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DC protector board/device in amplifier?

684 views 7 replies 4 participants last post by  wersuss 
#1 ·
Hello. I'm buying DYI amplifier and seller told that it has Soft start protection aswell as Omron relay. Does these work as DC protection for speakers?
 
#2 · (Edited)
What you described does not prevent DC protection. 99% of all amps made put a capacitor in series (a.k.a. AC coupling). That blocks a DC signal and passes an audio signal. VERY few amps are DC coupled. Here are some: Anthem, Parasound, Simaudio, Krell, Plinius, and B&K. Nearly all others put that cap in series.

That said, Simaudio and Plinius have a micro controller that tests for offset. But Parasound and B&K for instance don't. So if a preamp is DC coupled and the amp saw that signal, it would automatically amplify the DC and potentially damage the drivers.
 
#3 ·
What you described does not prevent DC protection. 99% of all amps made put a capacitor in series (a.k.a. AC coupling). That blacks a DC signal and passes an audio signal. VERY few amps are DC coupled. Here are some: Anthem, Parasound, Simaudio, Krell, Plinius, and B&K. Nearly all others put that cap in series.

That said, Simaudio and Plinius have a micro controller that tests for offset. But Parasound and B&K for instance don't. So if a preamp is DC coupled and the amp say that signal, it would automatically amplify the DC and potentially damage the drivers.
Hi! Wow, thank for great answer. So i guess i shoulnd't worry about DC to speakers? How high is the possibility to get DC to speakers and damage them?
 
#7 ·
Not enough information IMO. A "soft start" circuit could be to control in-rush current from the wall plug (so it doesn't blow a fuse at power-on), to bring up the power rails gradually after the transformer or as part of the switching power supply circuit (depending on the type of power supply), or some sort of bias or output impedance control circuit in the output stage and/or connection to the speakers. Same thing with the relay; where in the circuit is the relay, and how is it controlled? If it is in series with the speakers, what is the control circuit sensing? If not, where is it and what does it do? If you are not a techie, ask the builder where it is and how it works in general terms.

A soft-start circuit will generally not provide any sort of DC protection IME; a relay might depending upon where it is in the amplifier. I have had amps with a relay on the AC line as part of the in-rush control circuit, reed relays to short the inputs (after a series protection buffer or resistor), power relays that are open to the speakers until the amp's bias has stabilized, etc. And as @SteveH said whether or not you even need DC protection is an open question. Also note some amplifiers have an input coupling capacitor to prevent DC inputs from being amplified but are still DC coupled at the outputs. And even if it is not DC coupled a shorted output device or other problem can still send a nasty surge through a speaker.

This is all true of all sorts of amplifiers; some of the worst problems I had were with commercial amplifiers, including one that seemed to destroy itself every few months and take whatever speakers were connected with it. The third time I repaired it and sold it "as-is" and told the seller about the problems I had. He used it in a band for about a year before it blew up again. Fortunately I had moved out of state so couldn't repair it (again).

Buying a DIY amp is always scary for someone without a reasonably high degree of technical knowledge. Some builders use kits that are proven technology, some are designers producing products as good or better than commercial products, and some slap parts together with little knowledge and experience. You can ask for references, listen to the amp in his system, and get a feel for how good the builder/designer is, but at the end you have to trust him or not. Same as with any purchase, of course.
 
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