mk60
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Hi all, I have a set of Klipsch La Scala AL5 speakers (nominally rated at 105 dB efficiency, IRL probably lower), and a couple of different Decware triode amp based setups. I feel like I've discovered that Decware's amps might not be a great fit for speakers this efficient, and I wanted to get some feedback on the community from this before I jump to conclusions and totally re-think my setup. Also, if my findings are generally correct, this post could also act as a PSA for people to think hard before chasing Decware amps to pair with very high efficiency speakers.
I'll first say that when I first got my La Scalas which were my dream speaker at the time, I did research and found that many people were saying that it's a no-brainer to pair high-efficiency speakers like this with good low power SET amps -- a perfect match. This is around the time that Decware's wait list really started to blow up (thanks partly to Andrew Robinson, who highly sung the praise of the SE84UFO with his La Scala AL5s). I decided to jump in and see what the fuss was about.
Since then I've been able to get my hands on two different Decware amps to pair with my La Scalas, with limited success.
1) A pair of SE84UFO25s, which I have run in three different configurations: a) just normal stereo from a single amp, b) unbalanced dual mono, and c) fully differential balanced mono (in this case fed balanced signal from a ZTPRE)
2) SEWE300B (just arrived last week!) running in standard stereo operation without any pre-amp.
I'll start by saying that everything that everyone has said about how nice these amps sound is true, they're lovely. But in nearly all cases, I'm getting what I think is an untenably loud 60 Hz hum from my speakers and subs -- this hum is about 46 dB at my listening position, about 10 feet from my speakers. While this isn't noticeable when playing many different genres of music at sufficient SPL, it is ever present in quiet moments, and for example when listening to classical music (either solo piano or larger orchestral works) instruments fade into the 60 Hz hum instead of into silence which I think really hurts the music.
Of course, I've done research on these forums and there are many threads about hum and how to, in some cases, eliminate it. I've also had the pleasure of having a few long phone conversations with Steve about it, what my expectations should be, and how to troubleshoot it.
Often, hum is attributed to ground loops in your signal chain, and many people are able to substantially reduce and solve hum in their setup by figuring out which components are causing the ground loops, using DC blockers, etc etc. Based on my testing, I do not believe that I have any ground loop issues, or at least, by far the main contribution to the hum is not from ground loops. This belief is based on the fact that with any of the three amps (either of the UFO25s or the 300B), if I unplug absolutely everything from all outlets in the room, only plug the amp into an outlet, and then connect a speaker, the hum is there. It is completely unaffected by whether or not any input is connected to the amp, completely unaffected by whether or not I plug other things into other outlets, and is also completely unaffected by the volume knob on the amp -- it hums just as loud at zero gain as it does at full gain.
In my conversations with Steve, I explained my situation, and he explained that there is definitely inherent hum in these amps that is part of the nature of the design. He very carefully voices his amps and has specific design targets in mind when he does so, and although he could completely eliminate the hum, the amp wouldn't sound the way he wants it to if he did so. He said (and I may be misquoting here, sorry if I get this wrong, Steve) that he designs it such that when using ~100dB efficient speakers, whatever inherent hum exists is negligible/unnoticeable at a normal listening position, but detectable if you go right up the driver. Unfortunately, with my La Scalas, that is far from the case. The conclusion that we seemed to get to in our conversations was that the hum I'm experiencing is inescapable if I'm going to pair speakers this efficient with these amps.
This is a bummer. There's so much I like about the sound of my UFO25s and of the SEWE300B, but it honestly makes it hard to listen to certain genres of music (e.g. classical music with high dynamic range) without being bothered, and it also makes it that having the amp on in the background playing music at a social gathering is annoying, because the hum is constant and totally noticeable by everyone in the room.
There is only one situation in which there is no hum: running the pair UFO25s in differential balanced mono. This isn't a full solution, though, as it prevents me from hooking up my REL 212/sx subs using high level connections, which is frustrating (have confirmed this with Steve). But it really gives me a taste for how good these amps can be, and it really motivates me to see if there is any way to enjoy my SEWE300B without the hum ruining it for me.
What I would like to ask is whether anyone else has had any similar experiences, and have figured out a way to fix it? I guess I'm specifically asking people who have paired Decware UFO or 300B amps with La Scalas or similarly efficient speakers without having audible 60 Hz hum at listening position? I'm holding out some sliver of hope that perhaps I misinterpreted or misunderstood aspects of my discussions with Steve when I was troubleshooting, and there is a way forward! And if not, I really would like to have my experience serve as a warning to people who are on the waiting list for one of these amps to pair it with a pair of La Scalas or Klipschorns, because if this is really an unfixable issue, these people might end up disappointed with their purchase.
One thing that gives me hope that there's a way forward here is that Andrew Robinson gushed about the pairing of his La Scalas with his SE84UFO, and I have a really hard time believing that he would have done so if he was getting the same loudness of hum that I am, or at least would have mentioned it as a caveat if he did.
I hope that I've faithfully represented my experience and the content of my discussions with Steve, but am happy to clarify further, or hear clarifications from Steve or anyone else if not! It's always been a delight chatting with Steve about this, and I think he makes great amps, and I hope my post does not come off as an accusation of false advertising in any sense on his part.
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