least they hold up and stay consistant for a long time. They are 6n30p's I believe. I apologize for any heresy I may have commited, YMMV
PS my idea of gear with a lot of sparkle would be the equipment Zestos makes.

[pstrisik]

Peter,
In my experience since the early 80s,the sparkle, magic and quietness of the 12ax7/5751 family has greatly exceeded 6922s. Currently my lp 275s sound better than my premier 12s in the areas that more power benefits. However the 275s have a a lack of sparkle which i hope will go away when i get up to 800 hours. I am now at 400 hours and if it does not improve the 6922s will be suspect.
Previously when my 6922s did sound great it was for a short time only. Roger Majeski of music reference,who I deeply respect, told me that tubes do not have an enherent quality and the sound of the tube was dependent on the circuit that it was in. I seem to be very sensitive to tube deterioration and 6922s never seem to have a long honeymoon period before the sparkle is gone and the noise picks up. If I had the $ I would probably not go for a cj gat which is 6922 based. The tubes in my act 2 series 2 are a more robust varient with the same lack of sparkle but at least they hold up and stay consistant for a long time. They are 6n30p's I believe. I apologize for any heresy I may have commited, YMMV
PS my idea of gear with a lot of sparkle would be the equipment Zestos makes.

Interesting. I have the 11A which, aside from a mysterious hum through both speakers that cropped up recently, has been very nice. It uses 5751/6FQ7. Still waiting to get my new LP125M's set up. They use M8080 (CV4058) and 6922. Maybe the same as your 275's? So we shall see!

[rlw3]

Interesting. I have the 11A which, aside from a mysterious hum through both speakers that cropped up recently, has been very nice. It uses 5751/6FQ7. Still waiting to get my new LP125M's set up. They use M8080 (CV4058) and 6922. Maybe the same as your 275's? So we shall see!

One source of lack of happiness with the 275s may be that each amp has 4 sets of power tubes. Some AA members I have read believe that one set of power tubes sounds better/more pure than the same circuit with 2 sets of power tubes (pr12s) and by the same logic 2sets of power tubes sound better than 4 (lp275s).
Cause and effect is hard to ascertain.
My 275s use 3 6922s. Would love to know why the m8080 was used instead??

[pstrisik]

One source of lack of happiness with the 275s may be that each amp has 4 sets of power tubes. Some AA members I have read believe that one set of power tubes sounds better/more pure than the same circuit with 2 sets of power tubes (pr12s) and by the same logic 2sets of power tubes sound better than 4 (lp275s).
Cause and effect is hard to ascertain.
My 275s use 3 6922s. Would love to know why the m8080 was used instead??

Maybe an email to service@conradjohnson.com could get an answer.

[pstrisik]

Regarding my Pr11A hum....

My repaired LP125M will be back by the weekend, so I'm taking a last try at tracking down the hum before taking the 11A out of service.

The hum is a constant sound out of both speakers and is present even if the preamp is off. If I unplug the preamp interconnects from the amp, the hum decreases slightly, but is still there. I've played with all cables and power cords. Even just moving them around should create some change in the hum if the problem was cable interference, but it doesn't change at all. I tried grounding the amp to the power conditioner. I've changed power conditioners. I've plugged in the amp directly into an outlet separate from everything else (but may be on the same circuit).

When I hook up the 125M's, lack of hum will make the 11A suspect. If the hum is there, I've got some kind of ground or interference problem.

Any chance it is a tube problem? Since it is constant and in both channels, I assumed not. But I can swap out tubes to see.

[rlw3]

Are both amps plugged into the same wall outlet? Have you tried using cheater plugs to lift the ground on one or both amps?
Lifting the ground on powerful amps is not ideal. Lastly have you tried lifting the ground of everything but the amps?(much safer) Do you have anything digital on in the house that could be turned off?

