[addaz]

Hi, I just finished completing my bugle circuit and there is a very loud pop when I switch it on, a loud and persistent hum when operating and a somewhat quieter (but still loud) pop when turning it off. If I touch the metal enclosure or grounding nut it gets quieter but it is still there and it's still louder than my receiver's built-in phono inputs so I know it's still too loud. I've gone over the circuit with a DMM and found nothing suspicious. I reflowed some solder joints with no changes. I took it out of the enclosure and got the same results.

All components are Digikey per the parts list except the switch and RCA jacks:
RCA jacks: http://www.frys.com/product/647708?site=sr:SEARCH:MAIN_RSLT_PG
Switch: http://www.radioshack.com/product/index.jsp?productId=2062518

The RCA jacks aren't the isolated type so the assumption would be that when they touch the metal enclosure they create a problem. That would make sense except that I get the same results out of the enclosure. 

I'm at a loss!

[addaz]

I just re-soldered a new switch onto the circuit and still have the same problem so that wasn't the problem.

[addaz]

The new switch just sparked at me when I accidentally contacted two contacts with a wire. However, earlier today the switch sparked at the board when I was moving the wires, hence the replacing of the old switch and switch wires. So if it's not the switch causing the sparking, what could be causing this?!

[poty]

What exactly your measured (with the values)?
Have you measured DC offset on output?
I don't understand your message about "sparkled switch" completely. Could you describe your setup more thorougly? How do you connect the Bugle to power supply (what is the power supply too)? What switch? Maybe you can give us a photo?
My guess - either bad or misplaced opamps or wrong power supply (or its connection).

[addaz]

Me left channel is measuring 2.5mV and the right is measuring 1.6mV.

I'm running the circuit on two 9V batteries.

Opamps are correctly oriented.

Here are some photos of the build:









Anything look suspicious? Let me know if I can provide you with any more info!

[Speedskater]

When I read about hum and switch sparking (on a small unit like this), I think about problems near the power transformer. As a side note, it's not unusual for line level equipment to pop at turn-on or turn-off.  The rule in PA systems is: Turn the power amps on last and off first.

[addaz]

I kept coming back to the switch, so I desoldered the wires at the board. Lo and behold, what do I see but two lifted pads:







I'm not sure where to go from here. Can I repair this, or can I connect the leads elsewhere in the circuit or do I need to order a new board?

[poty]

If there is really no contact between a lifted pad and the circuit it should be connected to (easy check with DMM) you can repair it with help of a bare wire soldered across the pad and the stripped part of the nearest trace. It should cure sparking (now I know what it means), although it doesn't related to hum.
The only problem I can think of is the long wires to the RCAs. You can also try to look at which hole (from the three available for each RCA place) is really grounded (connected to the ground plane). I can't do that, because I do not have the Bugle PCB. You connected the "ground" wires to the center hole which may be not connected at all.

[addaz]

As for the lifted solder pads, it appears that solder is still sticking to them, so there's still a pad there. Maybe I've just abused them too much and they juts appear to look broken.

All three large holes around the input/output are grounded so I know they are fine. I snipped back the wires on the RCA jacks to the minimum distance I could work with (around two inches) and it's still noisy and the switch pop is still loud. If I even wave my hand near the inputs, the hum increases greatly.

The enclosure I intended to use this circuit with is a two piece aluminum box. I mounted the circuit on standoffs on nylon washers in the bottom half of the box to see if that would shield any noise. it didn't, but I touched the turntable ground to the aluminum chassis and things got a lot quieter, but there is still a definite 60 cycle hum underlying everything, regardless of where I move it and what outlets I plug it into, on top of the constant noise when I move my hand near the inputs.

[hagtech]

Yes, there may be a small thump during power on and off of a BUGLE.  The hum is an unrelated matter, caused by a missing ground or too many grounds (magnetic pickup via loop).  Does the BUGLE hum when input leads are disconnected?  Do you get hum with a different phonostage in the same setup?

