I've been using an amplifier based on LM3875. One problem with it is that it makes a very annoying "POP' noise whenever I turn the lights on/off. I guess this is due to a so-called "spike voltage" from the AC mains. I've checked some textbooks on basic electronics and found that TVS (Transient Voltage Suppressor) could be used to kill this kind of spikes. Now, I'm wondering if any of the DIYers here tried this. If so, please let me know the result. This POP sound is killing me. Thanks.
JAZZ2250
JAZZ2250
For AC transients I am not a fan of TVS Diodes (seen to many of them blown). I would use something like the Panasonic ZNR type (check DigiKey) or a MOV type.
Ultimate protection system would be:
Line IN
a gas discharge tube
a low value resistor
ZNR or Mov
line out
(for DC, best bet is TVS diode)
Note: TVS diodes fail to a short ckt - not nice on AC line!
ZNR & MOV fail open ckt.
Ultimate protection system would be:
Line IN
a gas discharge tube
a low value resistor
ZNR or Mov
line out
(for DC, best bet is TVS diode)
Note: TVS diodes fail to a short ckt - not nice on AC line!
ZNR & MOV fail open ckt.
What you really need is a snubber across the light switch contacts. A 47r 1w resistor and a 1uF 250 VAC X cap *ac rated* in series should help a lot. Something similar across the mains input of your amp would be good too. *Important* use an X type AC rated cap that has UL, CSA and other safety agency approvals. Put both the cap and resistor inside a small metal box just to be 10000% sure of fire safety.
Thanks, crown300.
I checked digikey for Panasonic ZNR (type D). I was able to understand what MAV (Maximum Allowable Voltage) means. As I measured, the AC mains is 120V, and hence MAV has to be higher than 120V. Right? Will 130 or 140V do? Then, what should I choose for Vc (Varistor Voltage) and Max. Clamp Voltage @ Test Current? Sorry for a dumb question and thanks for your help. BTW, I've lived in Raleigh, which is close from Pittsboro, for one and a half year. It was a pretty nice place to live.
Thanks, Circlotron.
It seems opening the switch box of the light will be a little bit difficult for me because I'm living in an apartment. But, thanks for your valuable advice. I'll file your recommendation for my future reference.
JAZZ2250
I checked digikey for Panasonic ZNR (type D). I was able to understand what MAV (Maximum Allowable Voltage) means. As I measured, the AC mains is 120V, and hence MAV has to be higher than 120V. Right? Will 130 or 140V do? Then, what should I choose for Vc (Varistor Voltage) and Max. Clamp Voltage @ Test Current? Sorry for a dumb question and thanks for your help. BTW, I've lived in Raleigh, which is close from Pittsboro, for one and a half year. It was a pretty nice place to live.
Thanks, Circlotron.
It seems opening the switch box of the light will be a little bit difficult for me because I'm living in an apartment.
But, thanks for your valuable advice. I'll file your recommendation for my future reference.JAZZ2250
JAZZ2250 said:So, 120VAC at mains is RMS value and MAV is not? Confusing. 120VAC RMS = 120*1.414 = 170V, and Vpp = 2*170V = 340V. Shouldn't I choose MAV = 350V or higher? Again, confusing.
170Volts to neutral, is worst case. Yes, it is 340Vp-p. Neutral is ground potential, and the hot goes from -170 to +170V. The maximum potential will be 170 volts peak, but the polarity will change.
-Dan
I'm not an expert either, but I've had to deal with this more then just a few time in my work.JAZZ2250 said:
In US homes, ground and neutral are the same (If they are not, they should be) so you need not connect one across your incoming ground and neutral. Also your 240VAC for electric stoves and such in US home are 120VAC either side of neutral/ground. That is +120VAC(RMS) - Neu/Gnd - -120VAC(RMS).
This may differ in industrial situations, but alway check with a volt mater before applying power
Rodd Yamashita
http://dkc3.digikey.com/PDF/T023/V5/0573.pdf
Take a look at this catalog page in Digikey. This is what you really want. A box with all the stuff inside. Just connect it and forget about it . I think these mainly have things like pi filters.
Darrell Harmon
Take a look at this catalog page in Digikey. This is what you really want. A box with all the stuff inside. Just connect it and forget about it . I think these mainly have things like pi filters.
Darrell Harmon
Thanks, dlharmon. I'm using an EMI filter, which is shown below, with my amplifier. Still, I have the annoying POP sounds. Is the EMI filter different from the RF filters? And, isn't spike voltafe different from RF interference and EMI? I'm beginning to feel shame at my ignorance.
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JAZZ2250 said:Thanks, dlharmon. I'm using an EMI filter, which is shown below, with my amplifier. Still, I have the annoying POP sounds. Is the EMI filter different from the RF filters? And, isn't spike voltafe different from RF interference and EMI? I'm beginning to feel shame at my ignorance.
This filter won't take large spikes, only RF and small spikes. You must add varistors also. Size K10 and up. If you have 230 VAC in choose 250 V varistor K10-K14 at least.
Example here
http://www.elfa.se/elfa/produkter/se/20/2012568.htm
P1 is not suitable for "normal" protection. Each time this tube disharges, lifetime is shortened. Neon tubes is good for lightning protection. The tube may also break the fuses if it's triggered, not so pratical....
I had an APC Surge Arrest Professional that died. It had a nice filter including 6 MOVs, 2 huge inductors wound with 12AWG, and AC capacitors. You might look at either using something like this or its guts. I think the MOV's shorted out and blew the fuse. The board was sort of burnt. It probably died stopping a big surge. The ac power here at my school is nasty. It looks more like a square wave than a sine wave on the scope.
Darrell Harmon
Darrell Harmon
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