[pstrisik]

Are both amps plugged into the same wall outlet? Have you tried using cheater plugs to lift the ground on one or both amps?
Lifting the ground on powerful amps is not ideal. Lastly have you tried lifting the ground of everything but the amps?(much safer) Do you have anything digital on in the house that could be turned off?

The hum is from the stereo 11A. I am waiting for the LP125M mono to return from warranty service after which I will try the amp pair.

Safe to lift the ground briefly on the amp just for a test?

Lifting ground on everything else would be quite a job. I suppose I can turn off everything except the source preamp and amp and lift ground on the first two.

I probably have about 50 digital things in the house! I can turn off everything in the immediate vicinity.

Doesn't sound like it could be tubes to you?

I'm racking my brain trying to recall what might have changed to cause this.

[Coppy]

It's probably an issue of un-equal AC between the grounds of your components. Equipment often leaks AC to its chassis or ground.

You may not want to do this but you'll have to to track down the hum. First, unplug everything from the amp, except the speakers. Turn the amp on. If the hum is still there, it's something in the amp... could be any number of things, maybe a tube but more likely a cap. You should at least try lifting the ground on the amp to see if helps. It won't hurt the amp but could be dangerous if high voltage shorts to the chassis. I have run my amps ground lifted for some time.

Okay, say the hum is gone with everything unplugged. You're going to work back from the amp. Now, plug in just the preamp. If there's hum, lift the ground on the pre and you're done. If not, plug each source in one at a time until the hum returns and then lift the ground on the offending source to kill the loop. In my case it turned out to be the Magnum Dynalab FM tuner. Now all is well.

Good luck,
Bob

[pstrisik]

It's probably an issue of un-equal AC between the grounds of your components. Equipment often leaks AC to its chassis or ground.

You may not want to do this but you'll have to to track down the hum. First, unplug everything from the amp, except the speakers. Turn the amp on. If the hum is still there, it's something in the amp... could be any number of things, maybe a tube but more likely a cap. You should at least try lifting the ground on the amp to see if helps. It won't hurt the amp but could be dangerous if high voltage shorts to the chassis. I have run my amps ground lifted for some time.

Okay, say the hum is gone with everything unplugged. You're going to work back from the amp. Now, plug in just the preamp. If there's hum, lift the ground on the pre and you're done. If not, plug each source in one at a time until the hum returns and then lift the ground on the offending source to kill the loop. In my case it turned out to be the Magnum Dynalab FM tuner. Now all is well.

Good luck,
Bob

Thanks Bob! I have tried running it with only speakers connected and hum is still there. Tonight I will try with ground lifted and won't touch the chassis! If that doesn't work, I guess I can swap out the tubes next.

[rlw3]

Are all the source components on the same circuit as the amp? Are they on the same wall outlet? If not perhaps put all source gear on a cheap power strip so that it can go on the same wall outlet, then float the ground on the power strip. I had a circuit in another room in my house where it hummed on one outlet but not if i hooked up the amp to the next outlet on the same circuit with an extension cord. It made no sense to me at all. Do you have one of those cheap tester 3 prong plugs that lights up in different ways to show if any connects inside the wall to the outlet are missing or reversed?

[pstrisik]

Are all the source components on the same circuit as the amp? Are they on the same wall outlet? If not perhaps put all source gear on a cheap power strip so that it can go on the same wall outlet, then float the ground on the power strip. I had a circuit in another room in my house where it hummed on one outlet but not if i hooked up the amp to the next outlet on the same circuit with an extension cord. It made no sense to me at all. Do you have one of those cheap tester 3 prong plugs that lights up in different ways to show if any connects inside the wall to the outlet are missing or reversed?

I've tried on a different outlet (likely same circuit). I do have one of those testers and will try that tonight.

That amp has been running fine for a year, so I'm skeptical that it is the power. Feeling like the amp itself. I'll come back with the results. Thanks for all the input.

