Would 1N3005A zeners work in this application?
this is probably a stupid question -
i have these 1N3005A zener's lying around, and a bunch of electrolytic caps from which i'm sure i can get 2 of the right ratings. would this work for the dc-rejection filter shown here? the 1N3005A is rated at 100V/100W.
i'd like to have an inkling *before* i blow up the capacitors! (it's a long weekend and i can't get the 1N5404!)
this is probably a stupid question -
i have these 1N3005A zener's lying around, and a bunch of electrolytic caps from which i'm sure i can get 2 of the right ratings. would this work for the dc-rejection filter shown here? the 1N3005A is rated at 100V/100W.
i'd like to have an inkling *before* i blow up the capacitors! (it's a long weekend and i can't get the 1N5404!)
psarin,
I say go for it. 100v/100watt means they handle a zener current of 1 amp. They probably handle more than that forward biased. If they did happen to blow, they would simply short, and that would have the same effect as if the dc filter circuit were not in series with the transformer primary.
I say go for it. 100v/100watt means they handle a zener current of 1 amp. They probably handle more than that forward biased. If they did happen to blow, they would simply short, and that would have the same effect as if the dc filter circuit were not in series with the transformer primary.
Hi Mohan,
I'm not a very technical person and don't understand why a balanced power drain would introduce DC, but does it mean that 1 in 3 houses will have this problem? When other electrical things in the house get used the hum gets noticeably louder (especially a hair dryer!).
I am in melbourne as well - this could be a solution, but I would imagine that if stuff like hairdryers and lights and sending it crazy then perhaps I should opt for a power filter.
To clarify this configuration:
<font face=courier>
AC Live ----- -ve Cap A +ve ---- +ve Cap B -ve ---- AMP ---- AC Neutral
</font>
I am experiencing this problem big time since I moved home (no hum through the audio - all mechanical) - <a href="http://www.diyaudio.com/forums/showthread.php?threadid=914">my amp</a> is pretty loud at low listening levels, very annoying.
I'm not a very technical person and don't understand why a balanced power drain would introduce DC, but does it mean that 1 in 3 houses will have this problem? When other electrical things in the house get used the hum gets noticeably louder (especially a hair dryer!).
I am in melbourne as well - this could be a solution, but I would imagine that if stuff like hairdryers and lights and sending it crazy then perhaps I should opt for a power filter.
Any recommendations as to what rating caps I need and/or if there is a particular type of filter that would suit my hardware?
To clarify this configuration:
<font face=courier>
AC Live ----- -ve Cap A +ve ---- +ve Cap B -ve ---- AMP ---- AC Neutral
</font>
Jason,
It is rather hard to guess what is causing the interference in your electricity supply. This is because, there are too many variables. I would only resort to filters as a last measure. I have one filter that you could borrow and try.
No doubt you would have checked your earth for power lines.
Do you have any light dimmers, electronic pest control units.
Perhaps you could give me a ring (03) 9720 8730 or (03) 9720 8729 or on my telepath number 0500 566 616. Telepath is standard call charge and you need to dial the zero in front.
Mohan
It is rather hard to guess what is causing the interference in your electricity supply. This is because, there are too many variables. I would only resort to filters as a last measure. I have one filter that you could borrow and try.
No doubt you would have checked your earth for power lines.
Do you have any light dimmers, electronic pest control units.
Perhaps you could give me a ring (03) 9720 8730 or (03) 9720 8729 or on my telepath number 0500 566 616. Telepath is standard call charge and you need to dial the zero in front.
Mohan
DC blocking circuit ....
Just wanted to tell that I have built the DC filter that "mlloyd1" posted schematic for. It seems to work really good. My toroid transformer is very quiet now.
I've also got PCB layout for it if someone is interested, but it is so simple that a PCB is not needed.
/Freddie
Just wanted to tell that I have built the DC filter that "mlloyd1" posted schematic for. It seems to work really good. My toroid transformer is very quiet now.
I've also got PCB layout for it if someone is interested, but it is so simple that a PCB is not needed.
/Freddie
DC noise in the mains
Hi,
If I build enough of this filter, one for each appliance in the house will it then get rid of all possible DC in the mains?
I have two sets of child moniter, mic in one room and speaker in another, sometimes they buzz like crazy, yet sometimes they are very quiet. My Tor. transformer sing quite loud too.
May be all the filters and water pumps in my 100 gallon fish tank contribute a lot of noise into the house mains too?
