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Old 22nd August 2003, 12:36 PM   #21
grataku is offline grataku  United States
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Like most people on earth I own speakers that are made out of MDF with drivers in which the exposed parts are rubber, paper and silk...where exactly would I get shocked?

My future SE amp has no feedback... I don't recall ever seeing secondary connections to gnd in any SE design, maybe it's implied. For feedback designs it's a different story.
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Old 22nd August 2003, 02:04 PM   #22
EC8010 is offline EC8010  United Kingdom
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Default NOBODY expects the Spanish Inquisition!

Quote:
Originally posted by grataku
Like most people on earth I own speakers that are made out of MDF with drivers in which the exposed parts are rubber, paper and silk...where exactly would I get shocked?
From the loudspeaker leads.

Before you say, "but I never touch them when the amplifier is powered," let me just say that engineers expect the unexpected to happen - mainly because (in their case) it already has...
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Old 22nd August 2003, 03:38 PM   #23
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Quote:
The centre-tap of an 8R winding would be at 2R (impedances are transformed by "n" squared).
*slaps his head* After all the time I spent calculating what turns ratio I needed on my MC step-up transformer, you'd think I'd remember that.

Thanks, you pretty much answered all my questions.

I'm curious about grounding the speaker frames - some recent threads on speaker forums have been talking about this. If I ground the 0 ohms line of the OPT secondary, that gives me an easy way to experiment with grounding the speaker frame. I can just ground the frames to the -ve speaker terminal (and associated internal wiring), I won't have to run leads back to the amp chassis.
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Old 22nd August 2003, 05:35 PM   #24
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Oh, another question while we're on the topic of RF and instability.

* Do any of you add low pass filters (i.e., input shunt caps) to your amps to roll off at say 100KHz or so (or maybe higher)? This might be relevant for me because I'm considering a non-oversampling DAC, and based on my limited understanding, the output from this kind of DAC has ultrasonic (RF?) noise.

* If you do, is a cap to ground at the input the best way to implement this?

* I already have a series cap at my amp's input to roll off the bass going to my speakers. Is it a good idea to add a shunt cap too? Or should I implement the bass rolloff in a different point in my amp? The driver-output coupling caps are a candidate for this high-pass functionality.
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Old 22nd August 2003, 07:11 PM   #25
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by Saurav
If I ground the 0 ohms line of the OPT secondary, that gives me an easy way to experiment with grounding the speaker frame. I can just ground the frames to the -ve speaker terminal (and associated internal wiring), I won't have to run leads back to the amp chassis.
That's true, but remember that earthing is all about where currents flow and where earth connections are made. In your proposed scheme, any RF noise current will be forced to pass down the loudspeaker cable. If the amplifier's 0V isn't at true RF earth, you would now cause it to move up and down in sympathy with the RF. The ideal solution would be to screen the loudspeaker cables, and use the screen as the RF connection from the loudspeaker basket to the amplifier chassis.

As for non-oversampling DACs without output filters, yes, they subject innocent amplifiers to all manner of nasties above 20kHz. There, I've made my position clear, let's see what other people think...
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Old 22nd August 2003, 07:18 PM   #26
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Quote:
If the amplifier's 0V isn't at true RF earth, you would now cause it to move up and down in sympathy with the RF.
Would it do this even if I grounded the OPT secondary straight to the chassis/safety earth, instead of the audio/signal 0V?
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Old 22nd August 2003, 07:47 PM   #27
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Given that you don't have feedback, it should work. Give it a go.
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Old 22nd August 2003, 08:16 PM   #28
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Thanks for the help.
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Old 22nd August 2003, 08:30 PM   #29
dhaen is offline dhaen  Europe
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Hi,

It really is amazing how these threads just keep going on!
And here's my turn
If grounding one speaker wire affects performance, that will mean that performance will change according to:
RH,
Who's sitting near the cable,
Whether the cat's in or out!
In establishing a system, the aim is to reduce the variables, else it becomes art more than science to excel.
Also, we all need to remember that as builders of equipment, we are responsible for it's safety to other parties. That can include partners, children, visitors and even pets. None of whom can fully appreciate the potential dangers.

I've finished...I think

Cheers,
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Old 22nd August 2003, 08:38 PM   #30
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Quote:
Also, we all need to remember that as builders of equipment, we are responsible for it's safety to other parties. That can include partners, children, visitors
I'm vaguely familiar with the concept of children, but I've never heard of 'visitors' before. What's a 'visitors'?

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