[NeilR]

If you don't answer all my questions with each post, we are just wasting time.

 

[NeilR]

Just for future reference, you made a strategical mistake by wiring in the crossfeed board before you had the amp working. If you have any more problems, you have to debug that board, and all that switch wiring, at the same time. I wouldn't even do that.

 

[bperboy]

Its working fine now, and I really do appreciate all the help you've given me. The buzzing is still there, but I'll research more myself, and save you the trouble.

 

[NeilR]

Good luck. If it were me, I would pull the xfeed and temporarily wire in some jacks directly to the Millet inputs. Then I would measure every resistance in the circuit, comparing good channel to bad. Then power it up and do the same with DC voltages. Had you done that before, you would have discovered the discrepancy in the plate to ground resistance and narrowed the problem to the plate circuit. I'm just trying to teach you how to debug these things. With two stereo channels, as long as one is behaving properly, you have a point of reference and have to take advantage of that.

 

[bperboy]

I've taken out the xfeed, and rewired the output jack, but the buzzing is there, most noticeably when something is plugged into the input jack. I can't really notice it when nothing is plugged in unless I turn the volume all the way up, but when I plug something in, it immediately becomes a loud noticeble buzzing.

 

[Clutz]

Some sort of strange ground loop?

 

[NeilR]

With the source connected to input, does the volume control affect the level of the buzz?

If so, the problem is in your input side of the tube, which is where most buzzing seems to come from.

This is usually a ground issue. From your images it appears that the pot is grounded to the board via the pot case screw. (It almost always must be grounded). Verify this, and check resistance from the pot screw to ground via some of the other ground points.

Plug an interconnect into the inputs, without the source connected. measure resistance from the input pins of the interconnect to the volume pot input pads. Should be zero. Do the same with ground. Buzzing is almost always a ground issue- a lot of times it is an input pair reversed, with signal to ground and ground to signal input.

 

[NeilR]

Quote:

Originally Posted by Clutz Some sort of strange ground loop?

Good point, Clutz.

Pberboy- you have an ipod. Try that, working from battery (no charger connection and especially no USB/Firewire connection to your computer). Try as many different sources as you can.

 

[bperboy]

The tip and ring measure 0 resistance between their respective pads on the pot, but the ground sleeve to pot ground measures about 15K ohms, so thats not right.

 

[NeilR]

Everything you need to do is laid out in this thread. Let me know if you need help.

 

[bperboy]

I really don't know what else I can do. I'm really pretty new to electronics, and I'm just glad I got this far. I really just want to start listening to my Millett, and I'd like to know why its buzzing.

 

[bperboy]

Is it because both my input and output jacks are the big neutrik 1/4" locking ones, and they're both touching the case?

 

[NeilR]

You said you have 15 ohms between the end of your interconnect ground and the pot ground.

If so, your circuit look slike this (a little rough):

(ic plug) ---------> (ic plug) --> input jack------> board pad ----> board ground plane -----> pot ground pin.

The dashes are wire.

Something in there is not right. Easiest thing- swap interconnects and repeat measurement. If the problem stays in the same channel, it is not the interconnect.

Now, start measuring resistance. Stick a probe in the jack ground and the other to the pot ground. Still 15 ohms? Stick the probe on the board pad and pot ground. This gets tricky though, because you can get different resistance measurements on different parts of a pad, or get a good measurement on a cold soldered joint because you happened to stick you probe on a "good" place. Better to measure from leads on the top of the board to see how resistance runs up through the pad into the wire/part soldered to the pad. This method gives you an education and maybe highlight bad joints so you can recognize them in the future.

It would be easier though, to just reflow all the affected joints: 1) wire to input jack ground 2) Wire to input ground pad on board 3) pot ground pin. When you get done, remeasure.

If you swap cables and eliminate the cable, and reflow the joints and you still get 15 ohms and buzz, post back.

 

[NeilR]

Quote:

Originally Posted by bperboy Is it because both my input and output jacks are the big neutrik 1/4" locking ones, and they're both touching the case?

Those neutrik jacks should be isolated from the case. I used isolated DC power input, input jacks and output jacks for my Millet and I had no hum. My plan was to ground the jacks to the case (one at a time) but it never came to that. I later added a 3.5mm output jack, which was NOT isolated and that didn't cause a problem either. After doing some minor casing tweaks, I grounded the input jacks to the case, based on some thread I read here, and that was ok too. My Millet is not very particular about grounding, I guess.

The Millet does not use a virtual ground or a ground channel, so the grounding is pretty straightforward and there are a lot of options.

You could remove all the jacks (including the DC jack) from the case and see if the problem goes away, then start regrounding things to the case one by one.

The 15 ohms between IC ground and pot ground is screaming at you. Take care of that. Grounds are VERY sensitive to even small resistances. Especially input gorunds.

 

[NeilR]

Your output jack from the Steps (if you have a jack there) should NOT be grounded to the Steps case. Mainly in case you use the Steps for some other virtual ground amp, but in any event, that could cause a ground loop. Anything can cause a ground loop, even the color of your shirt. There is lots of voodoo in ground loops