[Joe Appierto]

If the cheater plug works, then you know that's the issue. Have you by any chance recently hooked up your cable service to your stereo system? I know I had to get one of those isolation transformers and hook it up to the cable lead before the hum went away in my system.

As I remember, even with the isolation transformer, the system hummed with both the Pr. 11A and the 140 unless I used a cheater plug.

[pstrisik]

Ha! Cheater plug worked. I didn't have time last night and gave it a quick try this morning, so I don't know more. My repaired mono amp will be picked up tomorrow, so I'll first see if there is a hum problem with them. If not, I'll be good. If so, I'll try to track down the ground problem more rather than depend on the cheaters.

Though it sounds like ground lift is acceptable practice. Some components have a lift switch even. Any cautions?

[ronenash]

Disconnecting the ground on tube components that have over 500 volts inside is not a good practice. Organizing your cables in a clean way usually solves he problem.

[pstrisik]

I'm doing my best!

If it is cables, it would seem that moving cables (while still connected) one by one should produce some variance in the hum but it doesn't.

[ronenash]

Try disconnecting the sources from you preamp one by one to see if you can get rid of the hum. It is usually coming from one of the sources. Its a tedious job to nail down hum problems but floating ground in a tube amp is not the solution imho. The risk is just too high.
I have done this in my system and the end result is that I have all amps and preamps Connected to one power distribution box (Wireworld Matrix), all digital sources and PC Connected to another distribution box and my analog sources and their marching phono stages Connected to a third distribution box. All distribution boxes are connected to a Torus power conditioner. This setup resulted in zero hum and noise.

I hope this will help out.

[klipschfan]

UNDERSTANDING, FINDING,
& ELIMINATING GROUND LOOPS
IN AUDIO & VIDEO SYSTEMS
http://www.jensen-transformers.com/an/generic%20seminar.pdf

[pstrisik]

Try disconnecting the sources from you preamp one by one to see if you can get rid of the hum. It is usually coming from one of the sources. Its a tedious job to nail down hum problems but floating ground in a tube amp is not the solution imho. The risk is just too high.
I have done this in my system and the end result is that I have all amps and preamps Connected to one power distribution box (Wireworld Matrix), all digital sources and PC Connected to another distribution box and my analog sources and their marching phono stages Connected to a third distribution box. All distribution boxes are connected to a Torus power conditioner. This setup resulted in zero hum and noise.

I hope this will help out.

Thanks Ron. It's all helpful.

Disconnecting sources from the preamp likely won't help as I have tried with the preamp disconnect from the amp. It seems like it is something about what is plugged into the wall. I will try the one by one method with things unplugged then plugging them in one by one. Hopefully the hum will disappear with most everything unplugged except the amp.

With your system it seems like everything is ultimately plugged into the same circuit. If true, it must be something about the power conditioning that is eliminating your ground issue.

[pstrisik]

UNDERSTANDING, FINDING,
& ELIMINATING GROUND LOOPS
IN AUDIO & VIDEO SYSTEMS
http://www.jensen-transformers.com/an/generic%20seminar.pdf


Thanks for this! I will dig in and see what I can learn.

[pstrisik]

Sorry, Ray. It looks like I did take over your thread! :redface: How's your transformer hum situation?

[rlw3]

No worries, my lp 275s are quiet in the mornings but get noisy by 5-6 pm. Dont know if this is a heat build up issue or the power out of the wall getting dirty as the day goes on. If noise growth remains during cooler weather this fall then i would have to think it is a heat build up problem. Peter i assume you tried using the 3 prong wall socket testing device and all was good?

[pstrisik]

No worries, my lp 275s are quiet in the mornings but get noisy by 5-6 pm. Dont know if this is a heat build up issue or the power out of the wall getting dirty as the day goes on. If noise growth remains during cooler weather this fall then i would have to think it is a heat build up problem. Peter i assume you tried using the 3 prong wall socket testing device and all was good?

