Almost let the magic smoke out of a CHN-70 - diyAudio
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Old 22nd September 2014, 02:18 AM   #1
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Default Almost let the magic smoke out of a CHN-70

Rule #1: Never hot switch components.

Rule#2: Amp on last -- Amp off first.

So I decide to do an FR plot of a test box. I plug the speaker into the amp, which is on. I plug the tester into the computer. I start the measurement program. The program comes up at 30Hz sine wave and 100% output. The poor little driver is excusing at least 1/2". It takes me maybe 15 seconds to figure out the situation and shut down the amp. There is that distinct burned resistor smell coming from the speaker.

Once I get everything settled down, I tested the Re of the CHN-70. Dead on spec. The coil isn't fried. I put the speaker back on line and play some music. Both speakers sound the same.

This is not exactly Mark's preferred break-in method, but I think I dodged a bullet here.

Bob
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Old 22nd September 2014, 07:56 AM   #2
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As The Librarian would say 'Oook.'

Good save Bob!
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Old 22nd September 2014, 08:47 AM   #3
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And that's why I like a tube amplifier - unlikely to fry my speakers. (Had a Cyrus amplifier where the output transistors failed, ouch - fried drivers on one side on a pair of speakers that cost us $5K.)
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Old 22nd September 2014, 12:31 PM   #4
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Excuse me, but exactly what does the type of amp have with my screw-up?

Bob
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Old 22nd September 2014, 02:06 PM   #5
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As you described the events, absolutely nothing - but the "letting out of smoke" remark likely dredged up fond memories for some of us in which the type of amp was critical in the causation - as in full DC supply rail voltage somehow magically finding its way to the speaker terminals - not so likely to occur with a tube amp.

Sounds like you definitely dodged one here - probably used up the good luck you'd like when buying your lottery tickets- I've generally found that it's only misfortune that comes in 3s
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Old 22nd September 2014, 02:32 PM   #6
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I always break in my MA drivers with "Never Understand" by Jesus and Mary Chain (on repeat, 36 hrs). They seem to sound better in the treble imo
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Old 22nd September 2014, 03:38 PM   #7
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Quote:
Originally Posted by Bob Brines View Post
Excuse me, but exactly what does the type of amp have with my screw-up?

Bob
Hello Bob,
I think us solid state boys are being "teased" .

Our weekly cleaning lady loved turning the amp's Vol control to Max to 360 degree dust it. She cost me 2 pairs of pre-arrestor drivers. Good job I had a bag of factory seconds.

Cheers
Mark.
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Old 22nd September 2014, 04:00 PM   #8
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I know the rule is amp on last and amp off first, but could someone actually explain in layperson's terms the principles underlying the rule? From a purely intuitive point of view one might think that it would be better to have the surge of power coming from the amp coming before you turn everything else on (hence amp on first), but the rule obviously says otherwise. I figure if I can understand at least some of the basic underlying the rule it might make it easier to recall it (especially for someone as forgetful as I can sometimes be).
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Old 22nd September 2014, 07:02 PM   #9
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Most competent commercial amps have turn-on delay relays. Power is not applied to the speaker until the amp has stabilized. There will be little or no turn-on thump. Most amps shut down gracefully, so little or no turn-off thump. Not all upstream components will power up and down gracefully and will produce a thump. My DAC's will. My music player will. Now, PA amps and monoblocks have no volume controls. They are at full power once they are on. If the amp is turned on first, any upstream thump will hit the speakers at full amplification. Will that high-powered thump damage anything? Your call.

Bob
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Old 22nd September 2014, 08:36 PM   #10
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Bob - I'd like to agree with you that "most competent commercial amps (should) have turn on relays", but since DIY speaker builders have also been known to roll their own electronics, either completely from scratch or kits, many the features of a mainstream product will be absent.

My most recent several acquisitions are interesting examples

- Onkyo surround receiver with onboard microprocessors that probably surpass the total computing power of the space shuttles (hyperbole, perhaps ) - it takes at least 20 seconds after powering up the system before any audio or video emerges.
- Yuan Jing TPA3116 digital amp, and DIYaudio store ACA kits - both excellent values in their own field - each exhibits minor transient thumps when powered up or down. As digital amps are so efficient, I'm ashamed to say I just leave it on all the time. The ACAs however, is a bit of a small heater, so they do get turned off. I'd be more than happy to incorporate some type of delay circuit, but have been advised that such could be a more elaborate circuit than the amp stages themselves.
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