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Old 27th July 2010, 06:10 PM   #1
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Default Thermistors and the F5

This past weekend I spoke with a well regarded turntable manufacturer and he got on the subject of NTC thermistors. He came right out and said it, 'Thermistors are terrible for audio.'. He suggested using a DPDT On-On switch to 'by-pass the thermistor once the power supply transient subsides'. Not his exact words. I'm paraphrasing.

So...I believe that power supplies are important to audio circuits. Considering people spend $40 on hi-end fuses and hundreds and even thousands of dollars on power cords, maybe there is something to this?
Can this one component in the power supply effect the quality of the overall sound on the F5?

I have 5 CL-60s in my dual-mono F5. They were also incorporated in the second F5 that I built. One option is to remove them. Not a good idea, I think. Another is to use a relay circuit. Probably has it's own issues.
Is the suggested DPDT by-pass a good option? Sounded simple enough when mentioned, but are there any pitfalls?

Like to hear your thoughts on this.

For what it's worth, I think thermistors are a simple, inexpensive solution to a big problem. They save us big time.

Thanks,

Vince
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Last edited by vdi_nenna; 27th July 2010 at 06:11 PM. Reason: spelling
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Old 27th July 2010, 06:38 PM   #2
juma is offline juma  Germany
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Quote:
Originally Posted by vdi_nenna View Post
... 'Thermistors are terrible for audio.'. ...
It's just plain silly, unfounded and insulting to fellow man's intelligence - a well known "audiophool's" talk

Run away as fast as you can from anyone who is proclaiming such an "absolute truth, known only to sacred circle of those blessed with a true knowledge" IME, that's how you recognise the genuine snake-oil salesman...
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Old 27th July 2010, 06:47 PM   #3
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Quote:
that's how you recognise the genuine snake-oil salesman...
You're more right than you know, because of the conversations I had with others afterward. I like to get more fact before judging anyone, but unfortuantely you might have hit it on the head first try.

Anyway, by-passing the thermistors wouldn't have any noticable effect in your opinion.
Juma, I'll take your earlier comments as a 'no, they don't make a difference.'.

Thanks,

V~
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Old 27th July 2010, 09:31 PM   #4
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Quote:
Originally Posted by juma View Post
It's just plain silly,........
grumpy lately ?

( well - I agree with every word you wrote .... )
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Old 27th July 2010, 10:13 PM   #5
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Maybe try it and hear for yourself.
I probably wouldn't use a thermistor in a class B amplifier, but for Class A there shouldn't be any issues.
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Old 28th July 2010, 01:33 AM   #6
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I'm glad I asked.
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Old 28th July 2010, 05:35 AM   #7
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I did the exact thing when I built SOZ, switched it out of the circuit after a good 3 second count after power on. Poor (lazy) man's soft start....worked great. Just need to remember to turn the soft start switch back to original position after power off. Now I just use a variac, less hassle.

See post #3
My new space heater

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Old 28th July 2010, 12:23 PM   #8
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Mega-amp,

Since you have used the by-pass, did you hear any difference with the thermistor in and out of the circuit?

Thanks,

Vince
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Old 28th July 2010, 01:26 PM   #9
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I believe the only influence a thermistor in series with the primary of a transformer will have, besides the inrush-current limiting, is that it adds a tiny(!) amount of Jhonson-noise, as it's residual resistance will be greater than that of a wire or relay.
I also believe that there are bigger fish to fry.
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Old 28th July 2010, 01:30 PM   #10
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Seems like I've heard bad press about thermistors as well, but with some Tubes and Class A, it doesnt seem to be as big a problem because of the steady draw?

russellc
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