Hi,
My gainclone has just moved from my workroom to the living room, and now I can hear a buzzing noise from it
I don't know if it's because the wall wart isn't grounded there, of if I wasn't able to hear it in the workroom because the computer is in the same room.
The noise comes from the amp itself, the speakers are dead quiet.
I think it comes from the transformer, loke a mechanical noise.
What can cause this? And how can I solve this problem?
Thanks
Alex
My gainclone has just moved from my workroom to the living room, and now I can hear a buzzing noise from it
I don't know if it's because the wall wart isn't grounded there, of if I wasn't able to hear it in the workroom because the computer is in the same room.
The noise comes from the amp itself, the speakers are dead quiet.
I think it comes from the transformer, loke a mechanical noise.
What can cause this? And how can I solve this problem?
Thanks
Alex
Hi Alex;
Transformer noise is an unfortunate fact of life (particularly for those of us using Hammond 200 series PS trafos on 120VAC mains!). Here are some of the causes:
1. too high AC mains voltage for the primary
2. DC offset in the AC mains
3. too high a current draw from the secondary
4. trafo is not in proper electrical contact with the ground (i.e. ungrounded core)
You might (CAREFULLY!!!!!) measure the AC mains voltage and see if the buzzing is a function of the time of day or season (in this area AC mains goes from a low of around 113VAC to a high of around 126VAC depending on time of day, season, etc. There is some regularity to it (i.e. when everyone is running air conditioners, the AC voltage drops considerably....at night the AC mains also is allowed to sag by the power company).
You can attempt to fix DC offset by a filter circuit, or by use of an isolation transformer (the isolation transformer may well begin to hum though, so it's best to put it in another room). Some have been posted in the tubes forum here, so you ought to do a search if you're interested.
Not much to be done except replacement by a larger current rated trafo if you're drawing too much from it.
If the trafo's core is ungrounded, expect both noise and hotter operation. Check the ground shackles to ensure that there's been no inadvertant change here during the move.
There is also a trick to minimise the amount of hum that's audible. Shock mounting the trafo on thick rubber rings seems to help, particularly if it was previously bolted securely to a large plate (that can act as a sounding board). Just make sure that you have a good ground tie if you mechanically isolate the trafo.
Obviously any circuitry or wiring on the primary side of the AC mains is a potential danger....please exercise all due caution and if any doubts exist about either the circuit or your ability to implement it, do not proceed!
Good luck and all the best!
Ja mata,
Morse
PS Sorry for the "boiler plate" safety warning, but the US has a hard earned rep as the most litigious society on the planet.
Transformer noise is an unfortunate fact of life (particularly for those of us using Hammond 200 series PS trafos on 120VAC mains!). Here are some of the causes:
1. too high AC mains voltage for the primary
2. DC offset in the AC mains
3. too high a current draw from the secondary
4. trafo is not in proper electrical contact with the ground (i.e. ungrounded core)
You might (CAREFULLY!!!!!) measure the AC mains voltage and see if the buzzing is a function of the time of day or season (in this area AC mains goes from a low of around 113VAC to a high of around 126VAC depending on time of day, season, etc. There is some regularity to it (i.e. when everyone is running air conditioners, the AC voltage drops considerably....at night the AC mains also is allowed to sag by the power company).
You can attempt to fix DC offset by a filter circuit, or by use of an isolation transformer (the isolation transformer may well begin to hum though, so it's best to put it in another room). Some have been posted in the tubes forum here, so you ought to do a search if you're interested.
Not much to be done except replacement by a larger current rated trafo if you're drawing too much from it.
If the trafo's core is ungrounded, expect both noise and hotter operation. Check the ground shackles to ensure that there's been no inadvertant change here during the move.
There is also a trick to minimise the amount of hum that's audible. Shock mounting the trafo on thick rubber rings seems to help, particularly if it was previously bolted securely to a large plate (that can act as a sounding board). Just make sure that you have a good ground tie if you mechanically isolate the trafo.
Obviously any circuitry or wiring on the primary side of the AC mains is a potential danger....please exercise all due caution and if any doubts exist about either the circuit or your ability to implement it, do not proceed!
Good luck and all the best!
Ja mata,
Morse
PS Sorry for the "boiler plate" safety warning, but the US has a hard earned rep as the most litigious society on the planet.
trafo isolation and grounding
Thanks a lot for the lengthy reply, Morse.
My 2 trafos are going to be 22-0-22VAC 150-200VA (not clear), one of these trafos per dual channel.
By dual I mean separate chip (channel) for tweeter and mid in each stereo channel, so two chips on each stereo channel. Going for an active x-over, you see.
So one of these trafos will be feeding two LM3875's but i do not expect high current draw from the one running the tweeter.
Do you guys think these trafos will be sufficient to run the chips optimally (ie with highest (output / heat) ratio, i guess)?
Also I've been ponderring on how to mount these trafos: my base is going to be 3/4'' MDF with alum heatsink covering the top. So I was thinking of flushmounting the trafos on this MDF (just make another layer of MDF with a hole for the trafo)
What kind of rubber or material should i use to 'line' between the trafo and MDF? It has to be pretty heat resistant, no?
Also how can one ground a toroidal trafo?
Thanks
Alex
Thanks a lot for the lengthy reply, Morse.
My 2 trafos are going to be 22-0-22VAC 150-200VA (not clear), one of these trafos per dual channel.
By dual I mean separate chip (channel) for tweeter and mid in each stereo channel, so two chips on each stereo channel. Going for an active x-over, you see.
So one of these trafos will be feeding two LM3875's but i do not expect high current draw from the one running the tweeter.
