[eric343]

I built a CHA47 with a gain of 2, plus the 47ohm R5s, and at certain volumes and a portable (non-grounded) source, the amp generates a "machine-gun" noise. Is this simply oscillation that would be fixed by a more stable chip, or is it a serious problem?

 

[Apheared]

What opamp? If it is stable at unity, then it could be oscillating from other things than itself. Only at certain volume rotations? Like just the middle? Is the soldering still turned on and within 15'? Can you move the input cord around and change the machine gun noise? etc...

If it's not unity gain stable opamp, it might be it's own oscillation. Take the power off the 2nd current buffering chip and listen to the output. If that IS the case, you can do a "true" parallel config.. that is, stack the opamps literally on top of each other so they share everything... same input resistors, power rails, etc... just bend the output pin(s) of the top opamp out so they don't touch, and add your load sharing resistors to all outputs.

This works fine, and is actually the *preferred* way for high-speed configs... audio is as slow as life gets in the electronics world, and you will never be bothered by something with a couple nS lag... but @ 500MHz, or 2GHz, or...

 

[eric343]

OPA2228s.

 

[Apheared]

Oops. It doesn't like gains less than 4. (says 5, but 4 works)

You MIGHT get it to work as a buffer unity, but probably not. it's hit or miss. If it's oscillating now, probably not. Build it as mentioned, really stacked... you still get the benefit of the current boost.

You're not using a hansen are you? If so, you're screwed probably. Might require different opamps, because the way carl laid out the board so each dual is a channel, not a stage.

 

[eric343]

ROFL, this is *so* funny...

Yes, I *AM* using hansens. I did say CHA47...

Boy I'm glad I ordered 4 2134s... (two for my CHA and two for my dad's)

 

[eric343]

Speaking of 2Ghz, do you know anything about making stuff for 2.4Ghz 802.11b DSS wireless networking?

 

[Apheared]

No I did not make a .11 sniffer, I swear!

No, man... I'm barely analog audio capable... digital stuff I'm a schematic sheet follower. Easy enough to understand now, but I'm not even really into electronics... cept for audio... and weaponry/surveil/counter-surveil. And gimmicky things like plasma balls and jacob's ladders and crap.

 

[eric343]

You forgot Tesla Coils. Those are *schweet*