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Old 23rd January 2004, 02:58 PM   #21
Morse is offline Morse  United States
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Hi Saurav;

I used some .1uF ceramic discs for snubbers - ancient Philips ECG's I had in my parts bins. The "X" cap is a Panasonic interference suppression cap rated for 275VAC that's available at Digikey for about $1 each. I wired mine directly across the AC mains at the IEC inlet (I also wired in an MOV at the same spot so the amp now has an integral surge suppressor! ).

One trick you can use for this kind of thing for finding any residual hum is to wire in a headphone jack (using a voltage divider). In my case I used a 150r in series with

One other late addition to the project was a pair of bounce caps (.02uF, 1.6kV discs) to the power switch. There was a significant "off thump" when powering down. It's gone now, so again I'd just fit bounce caps as a matter of course in the future.

Ja mata,
Morse
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Old 23rd January 2004, 03:07 PM   #22
Morse is offline Morse  United States
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Join Date: Jan 2003
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Ack! Sorry about that - I hit the "enter" key by mistake while finishing an addition to that post!

Here's the complete text:

>>>...One trick you can use for this kind of thing for finding any residual hum is to wire in a headphone jack (using a voltage divider). In my case I used a 150r in series with....<<<<

...a 10r resistor. The headphone inlets are wired between each channel's 10r and ground (that way the noise is reduced significantly and the headphone sees a 10 ohm output impedence). It works fine and will point out any residual hum in your amp quite ruthlessly. BTW, I can't claim credit for that trick - it was Jon Risch at the Audio Asylum who posted it some time ago; he recommended using 100r/10r pairs up to 270r/27r pairs. I modified it a trifle, based on the headphones I'm using. It will drive Sennheiser 570's quite nicely!

BTW, I used a jack with both NC and NO switches so that when you insert the phones it kills the sound to the main speakers and when you pull the phones, it takes the voltage divider out of the circuit.

Sumimasen for the foul up in posting!
Ja mata,
Morse
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