Well this is frustrating ...

[Deke609]

Hi Jamie - Yes, made of 3/4 copper pipe with some velcro stuff on the inside - greatly reduces microphonics. They're not wired to anything. I took the idea from another poster on the Quickie forum.

I'm going to step back and take a break for a week or so. Get some paying work done and then turn my attention to building the "Bigby" (Big Bee - get it?  ), starting with a plywood test build. I was going to rebuild the BP totally stock on the original chassis, and even started the process tonight, but my heart's just not in it. I will be very careful with the grounding, and will reread Jones and Blencowe, etc. on the issue.

In the meantime, I emailed Audac and Cinemag about getting some isolation transformers to make an rca interconnect isolation box. Even if that does nothing, it will be fun to build and worth having as a piece of troubleshooting equipment. 

Man ... I've read posts about people going nuts with hum issues, but I had no idea just how maddening they really are. I'm mentally, physically and emotionally exhausted! 

cheers, Derek

[Doc B.]

The whole touching the amps with your hand thing can be really confusing. Sometimes it gives you a clue of which way to head in correcting the hum issue and sometimes it leads you astray. But the first thing I try if I find that touching two pieces of gear kills the hum is to replace myself with a piece of wire that ties the chassis and/or signal grounds of the two pieces together.

We had a situation years ago at CES where an exhibitor asked us to provide three Foreplay III preamps to drive a 5.1 surround setup powered by Pass Labs amps and sourced by a prototype DAC that was three stereo DACs (MSB, IIRC) chained together. The whole setup was powered from some power conditioner, the manufacturer of which I don't remember. The system hummed like a m**********er, exacerbated by the high gain of the Pass amps. We tried all sorts of variations of grounding and floating things to kill the ground loop, and eventually ended up buying every cheater plug the local Radio Shack had. We isolated pretty much the whole setup from safety ground and the hum went away. This was not a particularly safe or clean way to address the issue, but it got us through the weekend. In telling this story I don't condone anyone floating the safety ground on our equipment. Clearly safety grounding is for SAFETY. If you float it, it is by your free will. Any result, good or bad, is your sole responsibility.

[Deke609]

Thanks Doc.

The whole touching the amps with your hand thing can be really confusing. Sometimes it gives you a clue of which way to head in correcting the hum issue and sometimes it leads you astray. But the first thing I try if I find that touching two pieces of gear kills the hum is to replace myself with a piece of wire that ties the chassis and/or signal grounds of the two pieces together.

The weird thing is, the touching the amps thing only happens with the Quickie. If I don't touch it, no hum. If I touch one tube shield, I get hum. If then also touch the chassis of the Kaiju, hum disappears. But with Nickel Wonder amp in front of any other amp (BH or retail-bought), I get hum no matter what: touching or connecting the two chassis, using cheater plugs, elevating circuit ground from earth ground, standing on one foot with my eyes crossed ... nothing makes a difference. And it is the same hum I got with the BeePre. 

At this point, I don't know what to make of it. The upcoming isolation transformer rca interconnect box project may solve things, or it may not. Mocking up the BeePre on plywood will provide an excellent opportunity to test what may or may not be causing/contributing-to the hum. I'll be using Wago-type quick connects for the mockup and that will allow me to easily swap parts in and out and play around with layout.  And I will eventually scope all the tube amps while shorting their inputs - I just need to find the shorting plugs I made that are around "somewhere". Maybe that will point to something.

Worst case scenario: I never solve the problem and just turn down the Kaiju trimpots and turn up the Beepre.  That will make the hum disappear. But I know myself and I'll never be satisfied with that: I'll keep chasing the problem until I solve it or go mad trying to. So stay tuned -- If I start posting about moving to a spot between the earth's magnetic bands, you'll know I've begun my descent. 

cheers, Derek

[Jamier]

Derek, google:Analog Devices AN-347. This is an article on shielding, not specific to audio but the general concepts are probably applicable to audio. PJ mentioned that he thought your hum might be due to capacitive coupling and this article does speak to some of these issues.

Jamie

[Deke609]

Wow! Thanks very much Jamie. I've never seen shielding explained in such detail before, or even heard of some the methods of shielding discussed - e.g., using the shield (say, copper tubing) as the neutral return path for the shielded signal wire, thereby creating a cancellation circuit rather than a true shield circuit! Cool!  If this application note is correct, then I have been taking at best a half-assed and often ass-backwards approach to shielding - e.g., with respect to where the shielding is grounded, and how some shields are best daisy-chained and then grounded from one end of the chain.  Fascinating!

