Bottlehead Forum
General Category => General Discussion => Topic started by: Deke609 on October 17, 2019, 12:17:25 PM
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I don't think the hum was originating in the BeePre (which I have since dismantled and bought a whole bunch of parts for rebuilding).
I've been jonesing for music, so today I hooked up the Nickel Wonder preamp which has litlerally been gathering dust in a corner since I put it together. Fed it to the Kaiju. Headphones on: instant hum. So I think "!@&$ ^$%!@ **&%^# It's the Kaiju! I must of $#%&ed something up when I installed the snubbers!" So onto the worktable it goes but I don't see any problems. So I put the SII-45 after the Nickel Wonder - same hum!
So then I'm thinking I've blown the drivers in my LCD4s and that kinda freaks me out. So I rig up a headphone amp fed by the Nickel Wonder and try different HP's - same hum.
Then I changed all the cables and power cords. Same hum. Took everything off the dedicated 20A line from the box and put everyting on a regualr 15A line. No change.
Tried unplugging just about everything in the house. No change.
So I thought maybe there's something wrong with the grounding in my house wiring. But my Emotiva dc-offset filter indicates that ground is a-ok. Is there a better way to test the house ground?
So its some other noise on the mains? But what are the odds of the mains going wonky at the exact time that I install snubbers in my BeePre and Kaiju? The City was rewiring the mains over the summer (resulting in even lower mains voltage!), so maybe that's it. But I'm pretty sure I had both amps working silently after they did much or all of that work. So I'm doubtful. But maybe.
But it just occurred to me as I type that I did change something in the amps: I removed PB's chassis ground elevator diode mod b/c I was worried it might be interfering with all my shielding wired to chassis ground. I'm going to reinstall them and see.
What's weird to me is that I only hear the hum when the power amp (Kaiju or SII-45) is connected to a preamp (BeePre or Nickel Wonder). Remove the IC's and the hum disappears. Does that point to anything in particular as being the culprit.
Man ... I can't believe I tore down what I'm thinking was likely a perfectly working BeePre :(
Any and all suggestions for how I should troubleshoot this will be appreciated!
cheers, Derek
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If you have an oscilloscope that is the best way to sniff out hum issues. You can see the shape and frequency of the waveform and that helps a lot to determine the source.
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If you have an oscilloscope that is the best way to sniff out hum issues. You can see the shape and frequency of the waveform and that helps a lot to determine the source.
Thanks Doc. I do have a scope. I will take a look at the mains.
cheers and thanks, Derek
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Well, the reverse paralleled diode mod didn't help. And just to be sure, I listened again with a solid state headphone amp and different headphones -- and yup, the same hum.
So on to scoping mains power. This is so weird.
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Well, I tried one more thing in an effort to narrow down the source to either inside the house or outside. I cut the breakers to everything except the dedicated 20A line that's used only for audio - no change. Still hums. So I suspect it really is something on the mains.
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You might want to try the inverse. Cut the breaker to your 20A circuit for the audio equipment and then connect a very basic audio setup to one of the other [regular] circuits in your house. Hum of no hum?
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Good idea. But no luck. Still get hum.
I'm now wondering whether someone might have inadvertently disconnected the house earth ground. I live in an old duplex circa 1895. The guy in the lower unit was doing a bit of reno in the basement over the last couple of months. I wonder whether he saw an old wire connected to a pipe and cut or removed it. He's away until sometime next week - but I'll ask him when he gets back. Maybe I'll need to get an electrician to put in a new earth ground.
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Earth ground is not important for noise (only for safety ...)
What is connected to the input of the preamps?
BTW, Doc B's suggestion of using a scope to look at the device outputs and even the power line is still worthwhile. Post screenshots to crowdsource the analysis ...
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What's weird to me is that I only hear the hum when the power amp (Kaiju or SII-45) is connected to a preamp (BeePre or Nickel Wonder). Remove the IC's and the hum disappears. Does that point to anything in particular as being the culprit.
On your nickel wonder, the output is one winding of the transformer, is that floating in your build or did you ground one end?
