[n_maher]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif As far as I know, the 627 and 637 are not picky opamps, other than one of them (637??) is not unity gain stable (or is that gains below 5?). I would think you have some bad ones. I'd be contacting the seller...

TI specs it as >or= 5 so I think in some circuits a gain of more than 5 can be required to keep the 637 stable.

 

[rogerlike]

Quote:

Originally Posted by n_maher /img/forum/go_quote.gif TI specs it as >or= 5 so I think in some circuits a gain of more than 5 can be required to keep the 637 stable.

So is it pretty safe to assume the 637 are dead?

 

[Pars]

Uhhh.... yes

Not accusing anyone of anything, but high dollar parts such as the OPA627 / 637 are targets of fakes. Others would include stuff like TDA1541a, 2SJ109 / 2SK389 FETs, etc.

 

[n_maher]

I'm with Pars, I can't imagine anything other than dead chips resulting in the conditions you have. Hard to understand why they'd both be toast though...

 

[rogerlike]

Quote:

Originally Posted by n_maher /img/forum/go_quote.gif I'm with Pars, I can't imagine anything other than dead chips resulting in the conditions you have. Hard to understand why they'd both be toast though...

Yes, it is strange they are both dead. The seller is only willing to refund me 50% of the cost. I guess this is a bit off topic now, but any recommendations?

 

[Pars]

That's bullsnit... 100% less shipping is appropriate. He sold the damn things to you and from what you have posted, this is not your fault. One bad chip I could suspect that maybe you zapped it, but in a known working amp (which goes right back to working with known good chips) I don't think so.

 

[luvdunhill]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif That's bullsnit... 100% less shipping is appropriate. He sold the damn things to you and from what you have posted, this is not your fault. One bad chip I could suspect that maybe you zapped it, but in a known working amp (which goes right back to working with known good chips) I don't think so.

what he said.

 

[rogerlike]

Thanks guys. I've asked the seller to read your comments.

 

[rogerlike]

Quote:

Originally Posted by rogerlike /img/forum/go_quote.gif Thanks guys. I've asked the seller to read your comments.

I'd like to make mention of the seller, who only refunded me 50% of the value of the dead-on-arrival chips. Otherwise a nice guy, I feel as if I've been conned into buying expensive and dead chips.

The seller was MatthewK, and appropriate feedback has been left.

 

[00940]

I feel at the contrary that the buyer was quite honnest. The electronic shop in my city wouldn't ever refund me a cent for defective opamps. There are too many ways to blow up a chip.

Especially when you say you did blow a ad8620.

Btw: http://www.head-fi.org/forums/f11/pl...ispute-376877/ , the seller point of view.

 

[rogerlike]

OK, concerning the transaction, well blah.

I may have been hasty to call the chips as dead. They do *something* and I hope that they do work, or can get them working in my design.

This is what I've found out:

First up, turning the volume pot to about 90%, I get a signal, a faint signal. Turning it further to 100%, I continue to hear the signal but becomes clipped on bass. This doesn't happen with no op-amps present.

Secondly, nominally I run the META42 at +/-6v on the op-amp rails. Turning the rail voltage down from +/-6v to about +/-4v, the music signal on the output rises slightly. Increasing the rail voltage, the signal disappears.

Changing the global gain with R3/4 seems to do nothing to the level of the signal, although with a higher global gain, the signal saturates at a lower volume setting.

Could it be the op-amps are in some capacity working, or could it be due to signal leakage within dead chips? Both chips exhibit the exact same behaviour.

 

[tangent]

Grasshopper, it strikes one as suspicious that these are 'B' grade chips. No one who's paying attention goes out and buys such chips at a distributor; a single search will tell you there's no benefit over the 'A' grade for audio, so there's no point in spending 45% more on them. I suspect most of the B's buzzing around in the audio DIY world are samples. Free OPA637s may not always receive the reverent treatment they deserve; Confucius say, free product often confused with worthless product.

Being about the most expensive op-amp you can buy for audio purposes, this chip is also a ripe target for counterfeiting.

Can you post a macro shot of your BrownDog assembly?

 

[00940]

Tangent: I understand what you're saying but ... what does grasshoper mean in this context ?

rogerlike: the very first steps in troubleshooting the amp would be to get a cheap tl072 or tl082 and see what's happening. These should be available at any electronic shop near you.

 

[tangent]

"Grasshopper" is a reference to an old US TV show, Kung Fu, where the Oriental loremaster addresses his student, the star of the show, this way. If I am sensei (see the start of the thread), rogerlike is Grasshopper.

 

[rogerlike]

Quote:

Originally Posted by tangent /img/forum/go_quote.gif "Grasshopper" is a reference to an old US TV show, Kung Fu, where the Oriental loremaster addresses his student, the star of the show, this way. If I am sensei (see the start of the thread), rogerlike is Grasshopper.

Yes, Tangent knew what I meant

I will try and take a photos tommorrow... :/