I'm a little scared to try the shield-as-neutral-return-path (b/c I don't understand how it works), but the recommendations about where and how to connect shield grounds make some sense to me and seem like safe things to experiment with. 

Many thanks for this.  cheers, Derek

[Jamier]

Derek,

     For me the take-home message of this and other things that I have read concerning shielding is, that it should be as "simple as possible, but no simpler" as AE would say. If your have more shielding than necessary you might be adding a possible problem that your amp has to deal with( I think, I hope PB or PJ will correct this if it is wrong). This just seems intuitive to me (capacitive coupling w/ the PT?) but it could be all wrong.With respect to your power line issue, If that is the only real change that has occurred in the last month or so (you have sort of ruled out the water leak damage) then that is most likely the problem. I know very little about municipal power distribution, but since it is a new line, I would investigate the possibility that "modern" power lines may have "modern" devices put on the lines by the  power distributor to keep tabs on the condition of their grid, devices that might inject even more noise and crap. This is a complete guess on my part, but it might a possibility.If that is the case a PS Audio P5, or some other P model may be your best bet?

Jamie

     

[EricS]

Total guess here given your journey so far:  If the hum is confined to the Nickel Wonder pre, have you tried changing the PSU caps in the pre?  I've had some trouble with hum from old/dry electrolytics in a Class-A power supply before.  Maybe some AC Mains transient sent them over the edge...

[Jamier]

Derek,

     There is this book, Electromagnetic Compatibility Engineering, by Henry Ott. Publication date 2009. This shit is way over my head but it might be right down your alley. This is supposed to be the "Bible" on this sort of stuff.

Jamie

[Deke609]

Thanks guys.

... it should be as "simple as possible, but no simpler" as AE would say. If your have more shielding than necessary you might be adding a possible problem that your amp has to deal with( I think, I hope PB or PJ will correct this if it is wrong).

I suspect at least PB would agree    And I don't dispute that adding stuff creates new possibilities for problems. But ... if it is the shileding, that still suggests that some new environmental factor (exogenous to the amps) is making my shielding an issue now. Each of the SII-45, SII-2A3, BeePre and Kaiju have similar amounts of additional shielding, singly wired to chassis ground in pretty much the same way. None of them hummed after the shielding was installed.

The hum only started after I installed the transformer snubbers in the BP and K - I had previously installed CLCLC filters in both with no hum. I think the BP and K were out of commission for a week or two while I removed the transformers, did the snubber testing and then reassembled them and installed the snubbers. During that same time the City was hooking up the new mains line on my street. I finished the snubbers around the same time the City finished working on my street (but my buddy told me the City kept working on his street for a week or so after mine and we live very close to one another). So, you would think it was the snubbers - but that seems to be disproved by the fact that I get the same hum with the NIckel Wonder and the SII-45, neither of which has CLC type filters or snubbers (I'd have certainly added CLCLC filters to the SII-45 but there is zero available real estate under the hood  )

I would investigate the possibility that "modern" power lines may have "modern" devices put on the lines by the  power distributor to keep tabs on the condition of their grid, devices that might inject even more noise and crap. This is a complete guess on my part, but it might a possibility.If that is the case a PS Audio P5, or some other P model may be your best bet?

Yeah, that's the next step if (a) the isolation transformers don't kill the hum, and (b) a stock test rebuild of the BP on plywood gives me hum (I'll build it stock first, and if no problems, then add in other stuff one at a time: new filament supply, CLC for fil supply; CLCLC for HV supply, snubbers - testing as I go).

I really hope I don;t need a regenerator. The 300W PS Audio model, which is their cheapest, retails for $3000 CDN. That is a chunk of change and would wipe out most if not all of my budget for audio fun for quite a while.  I've been planning to rebuild the SII-45 with Lundahl 70H plate chokes and Sowter 5K M6/Mumetal parafeed OTs on a Kaiju size chassis - and would be a bit bummed if I had to put that off.  And spending $3K just to get back to where I was would be painful. But things are what they, and I'll do what I need to do ...

Total guess here given your journey so far:  If the hum is confined to the Nickel Wonder pre, have you tried changing the PSU caps in the pre?  I've had some trouble with hum from old/dry electrolytics in a Class-A power supply before.  Maybe some AC Mains transient sent them over the edge...

I guess that's possible. But the NK preamp is relatively new (built I think 2 years ago, maybe less). All caps were new and good quiality: Nichicon. And the amp has maybe a total of 5 hrs on it. I listened after the initial build, was satisfied that I had managed to follow the simple schematic and get a amp that played music without hum or other noise, and shelved it b/c it only sounded ok (nice treble, no bass).