The symptoms you are reporting are consistent with a grounding issue, and when you make your system more and more complicated, you provide more points where these issues can originate. Your instinct to get things down as simple as possible is a good one. I would follow Doc B's directions to see if that leads you anywhere.
If you have just one interconnect plugged in, do you still get hum? If you just touch the shell of one RCA cable to the shell of the jack (leaving the center pin doing nothing), does that activate the hum?
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Many thanks PJ and PB. I'm confident that I will *eventually* get to the bottom of this.
Earth ground is not important for noise (only for safety ...)
This is good information to know. I didn't see your message until late at night, after tracking down where the main panel in the basement makes an earth ground connection: on the city water service pipe that runs about 10 feet below grade under my front yard.It was loose and corroded. So I spent a couple hours cleaning all the parts, filing to get shiny metal, and re-attaching. So hopefully my house is now safer!
What is connected to the input of the preamps?
My DAC. But the hum happens even when there is nothing connected to the inputs of the preamp.
BTW, Doc B's suggestion of using a scope to look at the device outputs and even the power line is still worthwhile. Post screenshots to crowdsource the analysis ...
Yes, this will be this morning's project. I will post screenshots of everything later today. Everyone's expertise (or even wild guesses) as to the meaning of the results will be much appreciated.
On your nickel wonder, the output is one winding of the transformer, is that floating in your build or did you ground one end?
I will check that later today and report back.
If you have just one interconnect plugged in, do you still get hum?
Yes, I still get hum.
If you just touch the shell of one RCA cable to the shell of the jack (leaving the center pin doing nothing), does that activate the hum?
No. it only happens when the center pin is connected.
Different idea: I remembered this morning that in August I had a water leak upstairs. I didn't notice any effect on audio at the time. But seeing the corroded earth ground connection last night got me thinking this morning: corrosion takes time. Maybe one or both of the outlets near my audio or elsewhere on my main floor are corroded. I will safely investigate this after scoping.
cheers and many thanks, Derek
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Derek, do you have one of those test plugs with the three lights that analyzes the configuration of an AC receptacle? It will tell you if you have an open ground. It won’t tell you about the quality of the connection, but it will indicate if your grounded or not. I always thought earthing of circuit grounds made a difference with respect to noise too, especially signal input grounds.
Jamie
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Scope shots attached.
Mains looks fine. Interestingly, the scope says I'm getting 121V RMS, whereas my Fluke 117 says 117 (perhaps it's biased in favor of itself). So maybe I need a new battery (again!). And maybe this explains why my voltages on checkout are always slightly on the low side.
Hum is a jagged 60Hz wave. With preamp connected but not powered on: no hum and no hum waveform. With preamp on: jagged 60Hz waveform that varies in amplitude by the SII's attenuator setting.
Please let me know if the waveform isn't clear enough, or if you want something else.
All input/thoughts welcome and appreciated.
I still suspect that my upstairs water leak in Aug has something to do with this - the water went right through the floor into the ceiling (and presumably the walls, perhaps using mains wiring as its conduit).
I am going test whether the hum is still there if I plug the amps into the wiring from the main panel rather than the sub-panel.
@Jamie - I had one of those at one time, but it's either lost or buried in some box/bin somewhere (which is as good as lost - I'll find 5 years from now when looking for something else)
MTIA, Derek
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On your nickel wonder, the output is one winding of the transformer, is that floating in your build or did you ground one end?
Forgot to answer this: It looks like I grounded it.
cheers, Derek
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Derek,
Is your house wired through galvanized conduit, completely? You mentioned having a dedicated 20 amp audio circuit. Is that something you added or was it present when you moved in? In those circuits that are wired through the conduit are there no ground wires ( is conduit the ground pathway)?
Jamie
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Is your house wired through galvanized conduit, completely? You mentioned having a dedicated 20 amp audio circuit. Is that something you added or was it present when you moved in? In those circuits that are wired through the conduit are there no ground wires ( is conduit the ground pathway)?