Yes, the circuit tests ok at the outlet.

Regarding yours, though this may be stating the obvious... Have you tried waiting until four or five to turn them on to see if it is time of day or length of time on. You could also wait until the hum is at its loudest, turn them off until they cool and turn them back on and see what you get.

If it is a heat build up problem, you can get great little quiet fans that can plug into a switched outlet on your power center (if you are using one). Coolerguys.com -- Your Computer and Home Theater Cooling Source for Over 10 Years (http://www.coolerguys.com) seems to have about the best selection. They also have them with a temperature probe so they will turn on and off at a certain temp. You can get a pair of fans that run under 20db. Call them for recommendations as the website can be a bit overwhelming with all the choices. I can't hear mine at all from the listening position.

[rlw3]

the amp is not that warm especially in comparison to my 2 previous music reference amps, there is nothing above them and the ac vent is directly behind the rack which is between the amps so there is good air flow. i bet my problem goes away or is greatly reduced when the weather gets cooler. i may try turning it off then back on this saturday.

[pstrisik]

:thumbsup: CJ Detectives at work r us

[pstrisik]

Ha! Some progress! Though I am a bit embarrassed that I didn't find this earlier. I did too much assuming. The trouble was that much in my setup was the same and I mostly fiddled with things that had changed recently.

So, a cheater plug makes the hum go away. I plugged the 11A back in without the cheater so the hum was there and methodically unplugged other equipment one by one. It turned out to be my Onkyo pre/pro. I've had this in the system for a couple of years and longer than the 11A. So, maybe it is something connected to the Onkyo. That will be my next project - to unplug interconnects at the Onkyo one by one. There is a ground lug on the Onkyo. I have two Panamax' with the Onkyo on one and the 11A on the other. I wonder if connecting the ground lugs on the Onkyo with the Panamax that the 11A is plugged into, or connecting the ground between the two Panamax' would work.

On another note, I just picked up my repaired LP125M today, so will put those into service tomorrow afternoon. If the hum is not there with them, I may not pursue it anymore knowing that it isn't something wrong with the 11A.

[pstrisik]

Got it diagnosed!

Turns out to be one of the most common sources of hum that I didn't know about (learned a lot through this). It is caused by the cable tv connection. When I disconnect the coax cable from the cable box, the hum goes away.

I also now realize that the hum started when I changed my power distribution arrangement. I have two Panamax power units. One has my power amp(s), usb fans, turntable, and phono stage plugged into it. The other has everything else (digital sources, plasma, preamp, pre/pro, etc.). I used to have the unit with the amps plugged into the other unit. When I got mono amps, I decided to plug in the units separately due to the extra power draw, though into the same outlet. Evidently, plugging one into the other prevented the ground loop. Separating them, even when in the same outlet, allowed the loop to occur.

For now, I disconnected the cable and have ordered the Jensen Transformers ISO-MAX Cable TV Ground Isolator (ZVRD-1FF). Post after post said it works. It better at $50 for that little thing!

In the process of diagnosing this, I called Panamax for some advice. The tech suggested that there was nothing wrong with plugging one panamax into the other as far as load is concerned. Each one is 15A. But, since they are both plugged into the same circuit anyway, the max draw is 15A whether they are plugged into each other or separately in the same outlet.

Whew!

And, I have my LP125M's up and running. I think I have a thread going on those, so I will post there.

[pstrisik]

Looks like final update for my hum. Installed the Jensen Transformers Ground Isolator. It works! :thumbsup:

No hum whatsoever...... except for me going Mmmmhmmm!! :music:

[rlw3]

My hum problems have greatly reduced now that air conditioners are no longer needed.
Had the system running 9 hours and at the end it had a little 60 hz hum which i will try to kill by changing where things are plugged in and maybe using a ground cheater to test for that.

