Basic chipamp component selection

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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
 
bcdzt5 said:
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!
 
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.
 
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

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...
 
bcdzt5 said:
\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/showthread.php?postid=584425#post584425
 

Attachments

  • b3.jpg
    b3.jpg
    62 KB · Views: 1,110
Hi,
for 8ohm speakers you should be using around 25Vac for maximum power.
You can use upto 28Vac but check that this is at your rated mains voltage. eg a 230:28+28 running from a 240Vac supply becomes 29.2Vac.
Add on regulation of 6% and you have an open circuit voltage of 31Vac. That is far too high.

If you do go for >25Vac then you must use a very large heatsink to keep the chip cool.
 
If you do go for >25Vac then you must use a very large heatsink to keep the chip cool.

I guess this must have something to do with the load involved but I am using 25VAC traffos and my (smallish) heat sinks hardly get warm (after hours of continuous use).

An externally hosted image should be here but it was not working when we last tested it.


I don't think this is a fluke because most of my GC's have used similar heat sinks, probably the smallest being on my original monoblocks. A half-inch thick. semi-circular piece of aluminium, again with no fins. And they never get more than slightly warm either.

An externally hosted image should be here but it was not working when we last tested it.
 
Sanity check

I am preparing to power on the amp for the first time ( :D ) and I would appreciate some experienced eyes looking over the layout.

I have read much about hookups throughout the forums but I still unsure about the Antek transformer wiring. Below is a pic hobbled together from other DIYaudio posts. Is this hookup correct? I have drawn pink arrows where there could be a switchup...
 

Attachments

  • hookup.jpg
    hookup.jpg
    96.2 KB · Views: 748
For starters you first want to run the PSU on its own, and measure the voltages it is putting out, to eliminate PSU problems destroying your amp... (speakers)

Once this is done and it looks ok, connect it to the amp boards...

Short the input and measure DC level between amp output and ground... this should be very low, a few mV or so... now connect and old speaker and make sure it plays fine at low volume for a while without seriously getting hot etc...

Regarding the pot....

WAY WRONG WAY TO GO THERE....

input goes to pin at max volume side, output from pot goes to middle pin, 0 volume side pin connects to ground...
 
Re: Sanity check

bcdzt5 said:
I am preparing to power on the amp for the first time ( :D ) and I would appreciate some experienced eyes looking over the layout.

I have read much about hookups throughout the forums but I still unsure about the Antek transformer wiring. Below is a pic hobbled together from other DIYaudio posts. Is this hookup correct? I have drawn pink arrows where there could be a switchup...


Hi,
remove the risk of damage due to a wiring error.
Use a mains light bulb tester for first power up of your transformer.
If all OK, then add the rectifier PCB. Power up again through the tester.
If all OK, add on one amplifier and power up again through the tester.
Get the idea?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.