Hi Jamie - no metal conduit that i know of. I should have chosen a different word. I just meant that I suspect the wiring in the walls would make an easy means/route ("conduit") for water to follow gravity.
I had electricians add the 20A line a couple of years ago and watched them put it in. They snaked a new wire directly from the box to the wall outlet.
cheers, Derek
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Is that wire romex? If it is it’s not likely be a problem except on the stripped ends which you can check easily. Did you turn off the circuit breaker and pull the duplex out of the wall box?
Jamie
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I'm not worried about the wires so much as I am about the receptacles and receptacle boxes.
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If it is dedicated it only has 2 ends. The duplex in your listening room and the connection at the service panel( unless it is connected through one or more service points, which should also be in metal or possibly plastic boxes).
Jamie
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Derek, turn off the breaker, AND BE SURE it is off, and pull the duplex out and inspect it. It’s possible that the problem could be as simple as a ground wire that’s become detached from the duplex. Not all electricians are as careful as others. Make sure when using the Sideties on a duplex to make a “J†loop on the wire in a clockwise direction so the screw pulls the wire in toward the screw shaft and thus cannot come loose. MAKE SURE you check those wires with a meter before you handle them.
Jamie
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With preamp on: jagged 60Hz waveform that varies in amplitude by the SII's attenuator setting.
That's a new piece of information. If the attenuator is all the way down, is the hum nearly inaudible? Is everything plugged into the same outlet?
When you figure out what's actually wrong, it's likely to be something incredibly simple.
Something I've had happen that could cause this would be one of the two connetions on an RCA jack not being connected. Or, for instance, if somehow you swapped ground and signal hot, that could make a weird problem like this.
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If the attenuator is all the way down, is the hum nearly inaudible?
Yes, at about -27dB it is barely audible. If I wasn't looking for it, I wouldn't notice it.
Is everything plugged into the same outlet?
Yes. And I've now tried 4 different outlets. 1 off the main panel, 3 off the sub-panel, including the 20A dedicated. All give me hum.
When you figure out what's actually wrong, it's likely to be something incredibly simple.
That would be nice. I need to take a fresh look at the problem.
Something I've had happen that could cause this would be one of the two connetions on an RCA jack not being connected. Or, for instance, if somehow you swapped ground and signal hot, that could make a weird problem like this.
I will look. But for that to be the case, I'd have had to make the same error at least twice and at least 1 year apart. B/c I got the same hum with BeePre (built in the last year and tinkered with) and Kaiju (built recently and tickered with), and BeePre and SII-45 (haven't done anything to it in a while - no snubbers, no CLC filters, etc.). And I get it with the Nickel Wonder (built from schematic a while ago; made no mods) w/ Kaiju, SII-45 and a retail-bought SS HP amp. In mid Sept I had no hum (other than reg dropout in the Beepre) and had never experienced hum. So I think something has changed ... I just have no idea what.
I'm stumped. THe only thing I can think of is the water leak. But I don't know how that would lead to what I assume is a ground loop somewhere. Or is not a ground loop?
Please keep the ideas coming!!!
thanks, Derek
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Derek, have you tried different interconnects/ cables, including power cables?
Jamie
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Derek, have you tried different interconnects/ cables, including power cables?
Jamie
Yup - four different interconnects, including 2 store bought to rule out me having made the same mistake in building the cables. And different power cords - diy and stock/commercial ones. No difference in hum.
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Does anyone see any clues in the jagged 60Hz waveform that I posted on the first page of this thread?
many thanks, Derek
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It's not just 60. Looks like 120 and maybe 180 on there too. Just hook a bare wire to your scope input hot and see if it shows the same kind of waveform. Since you seem to hear hum with every piece of gear, that will tell you if every piece of gear is picking up something in the environment.
Also, I don't see anywhere that you have shorted the inputs and looked at the waveform. Turning down the level pot is almost the same thing, but just almost. That will help to determine if the root problem is within the DUT.
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... hook a bare wire to your scope input hot and see if it shows the same kind of waveform. Since you seem to hear hum with every piece of gear, that will tell you if every piece of gear is picking up something in the environment.