[pstrisik]

Hi Ray,

That's good news! You'll have to move up here to Alaska where air conditioning isn't needed! :D

[rlw3]

On Briz's summer tubes winter tubes thread member microstrip reports a hum problem reduced by removing the tranny cage/heat and working on the physical mounting of the tranny/vibrations. 2 problems both contributing minus only the bac air conditioning season electricity which makes the hum a lot louder than it is now. Good possibility of killing hum with a little work. Will make sure caps are discharged before touching anything.

[ronenash]

On Briz's summer tubes winter tubes thread member microstrip reports a hum problem reduced by removing the tranny cage/heat and working on the physical mounting of the tranny/vibrations. 2 problems both contributing minus only the bac air conditioning season electricity which makes the hum a lot louder than it is now. Good possibility of killing hum with a little work. Will make sure caps are discharged before touching anything.


Not sure you want to get into this Ray. These amps are not very easy to take apart and I personally would not leave any loose screws inside. If you find a loose screw that you can tighten, that's another story.

[rlw3]

Ron, you are right about the difficulty of opening the amp up. The hum was extremely low yesterday when it was very cool. Today was warmer and had a little encrease in hum. Thinking all of my problem might be air conditioners. I live very close to a military base so I wonder what it contributes. Read Briz's thread, the problem of hum was helped by loosing the trannies and giving them shock obsorbers. Sounds great but very hard to do

[ronenash]

If you want to go in to this you can take the cover bottom cover off. You will find the screws that hold the tranny cover underneath. I would put a piece of rubber or something between the tranny and the cover. I would definitely not loose the screws. Remember, these transformers weigh a lot and if they are not well attached they can deform the chassis when you move the amp.
A more sensible solution in my opinion would be to get a good power conditioner such as the Torus.

[microstrip]

IMHO, putting rubber between the transformers and and the cage will only make it worst, as it will thermally insulate the power transformer, increasing its temperature. As I do not have children or pets around, my amplifiers are now operating without the transformer covers. BTW, releasing the transformer mounts a few turns is not dangerous, as the nuts are self locking and will stay attached.

As I suspect that the mechanical hum is caused by the increase of the temperature that dilates the iron blades, every thing you can do to circulate the air in the vicinity of the transformer will reduce hum. I have also tried decreasing the tube bias by 30% and the transformer immediately became silent - but sound decreased quality.

But my greatest hope is still on putting new silent blocks for the transformer and for the cage mount that will rise height about half inch.

[rlw3]

Why does releasing/loosening the transformer mounts work?
Please describe the silent blocks you write about?
Would placing small wood blocks like ayre myrtlewood blocks under the tranny cage be good?
How do you remove the tranny cage safely?

[microstrip]

Why does releasing/loosening the transformer mounts work?
Please describe the silent blocks you write about?
Would placing small wood blocks like ayre myrtlewood blocks under the tranny cage be good?
How do you remove the tranny cage safely?

Releasing/loosening the transformer mounts can help to decoupling the transformer from the chassis, avoiding communicating the vibration to the whole structure. The silent blocks I consider are small soft rubber cylinders with decoupled metal inserts or screws. Wood blocks will not decouple the transformer from the chassis as they are not isolators between 50/60 and 300 Hz.

The transformer cage is easily taken out after the four screws holding it are taken. You have to take out the bottom plate to have access to them. In my case it lead to the the most significant improvement.

BTW, as the amplifier is very heavy I always manipulate it on a large two inch thick foam plate on the floor.

[erfurt]

I'd had some issues with my plasma tv injecting dc into the ac line which unfortunately is common with the stereo gear. The transformers in my mono amps would hum in a cyclical type pattern about every 20 seconds.
Gilbert at Blue Circle Audio devised this hum killer device with built in 1/2 BC6000 conditioning and a bypass switch to bypass quiet device when tv is off.
Hooked both amps to this unit and plugged it into wall - superb results.
Very cool and works like a charm.
Added a couple of 6x filters into thr spare outlets for good measure.