Since I really don't care about the NK amp, I figure I'll focus on the BeePre rebuild (the "Bigby"). I can explore the hum issue as I do so.

And as an aside: if anyone knows of a cool project for which the NK's tiny Hammond 124B (mumetal) OTs can be repurposed, please let me know.

cheers, Derek

[Deke609]

     There is this book, Electromagnetic Compatibility Engineering, by Henry Ott. Publication date 2009. This shit is way over my head but it might be right down your alley. This is supposed to be the "Bible" on this sort of stuff.

Yeah, thanks Jamie. I've seen a couple references to that text in my recent reading about hum. All of this stiff is way over my head too - I'm just undaunted and determined to plug away at it until it sinks into my thick skull.

I like to tell myself that this newfound perseverance is a sign that I have become more patient. But I suspect the more accurate explanation is that I've just become more stubborn. I get as frustrated as ever when I read stuff that I can't make sense of (about 90% - used to be 99%), but the frustration is now counterbalanced and maybe even outweighed by a grim determination to figure it out.   

cheers, Derek

[Jamier]

Derek,

     Keep us up to date on what you find. If it turns out to be an issue with the mains power, we will all need to know as this will probably effect us all eventually, as our power lines are updated. Although, here in California, the power companies are all bankrupt or nearly so, so our infrastructure updates are probably a way off.

Jamie

[Deke609]

Will do, Jamie. But in the end it'll probably prove to be something dumb that I did and that I just can't see right now. [edited to correct typos]

[Deke609]

Well, I found my shorting plugs (and even made some fancy new ones), but I am not much closer to figuring this out.  I came across an expanded version of Bill Whitlock's paper (see attached) that provides a 4 step test to figure out where the hum is coming from. The test requires special rca shorting plugs that tie together a male and a female rca connector. For each connector, the pin is connected to the ground/shield via a 1K resistor, and the grounds of the connectors are directly connected to each other (you'll see what I mean if you look at the paper). This results in 2K ohms from pin to pin and 1K ohms from either pin to shield/ground.  The "fanciness" of this arrangement is that allows the shorting plug be inserted as a intermediary between your regular rca cable and the amp.

Long story short: the hum is not coming from the Kaiju, it is coming from the preamp. This is a small bit of progress, b/c I wasn't sure before whether the hum (noise signal) might have been originating in the Kaiju, travelling to the premap via the shield/ground/neutral wire of the rca interconnect, and then returning to the Kaiju via the signal wire of the rca interconnect. So now I know that that's not the case - which is something, I guess.

But I have no idea what to investigate next.   

Really hoping the hum doesn't return when I do the test rebuild of the stock BeePre on plywood.

cheers, Derek

[Deke609]

Progress has been made! It's not my mains power - which is great news b/c that means I don;t need to shell out for a power regenerator. Turns out that the Nickel Wonder has its own grounding issues. Took the NW and my SII-45 to my folks' place today - different municipality, so different mains line.  Result: same hum.  And then I remembered something that PB had asked earlier in this thread: whether the unused OT tap wires were connected to ground or left floating in the NW. As per the schematic, I had connected the wires to chassis ground (star ground in my case).  So I cut them and, poof, hum disappeared.

When I first used the NW I must not have had the SII turned all the way up, and so didn't notice the hum which disappears at about -18dB on the SII.

So i figure my problem was a grounding issue in the BeePre.  I'm just waiting on some replacement 10mF caps and then will breadboard the BeePre on 16 x 20 plywood - same dimensions as the new chassis. Will start stock and listen, and then add bits one at time: PT flux bands, extra shileding for the wiring, CLCLC HV supply, separate LV supply, snubbers - listening after each new step.

Sheesh. The mystery of the hum has been driving me nuts. Feels good to know that it is an issue with my implementation. 

cheers and thanks to all who chimed in with help and encouragement,  Derek

[Deke609]

Oops. Spoke too soon. The wire I thought was an unused tap was in fact  signal -ve, so no wonder the hum disappeared. What confused me is that the Hammond 124B trannies also have a center tap black wire that is connected to B+ - I mistook that for signal -ve. But that gives me an idea: I had wired the signal negative directly to the star ground and then the rca output grounds/-ve to the star ground. I am going to try wiring signal -ve directly to the rca -ve tabs, and then from tabs to star ground. Maybe that will help.

[Edit: tried the above and no change. I'm at a total loss. Really hoping I hear no hum with the stock breadboard of the BeePre]