Regards,
Chris
Hi,
If I build enough of this filter, one for each appliance in the house will it then get rid of all possible DC in the mains?
I have two sets of child moniter, mic in one room and speaker in another, sometimes they buzz like crazy, yet sometimes they are very quiet. My Tor. transformer sing quite loud too.
May be all the filters and water pumps in my 100 gallon fish tank contribute a lot of noise into the house mains too?
Regards,
Chris
Chris:
My immediate response without a whole of thinking would be no, because the DC may be coming in from source externally to your residence.
Of more concern is safety; I'm thinking that some of the many household appliances wouldn't necessarily like to have such a filter in series with the supply
mlloyd1
My immediate response without a whole of thinking would be no, because the DC may be coming in from source externally to your residence.
Of more concern is safety; I'm thinking that some of the many household appliances wouldn't necessarily like to have such a filter in series with the supply
mlloyd1
maybe you can help
I followed the suggestions in this page -->> http://sound.westhost.com/earthing.htm.
I have the loop breaker and a mains filter. The casing of the transformer and the mains filter is connected
to the chassis. The chassis is then connected to the mains ground. The loop breaker is installed according to the diagram in the article.
If I remove the loop breaker, there’s a very annoying hum coming out of my DIY amp. With the loop breaker connected, the annoying hum becomes a low-pitch hum that it’s tolerable. But eliminating the low-pitch hum is very desirable even if it’s tolerable.
FYi, the amp I made is a headphone amp. Also, I observed that if I connected a higher impedance headphones on it, I cannot hear the hum. With lower impedance phones (e.g. 32ohm impedance like my Philips), it’s producing a hum.
Any suggestions?
Thank you very much.
Jayel
ps. Please don't point me to Headwize or Head-hi as I've been there already.
I followed the suggestions in this page -->> http://sound.westhost.com/earthing.htm.
I have the loop breaker and a mains filter. The casing of the transformer and the mains filter is connected
to the chassis. The chassis is then connected to the mains ground. The loop breaker is installed according to the diagram in the article.
If I remove the loop breaker, there’s a very annoying hum coming out of my DIY amp. With the loop breaker connected, the annoying hum becomes a low-pitch hum that it’s tolerable. But eliminating the low-pitch hum is very desirable even if it’s tolerable.
FYi, the amp I made is a headphone amp. Also, I observed that if I connected a higher impedance headphones on it, I cannot hear the hum. With lower impedance phones (e.g. 32ohm impedance like my Philips), it’s producing a hum.
Any suggestions?
Thank you very much.
Jayel
ps. Please don't point me to Headwize or Head-hi as I've been there already.
While working in the final stages of a pair of active speakers,
I encountered mechanical hum from the transformer, as
described in previous posts.
Being slightly baffled by this, as I knew the transformers were
dead quiet if connected to mains while unloaded, they were at
this point connected to the bridge and the reservoir capacitors
only.
After a little head scratching I had to verify by disconnecting the
bridge, and sure it went mute. Scratch!
So, connect the bridge without the caps, Hum... hum?!
So here I have a 1KVA Toroid transformer that is silent while
unloaded, but complains quite loudly if connected to an unloaded
bridge!!
Discovering that loading the transformer brought the noise down
the solution proved simple.
Connecting a 1uF polyprop pulse cap across the secondaries that
connect to the bridge, I had a suitable load to bring the
transformer out of saturation and into its operating range, while
at the same time providing some HF filtering for bridge and mains
noise.
My Magnetics theory needs a little work, but I guess bridge
leakage is part of the answer, as the audible hum had an
intensity buildup period of about 1 second.
Meanwhile if someone in the know could explain how a regular
unloaded bridge rectifier can bring a transformer into saturation,
it would be appreciated
I encountered mechanical hum from the transformer, as
described in previous posts.
Being slightly baffled by this, as I knew the transformers were
dead quiet if connected to mains while unloaded, they were at
this point connected to the bridge and the reservoir capacitors
only.
After a little head scratching I had to verify by disconnecting the
bridge, and sure it went mute. Scratch!
So, connect the bridge without the caps, Hum... hum?!
So here I have a 1KVA Toroid transformer that is silent while
unloaded, but complains quite loudly if connected to an unloaded
bridge!!
Discovering that loading the transformer brought the noise down
the solution proved simple.
Connecting a 1uF polyprop pulse cap across the secondaries that
connect to the bridge, I had a suitable load to bring the
transformer out of saturation and into its operating range, while
at the same time providing some HF filtering for bridge and mains
noise.
