I just got an H300 and a chance to compare it to one of the A30Pro's I've been using the last few weeks. The sound reminded me right away of the Sabaj A20H which is 1/3rd the price, has digital volume control for perfect channel matching, and doesn't run as warm. The design is sturdy and vented on the side, it's warm but no more so than the A30Pro. I've had a Gustard X26 Pro which runs hot, these aren't even close to that.
The H300 sounds fine, if you have an A30Pro I wouldn't suggest switching though. The volume wheel on this was scratchy/grindy after 3 oclock and felt like it got stuck towards the end. Will be sending this model back, but at least I could do a comparison to the A30Pro while having them both. The switches are fine except the gain switch. I learned right away to turn the volume wheel down before snicking the gain switch, because it's ridiculously easy to overshoot into high gain when aiming for medium. I was able to measure channel balance and it never deviated more than .2db and most times it was .1db or even. I use a 3.5mm male to male cable into the line in on the sound card, and on digital amplifiers both channels are a perfect match through the range, so I think it's fairly accurate. Every model is different, but it's within factory spec.
It's a simple design, transparent like most amplifiers out there today, and I'm sure if it gets measured it'll do well. This doesn't have venting on top, so if you have a cat, at least you'll never have to wonder where they're sleeping ever again. The volume wheel is small but not as annoying as I thought it would be (despite this one is defective like several of the Schiit Magni's I've had over the years with the scratchy/grinding problem).
If you get one, I'd order some thick round rubber feet on Aliexpress or Amazon to give it some airflow underneath. These are the ones I use. Just little speaker feet, but small enough to fit under an amplifier too. They come with 3M sticky pads to attach them.
Comparison:
Sabaj A20h has digital volume, 1/3 the price, almost exact same sound, less power (but still enough for the He6se with a 5 volt DAC). They're becoming hard to find, and the connectors on the back are annoying, also the XLR on the back are upside down, so you need a 3ft cable to twist enough usually.
The A30Pro is pretty evenly matched for power, better controls, and much better volume wheel. The vents are a dust magnet for pets. Also it has the same power on all headphone jacks, the H300 has different gains on SE and balanced. In low gain it's amazing with sensitive IEMs (95 on the 50mv test, completely silent noise floor).
The H300 gain switch is a recipe for disaster if you have easily blow-uppable headphones like the DT900/700 Pro X and use the switch often. Both the A30Pro and this will raise a 10x12 room temperature by 1 degree F if you leave them on all the time. Both surface temperatures measure with a laser thermometer too close to call on the hotspots.
Personally, I would save money and get the Sabaj A20H since they sound identical and perfect channel matching. The A30Pro is a sure thing as long as you don't have dust issues.
The best headphone amplifier stacks I've heard are my current SMSL SP400/M400 and also the Topping A70Pro/D70Pro Octo I just put together this month. I'd either scale back to the A20H or save up for the SP400 or A70Pro and sit either on the SMSL DL200 which is my permanent DAC, since it's big enough to sit almost any amplifier on. The H300 is a good amplifier in a crowded field, there's just no standout feature that makes it a must buy. It looks really nice on the SMSL DL200, but at this price so does a used Topping A90. Even the Topping L70 would be a great choice at the right price in comparison.
For myself, I've got a Topping A70Pro coming next week for $362 during the Aliexpress sale running through March 27th. It's going to be my permanent amplifier at that price with the DL200 under it.
In case you miss it or need to save up, the next ones are:
June 12th Summer Sale
Brand Shopping Week (August 18-21)
Then Singles day November 11
Black Friday Nov 20th
Those are the really big discount sales each year, the others are pretty minor for discounts compared to those.
The H300 is a nice amplifier, but you won't hear anything you likely haven't heard before. The headroom is great if you actually need it, but the thermals might be an issue for some unless you love all day warm coffee without having to go heat it up... I also have the Topping A50 III / D50 III stacking coming next week, will write up impressions when I get them to compare value for money and if the built in parametric EQ the DAC has works well.
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