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Firstly, that is great news that you fixed the hum issue. Hum is a trigger for me, so I totally understand the celebration.

Now, to off grid power sources. My experience is mostly using uninterruptable power supplies (UPS) i.e. battery backups for computers and networking. And I know the power supplied by them is extremely dirty. The issue is the inverter (the gizmo that changes DC battery power to AC, the inverse of a rectifier) is essentially a switch that produces an on/off square wave rather than a smooth sine wave. The output can be smoothed to be more sine-like using capacitors but that has other undesirable side effects. So my takeaway has always been: avoid inverted battery power for my stereo.

I also live in an area where wildfires can cause (extended) power outages, and have been considering some kind of solar/battery system for a while, mostly to keep the fridge running. But I'm always looking for an upgrade to my system and power is an obvious place to look. I've been looking for an explanation of how a "pure sine wave" inverter is different from a regular one, and pretty much the only thing I can find is "pure sine wave" is just a better filter on the inverter. Which doesn't seem that great, but your story is intriguing. I'm curious if anyone else has a story?

I lived off grid for ±28 years in the NC mountains. After no electricity for several years, we made a little hydro system with a large battery bank and inverter, that system slowly shifting as tech and climate changes evolved, both changing notably over that time. The annual rainfall remained about the same, ±60 inches a year, but as things changed, it became less and less regular. For years, in the hotter times of summer, about once a week it would rain, seemingly in part from evaporative localized cloud development. But gradually, weather patterns shifted, and there were longer and longer dry spells between heavier downpours. The ground dryer, and rains bigger, unable to take it in, less and less was retained, and more and more ran off down stream. Though still 60 inches of rain per year, my lowest gallon/minute average in high summer went from 90 gpm in ’83, to about 20 gpm over the about 24 years we used that system.

Luckily tech changed also, though in this case for the better. Relative to inverters, I went from a pretty good (for the time) “modified sine wave” that mimicked a sine wave by overlaying a lot of squares to look sort of like a sine wave, but still with a lot of noisy corners on those square’s edges. I used an isolation transformer with it for the stereo, and this helped, but the inverter, in a small building well away from the house, buzzed a lot, and the iso transformer buzzed a lot too, presumably from the noisy power it received, so I had to make a little house for it outside also. Not surprisingly, my then NAD amp transformers buzzed notably too, and you could hear the buzz without music from the ADS L1090, 90 db speakers. Still, considering this was the best I could do, I got used to it, loving the music while watching for better tech.

Next was a Trace modified sine wave inverter that was supposed to be much closer to true sine, and it was notably less noisy than the earlier behemoth. But still buzzing transformers, in the inverter, iso transformer, and the amp.

Getting closer, and over noise, I found an Exceltech (sp) “true sine wave” inverter, designed for sensitive equipment, especially medical, and supposedly steady and quiet. And though getting this close to a true sine was really expensive then, they made smaller units, and I got one just for the audio circuit. The best yet by far, no more Iso Transformer, but still noisy transformers in particular.

In the later 90s, after a lot of back and neck damage from being rear-ended by a tractor trailer at high speed, and us nearly stopped, I needed a pugmill to wedge clay for me in our pottery, and an electric wheel I could stand up at. The pugmill needed a lot of power (for a small off-grid system anyway). So I got a “close to” state of the art, larger Trace “pure sine wave” inverter. Designed to be tied to the grid, its power was said to be as, or more, reliable and good quality than the grid, making interchangeability possible. The relatively low measuring noise was acceptable by the grid standards, but I don’t think the noise nice audio can pick up and convey was the criteria. It was less noisy than the previous setups, but I guessed part of that was that the whole system was making less noise, including reduced, but not gone and EMF and RFI from the Inverter. I still had amp transformer hum and minor noise from the speakers… more than I have now, but finally getting pretty good (though I bet it would drive me nuts with my 97-98 db speakers now).

With MMs experience, it looks like this tech has progressively continued to improve. But I also know there are a lot of inverters and small backup systems out there, and there will be those that are less noisy than others, so research makes sense to me. And as I pointed to, seems to me it is not necessarily just the inverter in a lot of cases, but how it, and the battery are fed. Also, from researching and seriously upgrading my RV solar system recently, I gather it is still true that “true” or “pure” sine wave inverters are “flexible” relative to noise… So though I don’t have good answers, I feel confident that for very low noise audio, checking pretty carefully into various inverter based backup setups is a good idea. Aside from audio folks that maybe MM can point us to??? off grid Hamm radio operators seem to be pretty good “noise sniffers.”

Yours is an exciting story for me MM! Glad you broke through!

Maybe everyone is looking at the AC noise problem incorrectly.

Perhaps taking DC from a battery and then converting it to AC to then send it to the amplifier to be converted back to DC is adding way too many steps to the process?

My feeble knowledge of electronics will probably be displayed here, but why couldn't a amplifier be designed to take and use the DC power directly from a battery?
Something like a Tesla Powerwall could be stepped down to the correct rail voltages and ta-da you should have a silent power source.

Am I wrong in my understanding of such things? It sure wouldn't be the first time I was wrong about things I didn't understand.

"Any technology that I don't understand must be magic"!

One of the IanCanada DAC kits have been on my short list for DIY projects for some time. They do just that, Donnie- run on DC cells to skirt the power supply AC to DC conversion.

Tube heaters are no problem if they are dc heated at ~6v but getting 300-400v for plates at the correct mah would be above my computing ability. Not to mention, I’m trying to get less projects and less stuff. I sure would like to hear the end result though.  [smiley=peanuts21.gif]

Good points Michael.

I may be mistaken but there was a series of posts, not on this thread but earlier posts, where the hum in the SEWE300B seemed to be causing angry frustration and was deemed unavoidable after all kinds of attempts to eradicate it. . . and for those of us who have experienced minimal hum that has been able to be reduced this seemed a false representation of the SEWE300B, and might scare off potential interest.

I'm not sure it was your posts in another thread or someone else's. . . and the search function is not helping me find it. But it did seem an unfair presentation of the amplifier to me. (I know that The Other Lon has expressed similar frustrations with the hum). I thought Michael was making a good point or two along these lines.

I also don't think it's unfair to discuss hum. But the discussion I remember was really damning of the amp for hum, and dismissive of owning one. . . hum I've never experienced in any intrusive way except when my power regeneration was not working properly, or when I was using a particular tube that had more than a year on it. . . I retired that tube pair and then went back to it weeks later. . . and the hum was gone.

So . . . the 300B tube itself is going to be a noisier tube than most, but some are better in this regard than others, feeding it clean power and it does not have to be a problem (my experience tells me so). And tastes may differ, but for some like me this is the best amp I've ever heard. PERIOD. In my 25 plus years of Decware experience there are not better sounding Decware amps.

Anyway, I'll bow out of the discussion as if hum were to be an issue in my system it is mitigated to the point that I don't think of it at all, and I have never been happier with the sound of an amp. And it has just the right amount of power for me when operating in about the medium point of its power potential.

You are absolutely right about there being many factors for hum. I live in the most quiet neighborhood i ever have with few neighbors, pretty clean power untreated, and my system has a low noise floor. If the amp had a lot of hum I should hear it, even with HR-1s. But I don't. I do hear significant noise with some tubes, more than others for sure, but still hum is not audible at the listening seat. I just don't think the amps are big hummers, and I hate that there's a reputation that is building along those lines. But what is is what is. Have a great holiday and so glad you have the hum handled, and thanks for mentioning the battery unit.

I've heard nothing but great reviews about AGY's power filters.
https://www.angela-gilbert.com/ac-power-line-filters

I just know that their solid state amps are silent.