Great — again, indebted to all of you for taking the time. Please don't apologize for asking basic questions. I agree that it's easy to overlook something obvious and I take no offense. It also occurs to me that I never actually tested the outlets with a receptacle tester. I'll do that as well — having met the previous owners of this house, anything is possible.
I got the preamp a while ago and honestly don't remember if it ever played nice, though obviously Rowlands have a reputation for being pretty tightly engineered. I like the earlier suggestion to try it elsewhere and I'll figger how do that tomorrow.
The preamp has one RCA and one XLR output (one pair of each, but you knew that's what I meant). The amps are connected to the RCAs; the sub is connected to the XLRs via adapter and then by RCA cables. I'll disconnect it from the preamp and try again — another good suggestion — and I'll try switching the two sets of outputs.
There is no CATV in the house at all. (I have two teenagers. They think I'm Stalin.) |
Thanks to both of you for trying. I haven't tried the preamp in another system because I don't have a second one, but I'll rig something up in another spot and report back. Good suggestion.
No dimmers, LEDs, TVs on the same circuit.
Dill: I inserted the Monster because of the hum, hoping it might give everything a single ground spot. D'oh! :)
Thanks again. Keep 'em coming. This is a pain! |
Oh, and @mcroth — thanks for the suggestion, but you're right, when the sub is totally unplugged the hum is diminished slightly, but still pretty audible from several feet. I appreciate your raising the idea! |
Again, thanks to everybody for taking the time. Here are new data as of this morning:
@cleeds I never think of my video stuff as a separate system, but it obviously is. I ran the preamp through a Meridian 551 integrated amp and then to a pair of Totems. All but dead silent, so it doesn't seem to be a noise problem with the preamp itself.
@almarg I was so hopeful it was the XLR/RCA adaptors, as Al suggested (the easiest fix, after all). Alas, unplugging them changed nothing. While I was at it, I switched the amp runs from the RCAs to the XLR/adapter outputs. Again, no change.
@xti16 I did try lifting preamp ground only, with and without using the Hum-X on the preamp. Slight changes, nothing significant. I'm resisting the circuit-breaker dance for two reasons: first, see data below. Other circuits don't seem compromised; and, second, the breaker box is three stories down and while I'm in decent shape, I am no longer 25 years old. ;)
Okay, here are some more data.
Plugged the amp and preamp in two other parts of the house, using the same cabling each time. Here's what I found:
Location 1: Recent construction, new electrical service 2004.
Wiring is correct.
No hum at all.
Neutral/ground voltage: 0.1VAC
Location 2: Original construction, 1936 wiring but service upgraded, probably 1990s. Not the same circuit as #3 below.
Wiring is correct.
Barely audible (acceptable) hum
Neutral/ground voltage: 0.0VAC
Hot/ground voltage: 0.8VAC
Yes, those are right; I measured several times and re-checked wiring
Location 3: Listening room
Wiring is correct
Hummmmmmmmmmmming bird Farms, may we help you?
Hot/ground voltage: 0.9VAC
I'm now wondering if it's something to do with the circuit that feeds the listening room — but, again, that's just logical speculation, blissfully free from the constraints of actual circuit knowledge.
Anybody see anything helpful here? Thanks again!
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@xti16 Hell, sorry. That should be neutral/ground in #3 above. Anyway, it’s 124.5 in both spots. Also, the receptacle tester reports normal service in all three locations. |
@xti16 No, all service is on the same panel; circuits were added in 2004.
Given the different dates of installation, I totally agree that it's possible that location 1 and 2 (and even 3, perhaps) are on different phases.
Um... what does that mean? (Sorry!)
Does the normal performance of the SS amp put any holes in that theory?
Is there something to try short of having an electrician check?
Thanks so much! |
Okay, here’s a little more info. (I work at home. You can see I’m getting a lot done today. LOL.)
I have a SS amp with balanced inputs as well. When I substitute it for the Quicksilvers, the hum disappears, even with the sub connected. This is true whether I connect the SS amp directly to the XLR outputs or to the RCA outputs via RCA-to-XLR cables.
This suggests some kind of issue between the Rowland preamp and the Quicksilvers, yes? It also suggests that the AC power by itself isn’t really a problem. But whaddo I know? Any ideas?
And to answer the obvious question: Yes, the Quicksilvers sound about a zillion times better, so keeping the SS amp instead isn’t really an option. |
@swampwalker Good deductive powers, my friend, though the difference is pretty drastic and the sensitivity would have to be really, really high. With the Quicksilvers I can hear the hum from 15 feet. With the SS amp it's quiet as a tomb from 6 inches.
Others: I've searched online and wonder about grounding the chassis of the Quicksilvers to the chassis of the preamp. I understand that my lack of understanding may lead me to ask this question, and that may be the dumbest suggestion you've heard since breakfast (I mean since breakfast time, not the idea of breakfast). If so, feel free to put me straight. |
@xti16 Hey... I think I agree with what you're saying but I'm not understanding the first line.
Are you saying: "Since locations 1 and 2 don't have a problem, but location 3 DOES..." etc.?
