I understand that if you drink enough Mad Dog 20-20 (Ripple) you will not hear any hum. You will of course wake up the next morning with a headache. It's all about trade offs😂.

HK

My speakers are homemade using MarkAudio Alpair 10-P drivers, but I've also tested with Klipsch RP-600Ms too, exact same result. I've tried multiple different rectifiers, power, input, and voltage regulator tubes, nothing has had any effect on the hum. Like I said, it's barely noticeable at the listening position, but it is there in a quiet room. I feel like a plausible explanation here would be that filter capacitors in the power supply vary slightly even within spec, so the ones in my amp don't smooth out the ripple quite as well, but otherwise, I've got nothing. Believe me I've tried it all!

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Was it 120 Hz hum?

I did reduce some 60hz hum by sliding rubber washers underneath the transformer feet, which helped stop them transferring their vibrations to the chassis, that was a relatively simple upgrade/fix! But yeah the 120hz hum is most definitely electronic and not mechanical.

Interesting, thanks for doing that! The plot thickens! I wonder what could be the issue/if there's hope. Like I said, maybe the filter caps on the power supply? Dunno if anyone has any other ideas...

Hi everyone! Sorry for the long delay in updating, I had a few days out camping/hiking that was bookended on either side by intense work situations that I needed to put all of my attention into.

So, since I last posted, I regrettably haven't made much progress in resolving things.

When my landlord heard that I'd had an electrician over, he insisted on bringing his own electrician over just to double check everything for me. Everything checks out, the wiring is actually much more modern than the rest of the house, and the ground is definitely good. I feel pretty satisfied that if there is a problem with something, it is not the wiring in my home. I had a back and forth with Rex, the audiophile oriented electrician someone linked earlier in the thread, and that seemed to be his conclusion as well. I also got my own outlet tester, and no problems detected anywhere.

I did try lifting the ground with a 3->2 prong adapter, it made absolutely no change.

I also tried shorting the two input RCA jacks (something that Rex and people in the Klipsch thread suggested is important to accurately characterize the hum), it made absolutely no change.

Steve asked me to send him a video recording of a decibel meter recording the room with the amp off then on. I obliged, and he replied that he really thinks that there's nothing wrong with the amp, and that this is just the unfortunate consequence of the super high efficiency of my speakers. He also suggested that speaker placement and room acoustics could be contributing to the problem -- but fwiw, the hum is bad anywhere in the room, and not any worse at my listening position. Room is 400 sq ft.

I've gotten confirmation from someone over at the Klipsch forums that they had the SEWE300B and tried pairing it with ~100 dB speakers. He troubleshooted the situation with Steve and it seemed like they came to the same conclusion, and he ended up selling the 300B.

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When I hear something like this, it gives me pause/hope. The hum I get from my pair of UFO25s, although ~3dB less than what I get from the 300B is definitely still unbearable (mid-50 dBs at listening position). But then, James, your speakers are ~94.5 dB, and that is a huge difference. Even so, though, I wouldn't expect "heat death of the universe" silent even at 94.5 dB efficiency, given what I'm experiencing at 105. Indeed my 95 dB Zu DW6s have faint hum at listening position when hooked up to the 300B. But I actually haven't ever tried the DW6s with the UFO25s. I'll try that when I get home on Monday!

Again I really appreciate everyone's suggestions and investment in helping me troubleshoot and understand what's going on. At this point it seems like we're trending towards certain Decware amps (300B, UFO25) not being a correct match for anything around 105 dB efficiency (and anecdotally maybe the 300B isn't a good pairing for even 100 dB?). If we do determine that this is true, this is really good information to be out there for anyone on the waiting list who has been planning on pairing the 300B with La Scalas and Klipschorns (I've spoken to a couple already), and it gives them an opportunity to re-think their plans!

I feel like I've tried all of the troubleshooting suggestions people have put forth so far except for balanced isolation transformer. But I'm still open to trying things and if anyone has any other suggestions I'm happy to hear them

(also, again, for anyone that's still suggesting ground loops, I think I have pretty conclusively ruled that out: the hum is exactly the same even if there is no input to the amp, and the amp is the only thing plugged in to power -- feel free to let me know if this doesn't rule it out!)

Yes, I do still want to take it somewhere that has La Scalas or KHorns set up to try it out and get peace of mind, but that's easier said than done. Unfortunately, I don't have any friends with passive speakers (young people...) and dealers don't usually have LS or KH set up to demo, and would only want to do so if they think they might make a sale.

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My understanding of what Steve has told me is that there is absolutely inherent hum in his amps that is designed to be quiet with less efficient speakers.

Sorry about that mk. It takes a while for me to complete a paragraph, and you had a reply all set.  :D .

I'm in Los Angeles!

Thanks! I'll actually probably have a chance to try the amp on a set of Klipschorn AK6 (exact same drivers and efficiency as my La Scala AL5) next week in another location. Assuming the hum is the same there, I'll feel pretty confident with the conclusion that what I'm experiencing is just the inherent hum of the amp, meaning it's just not a great match for super high efficiency.

I'm still curious if there is anything that can be done (filter cap swaps, etc), since it seems like some amps are dead quiet with high efficiency speakers ... Like, one of 2 things must be true: 1) All the Zen Amps hum but for some reason some people don't hear it, or 2) Some of the Zen Amps hum, and there must be some reason as to why. If it's #2, I'd love to know what the reason is!

Sam, so I think that everything that I've found so far is mostly number 1, but with a little bit of number 2! My understanding comes from my discussions with Steve, my own experiences with several different Zen amps, and discussing with others who have had experiences pairing Zen amps with extremely efficient speakers. But I don't claim to know for sure that everything I'm saying here is true.

