Disclaimer: I received a free sample from Audinst, and they are also a site sponsor.
I wasn’t aware that Audinst was working on a newer replacement product for the HUD-MX1, but the moment that I received an email from Audinst about the HUD-Mini, I was very excited because I expected to see an upgrade to the HUD-MX1 (which by now have been in the market for two years). The HUD-MX1 gave us an affordable yet solid performing entry level USB DAC, and I had this expectation that the newer and better looking Audinst HUD-Mini was going to top that.
As I received the product in my hand, my impressions were quite positive. The enclosure design has improved over the HUD-MX1, and is also slimmer and smaller compared to the predecessor. Even though the smaller form factor isn’t going to be a big deal once you put it on your work desk (where you’ll be using it with your laptop), it was enough of a design change to make it look like a more modern product. Aside from the lack of the DC power input (which I never use on the MX-1, anyway), the HUD-Mini was mostly the same front and back. Up till that point, I wasn’t even aware of the price that Audinst was going to charge for the Mini. I simply thought that given the better looking, and the sound (which I thought would surpass the MX1), they can charge a higher price and it would still be a good value.
I was so surprised when I started to listen to the HUD-Mini. I didn’t understand the sound that Audinst was trying to create here. It had a good bass, but nothing else. The sense of space was non existant, the midrange very congested, the sound extremely grainy. Immediately I was disappointed. Not only did the Mini fall short of the MX1, but I would even choose the Fiio E10 over this. I tried listening to it for a few days, and still my impressions were the same. There is no way I can recommend something that sounds like this.
I don’t remember what happened next, perhaps I was flipping around the manual and discovered the fact that the op-amp is replaceable, or perhaps I was taking internal shots of it when I discovered a socketed op-amp, but what follows is that I suddenly found myself listening to the HUD-Mini with an OPA2227 and being very pleased with the sound. Gone is that grainy, congested sound, replaced with a much grander sound with a clear and full mids and a very nice soundstage depth. I listened to the Mini with this set-up for a week or more, and I’m still convinced that the Mini is now an entirely different product.
This is the second time that I’ve chosen the OPA2227 over the stock op-amp from the manufacturer. No, I don’t think that the OPA2227 is the perfect answer for everything. It’s just that in this case, that’s the only op-amp I happen to have available. Somehow I have misplaced my box of op-amps with the super-nice 2111KP and other popular options like the OPA627 and AD797, so the only op-amp that I can use is the OPA2227 which I simply pulled from JDSLabs’ CmoyBB. And while the stock LME49860 worked really well with the HUD-MX1, it simply sucks on the HUD-Mini, and don’t ask me why that is. What I’m saying is that the HUD-Mini, currently priced at $129, is quickly becoming my new recommendation for an entry level USB DAC/Amp in this price range, even besting the HUD-MX1 and the Fiio E17, as long as you are using the OPA2227. Another op-amp that I happen to have around is the MUSES 8820 (from the Audinst AMP-HP portable amp), which I believe is a more rare op-amp and perhaps also more expensive than the OPA2227. The MUSES 8820 is a better technical op-amp with a stronger low bass performance, more spacious sound, cleaner and blacker background, and overall more laid back than the OPA2227. I still think that the OPA2227 with the fuller mids down to the midbass is the better all rounder, but if you want to give the MUSES a try, it’s also an upgrade from the stock LME49860.
The bottom line is that you can try rolling other opamps and perhaps you’ll find a better combination. The only thing that you need to know is to get an op-amp that can accomodate a 9V supply voltage. How to find out: Google the op-amp code (i.e OPA627), open the datasheet document which usually comes in a .PDF format. On the specifications page, locate the power-supply voltage range (in the case of the OPA627 it’s a ±4.5V to ±18V, so you’re good.
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