I've assumed for awhile that I've got some DC on my line. At least half of the power transformers that have passed over my bench or system have buzzed. I'm working on a new amp, and my latest PT buzzes pretty obnoxiously. When I touch one lead of my DMM to Line and one to Neutral with it set to "DC volts" I get 18.3 volts. That seems like a great deal of DC, right?
So, I built a DC blocker according to this schematic. I used a high current bridge and a pair of 6800uf 16V caps from my parts bin. (Of course, the thread does say to not just use parts from the bin . . .) Nothing changed (18.3VDC, buzzzzzzz). Similarly, would my variac block DC if I had it? I still measure 18.3VDC on the back end of it, but maybe autoformers don't block DC like transformers.
So, there are two possibilities. One is that my DC blocker doesn't work, the other is that I don't really have DC on my line, just buzz-y transformers.
I could maybe live with the buzz, but I'd like to figure it out. I just purchased this PT, a NOS Stancor. If it does indeed buzz this loud (I am using it well within it's current rating and for its intended application), I'll consider trying to return/exchange it. I know similar questions have been asked frequently, and I'm trying to dig through old posts. The likely search terms are so common that it is tough to find applicable info.
thanks for your help!
pj
www.wildburroaudio.com
So, I built a DC blocker according to this schematic. I used a high current bridge and a pair of 6800uf 16V caps from my parts bin. (Of course, the thread does say to not just use parts from the bin . . .) Nothing changed (18.3VDC, buzzzzzzz). Similarly, would my variac block DC if I had it? I still measure 18.3VDC on the back end of it, but maybe autoformers don't block DC like transformers.
So, there are two possibilities. One is that my DC blocker doesn't work, the other is that I don't really have DC on my line, just buzz-y transformers.
I could maybe live with the buzz, but I'd like to figure it out. I just purchased this PT, a NOS Stancor. If it does indeed buzz this loud (I am using it well within it's current rating and for its intended application), I'll consider trying to return/exchange it. I know similar questions have been asked frequently, and I'm trying to dig through old posts. The likely search terms are so common that it is tough to find applicable info.
thanks for your help!
pj
www.wildburroaudio.com
Besides a sucky multimeter, 
you may have an asymmetrical load somewhere in the house (e.g. an electric blanket or space heater set on medium). These can distort the AC waveform to some degree and cause some transformers to buzz. It may also fool a meter into thinking there’s an offset, as the asymmetry integrates out to an offset in the meter.
you may have an asymmetrical load somewhere in the house (e.g. an electric blanket or space heater set on medium). These can distort the AC waveform to some degree and cause some transformers to buzz. It may also fool a meter into thinking there’s an offset, as the asymmetry integrates out to an offset in the meter.
It is indeed a sucky multimeter. I don't think I've got anything problematic running in my house right now. I had a couple of lamp switches with dim and bright positions. In the former, they caused my chip amp transformer to hum somethin' fierce. I changed them to regular old on/off switches.
If only getting a better DMM would stop my transformers from buzzing . . .
pj
If only getting a better DMM would stop my transformers from buzzing . . .
pj
Then, IMNSHO, you have no DC on your line.
Lots of transformers hum for other reasons, mostly poor winding, than DC on the line. I've had a lot of trouble with it, to the extent that I bought a little venturi-type vacuum pump on ebay and built a chamber so I can vacuum impregnate with varnish. It's a bit of a pain, but has cured it every time so far.
Aloha,
Poinz
AudioTropic
Lots of transformers hum for other reasons, mostly poor winding, than DC on the line. I've had a lot of trouble with it, to the extent that I bought a little venturi-type vacuum pump on ebay and built a chamber so I can vacuum impregnate with varnish. It's a bit of a pain, but has cured it every time so far.
Aloha,
Poinz
AudioTropic
Okay,
I put the varnish in a dedicated pan on the stove, on 'warm', or whatever it takes to get it hot enough that it's hot, but I can touch it. The transformer goes in the oven on 200° or so, same deal. When they're warm, I put the trans in the vacuum container upside down, and pour varnish in there until it's almost full. If it's an open-frame transformer, I put it in a can that's not too much bigger than the trans and pour the varnish in there.
The pump I use is the kind you see millions of on ebay, a red box with a venturi inside. These will actually pull a pretty good suck, about 28", but they take a lot of air, more than my compressor can deliver, so I have to plan it out. I pump the compressor all the way up to 150lb. max, and set the regulator to about 60lb. I put the top on the vac container and plug in the air. I then dial the air up as I watch both the gauge and the transformer. When the varnish is fizzing, I leave the air where it is, and dial it up to just keep the fizz going and not let the varnish geyser all over the inside of the vac bottle (which it will, and is an amazing cleanup chore), until the compressor has started up again and can't pull any more vacuum since it's running out of air. I can usually get up to 26-27" if I'm careful and quick, which is pretty good (30" is outer space, brah). I dial down the pressure, unplug the air, and dump the excess varnish back in the can, setting the transformer on top so it can drain a few minutes. The gear gets cleaned up, and the trans set in the sun to dry a day or two.
