OPA627 and possible ESD damage

[madisonears]

I recently installed SOIC OPA627's at the input buffer of my active xovers. The circuit is proven, and all the components are very high quality with verified values. The power supply bypassing is everything or more than what the spec sheet and common practice require, and is identical between channels. Yet one crossover sounds beautiful, with rich midrange and delicately detailed highs, while the other one sounds shrill and wiry, obviously distorted. I know the speakers, amps and source are not at fault.

These are legit parts sourced from Mouser. The only variable is that the good channel was installed a couple weeks ago when the weather was warmer, but the bad channel was installed a few months ago when the outside temps were frigid and hence inside air much more dry. Is it possible I damaged the OPA by ESD? I admit I took no precautions because it's never caused a problem before. What might that do to the chip if I didn't totally kill it, and what would that sound like?

Peace,
Tom E

 

[sgrossklass]

It's a FET input part, so it's certainly possible to damage it by ESD if handled without adequate care. However, dry joints seem just as likely, have you checked for those yet?

 

[madisonears]

Thanks for your suggestion. Why is a dry joint "just as likely", and how would that contribute to what I'm hearing? I believe the joints are all fine. I use a bit of flux on each pad and very good quality, fine gauge solder with quick application of high temp iron, allowing plenty of cooling time between soldering each lead.

I suspect ESD because of the FET inputs. I have no way to prove that, so I was wondering if anyone else has experienced the same thing and what it sounded like. It seems to be getting worse, which agrees with one description I read about "latent defect" ESD damage.

Peace,
Tom E

 

[pinkmouse]

ESD damage can present in many ways, right from complete faliure to stuff that's only noticeable with high grade measuring equipment. If all joints are okay, and the rest of the circuit checks out then all you can do is try replacing it, this time using appropriate precautions.

 

[madisonears]

SHOUT OUT to Mouser.

Sent them an e-mail late last night, explaining the problem I'm experiencing, alerting them that I thought their method of shipping these tiny opamps loose in a plastic envelope may have caused static charge build-up. I was very nice and did not request any special treatment. I politely suggested they revise their packaging and let it go at that.

Today I got a call to inform me that they're sending me two replacement parts at no charge. I call that pretty amazing customer service.

Peace,
Tom E

 

[AndrewT]

A plastic bag made of the correct semiconductive film will protect sensitive components from static charge, when inside the bag.

It's the handling when it's out of the bag that can be the damage problem.

 

[madisonears]

Andrew, that's what I thought, too. Now I'm no longer certain about the efficacy of the plastic anti-static envelope. Those little chips may have rubbed around in there thousands of times in the mail between Mouser and my house, during cold weather with very low humidity. Is it indisputable that there would be no static generated?

Perhaps I did wreck them, but it's never happened before. If nothing else, take this as a cautionary tale when handling FET devices.

The first replacement part from Digikey arrived in a hard plastic tube with stoppers on each end to prevent movement of the chip within the package. That opamp is working perfectly, whereas both opamps shipped loose in an envelope have gone bad.

Peace,
Tom E

 

[AndrewT]

The "hard plastic tube" would need to be semi-conductive to protect the internal from static build up.
An ordinary non-conductive plastic does not protect from static.