Many thanks Doc. Will do.
Also, I don't see anywhere that you have shorted the inputs and looked at the waveform. Turning down the level pot is almost the same thing, but just almost. That will help to determine if the root problem is within the DUT.
So short the preamp inputs and connect to amp and test? Or short inputs of unconnected preamp/amp and test? Or all of the foregoing?
Many thanks, Derek
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Start by looking at one piece of gear at a time in order to narrow down where the problem lies. Disconnect the preamp from the amp, short the preamp inputs and look at the output of the preamp. Then do the same with the amp, short the inputs of the amp and look at the amp outputs.
Note that this applies only to Bottlehead products. I don't take any responsibility for the stability or functionality of anyone else's amps with the inputs shorted
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Ah hah! Should have tried this earlier: DAC straight to the SII-45, no preamp. NO HUM! ZIP, ZILCH, ZERO. PERFECT SILENCE! (And as an intesrting side note, it sounds much better by itself than with the Nickel Wonder in front of it ... which, come to think of it, I think is the reason why I put it in a corner to collect dust in the first place).
So there's something about the interaction of the preamps and the amps. Maybe I reallly did make the same mistake multiple times. So I think I need to look for possible sources of a difference in ground potentials between preamps and amps. I wonder if the "balanced outputs" mod (+ve and -ve of both speaker out referenced to ground via resistor) might do this? Or interact with the diode chassis ground elevation mod? I am going to enjoy listening to the SII-45 by itself for a bit and look over schematics and photos of my builds to see if I can spot anything.
Feeling more relaxed now and confident that the riddle will eventually be solved.
Start by looking at one piece of gear at a time in order to narrow down where the problem lies. Disconnect the preamp from the amp, short the preamp inputs and look at the output of the preamp. Then do the same with the amp, short the inputs of the amp and look at the amp outputs.
Many thanks Doc. I will try this tomorrow morning. I'm pretty tired today - at 2 am yesterday I scrubbing/filing heavy gauge ground bus wire in an effort to improve earth ground :)
Note that this applies only to Bottlehead products. I don't take any responsibility for the stability or functionality of anyone else's amps with the inputs shorted
Hah! I don't care about the other ones. And I'm neither litigious nor the type to blame people for trying to help me (for which help I am thankful and appreciative)! :)
I hereby absolve and agree to hold harmless all who post or have posted advice, opinions, suggestions etc., of whatsoever kind, on this thread or other any other on this forum; and for greater clarity, declare that I am solely responsible in law, equity or otherwise for any actions or inactions I have taken or may in the future take, whether in reliance up on or influenced by such advice, opinions or suggestions. Seriously. Not joking.
cheers and thanks, Derek
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That's a new piece of information. If the attenuator is all the way down, is the hum nearly inaudible?
Yes, at about -27dB it is barely audible. If I wasn't looking for it, I wouldn't notice it.
@PB: I should clarify that only the attenuator on the SII has this effect. Not the volume pots on the BeePre (pre-dismantling) or the Nickel Wonder. Changing the coarse attenuator on the BP had little effect on the hum: slightly changed the tone, but not the volume. With the Bp attenuators set to minimum volume, I got pretty much the same hum loudness. Same thing with the Nickel Wonder: same hum with volume all the way down as nearly fully open - except that turning it all the way up seemed to shift the hum to one side and change the tone a bit - but I figured this was just weird bahavior of a $10 pot turned too far (literally forcing it to point it wouldn't turn any more).
And I need to correct a previous misstatement: the hum becomes nearly inaudible at -18dB, not -27dB.
Does the fact that the SII attenuators, and only the SII attenuators, affect the volume of the hum point to anything?
many thanks, Derek
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Last observation for the day: no hum with the Quickie as preamp in front of the SII-45. I assume the same will hold true with the Kaiju. I will try that tomorrow.
