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Old 20th February 2017, 09:19 PM   #2191
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alright, will try this out as soone as I get the parts.

Am I crazy? no ground connection on load side? : AC115-250V 6A Unipolar Solder Lug Terminal Power Line EMI Filter CW3-6A-T | eBay
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Old 25th February 2017, 10:44 AM   #2192
AndrewT is offline AndrewT  Scotland
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Quote:
no ground connection on load side?
what re you trying to say?
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Old 28th February 2017, 11:44 PM   #2193
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I see a connector for ground on LINE side (based on the picture on the ebay link). However, ON the schematic drawn on the part, I see a ground connection between the 2 caps in parallel near the LOAD side.

Just want to make sure that I have a proper earth ground connection If I use such a device on my AC wall connection.

Last edited by MartyBoy; 28th February 2017 at 11:46 PM.
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Old 8th March 2017, 09:50 PM   #2194
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Quote:
Originally Posted by AndrewT View Post
attach the two resistors in series. That gives you 101r
Attach the 100r to the Hot/Flow output.
Attach the 1r to the Cold/Return output.
The headphone Hot/Flow output comes from the junction of the 100r & 1r
The headphone Cold/Return output comes from the amplifier Cold/Return.

This way the headphones see a source impedance of a tiny bit less than 1r
and the amplifier sees a load a bit higher than 100r

If the 100W amplifier were turned up to just reach clipping the 100r will dissipate less than P=28.2VČ/100r = 8W
Use at least 16W of resistor for this arrangement to get 40dB of attenuation from a 100W amplifier.

Use your own values to determine your attenuation and impedances and dissipations.
mmm ok .

My headphone jack has 1x left, 1x right, and the ground. Both my output ground are connected togheter at the jack. How do implement the 1r resistor? I'm confused...

So far, I've just connected 1x 100r to both left and right channel hot signal.

Last edited by MartyBoy; 8th March 2017 at 09:58 PM.
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Old 8th March 2017, 11:16 PM   #2195
udailey is offline udailey  United States
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So you nearly short out each headphone speaker with a 1R resistor? Best case scenario is that you have 32ohm headphones. Worst case is 600ohm headphones. So 28V out of the amp gives you around a quarter of a volt to drive the headphones? This won't provide enough volume.
If I wanted to drive headphones with a chip amp I would change the gain of the amp to 10 for lm3886 or lm3875. Then I would add a permanent attenuation circuit on the input. If I were super cautious I might put a 100R resistor on the output of the amp and it would be a low wattage resistor because headphones inherently contribute to the total resistance seen by the amp resulting in very low power output.
Unless you have some way to mute the amp on power up and down I would not leave my headphones plugged in during turn on and off.
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Old 8th March 2017, 11:32 PM   #2196
udailey is offline udailey  United States
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Maybe something like this schematic. This schematic ignores capacitors and power supply. Just giving an idea for attenuation and gain as well as current limiting the output.
If you have a pop on turn on then it could blow the headphones if they are plugged in when you turn it on. If you turn it off with headphones plugged in you could have a problem with too much DC getting to the phones as a lot of times the amp can have large DC offset while turning off.
Attached Images
File Type: gif headphone example.GIF (3.6 KB, 61 views)
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Old 9th March 2017, 07:49 AM   #2197
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by udailey View Post
So you nearly short out each headphone speaker with a 1R resistor? Best case scenario is that you have 32ohm headphones. Worst case is 600ohm headphones. So 28V out of the amp gives you around a quarter of a volt to drive the headphones? This won't provide enough volume.
If I wanted to drive headphones with a chip amp I would change the gain of the amp to 10 for lm3886 or lm3875. Then I would add a permanent attenuation circuit on the input. If I were super cautious I might put a 100R resistor on the output of the amp and it would be a low wattage resistor because headphones inherently contribute to the total resistance seen by the amp resulting in very low power output.
Unless you have some way to mute the amp on power up and down I would not leave my headphones plugged in during turn on and off.
if 100r+1r gives too much attenuation (-40dB) then change to 100r+3r3 to give -30dB
Don't go and change the stability margins of the chipamp by reducing it's gain.
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