In case of OPS transistor failure the power regulator will switch off the power much faster then relay will disconnect output. The DC control is separate part detection, nothing to do with OPS transistors.
Switching off mains supply is not good solution, big power supply capacitors still have enough charge to damage loudspeaker. My regulator is connected after big power supply caps, only much smaller caps situated on the amp board will discharge via loudspeaker, and this is not danger for woofer but could be to twitter. Normally in passive crossovers twitter is connected via a capacitor. In case of active crossovers I always connect twitter via additional capacitor.
BR Damir
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I believe you. I have only been referring to why relays are used at all for protection. There are relays which do not deteriorate at the contact point. Maybe not used in audio amps, though.
One of my Go-To books on contacts is the early work by Ragnar Holm. "Electric Contacts" 1981 4th edition Another from my library is "Switch Engineering handbook" John R. Mason. 1993.
Hard gold over silver over copper with wiping action of contacts upon open and close and of contactor construction can be very good for a high number of cycles.
However, as suggested it might be good to replace any relay or contactor in the event of OPS failure which can exceed the contacts normal rating.
Though I have not seen it used on speaker relays -- only power switches -- an RC across the contacts will minimize arc burn/pitting.... a real concern for creating poor contact performance over time.
The peak discharge current of even caps in bypass right at the OPS devices can produce very high current peaks..... beyond any tweeter can usually handle..... limited only by the esr of the cap and pcb trace. But less to the speaker due to cable/interconnect Rs. but still.... PS voltage dumped into a fraction of an Ohm is still a lot of current even if the period is short. The speed at which a dynamic tweeter VC can act as a fuse is amazingly fast.
THx-RNMarsh
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Hi Richard,
I've made it a point to replace the relay with output failures. It is pretty much a certainty that the contacts will be burned or badly pitted as a result of the failure. Marantz receivers were capable of melting the contacts together. Seen that more than once.
I have seen permanent magnets glued or taped to the sides of some relays in an effort to blow out the arc. I'm not sure how effective that is, but when replacing those I'll move the old cover to the new relay to retain that feature.
-Chris
I've made it a point to replace the relay with output failures. It is pretty much a certainty that the contacts will be burned or badly pitted as a result of the failure. Marantz receivers were capable of melting the contacts together. Seen that more than once.
I have seen permanent magnets glued or taped to the sides of some relays in an effort to blow out the arc. I'm not sure how effective that is, but when replacing those I'll move the old cover to the new relay to retain that feature.
-Chris
Totally not making fun of you in the least (I admire your clarity in what is not your native tongue!) but "twitter" versus tweeter amused me.
And, yes, I'm also doing active but made one of the poles a series capacitor for insurance as well.
2.2 uF into 10K 1 VRMS. Just picked the physically smallest one from the 2.2 uF bin in my capacitor drawer. If I get around to it I can run a few more samples. But I did want one that was far from perfect. I did run a capacitor sold for audio use and it was much better but still showed the results expected.
Yes. And what is the dielectric for the cap under test that gives D=5% ? Replacing several of those in a system will make a noticable difference in sound quality.
THx-RNMarsh
Very true. Higher voltage caps measure better in almost every parameter. This is especially true for polar and bipolar electrolytic type. Also, 105C rated caps are much better than 85C caps.
I always use 105C rated when electro types are needed. They also generally have longer life.
THx-RNMarsh
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More fun. A 1.8 uF 160 VAC 250VDC Bennic brand metalized polypropylene capacitor into a 10,000 ohm 1% metal film 1/4 watt resistor. 5 volts RMS at 20 hertz and .5 volts RMS at 200 hertz. DC coupling out of the AP. Nicely shows the harmonic and intermodulation distortion. I will run the test again tomorrow to be sure it holds up.
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Nicely, really? Since the 60Hz can't be differentiated from hum no claims to its origin can be made and since 20 and 200 are exactly divisible there is no definitive proof of IM here either. You do love confounders don't you? Besides if the 60Hz is hum everything is -115dB or better not exciting.
EDIT - That's an 8.8Hz corner so there is considerable AC voltage on the cap and the fundamental magnitude is off on the plot.
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