Off-topic tangent: the Quickie w/ PJCCS is my son's and I'd never listened to it except connected to my son's Quicksand. It sounds insanely good in front of the SII-45. It beats the pants off the Nickel Wonder - which cost me about 2 X as much in parts (the tiny Hammond nickel transformers alone were $100 or more). Wow! It's no BeePre, but I could understand someone hearing both and deciding they could live with Quickie. Crazy good. And really fun to listen to.
cheers, Derek
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It sounds to me like the problem is capacitive coupling from a power transformer winding to the signal ground. The Quickie has no power transformer.
This is described in one of the Jensen Transformer white papers. These papers of course reflect the reasons you should use transformers, but it is perfectly true that isolation transformers will break such a current better than pretty much anything else.
It's too late (and I had too nice a wine with Friday dinner) to follow up in much detail, but a ground lift in one device and/or the other should make a difference, if my analysis is correct.
Usually we look at a preamp / amp, and because the power amp transformer is larger, we expect it to be the "source," but I imagine both contribute in the real world. That may be why reversing the phase with a cheater sometimes works and sometimes doesn't.
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Many thanks PJ. I will track down the Jensen white paper and see if I can make sense of it tonight.
cheers and thanks, Derek
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Here is Bill Whitlock's (Jensen) White Paper that PJ referenced. Since hum is a common problem this may be of help to others now and in the future. It is pretty accessible - no calculus, just a bit of simple algebra based on Ohm's Law and the formulas for voltage dividers, parallel resistors and capacitive reactance. And it's a really cool example of how you can use these simple formulas/concepts to work through a pretty complex problem.
Many thanks PJ for flagging it. I am still digesting it (as fully as I can) and will probably have a couple of follow-up questions (a) to make sure I am at least getting the basic idea, and (b) about the practical solution: which looks to be a diy interconnect box with a wideband, low distortion 1:1 isolation transformer.
cheers, Derek
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For what it's worth, you don't have to DIY; Jensen makes isolator boxes of many kinds; here's an example:
https://www.jensen-transformers.com/product/ci-2rr/
That's a little pricey, and some listeners don't like the resulting sound quality. I see it as a convenient diagnostic tool. If you like the sound, it's also a solution, but as I said a ground lift (back to back diodes shunted by a 10-ohm resistor and a small capacitor to bypass it at radio frequencies) in the preamp and/or in the power amp will often do the job. That's because the source impedance of the capacitive coupling is very high, so the 10 ohm resistor almost completely shorts that current. Merlin Blencowe's article on grounding has a treatment of the ground lift:
http://www.valvewizard.co.uk/Grounding.pdf
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Excellent! Thanks PJ. Yes, the Jensen "IsoMax" stuff is pricey - which is why I thought I'd diy, plus it's fun to make one's own stuff.
I will try the diodes/resistor/cap approach. If it completely kills all audible hum I will just go with that. Otherwise, I will look into getting a good 1:1 transformer.
cheers and thanks, Derek
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So, this is a slightly OT, but I’m a little confused about PJ’s comment that earth grounding is not important when it comes to noise reduction. I completely believe him, he has more experience than, well, maybe anyone, but a recent build that PB helped me on, led me to believe that earthing is important to noise reduction so I’m trying to understand. PB advised me to ground the signal input ground at the point where the input entered the audio circuit ( in this case it is a PCB). I ran a wire from the signal input ground connection to a star ground that I located next to the IEC. The star ground connects directly to the ground pin on the IEC. When I first powered up the amp(s), they are monos, this wire was not connected and I had some audible hum. When I connected this wire to the star ground that hum ceased. The amps are push/pull K-501s. Also, connected to the star ground are the signal input cable shield ( from the load end) and two wires from aluminum plates that the binding posts and input RCAs (these are on opposite sides of the amps from each other) are mounted in, they have insulated shoulder washers. If the earthing isn’t the reason for the hum reduction, what is? Can you help me understand? I haven’t used the amps in a few weeks so I will experiment with this connection and see if the hum repeats when disconnected but I remember that this connection reduced the hum considerably, I’m pretty sure.
Jamie
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Jamie - the noise reduction was because the signal ground connected to the chassis, not because the chassis happened to be connected to earth ground for safety reasons.