My Magnetics theory needs a little work, but I guess bridge
leakage is part of the answer, as the audible hum had an
intensity buildup period of about 1 second.
Meanwhile if someone in the know could explain how a regular
unloaded bridge rectifier can bring a transformer into saturation,
it would be appreciated
does your toroid still sing?
while roaming through some past threads, I found this version of the "dc_blocker" circuit some of us have been using to quiet our unhappy toroids.
this appears to be used in a currently marketed, very reliable amplifier. I'll leave the details to the reader
enjoy,
mlloyd1
while roaming through some past threads, I found this version of the "dc_blocker" circuit some of us have been using to quiet our unhappy toroids.
this appears to be used in a currently marketed, very reliable amplifier. I'll leave the details to the reader
enjoy,
mlloyd1
Attachments
I've done some measurements that show what's really hapening when you connect a transformer to mains
Using a lowpass filter [100k + 47uF] I have measured about 50mV average over time of DC on my mains supply
I also have an old electric heater that in half-power mode uses a diode in series with the heat element to pass only half of the mains waveform. When I plug this heater in half-power mode I get an additional 1V of offset on mains supply
To test the need and the efficiency of DC filtering, I've done some measuremens of the current through the primary of a 750VA toroidal transformer
This oscillogram shows what happens when I connect the transformer to mains and let it deal with the 50mV DC offset
Blue trace is mains waveform at 100V/div [230V AC], it looks more like a clipped triangle wave instead a sine wave due to the line inductance limiting the slew rate and all the rectifiying applications consuming all the current only during the peaks [30% of total time]
Red trace is the current through the primary at 200mA/div. Transformer saturation towards the negative side is evident, reaching 350mA peak of leakage current. The transformer buzzs slightly due to the saturation
The noise present in the current waveform is common mode and was suppressed in further measurements adding a common mode filter between mains and measurement point
The second oscillogram shows what happens when I plug the electric heater in half-power mode
Red trace this time is in 2A/div so the leakage peak current exceeds 6A. The transformer is heavily saturated towards the upper side and buzzs loudly.
The third oscillogram shows what happened when I placed a DC filter consisting of two 1000uF 16V and some diodes in series with the primary
This time, red trace is 20mA/div and shows the small leakage current due to both the magnetizing inductance and the parasitistic capacitance between adjacent turns. The transformer is no longer saturated and performs silently
the fourth oscillogram shows the induced voltage in a loop of wire of 10cm diameter placed vertically, paralell and 1cm away from the transformer [placed horizontally] obtained when the transformer was saturating with more than 6A peak [with the electric heater plugged]
The red trace is 2mV div and shows the induced voltage in the loop of wire
That measurement demonstrates that when a 50-60Hz transformer is saturating, it produces electro-magnetic-interferences that induce noise voltages on everything in the nearhood
Actually, I think that +-5mV of low frequencies induced in a loop of wire of 10cm diameter near the transformer is a serious thing since this EMI is at audio frequencies, it's not RF so it's 100% audible and it may be happening in all your transformers
In the other hand, all the tests were performed with open secondaries but if we add load so that primary current has peaks of 6A, then the EMI radiated would be the same or higher
With load, the EMI is produced due to flux in the leakage inductance, resonances due to parasitistic inter-turn capacitance, RF ringing due to diode turn-off characteristics and the fact that the peak current through the transformer is 3 times or more the average DC current after rectification
In conclusion : Rectifiying the output of 50-60Hz transformers produces EMI as any SMPS does and this phenomena gets aggravated when the transformer is saturating due to direct connection to mains without a DC filter
50-60Hz transformers are nothing but big, bulky and crappy antennas
Using a lowpass filter [100k + 47uF] I have measured about 50mV average over time of DC on my mains supply
I also have an old electric heater that in half-power mode uses a diode in series with the heat element to pass only half of the mains waveform. When I plug this heater in half-power mode I get an additional 1V of offset on mains supply
To test the need and the efficiency of DC filtering, I've done some measuremens of the current through the primary of a 750VA toroidal transformer
This oscillogram shows what happens when I connect the transformer to mains and let it deal with the 50mV DC offset
An externally hosted image should be here but it was not working when we last tested it.
Blue trace is mains waveform at 100V/div [230V AC], it looks more like a clipped triangle wave instead a sine wave due to the line inductance limiting the slew rate and all the rectifiying applications consuming all the current only during the peaks [30% of total time]
Red trace is the current through the primary at 200mA/div. Transformer saturation towards the negative side is evident, reaching 350mA peak of leakage current. The transformer buzzs slightly due to the saturation
The noise present in the current waveform is common mode and was suppressed in further measurements adding a common mode filter between mains and measurement point
The second oscillogram shows what happens when I plug the electric heater in half-power mode
An externally hosted image should be here but it was not working when we last tested it.
