Andersonix said:
The CL-60 style thermistors are made to limit inrush current. They are at their highest resistance when they are cold, which will keep the current draw reasonable as the caps charge, and once they heat up, their resistance decreases, letting more of the mains through, keeping your efficiency up.
You also get the benefit of a little mains filtering, because of the (small) residual resistance.
That's a win-win in my book, AND you can use smaller fuses for better protection of your amp.
Win-win-win
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well. let me be the idiot that screw that up
"blow" the main's fuse and pull it back on within a sec or 2(or 30) then it will blow the amp's fuse however. if that CL-60's are bypassed a sec whitinin startupThe CL60s and other Power NTCs used as current limiters need to be bypassed by a relay or similar to allow them to cool and to reduce the source impedance seen by the PSU.
If you don't bypass the NTCs then varying current in the amplifier will modulate the output voltage of the transformer due to the variable source impedance presented by the NTC/s.
If you don't bypass the NTCs then varying current in the amplifier will modulate the output voltage of the transformer due to the variable source impedance presented by the NTC/s.
Can that be interpreted as "starving" the amp of full power. After completing the thermistor system yesterday, that's the impression I'm getting.
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anyone caring to measure voltage across NTC , in use in common FW clone ?
if taking things purely academic , one need to say that observation is academic , so needing pro et contra confirmation in praxis
I made amps without them (NTCs) , with them as solo soft start element , with them instead fixed value resistors in regular relay equipped soft start circuit .......
if taking things purely academic , one need to say that observation is academic , so needing pro et contra confirmation in praxis
I made amps without them (NTCs) , with them as solo soft start element , with them instead fixed value resistors in regular relay equipped soft start circuit .......
I reported years ago about this voltage modulation when the NTC is not bypassed.
It is in the Krell KSA100 Klone Thread.
I could see the output clipping starting and getting worse as the (primary circuit) NTC varied it's resistance in response to varying output current.
It is even worse when powering a ClassAB amplifier.
It is in the Krell KSA100 Klone Thread.
I could see the output clipping starting and getting worse as the (primary circuit) NTC varied it's resistance in response to varying output current.
It is even worse when powering a ClassAB amplifier.
one thing is 50W A class with oomphteenth watts of B class capability , another thing is 25W A class amp
however , if Pass is using them in all FW products , same as in many PL ones - in exactly same manner , that's good enough in my book , and everything else is in purely academic domain
so - I'm using the same in my amp , if sissy power and A class are in question
in case that I'm going to make more muscular amp , or even having substantial B class capability , I'm going to use relay based soft start , strictly having NTC chain instead of fixed resistors chain
however , if Pass is using them in all FW products , same as in many PL ones - in exactly same manner , that's good enough in my book , and everything else is in purely academic domain
so - I'm using the same in my amp , if sissy power and A class are in question
in case that I'm going to make more muscular amp , or even having substantial B class capability , I'm going to use relay based soft start , strictly having NTC chain instead of fixed resistors chain
FWIW: I ended up using Andrews formula (500 VA X 3 = 1500 / 120 = 12.5 A) and put two 6 A Slo-Blo in the dual fuse inlet. That prevented the blown fuses. I re-installed the thermistors and found no degradation of of sound quality. I did remove both F5 modules and test them on a chunk of standard heat sink. The output on each was back up to the proper level and that remained when I reassembled the entire amp build. The "starved" distorted sound probably had nothing to do with the CL-60, but rater some fault in the connections. I'm actually now getting the best sound quality and highest output since the beginning of the project. Might try to lower the fuse size back down a bit to increase safety margin now that I know the thernistors are working as designed.
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I wouldn't put a relay between the output and the speakers.
Probably not a bad idea to bypass the thermistors with a relay after a short period so they cool down.
Even if the relay is very high pressure connection, and very low resistance?
I wouldn't want anything in the signal path. What you do is up to you. Try it and listen.
Hi guys,
Some questions that are stupid and certainly asked before, but the answers are hard to find due to the amount of info:
Where do I put the cl60 when there is only one primary winding? In series after the switch and mains capacitor i guess, but just confiming here.
What do I do with signal ground? I´m doing this p2p, so its not given by the board and wiring sketches. They are obviously connected together at two points in the circuit itsfelf, but does it go chassis or psu?
Thanks a lot. Will be providing pictures to redicule soon!
Some questions that are stupid and certainly asked before, but the answers are hard to find due to the amount of info:
Where do I put the cl60 when there is only one primary winding? In series after the switch and mains capacitor i guess, but just confiming here.
What do I do with signal ground? I´m doing this p2p, so its not given by the board and wiring sketches. They are obviously connected together at two points in the circuit itsfelf, but does it go chassis or psu?
Thanks a lot. Will be providing pictures to redicule soon!