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PJ,
Thank you for correcting my misunderstanding. If I had made the chassis from something metallic that might have occurred to me, but I used wood and created the star ground from a screw terminal block, which became, I guess, the conductive part of the chassis. At least I had the good sense to attach everything metal to it. Well, at any rate, I’m learning, albeit slowly. Apparently, I ‘m not afraid to ask stupid questions, so for those of you who are, stay tuned and I will probably ask every one of them and probably some twice.
Thanks again, Jamie
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I scoped the voltage of mains neutral to mains ground a few minutes ago. It looks a lot like what I saw coming out of the SII-45 when it was fed by the Nickel Wonder.
Top attachment is mains neutral:ground. Bottom is the SII-45 output I posted before.
Any thoughts?
I tried adding one diodes/resistor/cap combo to the SII-45 and it did nothing. I will try adding one to the nickel wonder tomorrow (ran out of time today)
cheers and many thanks, Derek
[Edit: COuple of additional points. (1) If you look toward the bottom of the images, there are some basic stats about the waveform. (2) The hum has gotten worse over the last month. It started as a barely audible hum coming out of the Kaiju a month ago. It is much louder now.]
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No change with with the diodes/resistor/cap ground elevators installed in both SII-45 and the Nickel Wonder.
Don't know how to make sense of this. No hum with DAC directly connected to the SII-45. And no hum with DAC -> Quickie -> SII-45. But connect the Nickel Wonder (which when originally built caused no hum) to the SII-45, or a retail purchased and unmodified SS headamp, and I get hum. Had the same issue (but not as loud) when the Beepre was still put together (but didn't test it with other amps - just the Kaiju -- b/c disconnecting the BP made the hum go away and so I assumed that it was the source of the problem). So something has changed in the environment - maybe corrosion in a receptacle or at the mains sub-panel caused by the August upstairs water leak; maybe the City's new line on the street; or a host of any other things -- Arghh!)
In Bill Whitlock's White Paper, he suggests that the power transformer in each connected amp produces a parasitic capacitive coupling with the amps's chassis ground, and that the interconnects then connect the two chassis, and that this opens the door to a ground loop that becomes part of the signal going to the second amp (b/c somewhere in the amps the signal wire is referenced to ground).
If the above interpretation of the white paper is correct, then doesn't it follow that elevating the chassis ground from earth ground in both amps leaves what I'll call the "Whitlock problem" untouched - can't a loop still circulate between the two chassis by way of the interconnects? If so, then maybe I need to try isolation transformers. The specs of the Jensen CI-2RR look good on paper: frequency range of <10Hz to >40kHz and low distortion - but is $200 USD. [Edit: and I'd really like to diy them]. Does anyone know of equal or better isolation transformers (wideband, low distortion) that would be suited to the task? I came across a couple pcb-mount transformers made a company called Audac that look even better to me on paper (models TR106 and TR266: http://audac.eu/products/c/transformers/line-transformers (http://audac.eu/products/c/transformers/line-transformers), but I can't find any reviews of them and haven't figured out where/how I could buy them.
cheers and many thanks, Derek
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Derek, you mentioned in some of your previous posts, in other topics, that you experimented with shielding, it seemed like a fair amount of shielding. Do you have more than the “stock†shielding in the SII, and do you have it in the NW pre? If so, is it the refrigeration tubing type that you experimented with in other builds?
Jamie
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Thanks Jamie - I thought of that too. There is one piece of copper tubing in the NW that shields the incoming signal wiring (from DAC) to the vol. pot. But it is wired to star ground at only one end and otherwise doesn't make contact with anything conductive (chassis is acrylic). I suppose it could act as an antenna, though, but I didn't see anything when I scoped a 1 ft piece of wire (used as an antenna) - a bunch of stuff in the really high kHz and MHz that is likely coming from my wireless internet, but nothing in the 0-200 Hz range. Plus I get the same hum 1 floor down - so if it's RFI, it's a pretty powerful and consistent signal - so I doubt that's it.
But yeah, I have a ton of extra shielding in all my BH amps - but none of them has hummed before.
