Mapman,
Actually, I don't need the amp on to play the stereo, I can use headphones! With the amp powered off, and using 'phones, I heard the hum. After about 1.5 hours, the preamp must have warmed up enough to kill the hum, because it did go away. Hence, my theory that the problem was thermal.
Lee |
" If I turn off the amp, but leave the preamp powered up, there doesn't seem to a problem."
Well, you need the power amp with accompanying hum on to play, don't you?
Sounds like the transformers in the power amp is the cause of teh inductance hum in the phono-pre....same problem I had.
Try separating them further apart physically and see if that helps. if your IC is too short, use a cheap longer one temporarily just as a test to see if it helps. If it does, get a longer good IC to your liking and keep them apart. |
An Update - which I hope is final.
The hum doesn't appear to be grounding related. Instead, it appears to be thermal in nature. If I turn off the amp, but leave the preamp powered up, there doesn't seem to a problem. For 2 days in a row now, there's been no hum.
If it ain't broke, I won't fix it.
Thanks to those who helped.
Lee
The problem appears |
After looking at the website, I'm wondering if I can anything like that at Home Depot, or Lowes. |
You may have a different problem yet this site provides some potentially useful shielding and measurement solutions.
http://www.lessemf.com/mag-shld.html |
The only moving of the preamp has been to move it to a separate shelf by itself (no discernible difference). When I connected different amp, they were about 3' apart. No difference then either.
This morning, I put a metal widow screen behind the stereo to act as a shield, hoping the noise was coming from that direction. It was a no go. |
Have you tried physically moving the pre-amp with the phono stage around to see if the hum level changes with location?
If so, it is inductance hum from some nearby power transformer, possibly in power amp or other component(s) or other external source.
If you haven't already, try this first to determine if that is the problem. If so, switching to an external phono stage is not necessarily the solution. Addition shielding and/or relocation of components for better separation is. |
When I separated the amp and preamp (twice now), they are currently separated by a shelf, and a CD player. They used to be right on top of one another. The 1st time was when I tried to eliminate the amp by connecting my old Carver M-500T. It buzzed like crazy when I did that (3' apart).
Each thing I do requires extraordinary effort. About 5 years ago, I had a massive stroke. The doctors didn't even think I'd make it through the night. Now, I'm chasing little, annoying buzzes. I may have lost a few brain cells, but they weren't audiophile related. |
Well I see I came late to your 'party'.
At the end of your other post you seemed to have solved your problem which you traced to an interaction between the amp and the pre-amp. -You referred to RF if I recall - I've a very short memory :-).
Going back to my original post - you seem to have seperated your amp and pre-amp in a quest to correct your problem. To what extreme have you taken this? When possible and necessary I try to keep the amp and phonostage (of what ever kind) at least 6ft apart. A couple of my pre-amps with phono stages come with seperate power supplies with long cords to allow a distant seperation to avoid hums - and it makes a difference believe me. Long winded way of saying, get some 6ft long IC's (cheap variety will do) and put your amp as far away from the pre-amp as possible. BTW, I don't think you are dealing with stray RF from anything, I think you are dealing with magnetic fields - I think.
May not work but gives you something to do! :-) |
Newbee,
I shorted the ICs by jamming a piece of tinfoil into a cheapo pair of ICs (very high tech), and then putting that IC into the phono inputs of the preamp, which is a NAD 1155, which is solid state. I'd like to go tubes, but I can't afford it, and I'd need a divorce first.
This may be important in isolating the buzzing noise. Then again, maybe not. I just powered off the B & K amp, and put a pair of headphones into the preamp. There was still a buzz present. That means that the amp isn't the source.
It gets weirder, and weirder. BTW, this morning, I powered off my wireless router, and DSL modem in the slim hope that they were the cause. As expected, they weren't. |
Newbee -- Here's his original thread: http://forum.audiogon.com/cgi-bin/fr.pl?htech&1233446646His preamp is a NAD 1155, which I assume is solid state. I think he shorted the phono inputs by connecting interconnect cables to them, and at the other end of the cables putting a piece of foil between the center pin and the ground of the male rca. The hum was not present when he did that. Regards, -- Al |
What kind of pre-amp are you using? If it has tubes in the phono stage you could be getting hum from them. I'm not sure I understand what you mean by shorted interconnects - are you saying that you in essence shorted the phono inputs by using IC's and the noise went away? Or are you saying that you connected the TT IC's to a line input and there was no hum. How did you short the IC's - I've never seen female shorting plugs. Interesting, anyway........ |
I thought that the problem may be thermal, that's why it lessens to a degree when the preamp/combo are left on for a while. Now, I have the preamp on a separate shelf. The amp can no longer provide a measure of heat. Maybe a heating pad on the preamp will goose it along. If I want to get the preamp really cold, all I have to do is put it outside. |
Lee -- Towards the end of your original thread about this problem the hum disappeared, returned, and disappeared again as you did various things (reversing plug polarities, separating and shielding components, etc). Obviously it has now returned once more.
Therefore, what I'm thinking is that it may be an intermittency in the phono stage of the preamp, which happened to not be occurring when you shorted the inputs. So ruling out the preamp on the basis of that experiment may not have really been conclusive.
If it is an intermittency in the preamp, my suspicion would be that a capacitor may be on the edge of failure, as you were led to believe way back at the beginning of that other thread.
Does the problem seem to be temperature or warmup sensitive? If you are not sure, try putting the preamp in either a cold basement or a warm attic for a while, and see what happens.
Beyond that, I agree with Newbee's suggestion to try to get a separate phono stage with return privileges.
Regards,
-- Al |
You should be able to determine what is causing the hum through an organized trial and error. Don't live with it. Isolate it and fix it. |
Newbee,
The phono input even hums when no phono is even there. After seeing that, I tried the shorted interconnects. When I got no hum then, I proved that the preamp wasn't at fault. I haven't been able to identify an extraneous source, so I wrestling with the question of buying an outboard unit. I may just have the same problem with that, however.
Lee |
It can be, but often a hum can be caused by a phono stage, one that is in the pre-amp, or an outboard one, that is too close to transformers, especially in amps, and the cables from the TT to the phono stage must also be placed carefully so they do not come close to a transformer or PC. If you haven't already tried that, be sure to do so before you buy an outboard unit. Often just getting space (as much as possible) between the phono pre and or cables from other electronics will do the job. You probably already knew that and eliminated these possibilities. So....
If you can get one that will match your cartridge and have a return privilege, why not - the ones you mention are inexpensive enuf. |