If that's what you're suggesting, it makes sense to me. I've tried nearly everything else and the fact that the equipment works in some locations certainly suggests that the equipment isn't the problem. Just confirm that I've got it right above.
All of that said, what continues not to make sense is that the voltage potential in location 2 and 3 is the same (and too high), but only location 3 has the killer hum, where location 2 is basically okay (at least sonically).
Thanks!
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@edwyun Thanks for the input. I'm pretty sure it's a ground loop, since lifting grounds does have some clear effect. There is the slightest trace of RFI if I put my ear an inch or two from the speaker. I'm not sure I can slay that, but I can tame it a bit with cable choice.
If you think my analysis is off, by all means say so — I'm not an expert here. |
Hi, folks. Sorry to be unresponsive; had some actual work to do there for a while. Thanks as always for the input. Phase: All three circuits I checked are on the same phase — if I understand correctly — meaning all three are on the left half of the panel. @ toddverrone I think that answers your first question, yes? As to the dirt or loose contact: Are you talking about a contact at the breaker in the panel? The breaker has only one leg, doesn't it — is there a neutral or ground lead there? If you're talking about a problem at the outlets themselves, the problem is the same on two different outlets in my listening space so it seems unlikely that's it. @gs5556 Yes I did, but thanks for the suggestion. @almarg Yes, either amp behaves the same way with the other amp clear of the system. Thanks, fellas! |
@edwyun Acknowledged, and thanks. What I should have said is that there's a little bit of RFI that I can hear, and a LOT of hum that sounds like a ground loop. I'm trying to attack one thing at a time. (I'm not that bright!).
@toddverrone Got it. But wouldn't the acceptable performance in locations 1 and 2 seem to indicate it's not the entire electrical service?
Doesn't seem to be any harm in pulling the panel, shutting off the main breaker, and having a look tomorrow. I'll disconnect and reconnect the relevant breaker (#3) while I'm in there. If I don't reply further — well, you'll know I skipped the second step. |
Thanks to all of you, especially @toddverrone, @almarg, and @xti16, I think I have it figured out.
The original circuit feeds the two outlets at the system end of the room. I don’t think that was installed in 1936, but it’s in metal conduit, so it definitely isn’t too recent. Not surprisingly, one outlet box connects to the other, so any shortcomings in the circuit are shared.
Mais voilà. There is a four-gang outlet at the opposite end of the room that we added upon buying the house in 1998. (The room doubles as my office.) It’s Romex-fed, and I think it even has its own circuit. There’s some other stuff on it (most unfortunately a laser printer), but when I run a long extension cord from the system to the 1998 outlets, the hum is almost totally gone. At any rate, it’s acceptable.
From there isn’t not too hard for me to run some Romex about 20 feet and install a new outlet at the other end. Some day somebody is going to ask what the hell went on, but for now it should solve the mystery.
If anybody thinks I’m wrong, please let me know. Otherwise, for now, I think it will work.
Thanks again for all the time and advice. I’m truly grateful. |
I've been busy but have read through everything each of you contributed. I'm very grateful to everybody for taking the time to offer thoughts. Thank you.
Here's the update:
I used what time I had to reroute and reconfigure the two electrical circuits in the house per my last posting. My back is sore, my fingertips roughed up. And when I finally had everything put back together... Can you wait?! ... No change. I kinda expected that, being a pessimist at heart, but was still disappointed. Hey, at least I lowered the ground resistance to near zero in the system's circuit.
So I kept poking and think I have probably found the real culprit: the Rowland preamp.
I should have tried some of these things first, as they're simpler, but alas, we all learn by experience, yes?
Turns out that when I run my DAC straight into the amps, the hum is barely audible. (It's a Mac server, so I can control the volume through iTunes.) That also seems to eliminate that digital equipment as the cause per se.
But here's the salient clue, something I hadn't tried before: If I disconnect all source cables from the preamp, and then disconnect the preamp from the AC power, leaving the preamp and amp connected ... the hum remains. Yikes.
I opened the preamp and looked at the power board. There is a cap with one leg connected to the ground screw via a PCB trace, but the solder connection is hair-thin. I've contacted Rowland to ask if that trace is supposed to be stronger, which I'm capable of addressing myself. But if that's not it, I'm awaiting their response, which I assume will include sending the preamp to them.
The greatly reduced hum has also allowed me to identify a little RFI in one channel, but I'll take one thing at a time.
If this stimulates any thoughts, I'd be glad to read them. Otherwise, this feels more solid to me and I hope it's the beginning of the solution.
Thanks again, all. |
@edwyun I haven't received a response from Rowland, so that would actually be super-helpful if you'd be willing to check. (I'll holler at them if I don't hear by tomorrow.) The thin trace is on the top side of the power board, in the corner where the ground ring connects to the AC receptacle two inches away. (Since the cover is on the bottom, you can't see the top side without unscrewing the board, but it's super-easy, just four hex bolts.) Here's a photo of the board and the ground I'm wondering about: https://www.dropbox.com/s/xkhm3lnsog45auy/Capri-ground-7D2_4666.jpg?dl=0If you get a chance, let me know if yours looks the same. Thanks a lot! |
