[Dreamslacker]

As above...

Just received my UPS package from T.I. about ½ hour ago and replaced my OPA134PA's.
I'll be building a new voltage splitter with the TLE2426's (not available in Singapore at all) I got in the package later tonight.

Initial thoughts:

Sound:
A little more detailed than it's younger brother.
Bass seems to be improved slightly. Not as boomy..
Soundstage definitely improved.

Power:
It's sensitive to wall warts. I get a humming if the setting is too low on the pot. It goes away once I turn up the pot a little.

Gain:
This is the 637; No compensation (non-unity stable) and is supposed to be stable at gains of 5 or more.
On my setup, it was initially at a gain of 5.67 (according to the tangentsoft calculator). Not good.
The opamp doesn't like it much and I get clipping. The opamp also oscillated & heated up. Increased the gain to 9.84 and the problems go away.

Anyone else has anything to add?
Interested in any tweaks that might improve the sound quality when using the OPA627/637?

 

[puppyslugg]

Class A biasing thru a switch.

 

[tangent]

I don't know about your "sensitive to wall warts" diagnosis. Did you try batteries and high-quality wall warts? If you did and the hum goes away, it's possible that you're using a nasty unregulated power supply, or an especially ugly switching power supply and that the PS noise is coupling into the signal stage in audible amounts. But, it could also be that your power supply is causing low-level oscillation or some other thing.

Quote:

supposed to be stable at gains of 5 or more.

That's not quite what the datasheet says. What it says is that without external compensation, the lowest gain level at which you can expect to have stability is 5, in the best case. It does not say that at a gain of 5+epsilon that you're guaranteed to have stability. It's merely possible to get a stable setup with a gain of only 5 with this chip. The higher you take the gain, the more stable it will become, because you're narrowing the chip's bandwidth and increasing its phase margin.

This applies to all op-amps, by the way, not just the OPA637.

 

[Dreamslacker]

Quote:

Originally posted by tangent I don't know about your "sensitive to wall warts" diagnosis. Did you try batteries and high-quality wall warts? If you did and the hum goes away, it's possible that you're using a nasty unregulated power supply, or an especially ugly switching power supply and that the PS noise is coupling into the signal stage in audible amounts. But, it could also be that your power supply is causing low-level oscillation or some other thing.

The humming doesn't exist with batteries when I turn the pot. down. With the wall wart, it does. Turning the pot. up a little solves the problem totally. It's not a switching wall wart for sure.

Funny thing is that this did not exist with the OPA134P. Nonetheless, the problem is gone now (with the volume at audible levels) and I'm cool with it.

The amp. is biased into Class A with cascoded Jfets. No coupling FET's since my sources don't have DC offset.