Red trace this time is in 2A/div so the leakage peak current exceeds 6A. The transformer is heavily saturated towards the upper side and buzzs loudly.
The third oscillogram shows what happened when I placed a DC filter consisting of two 1000uF 16V and some diodes in series with the primary
An externally hosted image should be here but it was not working when we last tested it.
This time, red trace is 20mA/div and shows the small leakage current due to both the magnetizing inductance and the parasitistic capacitance between adjacent turns. The transformer is no longer saturated and performs silently
the fourth oscillogram shows the induced voltage in a loop of wire of 10cm diameter placed vertically, paralell and 1cm away from the transformer [placed horizontally] obtained when the transformer was saturating with more than 6A peak [with the electric heater plugged]
An externally hosted image should be here but it was not working when we last tested it.
The red trace is 2mV div and shows the induced voltage in the loop of wire
That measurement demonstrates that when a 50-60Hz transformer is saturating, it produces electro-magnetic-interferences that induce noise voltages on everything in the nearhood
Actually, I think that +-5mV of low frequencies induced in a loop of wire of 10cm diameter near the transformer is a serious thing since this EMI is at audio frequencies, it's not RF so it's 100% audible and it may be happening in all your transformers
In the other hand, all the tests were performed with open secondaries but if we add load so that primary current has peaks of 6A, then the EMI radiated would be the same or higher
With load, the EMI is produced due to flux in the leakage inductance, resonances due to parasitistic inter-turn capacitance, RF ringing due to diode turn-off characteristics and the fact that the peak current through the transformer is 3 times or more the average DC current after rectification
In conclusion : Rectifiying the output of 50-60Hz transformers produces EMI as any SMPS does and this phenomena gets aggravated when the transformer is saturating due to direct connection to mains without a DC filter
50-60Hz transformers are nothing but big, bulky and crappy antennas
Great Measurements!
I am also thinking about SMPS for my next project,
but I am still convinced that they are even more critical
in EMI, because the voltages inducted to a loop are proportional
to the speed of the change in the magnetic field (d phi / d t )....
May be one positive point in SMPS is that these signals are above
audio frequencies. May be I know more about SMPS for Audio
in one year.... ;-)
I am also thinking about SMPS for my next project,
but I am still convinced that they are even more critical
in EMI, because the voltages inducted to a loop are proportional
to the speed of the change in the magnetic field (d phi / d t )....
May be one positive point in SMPS is that these signals are above
audio frequencies. May be I know more about SMPS for Audio
in one year.... ;-)
Have you seen this:
I have made a DC trap with one or three diodes in series.
If the interest is huge (> 50 pcb's) maybe we can do a group purchase. I have got only a few a these pcb's.
An externally hosted image should be here but it was not working when we last tested it.
I have made a DC trap with one or three diodes in series.
If the interest is huge (> 50 pcb's) maybe we can do a group purchase. I have got only a few a these pcb's.
Great idea, but 2x10.000uF is way too much capacitance
I've noticed that line offset fluctuates and capacitance should be small enough to accomodate these fluctuations, I tested bigger capacitors but selected 2x1000uF for this reason
When you rectify the output of the transformer, current consumption is at 100Hz, 300Hz, 500Hz, 700Hz, etc.. But mainly at 300Hz and 500Hz, so 500uF [2x1000uF] has low enough impedance [1 ohm] and still allows faster DC changes with less transient saturation [for 120V AC capacitance should be doubled]
The problem may be ripple current in the capacitors, but placing more 1000uF in series-paralell solves it
Using smaller capacitors also has smaller space and cost requirements
I've noticed that line offset fluctuates and capacitance should be small enough to accomodate these fluctuations, I tested bigger capacitors but selected 2x1000uF for this reason
When you rectify the output of the transformer, current consumption is at 100Hz, 300Hz, 500Hz, 700Hz, etc.. But mainly at 300Hz and 500Hz, so 500uF [2x1000uF] has low enough impedance [1 ohm] and still allows faster DC changes with less transient saturation [for 120V AC capacitance should be doubled]
The problem may be ripple current in the capacitors, but placing more 1000uF in series-paralell solves it
Using smaller capacitors also has smaller space and cost requirements