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Topics - Joe

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Tubes and Hybrids / power attenuator
« on: June 26, 2015, 06:17:41 PM »
Looking to make a power attenuator for my Dual Rectifier amp. After looking over some schematics, some things are not clear to me. I would like to use silicone wirewound resistors for cost reasons, if that's ok. Also, some circuits are purely resistive and others have bipolar capacitors in addition to the resistors. Do the capacitors matter enough to bother with? Thanks.

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Preamps and Effects / Radio Shack Perfboard
« on: October 13, 2009, 10:49:39 PM »
Just got one of these, seemed like the perfect thing for wiring a preamp, since it works like a breadboard:
http://www.radioshack.com/product/index.jsp?productId=2102846


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Amplifier Discussion / Safety Tips
« on: August 24, 2009, 05:16:42 PM »
(Updated 11/02/09)

-When wiring panel-mount fuseholders, it's important to wire them correctly. The hot line from the switch goes to the back terminal, and the side terminal goes to the transformer primary. This prevents the hot line from being connected to the cap/exposed metal if someone forgets to unplug the unit before attempting to change the fuse. Also make sure the fuse comes out with the cap, and doesn't stick in the hole.

-It's always a good idea to use a hold-down footswitch when probing around a live chassis. This way your foot will release the electricity in case of a shock. Harbor freight sells these switches for like $10. (Two kinds are available, make sure it's the hold-down kind not the on-off kind.)

-Always wrap electrical tape or use heat shrink around mains connections, and wire-tie them in enough places to keep them secure. Tie things in such a way that if the ends come loose, they can't fall down and hit the chassis. Also, loose AC wires can get pinched between lids/covers/etc and create a shock hazard.

-Make sure the green ground wire from the AC cord is attached using a star-type lockwasher, maybe some lock-tite also. Grind any paint off the inside surface where the ground wire is to be mounted. It needs to be secure and in conduction to the chassis.

-Extra screws/nuts left in the chassis can cause shorts. Hold the chassis upside-down and shake it hard to (hopefully) get rid of them.

Please add to the list...

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Amplifier Discussion / power amp questions
« on: May 11, 2009, 01:34:05 AM »
Ok, I am working on a design similar to this:
http://depalma.pair.com/Analog/analog3.jpg

I've built a couple of cap-coupled jobs, now working on a direct-coupled version in simulation. I want to add short-circuit protection, and I'm down to three options:

1. Forget it, and use the caps/single supply.
2. Use typical VI limiting and hope it works.
3. Place zener diodes from output to driver bases, hoping to limit the current to a known maximum.

Also, I can't guarantee that the bias won't shift very slightly with temperature. It's not much at all, but possible to get 1/8V or something if it gets really hot.

My first two builds (one 6W/channel stereo and one for headphones) sound nice and punchy, so I feel it's a design worth exploring a bit more.

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