I make these statements assuming that there are no power issues or ground loop issues which will also independently cause hum problems

1) All Zen amps do hum, to a certain extent. Different models hum have different levels of hum which are inherent to the design of a Zen amp, and is tuned differently for different models/designs (e.g. in my testing and confirming in discussion with Steve, SEWE300B > SE84UFO25 > SE34I.5), and this hum can not be eliminated. Based on reports/reviews I've heard from a couple of other people, I suspect, but have not confirmed, that the inherent hum level of the SE84UFO2.1 is less than the SE84UFO25.

2) The extent to which you will hear this inherent hum depends entirely on the efficiency of your speakers and how far you're sitting from them. I think that the reason that some people say that they don't get any hum from their Zen amp is that the level of inherent hum of the model that they have, combined with their speaker's efficiency rating (usually mid to high 90s), leads to a hum that isn't loud enough to hear at normal listening position, and can probably only be heard by listening right next to the driver. Or, often in the worst case, a low level of hum is audible at listening position, but not enough to be a problem.

3) My case is the worst possible scenario because of the 105 dB efficiency of my speakers, and it makes the SEWE300B and SE84UFO25 (unless in differential balanced mono) unusable. I will say, though, that the amount of hum that I'm getting through my 95 dB efficient Zu DW6 paired with the SEWE300B is definitely noticeable at listening position, although not nearly as bad as through my La Scalas. Still a surprising amount, though. If Steve's spec is that on a 95 dB speaker I shouldn't be hearing hum at my listening position, then it really does seem like something is wrong here. He doesn't seem to think so, though.

Anyway, Sam, do you think there's info/evidence that contradicts the understanding that I've come up with?

I would also really like to understand what's happening

Yeah, I tend to agree with your assessment, I've got the UFO25 in a small room with relatively sensitive speakers (not 105dB, probably low 90's, so I'd imagine with 105dB ones it would be not great)... the only reason I'm not 100% sure is because we've got eyewitness testimony to them being "heat death of the universe" silent, and they're low wattage amps so I'd assume most people aren't using sensitive speakers, not like, 85dB. Hopefully we'll find out!

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I will say this, if it is 120 Hz ripple from the power supply, I think that would be more or less the same in both channels, so it would cancel out if you were doing balanced differential. I was one of those who claimed that my UFO25s were silent with my 95ish dB speakers. And I believe they were when I first got them, but I stuck my ear against the speaker cone the other day and there was barely audible “noise.” Some of it is tube noise, but there was a little bit of hum as well. It isn’t audible 6 inches from the driver, but it is there. Perhaps it is a function of many more hours on the amp, and/or my current tube set.

Excellent post cmdc. Really has me thinking....which is what caused all of my problems in the first place..  This thread has had me checking for hum many times now on our own setup. We both hear none through the speakers (101db as well). The sub when it is on puts out a very faint hum when your head is right next to the driver. 3 feet away though..quiet. Our son purchased Forte4's a couple years ago. 99 db, no hum either. We both now own recent Zen UFO amps. This is an interesting topic. I cannot stand hearing hum at my listening positions at all~ I have an older analog radio shack db meter and out of curiosity am going to compare the hum from the sub and any from the speakers. Second guessing I guess..

Thanks, cmdc, for taking the time to do that, this seems like an important data point for this conversation!

That you're getting basically no hum from 101 dB speakers on your UFO25 is definitely interesting (and encouraging) to me. Both of my UFO25s hum the same, and loudly, on my 105 dBs, and you can hear that hum anywhere in the room (12x30). But your report is consistent with, for example, Steve Guttenberg really enjoying the UFO25 on his Cornwall IVs (also 101 dB).

Does anyone know the math on SPL as a function of distance and efficiency off the top of their head? For example, I've got my pair of 105 dB speakers set up ~10 feet from my listening position, and I measure, say, a 55 dB hum at listening position (that's about what I get from each of my UFO25s). Leave all of the geometry the same, and replace the 105 speakers with 101 dB speakers -- if everything else is the same, how loud would one expect the hum to be at listening position? I'm too tired to think about it right now, but may figure it out tomorrow. I actually don't think I've ever hooked either of my UFO25s up to my 95 dB DW6s -- I'll do that when I'm back at home next week. I expect no hum at listening position. Otherwise, it really seems like something is up.

Also, I'll emphasize again that unlike the hum that cmdc seems to be describing (seemingly changes with cables, pre-amp, and volume?), mine is dead constant when you switch out cables connect or disconnect a pre-amp, turn gain up/down. Ground lifted or normal. Doesn't matter, hum's the same (only changes with amp, UFO25 vs SEWE300B).

One thing that really has me scratching my head here about the 300B amp is that Steve seems to have confirmed that it's an absolutely wonderful match for his 103 dB headwreckers. With how loud the hum I'm getting on my La Scalas is, I would imagine it would have to be pretty similar to what you would hear out of the headwreckers, and yet that seems not to be the case? This points me back to there being an issue elsewhere external to my amp. But then Steve has told me explicitly that the hum I'm hearing is purely a result of my speaker efficiency (and possibly speaker placement and room). So at this point, I really have no idea. But I continue to endeavor to figure it out by getting more data!

What, wait....the "Sound Inverse Square Law?" This explanation may be precisely what MK60 needs, but I'm going to need another cup of coffee this early Sunday AM before going any further with this one

Good luck pursuing an answer, MK60. Your patience and ability to stay focused and optimistic are admirable and instructive.

new to this forum and thread. hum is super frustrating, i feel your pain. i didnt see that you ever tried an isolation step down transformer. get a 1000w 120-120 isolation step down transformer. if the hum is coming from house/wiring it will fix it. ive battled a couple of recalcitrant hums over the years and this fixed them.