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Old 7th November 2007, 07:25 PM   #1
bcdzt5 is offline bcdzt5  United States
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Default Basic chipamp component selection

Hello all,

I am new to DIY audio and I am preparing to make first leap into the hobby. I am assembling a chipamp with the following components.

Audiosector 3875 Chipamp
-2 separate amp boards
-Chosen over the 3886 for its higher output at 8ohms
-Reasonably priced and easier to assemble than point to point

Audiosector Unsnubbereized PS board
-single pcb for both channels
-I am currently indifferent on the PS being snubberized or not (haven't established a taste yet)

AnTec toroid transformer (45USD w/shipping)
-single 300VA with 2 32volt secondaries (one per channel)
-chosen over 200VA because price was not much more

Typical PC-style power entry module/switch with 3amp slowblow fuse

Plate aluminum enclosure w/ RCA in/out connectors / 18 gauge wiring

Soundblaster External USB soundcard as a preamp
-already has a pot for vol. control
-okay DAC
-fewer grounding troubles

And that's it!


How could I add a power-on indicator light on this circuit? The lowest voltage I can tap is 32volts, and that would take one heck of a resister to regulate an LED. Any ideas? Incandescent in parrellel with 32 volt powersupply output?

Anyone know the dimensions of the Audiosector boards? (Especially the distance between mounting holes)

Speaker power suggestions? (50-100 watts/channel correct? Is it that simple?)

I appreciate any suggestions any of you can make. It seems to be a typical setup, so I hope I haven’t made any glaring mistakes.

Thanks,
-Brandon
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Old 7th November 2007, 07:51 PM   #2
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Default Re: Basic chipamp component selection

Quote:
Originally posted by bcdzt5
How could I add a power-on indicator light on this circuit? The lowest voltage I can tap is 32volts, and that would take one heck of a resister to regulate an LED. Any ideas? Incandescent in parrellel with 32 volt powersupply output?
Would it? Correct me if I am wrong but... assuming the LED has a voltage drop of 2v

R = (32v - 2v) / 0.01A (aka 10 mA)
R = 30 / 0.01
R = 3000 = 3k

Then wattage would be

P = 32v^2 / 3000R
P = 1024 / 3000R
P = 0.34W

Take in to account mains fluctuations etc it may be wise to go with 0.75W - 1W maybe. They're not really that huge!
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Old 7th November 2007, 08:06 PM   #3
BWRX is offline BWRX  United States
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You could just use 3 common 1k 0.25W resistors in series instead of a 3k 1W resistor.
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Old 7th November 2007, 08:18 PM   #4
wboyd is offline wboyd  United States
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You can always add another winding to your transformer...grab some wire...wrap it around transformer until you get the proper voltage needed.
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Old 7th November 2007, 09:38 PM   #5
Sherman is offline Sherman  United States
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The easiest way to add a power-on indicator light is to use a rocker switch with a light built in. You can pick them up at almost any electronics store for a buck or two. They are usually available with red, orange, green or blue lights. I've used them in everything from chip amps to tube amps with no problems at all.
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Old 7th November 2007, 09:49 PM   #6
Nordic is offline Nordic  South Africa
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1/4W 10k will do

3mA is more than enough for an LED.
More appropriate rails are about 35V.
So, lets say 35-2V = 33V
33V x .003= 0.01W

Quote:
single 300VA with 2 32volt secondaries (one per channel
Return this... voltage way to high. Transformer voltages are normaly quoted in AC.. unless it has a built in (screwed on) bridge rectifier.

To get the DC voltage you take AC voltage and multiply with the sqaure of 2, which is roughly 1.414... or take the DC voltage and divide by 1.414 to get the required AC transformer voltage.

To save you some time, for 8R loads, a 25 to 26V ac transformer will give you about 35V volts when all is said and done.

Your 30V transformer would give over 42V of DC...
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Old 7th November 2007, 09:57 PM   #7
BWRX is offline BWRX  United States
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Quote:
Originally posted by Nordic
To get the DC voltage you take AC voltage and multiply with the sqaure of 2
Nordic, I think you meant to say square root of 2.
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Old 7th November 2007, 09:58 PM   #8
Nordic is offline Nordic  South Africa
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Old 7th November 2007, 11:25 PM   #9
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Default Re: Basic chipamp component selection

Quote:
Originally posted by bcdzt5
\How could I add a power-on indicator light on this circuit? The lowest voltage I can tap is 32volts, and that would take one heck of a resister to regulate an LED. Any ideas? Incandescent in parrellel with 32 volt powersupply output?

Anyone know the dimensions of the Audiosector boards? (Especially the distance between mounting holes)
Audiosector PS board has LED output with a spot for voltage drop resistor. With 34V rails, I use 62k, 1/4W resistor (small Panasonic LED)

The board size (both amp and PS) is 1.2 x 2.9, distance between mounting holes 2.6" .

More info here: http://www.diyaudio.com/forums/showt...425#post584425
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Old 8th November 2007, 07:33 AM   #10
bcdzt5 is offline bcdzt5  United States
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I'm glad I posted here before I sent out the order.

That would have been an expensive slip up with the transformer. Nordic, you just saved me a bunch of frustration.

Thanks a lot!
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