Do you guys think these trafos will be sufficient to run the chips optimally (ie with highest (output / heat) ratio, i guess)?
Also I've been ponderring on how to mount these trafos: my base is going to be 3/4'' MDF with alum heatsink covering the top. So I was thinking of flushmounting the trafos on this MDF (just make another layer of MDF with a hole for the trafo)
What kind of rubber or material should i use to 'line' between the trafo and MDF? It has to be pretty heat resistant, no?
Also how can one ground a toroidal trafo?
Thanks
Alex
Hi Bricolo;
Ahhhh, a toroid core. I have vanishingly little experience there (I almost universally use EI types). Darned if I know how you're supposed to ground the thing's core, but providing a pathway for the potential that builds up has helped on EI's.
Christer DEFINITELY has a point. It could be that the room you were in has something to do with it. Perhaps the wiring is on a different circuit, and it's not got a DC offset (or some ugly reactive components). Perhaps the act of moving it caused something to shift. Perhaps you tightened down the trafo a bit after you moved it (definitely want some kind of shock mounting so that the base of the amp does not act as a sounding board; similarly thick rubber legs from the amp to the table it's on will keep it from using the table as a sounding board).
Particularly if Carlos is right, and it's a loose wind (not much you can do about eliminating vibration from starting) then you have to try to isolate the transformer from the room acoustically. If it's inside a chassis that's lined with sound absorbing material (like what you'd use for sound deadening a motorcar's doors) and it's on thick shock mounts, that could help quite a bit - enough so that you will never notice it in the real world. Obviously you will have to allow for cooling, so there's a tradeoff between acoustic isolation and cooling that cannot be ignored.
Good luck! Hope it all works out for you!!
Ja mata,
Morse
Ahhhh, a toroid core. I have vanishingly little experience there (I almost universally use EI types). Darned if I know how you're supposed to ground the thing's core, but providing a pathway for the potential that builds up has helped on EI's.
Christer DEFINITELY has a point. It could be that the room you were in has something to do with it. Perhaps the wiring is on a different circuit, and it's not got a DC offset (or some ugly reactive components). Perhaps the act of moving it caused something to shift. Perhaps you tightened down the trafo a bit after you moved it (definitely want some kind of shock mounting so that the base of the amp does not act as a sounding board; similarly thick rubber legs from the amp to the table it's on will keep it from using the table as a sounding board).
Particularly if Carlos is right, and it's a loose wind (not much you can do about eliminating vibration from starting) then you have to try to isolate the transformer from the room acoustically. If it's inside a chassis that's lined with sound absorbing material (like what you'd use for sound deadening a motorcar's doors) and it's on thick shock mounts, that could help quite a bit - enough so that you will never notice it in the real world. Obviously you will have to allow for cooling, so there's a tradeoff between acoustic isolation and cooling that cannot be ignored.
Good luck! Hope it all works out for you!!
Ja mata,
Morse
Christer said:
I always assume that people test these things before building the complete amp (that is, putting everything together).
If your trafo gets extremely hot, of course, you should use a good rubber or something more appropriate for high temperatures.
I use mouse mats (pads?) and never had problems.
It absorbs vibrations very well.
Much better than the thin rubber they send with the toroids where I buy them.
I have used the expanded polymer that comes in certain packages to protect the goods inside. It is usually used with sensitive parts and I got mine from the package of a lab chromatography system. The characteristics I look for are air inside the material, like a foam, but not brittle neither too soft. If you squeeze it it yelds to pressure but not much, and in a way that resembles rubber. It cured my buzzing 800 VA transformer quite well, but I left it unbolted to cut the path of vibrations through the bolt...
Another idea I had at the time was to pot the transformer with low viscosity epoxy. But it is a bit radical.
Miguel
Another idea I had at the time was to pot the transformer with low viscosity epoxy. But it is a bit radical.
Miguel
I know what i will do!
As i mentioned my trafos will be sortof flush mounted on MDF.
I will make a donut shaped sand pillows for the trafos to rest on sandwiched between rubber washers. Also I will use thisk rubber washers on the mounting hardware, so the vibrations wont go thru them. Plus the MDF base should help.
Cheers
Alex
As i mentioned my trafos will be sortof flush mounted on MDF.
I will make a donut shaped sand pillows for the trafos to rest on sandwiched between rubber washers. Also I will use thisk rubber washers on the mounting hardware, so the vibrations wont go thru them. Plus the MDF base should help.
Cheers
Alex
Found one cause of transformer humming
F Y I - I finished my GC using Brian's boards the other day after locating a short from the mounting screws, it ran good and quiet. This morning I was listening to my GC when the toroidal transformer began to hum loudly for a few seconds then pulsed some ten times in ten seconds and repeated the pulsing every 5 to 10 seconds for about 10 minutes. Then quiet again. Asked my wife if she turned on her curling iron, and she said yes. Hummm.... Went over to the bathroom and turned on the curling iron and sure enough that was making the transformer sing again. I guess I'll have to implement one of the AC line filter circuits or just not listen when my wife is prettying herself up.
Matt
F Y I - I finished my GC using Brian's boards the other day after locating a short from the mounting screws, it ran good and quiet. This morning I was listening to my GC when the toroidal transformer began to hum loudly for a few seconds then pulsed some ten times in ten seconds and repeated the pulsing every 5 to 10 seconds for about 10 minutes. Then quiet again. Asked my wife if she turned on her curling iron, and she said yes. Hummm.... Went over to the bathroom and turned on the curling iron and sure enough that was making the transformer sing again. I guess I'll have to implement one of the AC line filter circuits or just not listen when my wife is prettying herself up.
Matt
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