Chris, note my comments before about precision timing. Rod's circuit will give you very repeatable and precise delays. Problem is, you don't need that, so why spend the extra money? (No reflection intended on RE- I think that 99% of the stuff he presents is terrific)
It's high end audio. Everything has to be more expensive and complicated than necessary. 0.1% resistors for bleeders. Teflon caps for the "on" light supply. Microcontroller surge protection.
It's high end audio. Everything has to be more expensive and complicated than necessary. 0.1% resistors for bleeders. Teflon caps for the "on" light supply. Microcontroller surge protection.
Yes, a thermistor is even cheaper and more simple and has been used in many pieces of equipment with success, however, the purist in me does not like the idea of having a permanent resistance in line with the TX ! (it most have resistance in order to dissipate the power to self heat).
The relay can of course be replaced by a suitable triac or anti- paralell SCR's but that would complicate matters considerably!
The relay can of course be replaced by a suitable triac or anti- paralell SCR's but that would complicate matters considerably!
That's funny jez, cause the purist in me perfers the thermistor... What if mains noise somehow was induced into the coil of the relay and back onto the rail voltage!
Just paranoid...
/Niclas
Just paranoid...
/Niclas
I don't see how that could happen myself. What is a much greater certainty is that with a class-b amp the large difference between average and peak current will mean that the thermistor is hardly at minimum resistance and therefore modulating the supply.
I think the main (ha) argument against the thermistor (other then a resistor in the mains line, which doesn't bother me) is this:
Power up your amp. Termistor heats up and drops in resistance, all is good. Now turn off your amp for a few seconds, and turn it back on. Thermistor is still warm (no resistance) and offers no inrush protection.
Circuits like peranders' take this into account, and offer repeat protection.
Now, how oftern do you turn an amp off and back on quickly? Not oftern. Do you ever do it though? Want to have to replace a fuse if you do it accidently?
Power up your amp. Termistor heats up and drops in resistance, all is good. Now turn off your amp for a few seconds, and turn it back on. Thermistor is still warm (no resistance) and offers no inrush protection.
Circuits like peranders' take this into account, and offer repeat protection.
Now, how oftern do you turn an amp off and back on quickly? Not oftern. Do you ever do it though? Want to have to replace a fuse if you do it accidently?
WorkingAtHome said:
In my case anyway we face power interuption very often. Either by nearby new houses building sites or by freezing rain in the winter or by power outage by air conditioners in the summer. That is often enough to treat it as a WHEN not a IF situation. All my fish tanks pumps has to be self primed too!
I had a soft sart with slow reset (not a thermistor) for a subwoofer, very annyoing with blown fuses if the music happened to increase just after the subwoofer was switched off. Still thermistor is Ok and a very easy solution but requires careful selecting and you mustn't have short "blips" in the mains voltage.WorkingAtHome said:
Interesting theorystappvargen said:That's funny jez, cause the purist in me perfers the thermistor... What if mains noise somehow was induced into the coil of the relay and back onto the rail voltage!
Just paranoid...
/Niclas
but can you give any scientific explanation? 
Have a look at picture 3 (Bild 3) at the bottom of this page.
It basically uses an NTC which is shortened by an AC relais whose coil is accross the transformer primaries:
http://www.elektronik-kompendium.de/public/schaerer/onilim.htm
It should also protect against short glitches in the AC mains.
It basically uses an NTC which is shortened by an AC relais whose coil is accross the transformer primaries:
http://www.elektronik-kompendium.de/public/schaerer/onilim.htm
It should also protect against short glitches in the AC mains.
We stumbled across this same solution on another thread. Still doesn't help with short turn-off/turn-on times, as the thermistor is still going to be hot.
shorted
Once the thermistor is shorted out by the relay, its gong to cool off. Then you don't have to worry about turning the amp off and on again in rapid succession.....once.
Do a bunch of rapid on/off's and it will probably still be hot.
Of course if you use an in-line thermistor you are going to have a problem with every off/on cycle that is short. Just FYI, the Pass Labs projects appear to use this. I know my Audio Research Dual 75A uses an in-line thermistor without a relay.
The good thing about thermistors for soft-start is that they are readily available and have sufficient power rating to take the surge, as opposed to the large underrated resistors.
There is another reason for creating a rather complicated time delay soft start circuit, the reason I am doing it is to LEARN. It interests me and I want to see if I can do it successfully. Its another chance to get to use some transistors and other circ. components, and do some math. For me its not about churning out amplifiers one after the next.... Then again, the alternatives presented are also interesting.
Once the thermistor is shorted out by the relay, its gong to cool off. Then you don't have to worry about turning the amp off and on again in rapid succession.....once.
Do a bunch of rapid on/off's and it will probably still be hot.
Of course if you use an in-line thermistor you are going to have a problem with every off/on cycle that is short. Just FYI, the Pass Labs projects appear to use this. I know my Audio Research Dual 75A uses an in-line thermistor without a relay.
The good thing about thermistors for soft-start is that they are readily available and have sufficient power rating to take the surge, as opposed to the large underrated resistors.
There is another reason for creating a rather complicated time delay soft start circuit, the reason I am doing it is to LEARN. It interests me and I want to see if I can do it successfully. Its another chance to get to use some transistors and other circ. components, and do some math. For me its not about churning out amplifiers one after the next.... Then again, the alternatives presented are also interesting.
You are corrdct about the thermistor cooling off. I forgot. that is how we arrived at it on the other thread.
http://www.diyaudio.com/forums/showthread.php?postid=592317#post592317
http://www.diyaudio.com/forums/showthread.php?postid=592317#post592317
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