I guess a good test would be to take a cheap headamp and the NW to my buddy's place down the street and try them there. Although I'm not sure if he's on the same City power line as me. Would be a better test if he was on a separate line (in case I were to hear hum at his place too).
This is driving me nuts!
cheers, Derek
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Follow-up: same hum at my buddy's place. Took the NW preamp and retail-bought SS amp there. So I thought for sure this pointed to the preamps and something about the way I built them. But ... I mentioned that prior to testing at his place I thought it might have been the new power line the City put in. Turns out they put a new line along his street too (perhaps the same line, since we live a 15 min walk from each other) and finished about a month ago (same time my hum problem popped up).
So, since I've already inspected both the main panel, sub-panel and a bunch of receptacles for water damage and found none, my next step will be to rebuild the BeePre completely stock. If I still get hum, it's the mains power. If I don't, it's my build mods.
cheers, Derek
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Some additional observations in case they mean something to someone.
As I mentioned before, I get no hum with the Quickie feeding the SII-45. Same goes for feeding the Kaiju. EXCEPT, today I noticed that if I touch either of the tube shields on the Q, exactly the same hum shows up in the touched channel. BUT if, while touching a Q tube with one hand, I then touch the Kaiju chassis with the other, the hum disappears.
Does this point to or confirm anything?
many thanks, Derek
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Derek, you have tube shields on your 3S4s? Are they connected to the ground bus?
Jamie
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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? ;D), 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! ;D
cheers, Derek
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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.
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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. ;D
cheers, Derek
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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
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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
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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
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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...
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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
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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 ;D)
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
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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. ;D
cheers, Derek
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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
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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]
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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
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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
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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]
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Success! Success! Success!
The breadboard of the stock Beepre took forever but it worked! Hooked it up to the SII-45 and NO HUM!!!! And look at the thing! A complete rat's nest - an invitation for hum at every turn. And there was no question it was working and producing sound b/c the microphonics of the rat's nest build were crazy (but clear, without buzz or hum -- just that beautiful Beepre "ping" and resonance)
So something went wrong in the previous iteration of my Beepre - I again suspect a short somewhere caused by a metal shard (swarf from all the drilling). But who knows -- and frankly, at this point, who cares. Now I can turn my attention to doing some proper breadboarding and then begin the actual rebuild in the new and bigger alumininum chassis (with CLCLC HV filter, dedicated LV trafos with CLC filters before the LM1085 board, cooling fans, snubbers, tons of copper shielding, and giant Nichicon 22mF 80V cathode resistor bypass caps -- in short: the works!)
I am a happy guy tonight ;D
cheers, Derek
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It looks like you took me up on the Wago clips. Aren't they just amazing for prototyping? You bought a bunch!
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It looks like you took me up on the Wago clips. Aren't they just amazing for prototyping? You bought a bunch!
I did indeed! I picked up a cheaper knock-off version after you posted about them. I think it was a 75-pack, most of which are doubles that are only good for connecting 2 wires. They work really well. What I most like about them is that you don't have to clip the leads of components and so everything is reuseable for the permanent build.
cheers, Derek
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Congrats, Derek! I've had a few problems over the years from stray single strands of wire, curly aluminum corkscrews, or a rogue solder bead that rattled around inside the chassis. I have found an air compressor to be a useful device before final assembly.
Now the fun starts of getting it back into a chassis. This is where I am, just now ordered the aluminum top plates after being tied up with work for weeks.
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Thanks Eric! Yeah, now the real fun begins. I've got a lot of metal work to do. And still need to settle on a layout. I think I'll build it in a wooden enclosure before making any cuts in the new aluminum.
cheers, Derek
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And +1 to PB's trick of using flat ceramic 4 pin sockets for breadboarding (mentioned in Eric's 300B build thread). As PB mentioned, you can insert 4 pin tubes from the bottom. Just remember to swap left and right pin wiring - maybe not such a big deal for pins 1 and 4 (filament) if you're using AC heating, but you don't want to mix up grid and anode!
cheers, Derek