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?

[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]

Originally Posted by 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?

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]

Originally Posted by Coppy

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. 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.