This has fixed every hummy transformer I've tried it on. It would be like magic, except that it's a PITA. Worth it, though.
Aloha,
Poinz
AudioTropic
I put the varnish in a dedicated pan on the stove, on 'warm', or whatever it takes to get it hot enough that it's hot, but I can touch it. The transformer goes in the oven on 200° or so, same deal. When they're warm, I put the trans in the vacuum container upside down, and pour varnish in there until it's almost full. If it's an open-frame transformer, I put it in a can that's not too much bigger than the trans and pour the varnish in there.
The pump I use is the kind you see millions of on ebay, a red box with a venturi inside. These will actually pull a pretty good suck, about 28", but they take a lot of air, more than my compressor can deliver, so I have to plan it out. I pump the compressor all the way up to 150lb. max, and set the regulator to about 60lb. I put the top on the vac container and plug in the air. I then dial the air up as I watch both the gauge and the transformer. When the varnish is fizzing, I leave the air where it is, and dial it up to just keep the fizz going and not let the varnish geyser all over the inside of the vac bottle (which it will, and is an amazing cleanup chore), until the compressor has started up again and can't pull any more vacuum since it's running out of air. I can usually get up to 26-27" if I'm careful and quick, which is pretty good (30" is outer space, brah). I dial down the pressure, unplug the air, and dump the excess varnish back in the can, setting the transformer on top so it can drain a few minutes. The gear gets cleaned up, and the trans set in the sun to dry a day or two.
This has fixed every hummy transformer I've tried it on. It would be like magic, except that it's a PITA. Worth it, though.
Aloha,
Poinz
AudioTropic
Hi folks,
poindexter wrote:
yes transformer like to hum because this:
http://hyperphysics.phy-astr.gsu.edu/Hbase/solids/magstrict.html
more reasons why trafos like to hum are unsufficícant core sizes by operate them close to the max induction near the iron saturation. In other words cheap trafos.
dc in the eletrical mains occurs from non linear appliances like triac controls like in a light dimmer, one way rectifiers in heater on " half". And they appears in vast quantaties as in SMPS without pfc and flourescent ballasts.
with humming regards
Wolfgang
poindexter wrote:
yes transformer like to hum because this:
http://hyperphysics.phy-astr.gsu.edu/Hbase/solids/magstrict.html
more reasons why trafos like to hum are unsufficícant core sizes by operate them close to the max induction near the iron saturation. In other words cheap trafos.
dc in the eletrical mains occurs from non linear appliances like triac controls like in a light dimmer, one way rectifiers in heater on " half". And they appears in vast quantaties as in SMPS without pfc and flourescent ballasts.
with humming regards
Wolfgang
Yes, that is the reason, and the reason that varnish impregnation will stop the hum. The magnetic fields generate physical forces on the windings, which move; and the varnish holds them in place.
I don't use special transformer varnish, which would be difficult to source around here. I use a spar (McCloskey Man O' War) which is readily available, dries slow, and stays a little soft.
The vacuum container I use is the inner container of a slow cooker, which is pretty sturdy, with a piece of ¼" polycarbonate over the top sealed by an alex caulk gasket and the pipe from the pump mounted in it. The gauge is mounted in the pipe on a tee. It's a very home-lash-up setup, and works like crazy.
Aloha,
Poinz
AudioTropic
I don't use special transformer varnish, which would be difficult to source around here. I use a spar (McCloskey Man O' War) which is readily available, dries slow, and stays a little soft.
The vacuum container I use is the inner container of a slow cooker, which is pretty sturdy, with a piece of ¼" polycarbonate over the top sealed by an alex caulk gasket and the pipe from the pump mounted in it. The gauge is mounted in the pipe on a tee. It's a very home-lash-up setup, and works like crazy.
Aloha,
Poinz
AudioTropic
astouffer said:
Shimming between the windings and the core seemed pretty easy, so I hammered a few toothpick halves in. It has quieted it down considerably. It is probably quiet enough to be tolerable now, especially because it will be in an enclosed power supply chassis. I'm tempted to pound a few more in. I don't see how they could hurt anything.
pj
Ha I have a diffusion pump in the garage that can go to 1 x 10 to the 9th torr, that should do a pretty good job LOL.
Oh and 30 inched of mercury isn't outer space. Outer space is in the micron or militorr vacuum range.
You can't get this with out a good 2 stage vane pump it's high vacuum, not ultra high.
Oh and 30 inched of mercury isn't outer space. Outer space is in the micron or militorr vacuum range.
You can't get this with out a good 2 stage vane pump it's high vacuum, not ultra high.
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