Disclosure: Received Gremlin from APOS for a loaner tour.
My chain is spotify playing from my PC to a Gustard U12 then a BiFrost 2/64 connected to the Gremlin via its balanced input.
Starting with the "core" set of ray tubes, this amp has plenty of punch and power. It has a lovely musical tubey sound. It's not terribly detailed but the sound signature is full and warm. Sound has a bit of a congested nature and instrument separation is a bit tough as everything sounds too full and hard to pick apart the details. The sound signature itself though is right up my alley. It is wonderfully warm with an emphasis on the mids and mid bass.
Changing over to the "select" ray tubes and the detail really jumps. It's very significant. The amp is still warm but it loses the "fullness" it had and instead you get a lot more detail and instrument separation is clear. I much prefer this sound profile. The bass detail increases which makes it sound more punchy. Of course, the detail extends across the mids and treble as well. Vocals clear up and the treble sounds less grainy. The price also jumps considerably.
Connectivity wise, the limitation for only balanced inputs is a bit rough I think for the budget market. I think the majority of budget DACs with this small form factor will likely have RCA outs. It makes it a bit difficult to pair. I like the balanced outs though, I think getting a balanced cable is a much easier ask.
For $120, the gremlin feels unbeatable. I can't think of anything else at this price point which is as enjoyable. Jumping up to $300 though and I still think it's quite a great value. I did compare this amp to my DIY project ember from garage1217. At the time I build that amp, the price was comparable as I recall. I feel like they really are at the same level but the project ember gives you selectable impedances, more tube compatibility, and a large power range. This shows for harder to drive headphones like the Sierra. Nowadays, the ember (even DIY) is $20 more without the tube. I think they both make a case for themselves. The gremlin and ember both sound amazing and I really couldn't pick one over the other. They actually sound very similar to me. The ember just ends up costing more with more features. If you don't need those features, then the gremlin is the better pick. I recommend the gremlin in both forms. I think the $120 version is a budget king, while the $300 version with the upgraded tubes would be my preference but the tradeoff for detail is a significant jump in price.
