Post by CyberGene on May 8, 2017 14:55:16 GMT
I have received my standalone amp and have been using it for more than a week now. So, here's a followup as I promised. Here's a description of the amplifier itself. It's a custom built solid state amplifier with discrete JFET transistors. It also has a built-in USB DAC (AK4490). The DAC part is galvanically isolated from the USB part. The DAC part and the amplifier part are powered through a toroidal transformer. There's a lot more details but anyway, what's important is the guy who builds and sells them is very respected engineer who has built a lot of them to audiophiles, the build quality is stunning.
So, I used my HD-650-s and compared the built-in headphone output of my 12" Retina MacBook 2015 model to both the Apogee Groove USB DAC/amp and the standalone custom built amp. I did a lot of comparisons and was ready to declare there's no difference at all to my ears. But then I played the Pink Floyd's "The Dark Side of the Moon (2011 Remastered Version)", specifically the first track "Speak To Me", which begins with a heart beat. In this specific sound it seems the bass is ever so slightly weak and not that detailed/clear on the MacBook's output compared to the two DAC/amp solutions. With that in mind, I started listening specifically to the bass in other recordings. I could discover similar differences in other bass-heavy tracks. However I would bre really hard-presses to tell the difference. It is there of course, but is barely audible. Furthermore, I think I can't hear any difference between the Apogee Groove and the standalone amp. We've discussed above the constant current drive, and it seems this might be overstated since on some other websites (Inner Fidelity and Ken Rockwell) they've done measurements and couldn't conclusively confirm it is a pure constant current drive amp, and rather a mix between a constant voltage and constant current. But in any case, it's hard for me to hear any difference between the Apogee Groove and the standalone solution. If there' some clever made setting where I can switch between both in an instant, then this might be another story but since I need to move the plug from one amp to the other and then switch the output in the computer, I seem to lose my audio memory
I will keep the standalone amp because I like the way it looks and it makes me feel comfortable since it has its own high quality toroid transformer and all the other stuff, but apparently this is more of an auto-suggestion rather than any objective feeling
In any case I really can't find anything wrong with it. Which is mainly due to HD-650 that sound terrific even from the MacBook's output 
Oh, and just for the fun of it, I am gonna build my first simple DIY project - Pete Millett's NuHybrid amp with a futuristic DHT triode tube made by Korg (http://www.pmillett.com/nuhybrid.html) This tube is made by Korg for use in their guitar effects and the measurements show it has some typical tube type of THD which is why I chose it I already have a very high quality, linear, crystal clear sounding amp, so for my first DIY I took the other path - that of the intentionally introduced distortions At least it's very simple and is relatively cheap.
So, I used my HD-650-s and compared the built-in headphone output of my 12" Retina MacBook 2015 model to both the Apogee Groove USB DAC/amp and the standalone custom built amp. I did a lot of comparisons and was ready to declare there's no difference at all to my ears. But then I played the Pink Floyd's "The Dark Side of the Moon (2011 Remastered Version)", specifically the first track "Speak To Me", which begins with a heart beat. In this specific sound it seems the bass is ever so slightly weak and not that detailed/clear on the MacBook's output compared to the two DAC/amp solutions. With that in mind, I started listening specifically to the bass in other recordings. I could discover similar differences in other bass-heavy tracks. However I would bre really hard-presses to tell the difference. It is there of course, but is barely audible. Furthermore, I think I can't hear any difference between the Apogee Groove and the standalone amp. We've discussed above the constant current drive, and it seems this might be overstated since on some other websites (Inner Fidelity and Ken Rockwell) they've done measurements and couldn't conclusively confirm it is a pure constant current drive amp, and rather a mix between a constant voltage and constant current. But in any case, it's hard for me to hear any difference between the Apogee Groove and the standalone solution. If there' some clever made setting where I can switch between both in an instant, then this might be another story but since I need to move the plug from one amp to the other and then switch the output in the computer, I seem to lose my audio memory
I will keep the standalone amp because I like the way it looks and it makes me feel comfortable since it has its own high quality toroid transformer and all the other stuff, but apparently this is more of an auto-suggestion rather than any objective feeling
In any case I really can't find anything wrong with it. Which is mainly due to HD-650 that sound terrific even from the MacBook's output 
Oh, and just for the fun of it, I am gonna build my first simple DIY project - Pete Millett's NuHybrid amp with a futuristic DHT triode tube made by Korg (http://www.pmillett.com/nuhybrid.html)
This tube is made by Korg for use in their guitar effects and the measurements show it has some typical tube type of THD which is why I chose it I already have a very high quality, linear, crystal clear sounding amp, so for my first DIY I took the other path - that of the intentionally introduced distortions At least it's very simple and is relatively cheap.