A well designed transformer will work as well as MOV's/ Zeners and even the more complicated stuff. Look at the OneAC stuff (Now Powervar) Standard Power Conditioners and Power Protection
This is part of why surge and noise issues were not as important 30 years ago.
Cascading an MOV and a gas discharge tube works but getting the right mix is not obvious. A 30V MOV won't stop a conducting GDT's plasma. We use that combination in some EU markets where the ground is not connected to power so its unpredictable.
If I can find some parts and some time I'll try some experiments. Most of the GDT's I have are 30V parts for coax and MOV are 130V or 250V parts. Neither are appropriate.
Current quality MOV's are much closer tolerance than the older GE parts. The products are much more consistent and higher performance. Those older parts would explode on occasion with the surge generator. I don't ever see that today. We still check them for spread periodically. Some vendors are not as good. You learn to be careful after being involved in a few fire investigations.
This is part of why surge and noise issues were not as important 30 years ago.
Cascading an MOV and a gas discharge tube works but getting the right mix is not obvious. A 30V MOV won't stop a conducting GDT's plasma. We use that combination in some EU markets where the ground is not connected to power so its unpredictable.
If I can find some parts and some time I'll try some experiments. Most of the GDT's I have are 30V parts for coax and MOV are 130V or 250V parts. Neither are appropriate.
Current quality MOV's are much closer tolerance than the older GE parts. The products are much more consistent and higher performance. Those older parts would explode on occasion with the surge generator. I don't ever see that today. We still check them for spread periodically. Some vendors are not as good. You learn to be careful after being involved in a few fire investigations.
This is audio, EMC regulation isn't good enough.
And... that's disturbing. Power factor on large scales is being twisted so bad because of things like that, who knows how much extra coal, nuclear, etc, is burned up because of that.
Protection --- A good isolation transformer is great for a number of reasons; noise atten and ground isolation as well as blocking HV transients. The isolation transformers i had made for Monster Power's -7000 series did the trick quite well. For protection, a smaller and less costly answer is a large series inductor. With a cap added, you have a nice filter as well. It will block transients for less cost than an isolation Xfmr. But, for protection the ultimate in size and cost, the GDT-MOV is a hard combination to beat.
THx-RNMarsh
Richard it seems a good suggestion but I have a question here.
The max current in the serial connection of GDT and MOV will be dictated by the lowish handling power of the MOV, so what’s the meaning of having the GDT there?
George
The sustained power of the MOV is not as good as the GDT.... however, the MOV can handle very high transient currents. You can also parallel the MOV's.
The GDT is to buffer the MOV's C from the line... no C leakage across the line or to ground.... with an MOV only, you have leakage thru its capacitance. [There is a UL limit to the leakage to ground]. An MOV alone will pass some ac line current and any other freq on the line thru its C.... and in doing this create harmonics as well from the non-linear C. More noise/harmonics is not what we want for audio.
THx-RNMarsh
Post 81214. Std app note linked there, does not match your description. Not sure how having a MOV in series actually helps as the speed of the MOV is not being utilised.
It matches just fine. For audio we usually need some additional filtering - if placed before the GDT-MOV it slows the response needed.
Other question --- the UL and other standards are not for audiophiles... The limits of EMI/RFI are established to prevent police, fire, medical and aviation interference . The RFI filter for UL/Gov is far from adequate needs for audio.
THx-RNMarsh
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Thank you Richard.
So the target is the elimination of the leakage current of the MOV during the non conducting periods and the forcing of the GDT to turn off.
The price to pay is on the worsening of the surge protection profile due to the sacrifice of the MOV’s fast response time and of the sustained high current handling capabilities of the GDT
God forbid
🙂
George
yes, the protection speed is that of the GDT in this case. However lightning Tr is not in the nano-sec range of the MOV.... it is slower. But like I just said.... a small amount of DM-CM inductance of other filtering will not only slow the transients Tr but its amplitude as well. So... Not To Worry. In practice and for ac power line apps, it does its job very well.
The filtering needed on the ac line is not of high voltage transients but very wide bandwidth.... including audio freqs.
THx-RNMarsh
I think the reason we don't have more EMI issues than we should is because of the FCC and the EU. I remember getting very involved in this stuff in 1990 through about 1995. Many hours in EMC chambers and with Schaffner test gear. The FCC led the way IMV and once the EU harmonization came into effect, it really brought the issue to the fore. I would hate to think how much worse it would be without the focus we had about 25 years ago on these issues. Pity then that with cheap imports and the authorities turnin a blind eye that issues again start to arise.
Beware of self-certification as well.
I was working with a company who were testing a wireless link. The place had recently "upgraded" their communal microwave oven to a newer model with a higher-efficiency switchmode power supply. It had a paralytic effect on the link, and from quite a distance away. I had tested the link with an ancient microwave of my own and found transmissions to be robust.
The link people got a sample of the oven and confirmed that it was very effective at interfering with their hardware. As well, they determined that it was very much over regulation limits for emissions. The large Japanese company was self-certifying.
re non-linear capacitance across the AC line. I would have thought DC o the line a far more important problem. And, we have not even begun to talk about noise and other crud . . .
This is a bit like the 'ferrites on the mains side destroy the sound' argument promulgated by the Sandman a few years ago which we know is utter drivel.
This is a bit like the 'ferrites on the mains side destroy the sound' argument promulgated by the Sandman a few years ago which we know is utter drivel.
AC line noise comes from --
If you put a wide band inductive probe next to an (DUT) equipments' ac cord and turn the equip On, you will see on a spectrum analyzer- from a quiet base line - all sorts of noise put onto the ac line.
The utility line is fairly quiet most of the time but you Always inject noise from your home equipment connected to the line.
Here are but a few examples --- video displays are pretty bad offenders as well.
View attachment AC noise-1.pdf
View attachment ac line noise-2.pdf
View attachment ac noise-3.pdf
Almost all the noise in the home comes from connected equipment within the home. That includes your audio and video systems.
I put an individual filter on each piece of connected equipment and use ground isolation transformers.
THx-RNMarsh
If you put a wide band inductive probe next to an (DUT) equipments' ac cord and turn the equip On, you will see on a spectrum analyzer- from a quiet base line - all sorts of noise put onto the ac line.
The utility line is fairly quiet most of the time but you Always inject noise from your home equipment connected to the line.
Here are but a few examples --- video displays are pretty bad offenders as well.
View attachment AC noise-1.pdf
View attachment ac line noise-2.pdf
View attachment ac noise-3.pdf
Almost all the noise in the home comes from connected equipment within the home. That includes your audio and video systems.
I put an individual filter on each piece of connected equipment and use ground isolation transformers.
THx-RNMarsh
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Noise coupled to ground from each line matters, of course. But I found most of this noise is DM, a cap across the line can reduce a lot of the noise.
But you know all that anyway.
Does reducing the line noise from connected equipment make an audible change in the sound of your system? Ask SY.
-RNM
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