Millet Hybrid problems

I'm confused as well. It looks like there are two potentiometers installed. Those smaller pads to the left were for the Panasonic EVJ volume pot, while the six pads spaced out into a rectangle to the right were for the RK27. What's going on above this stuff?

Secondly, did you just build this yourself? If so, there's a grounding error on the board that needs fixing. While it will have a pronounced effect on both channels, it's possible that the effect would combine to mess up the sound in just one. Refer to this diagram for the board fixes if that hasn't already been done:
DIYForums.org • View topic - Millet Boards: New Revs Fixes and Tweaks

We need some pics of the whole board, especially above that pot area.

Well, I still don't know what's going on with those dual pot pads that are both filled. Without seeing the top of the board except for the pot shaft, I'd have to guess that the guy had a Panasonic EVJ installed originally and simply snipped it off, then installed an RK27.

The board is the later version that has the grounding issue. It doesn't look like any attempt was made to ground the terminal block whose pins appear in the upper right corner of your photo. That would be the first step. Scrape some of the green mask off of the adjacent ground plane and solder a wire from the center pin to the scraped area.

EDIT: On second thought, that's what that one black wire is that is going from the switch pads to the input diode - grounding.

So, if that's OK - give us a pic of the top. There's nothing on the bottom that would be out of the ordinary - except those pot pins.

It varies depending on which terminal block on the board you're referring to, if I remember.

As for the black wire - yes, upon further reflection, it wouldn't have anything to do with the signal input terminal block, would it? Sorry about that.

So - yeah, you need to ground the ground pin on the signal input terminal block to the ground plane on the board. As I said, the simplest way to do this is just to scrape the mask to the side of the ground pin, then either solder a small jumper from the pin to the scraped area, or bend the pin over to the scraped area and solder it (assuming the pin is long enough).

You are correct - the ground pin on that terminal block is the one to the inside of the PCB.

Looks like the same one we were looking at over in the amp section, right? This is the one with the weird grounding arrangement on the back plate. I don't know how they expected it to work that way. What's the second set of inputs for (the ones with the resistors)?

As for the black wire on the diode pad on the bottom. It looks like the guy burned the pad up on the switch blocks on top - there's one pad empty on the area marked "SWITCH."

I still can't see that front area around the pot - that's where the double pins are that are showing on the bottom.

So you say the tube bias checks out on both tubes?

EDIT: Sorry, that's a bit of rambling, but I can't see anything that would be causing your problem except that funky grounding arrangment in back and the possible pot screw-up in front.

Actually, the ones with the resistors are the inputs. Strange - we use input resistors on the Starving Student, but I haven't heard of anyone doing it before then.

It confirms what I suspected - there was a Panasonic EVJ initially installed. The builder simply snipped the leads, removed the pot, and installed the Alps RK27 on the other pads. He left the snipped leads in there. I don't think there's anything wrong with the pot area.

That headphone jack installation is pretty weird - more so than the grounding scheme in back.

I'm at a loss if you say you've biased the tubes. Both of them light when you turn it on? If not, then that would cause the problem.

It's possible that one of the OPA551's has burned out. Have you tried switching them to see if that has any effect?

They're plugged into what's known as DIP-sockets. Simply grasp them between your thumb and forefinger lengthwise and wiggle back and forth slightly as you pull up. They should come right out.

If that's not it, then I would recommend re-wiring that whole backplate. Seriously, there's not a whole lot that can go wrong on the PCB - wrong part, bad soldering, etc., but I think we can dismiss both.

When you go switching the opamps around, note that the notch on the end goes on the same side as the notch in the DIP-socket. The notch is also drawn into the PCB silkscreen.