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Old 28th June 2013, 11:11 AM   #13211
AndrewT is offline AndrewT  Scotland
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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.
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Old 28th June 2013, 01:42 PM   #13212
Zen Mod is offline Zen Mod  Serbia
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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
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Old 29th June 2013, 04:05 PM   #13213
bcmbob is offline bcmbob  United States
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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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Old 30th June 2013, 04:14 PM   #13214
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What do you all make of the DIYAudio soft start and speaker protect boards?
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Old 30th June 2013, 04:57 PM   #13215
Renron is offline Renron  United States
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The CL60s have the ability to reduce the current at startup due to being "cold", perhaps mounting them on/near the heatsinks would minimize their potential of starving the amp when warmed up? Just a thought.
Ron
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Old 30th June 2013, 04:57 PM   #13216
labjr is offline labjr  United States
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Quote:
Originally Posted by LucasAdamson View Post
What do you all make of the DIYAudio soft start and speaker protect boards?
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.
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Old 30th June 2013, 08:24 PM   #13217
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Quote:
Originally Posted by labjr View Post
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?
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Old 30th June 2013, 10:58 PM   #13218
labjr is offline labjr  United States
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Quote:
Originally Posted by LucasAdamson View Post
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.
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Old 1st July 2013, 12:47 AM   #13219
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K.I.S.S. and use the NTC. Then experiment later when you have nothing better left to tinker with. I will be experimenting with the attached AC relay type ss (as attached Fig.2) one day, so I will leave some space in my next amps.
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Old 2nd July 2013, 09:13 PM   #13220
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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? Im 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!
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