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Old 6th May 2004, 08:44 PM   #1
diyAudio Member
Join Date: May 2004
Location: spånga
Talking Itīs alive!! or newbies first attempt!

Hi everybody!
I've been lurking on this list now for quite some time, picking up tips and pointer, learning a lot about chipamps. Well I've finally done it. My first attempt on a 3875 chipamp and it worked from the first powerup! Incredible!

Here's the parts i used. A single supply 150 va toriod(2x22 v =about +-31 v) followed by two beefy 35 A bridges. five 1000 uF caps per rail and a 1000 uF filtercap by the chip ( per supply pin). I used feddes chillamp schematic omitting the 50 k input pot and one of the 4,7 uF input caps( there is two on each chanel in the schematic) since i drove it with my nad 116 pre. all resistors were ordinary metalfilmtypes with 1% tolerance.

Allright but how does it sound?
Well, wired up on the floor on a piece of particleboard with a hasy starground, alligatorclips, the chips squeesed between a processorheatsink and a piece of aluminum with lots of rubber bands providing the pressure, qiute allright actually!

There is alittle hum and hiss when its no music playing , but considering the wiring i positive they will be sorted out by rerouting the wires and making a correct starground. It starts up without any pops or other nastiness and when i turn it of i keeps playng for like 2 seconds before falling silent. There is alittle pop right at the end but i can live with that.

All in all a very happy beginning on my road to chipamp nirvana.
Thanks for providing the imformation on this very good forum!

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Old 6th May 2004, 09:26 PM   #2
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Greg Erskine's Avatar
Join Date: Jan 2002
Location: Sydney/Australia
Congratulations! It's always good when it works as designed.

How 'bout trying it without the "five 1000 uF caps per rail".
Greg Erskine
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Old 6th May 2004, 09:36 PM   #3
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BlackDog's Avatar
Join Date: Feb 2004
Location: Wellington, New Zealand
Default Re: Itīs alive!! or newbies first attempt!

Originally posted by mcameron

when i turn it of i keeps playng for like 2 seconds before falling silent. There is a little pop right at the end but i can live with that.


This effect is caused by your supply capacitors taking some time to discharge when the power is turned off, and is quite normal. As you have more supply capacitance than is common (many people have just a single 1000uF cap on each rail, at the chip), your discharge time is therefor longer.

The noise you hear at the end (I'm assuming this is when you power off the amp when a signal is still being fed to it) seems to occur when the supply voltage has dropped to a certain level, (min. chip operating voltage ??) and I have also experienced it. Try removing the signal before powerdown, it should be much quieter......

Good luck with you gaincloning !

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Old 7th May 2004, 01:14 PM   #4
diyAudio Member
Join Date: May 2004
Location: spånga
I have to say i'm a bit sceptical about the whole single 1000uF per rail bit. I imagine that an amplifier will perform it's best when working in as good conditions as possible and an eccesive supply ripple even with good powersupplynoiseresist (is that the correct word?) is in my mind like inceriting a 50 hz signal at the ps. I dont think any amplifier designer in history have ever done that intentionaly.

But i might try it all the same, its not abig effort after all, and not all things follow my reasoning!

thanks for the input guys!

/ Micke
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Old 7th May 2004, 02:39 PM   #5
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Join Date: Apr 2004
Location: SE England
Same here - I'm sceptical about only 1000uf per rail.

10,000uf per rail every time!
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