Hum is usually a system level thing, cause by interconnects, other equipment, ungrounded turntables, etc.  It can be caused by either electric or magnetic fields, the former being much easier to fix.

jh

[Aerobat]

The Bugle is known to pop when the gain switch is moved - it's best to switch off the amp input when doing this.

[poty]

Does the Bugle have the gain switch?

[addaz]

Jim, with the Bugle turned on and the turntable disconnected I have a loud hum. The RCA cords I've tried using with the Bugle long and cheap, so I'll start there and see if that cures the hum. Would it be favorable to switch to a plastic enclosure instead of aluminum?

poty, this Bugle was built stock per the instructions and is running off of two 9v batteries.

FWIW, my turntable and receiver power cords do not have a ground prong (not sure how common this is) and they are plugged into a surge protector.

[addaz]

Well, I went out and bought the shortest RCA cable I could find and it seemed to help in eliminating some of the hum. I also bought a ground loop eliminator to test out the connections and it didn't help eliminate anything- go figure.

Touching the ground lug on the circuit really quiets it up, but no matter what I try to ground it to, nothing keeps it as quiet as when I touch it.

I'm beginning to wonder if the AUX input on my receiver isn't grounded properly.

...or maybe I've unknowingly turned into that annoying guy who gets driven crazy by the slightest little noise that comes out of his system. Ugh, I really hope not.

[Aerobat]

Does the Bugle have the gain switch?

Sorry, I was referring to the Piccolo, never mind   

[poty]

Well, I went out and bought the shortest RCA cable I could find and it seemed to help in eliminating some of the hum. I also bought a ground loop eliminator to test out the connections and it didn't help eliminate anything- go figure.

You are powering the Bugle from batteries - then the hum can't be directly related with the Bugle. Could you try the following:
- Connect just the RCA cable to your preamp's input (Hum: Yes, No?)
If "Yes" - something wrong with the preamp or with the cable.
If "No" at the prevoius step, then:
- Connect unpowered Bugle to the end of the RCA cable, connected to your preamp's input (Hum: Yes, No?)
If "Yes" - there is a source of strong electromagnetic field nearby or problems with connecting the RCA cable to the Bugle (I strongly recommend to double check whether the shielding of the cable is connected to the ground plane of the Bugle).
If "No" at the prevoius step, then:
- Power on the Bugle and close its input (Hum: Yes, No?)
If "Yes" - there is problems with the Bugle itself - maybe something wrong with the negative feedbacks? Or RIAA components?
If "No" - it seems you are picking the hum from the inputs.

FWIW, my turntable and receiver power cords do not have a ground prong (not sure how common this is) and they are plugged into a surge protector.

I think this is the first thing to try: eliminate the surge protector and ground the preamp properly. Battery-powered Bugle is grounded through your preamp through the interconnect, so if the preamp is not grounded the sensitive circuits (like Bugle) wouldn't work properly.

[addaz]

Last night I flipper over my receiver and opened it up to double check that the inputs of the AUX channel were grounded. As far as I could tell they were grounded fine by a tight wire wrapping and attached to the chassis by a metal screw. However, when I flipped it over and got everything plugged back in, I could swear it was a tad bit quieter, as now the hum was the same volume as the noise floor on the Phono channel. "I'm officially going insane..." I thought to myself.

So when I saw your post this morning, poty, I went through all your steps one by one and still had the hum. I was starting to get concerned about the cables from the turntable to the pre as they are permanently installed at the turntable and there's no way to easily replace them if something went wrong. As a last ditch effort, I dug through all my junk and found my old Proton receiver. I plugged everything in and it was silent as a church mouse! Even when I turn it on and off the thump is gone!

Apparently the problem is with my receiver.

I apologize for all the frantic postings as this is something I should have tried right off the bat. I got caught up in the over analyzing of building a circuit after spending too much time away from the soldering iron. I would have never guessed the old receiver was taking a dive and causing this whole mess.

It's great to know there's people like you folks out there who are nice enough to help folks like me through this sorta thing, and it's great to see designers like Jim chime in and help out. Thanks again, folks!