I've been flipping between the OPA627AP and the AD8620 for a couple of days now. Every time I come back to the OPA627, it's like my shoulders drop a 1/4"...there's something so smooth about this opamp, especially in the midrange and at the top. I think I'm stuck on this thing for a while...

Quote: Originally posted by tangent In a buffered design like the META42, the op-amp isn't driving the headphones directly, so the op-amp's load is the buffer, which only demands current on the order of microamps. This is why you can have just 1mA or so of current and still have the...

Quote: Originally posted by jeffreyj 1. Class A operation requires that the transistor be biased such that the quiescent collector current is equal to the peak current demanded by the load. For headphones, this will probably be somewhere around 15-20 mA. The peak output of many op-amps is...

1. How do I determine what current is required to optimally bias a given opamp into Class A operation? I'm assuming that this is something derived from the datasheet, but I need a hand knowing what to look at. 2. With the results of #1 in hand, how do I go about adjusting the Rs value in the...

Quote: Originally posted by Voodoochile Are you ****ting me? No. No, I'm not. Quote: You used one before the bath, and a different one after the bath? Yup. Other adapter was grounding out. Quote: It's always what you least expect, I guess! I...

Oh dear...somebody shoot me. Do you suppose it would help to use the CORRECT FREAKING WALL WART? "Bad nubie" <thwack><thwack> "Bad..." My sincere apologies and thanks to all of the innocent bystanders.

I was mistaken in my previous post. There's audio on both L & R if I connect only the center pin.

Just jumpered the other 2 buffers (L & R audio) in the same way. Same results. Still getting -12VDC between the jack ground and the RCA ground from the source.

Okay...jumpered pins 2 and 7 on the power buffer after carefully checking the datasheet for pin numbers. Same results - audio if only the center pin of the RCA plug is connected. Connect the ground of the RCA plug to the ground of the input jack and the amp goes silent. Turn the volume up and...

Quote: Originally posted by Voodoochile I follow you now. The jack refers to the power inlet. If you are getting 12vdc from the power inlet frame (ground) to the RCA ground, then you have +12v somehow getting from the positive rail to the virtual ground trace (runs the perimeter of the...

Quote: Originally posted by yejun there should be some external link between the source and meta, otherwise it cannot be any voltage between them. With the RCA input plugs disconnected, I'm simply metering between the jack ground and the RCA plug ground. That's where the -12VDC...

Quote: Originally posted by Voodoochile Is the board still mounted in the case? If so, is anything touching the case (any solder points)? Disconnect the front panel LED and remeasure. No, it's out of the case and has been throughout. As soon as I found voltage on the front face...

Quote: Originally posted by yejun your power supply has 3 pins? if so, try 2 pins supply. No. Power supply has 2 pins, not 3.

Here's a thing: a meter connected between the audio input ground and the RCA input plug ground yields 12VDC (!). There's a 12VDC potential between the input jacks and the input plugs. That can't be right.

Quote: Originally posted by yejun how is input DC voltage? do u have input coupling capacitor? Originally measured DC offset at 1-2mV, figured it wasn't anything to worry about, so bridged instead of putting in caps. Do I have to rethink that position?