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Old 8th March 2013, 07:34 AM   #21
JMFahey is offline JMFahey  Argentina
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Basically agree, but must correct the MOV ratings suggested.
A "300VAC" and even worse a "540VAC" will "do nothing" to save you from switch popping.
They are already Factory rated for use with a certain nominal line voltage, you don't need to calculate peak voltage or something, the safety factor is already "built in" the VAC rating.
I live in a 220VAC Country, so "normal" here is a "230V MOV" .
Since one of my amps can end up in a "230V" or "240V" Country, I use 250V rated ones.
Any higher and although it might be fine for some *gross* peak such as a lightning hitting a Power line , it won't help much in day to day spikes.

So as a basic rule: for 220/240V lines choose 250V MOVs ; for 120V lines choose 140 or 150V ones.
Why?
Because many times, modern "120V" lines are actually "127"

Anyway, for better protection must be used in combination with switch capacitors.
For a practical example, check what manufacturers such as Fender/Peavey/Marshall, etc. use.
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Old 8th March 2013, 08:02 PM   #22
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The Hot Rod Deville has this on the hot side of the power switch between the switch and transformer: 1 028503 THERMISTOR 10 OHM 5A C60-11 TH1

and numerous CP's but I'm not sure what they are, here is a schematic: http://ampwares.com/schematics/hotrod_deville.pdf

Please let me know what they are and if they will solve the problem.

I have 0.01uF/1000v and 1400v ceramic caps I will be attaching later today to see how that works.

And I don't understand why or if the MOV's or X/Y caps are for voltage spikes coming in or solving the pop problem, or both?
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Old 8th March 2013, 08:18 PM   #23
DF96 is offline DF96  England
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Quote:
Originally Posted by dscottguitars
I am finding really hard to believe I am the only one who has asked this question and there are no definitive answers for it, other than turn the standby switch off first?? I am not willing to settle for a solution that is not really a solution unless it just can't be done. If that is the case please state that.
I have already told you the answer.
- X cap across the transformer primary (to slow down the switch-off transient)
- check grounding (to avoid unwanted coupling)
- check induction between power and signal circuits (to avoid unwanted coupling)#

Quote:
The Hot Rod Deville has this on the hot side of the power switch between the switch and transformer: 1 028503 THERMISTOR 10 OHM 5A C60-11 TH1
That will probably be an inrush limiter. Reduces switch-on clicks.

Last edited by DF96; 8th March 2013 at 08:19 PM. Reason: extend
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Old 8th March 2013, 08:45 PM   #24
JMFahey is offline JMFahey  Argentina
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Quote:
And I don't understand why or if the MOV's or X/Y caps are for voltage spikes coming in or solving the pop problem, or both?
Same thing: a "pop" *is* a voltage spike (caused by reactive load switching ) getting uninvited into the audio path.
Whatever reduces spikes, whether by capacitively absorbing them, delaying turn off or absorbing peaks will help.
Same as mixed-drug therapy in medicine: none is perfect but combinations are better than the sum of parts, a.k.a. "synergy".
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Old 9th March 2013, 12:16 AM   #25
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MOV's start working way too big (300-500 v) to affect the turn off pop. They can save the input transformer wiring in a soft lightning strike , or more urgently the input capacitors of a switching power supply on the same AC circuit with a big motor that switches off.
The disc capacitor across the transformer input, or across the power switch, or both, is for the 10 -100 mv high frequency transient that make the pop. It is subject to the 1000 v motor turn off transients from appliances, though, which is why it needs a UL/VDE/CSA/CE rating for the wall voltage. UL knows about the 1000 v spikes on the 120 VAC line. I used to coordinate repair of a machine that overloaded (switched compressor off with a power interruption) a new refrigerator every 15 seconds on the test line of a factory, so you could watch the motor switch off transient pretty conveniently with an oscilloscope. BIG high frequency transient voltage.
Anyway, many manufacturers of amps with a big power transformer first rely on the wiring of the transformer and the iron to suppress that transient, instead of buying a $.30 MOV. Again, the MOV is not for pop supression. And the 10 ohm NTCR (negative temperature coefficient resistor) in series with the power transformer winding is for soft start, it collapses to 1 ohm or so when heated up. Look up CL-90, a GE part, on datasheetcatalog.com if you are interested. My PV-1.3K amp used to dim the lights in the room when I turned it on. Not any more, with a CL-101 in series with the transformer. Peavey had already suppressed any turn on pop with a JFET clamping the input to +15V power supply with a turn on delay timer, but I found the effect on the lights of room annoying. The PV-1.3k was designed (1994) before NTCR's were cheap.
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Last edited by indianajo; 9th March 2013 at 12:24 AM.
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Old 8th April 2013, 05:59 PM   #26
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I tried to follow this discussion but I find it very hard because of my lack of knowledge to be frank.
I have a old Classé Audio DR-3 amp that makes a nasty transient sound when I turn it off.
I'm afraid the Emits or Peerless midrange domes of my Q2 Infinity's will suffer someday and I can get them anymore.
Can you explain to me where I should solder Arc Suppressor or MOV?
Over the plus and minus pole of the toggle switch?
I found this PDF from CDE Arc surpressors I probably have to use a 600 Vdc / 250 Vac device but I have no glue which Ohmic value I should take, 22, 47, 100 or 200 Ohms.
Thanks in advance.
Attached Files
File Type: pdf Arc Surpressor - Snubber Network.pdf (193.0 KB, 9 views)
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Old 12th April 2013, 09:53 PM   #27
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Solved it with two 10000 pF, 500 Volts Ceramic discs (one for each channel) on the connectors of the on/off switch,
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Old 14th April 2013, 12:09 PM   #28
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Reread posts 25 and 23 and remove your 500 V rated caps immediately. One gets 1000 V transients on 120 VAC lines in the western hemisphere from air conditioners and refrigerators. I can't imagine what voltage they get in France. In case this is not obvious to you yet, 1000 v is bigger than 500 v. That means your cap might fail at any time.
Per df96 the necessary rating for caps across the power line is X 250 VAC in Europe. X caps are regulatory required to be non-flammable according to wikipedia. The rating agencies know how big transient spikes from appliances are on the AC lines, and test accordingly.
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Old 14th April 2013, 01:59 PM   #29
DF96 is offline DF96  England
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Yes, 10nF X cap will be much safer. In the 1960s people just used high voltage DC-rated caps, but that is all they had. If one of those shorts you get a big bang and hopefully a fuse or breaker will prevent a fire developing. X caps should not do that as they are designed to cope with over-voltage transients.
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Old 14th April 2013, 08:14 PM   #30
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Quote:
Originally Posted by indianajo View Post
Reread posts 25 and 23 and remove your 500 V rated caps immediately. One gets 1000 V transients on 120 VAC lines in the western hemisphere from air conditioners and refrigerators. I can't imagine what voltage they get in France. In case this is not obvious to you yet, 1000 v is bigger than 500 v. That means your cap might fail at any time.
Per df96 the necessary rating for caps across the power line is X 250 VAC in Europe. X caps are regulatory required to be non-flammable according to wikipedia. The rating agencies know how big transient spikes from appliances are on the AC lines, and test accordingly.
These are used for surpressing the transient at turnoff wich the do very well I must say. I do not use them for spikes or overvoltage. These require varistors if I'm right??
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