rg,
First let me say that I've owned and used a Soundtech mixer, and was very happy with it - I simply outgrew its capacity. Over here, they're a bit expensive (shipping across the pond), but probably worth it for those who need reliability on the road.
Based on that (admittedly sole) experience, I'd have to say that you probably won't go wrong with that EQ rig. First, note that the spec says ">" - that means "greater than", which translates to "at least as much as, and sometimes more than". 10K is a bit low, 4K is definitely low, but as the symbol denotes, that's a worse-case scenario.
Now, I think ash alluded to this facet awhile back, I'll refresh everyone's memory here and now.
It is a truism in Electronics that you get the maximum
power transfer when the impedance is matched on both sides, output and input. But note that
power is comprised of voltage and amperage. In the grand scheme of things, we've batted around the edges of this in several other threads lately, most notably the "Mystery Ribbon Pickup" topic started by ash. But it's only been stated once, in my memory on this board, that there are two corollaries - The maximum transfer of voltage occurs at an impedance mismatch of low into high, and the maximum transfer of current occurs at an impedance mismatch of high into low.
Now, let me take that last one further, and do it now, before anyone goes out and blows up some expensive equipment. Power is defined as volts times amps, right? But if the maximum
power transfer occurs when the impedance is matched on both sides, and if our amplifier's Power Stage (the four EL34's or the four 6L6's) is amplifying current (which it is), then how come we don't just set the output impedance high, and feed that into our low impedance speakers? Good question.
There are several factors limiting this, so I'll just hit one or two highlights. First, tubes have output transformers. Some characteristics of these things are: they're heavy; they're expensive to build; and no matter what you design for, they're a big pile of compromises. Designing a transformer to deliver a given amount of power (volts times amps) at some impedance value is easy. The hard part is to use the right materials such that they don't burn up when things get hot; they don't cause eddy currents that will come out as unwanted distortion products; and most of all, so that they don't over-stress those also-expensive output tubes. IOW, there's a world of things to consider when designing these things, they're not just a pile of iron and copper thrown together by a couple of science-fair school kids.
Solid state amps, the matters get even worse. Output transistors are finicky, period. Load them down too much, and things get hot, real fast. In fact, way too fast to have a fuse blow and protect them. In a flash, it's all over but the crying. So, since they're designed to amplify current anyways, they're also designed to deliver that current (and voltage, can't forget that), into an impedance that's commonly found on most speaker boxes.
I know that I've over-simplified all the foregoing, and I didn't do that with the intent of treating anyone as if they couldn't "get it" - I did it because going much deeper will start to invoke some math, and some serious background in EE fundamentals. IOW, how much time you got there, bunky?
OK, back to the topic more close to hand..... low level signals.
On this end of the signal chain, we aren't so concerned with treating power with respect in order to avoid expensive damage. Yes we're careful, but if we "blow it", we don't blow the wallet too badly. More likely, we'll just hammer our sound into a high state of Major Ugly, which of course can be fixed.
So, again (so you don't have to scroll back up all the way), you get the best voltage transfer when you have a low output impedance and a high input impedance. Whyzzat?
It's mainly due to the fact that as a load sees an incoming signal, it tries to reciprocate by inducing a voltage of its own, and sending that back to the source. IOW, it tries to match and balance whatever it sees coming in. It wants to make everything sit at equilibrium. Obviously, if that were allowed to happen, then no work would ever get done! So this "resonance", if you will, is a reflecting back to the source.
But recall the definition of impedance - it implies AC or frequency, does it not? And the moment you speak those syllables, you have variable response, as in the resonance is not constant. At this point, I
think it's obvious that you've just created a non-linear signal path - some portions of the signal will be stronger than others. What to do, what to do.
Well, what about making it so all the frequencies are treated with similar disrespect? That could be done by making sure that everything is so far out of resonance that the load's reflections back to the source would be fairly constant, or much closer to linear.... couldn't it? Why, yes indeedy, that would solve the problem just fine. How do we do that, you ask? Ahh, but I'm sure that you've already sussed that one out..... you simply unbalance the impedance equation, by a lot. Like an order of magnitude (x10), if you can help it. More's just as good, or perhaps a bit better, but there is a "law of diminishing returns" at play here. After about a multiplier of 10, the effort to ensure that it's much higher doesn't get you any better results..... you might as well leave it at that, and you'll be OK.
Of course, these are theoretical numbers I'm throwing around here. In practice, you might encounter a factor of up to x100, just because Source A was intended to be used with Load A, and you've gone and hooked it up to Load B, which was much higher to begin with. No worries, it'll still work just dandy. I'll leave it up to the reader to reason out why that is, but as usual, I'm here to answer questions on that point, if need be.
Going the other way, where the ratio drops below 1:10..... that starts to get dicey. If you must, you can go to 1:5, or even lower, but at that point, you will likely (not guaranteed, but the chances are high) encounter distortion. The signal is meeting little resistance, and the load is attempting to balance what it sees coming in, thus it's reflecting more of its own self-generated signal back to the source, attempting to reach equilibrium. Bad ju-ju.
So let's get back to the question, after all that mind-numbing crap. First, I've said that Soundtech's spec sheet is giving you the worst-case numbers - I'll hazard a guess that the true numbers are probably significantly higher, just knowing Soundtech's reputation for being conservative. That being so, based both on my personal opinions and on anecdotal reviews all over the web, I'd have to say that it'll work with your gear, and the chances of needing a buffer of some sort are low. Not zero, but certainly low. Remember, this isn't home-owner or car-owner hi-fi gear, this is working-stiff pro musician equipment. They know what we need, and why we need it, and they didn't just jump into the business last week - they've been around longer than me!
Good luck on that bid!!
HTH
sumgai
p.s. As usual, my meds kicked in when I was intending to drop a short note, then go outside and work. Instead, I've now got a 7,500 charachter treatise, and for what? I've just reinvented the wheel, something I don't ordinarily do. Gotta have a chat with the doctors about that.....
For a much expanded explanation on all the above, try the Wikipedia article:
en.wikipedia.org/wiki/Impedance_matching
> Guitar > Boss GT-G > Harmonic Converger > EQ > Amp Return
The other thing is, it's only 16 inches wide, and has no rack-mounting ears. You'll need to fabricate something to cure that situation. But if it's in a plastic case, and it weighs this much, you may be better off with a shelf (pull-out drawer) instead.
I'm open to having yes another device
