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I think the guy who sold me his sap9 via eBay was someone in this discussion board. Well, generally this is an interesting toy to play with and it’s the cheapest balanced headphone amp you can find (at least it looks like a balanced amp LOL).
Cokeman is right, this amp’s single-ended output is not really powerful but the balanced output has the strength to drive hd6xx/650/600/580. I honestly don’t know whether it’s “true balanced” or not (though SMSL clamis it’s true balanced) but I can tell when using its xlr inputs (if you have a DAC with balanced xlr out) the amp’s balanced output indeed sounds different than the single-ended out. For hd650, sap9’s balanced headphone jack could make the headphones‘ low end sound more “solid” than using the single-ended. And what about a better channel separation that a balanced amp is meant to have? I have to say not so much you can hear.
So what is its overall sound signature? Bright as someone here suggested? Yup, sort of bright. However IMO sap9’s problem is “thin and flat” rather than just “bright“. The thin sound sig actually makes you feel it’s bright.
So is it worth buying? Go for it if you happen to already have a balanced DAC and a pair of hd6xx/650/600 with balanced cable and you don’t want to spend at least $300 to buy a single-ended amp that is capable of powering the infamously hard-to-drive Senn’s 6 series. Sap9 won’t bring you those fancy terms such as “vast soundstage”, “deep bass”, “airy”-you name it; but it can at least give your balanced hd650 an acceptable solid sound that most sub-100 singl-ended amps wouldn’t be able to have. Plus, don’t forget it has a balanced 2.5mm jack for IEMs or some balanced portable headphones from Pioneer.
Ok, so far it sounds like sap9 is kinda not bad but why did I call it “toy” in the beginning? That’s because I am using it for my PC video game system LOL (check out my picture). Sap9 might not be good enough to match the word “audiophile“ but it can truly enhance your experience with the finest video games. A balanced system plus a pair of hifi headphones are better than those blinking 5.1/7.1 gaming headsets, IMHO.

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Yes it’s master feline set. I like the griffin too.
I’m using it right now for my gaming system. It’s a balanced 24/192 DAC with decent sound. It’s not fantastic because it doesn’t have great dynamics and wide soundstage, and imaging is just so so, and there is no DSD support. But it is truly the cheapest balanced DAC you can find ( preowned on eBay for about $100 to $150) and its sound is good enough for hd650. However there are not so many of them coming out for sale so you might have to wait for some time.
I would just like to point out for everyone buying this for the 6XXs that unless you are using balanced the Fulla 2 has more power out of the 1/4in and has a DAC.
does this work well with the AKG K7XX?
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will I need anything other than that?
eps... it seems a nice setup... How can I use a really portable system (like in dorm) without the need of a desktop PC (where I have all my powerful audio setup: Balanced HD650 and Jotunheim)? Is it possible using the lightning port of my iPhone7-8 to this Balanced Amp? no DAC need? obviously not so powerful and complete but useful to a medium-high degree?
Please answer you audiophiles out there.
would this amplifier drive foster t50rp mk3 ? is it a good match ?
This is great a balanced AMP for $85. But if you have the money to afford a fully balanced DAC, you probably have money for a nicer AMP.
Yep. I mean, I guess it's a cheap way to try balanced outputs if you haven't before.
Do these actually exists? I can't find a single review and hardly a mention anywhere, not even on Amazon. Can someone please report on the sound quality? Thanks!
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So a bit more feedback after listening to this all night. This is a bright amp. My LCD-2's have actually been a bit sibilant. I am running the setup off the ifi BL DAC which is fairly neutral in my opinion. The sound stage is great, but I am not sure this amp would be acceptable with anything but a dark headphone. I will continue to update once the amp burns in all the way, but first impressions are a bit bright.

Can you do XLR in to unbalanced out?
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Mine can't either. SAP-8 may have made more sense for me since I bought it for the XLR inputs.
Ok no big problem in my case because i have balanced headphones. Got cables from
How does this SAP 9 compares to the O2?
strange that it says " balanced and unbalanced output ports can’t be used at the same time " but I was able to hear on both headphones when plugged in balanced and unbalanced headphone out at same time...
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If you have only a balanced input (xlr); does the unbalanced out work?
Just tested balanced xlr in to unbalanced out and it did not work. However unbalanced in to balanced out works..