my budget is 100$
gonna pair this with my campfire audio cascade .
what that really important to me is it will be very small ,i dont want my pocket to be full with audio stuff this is wierd and uncomfortable
I’d up the budget a tad to $169 and get the Lotoo Paw S1 or maybe a Dragonfly?
I personally don’t like the feel of anything that attaches with a cord to my source if It’s going in my pocket. I always feel like I’m going to wear out the USB jack on my phone or DAP. Maybe that’s not a valid concern, but it’s what I think about. If I were commuting or listening on the go a lot I think I would pick up something like the BTR5 so there is no need for a wire between my audio source and the amp. Then when I got to my location I would plug it into my phone or laptop wired and use it that way.
That being said, I don’t have experience with the BTR5. I have owned the Dragonfly Red and I currently own the iFi Hip Dac. Both are solid devices and I chose the Hip Dac in the end because of synergy with my specific headphones. Plus XBass on the Hip Dac is one of my guilty pleasures, but from what I’ve heard about the Cascade I don’t think you would need any help in the low end department. 
Edit: If your budget absolutely has to be $100 I would probably be looking at the Shanling UP4. Similar functionality to the BTR5 and I haven’t heard really any complaints about it. Also it has a volume knob instead of buttons if that matters to you. (It should, knobs are great.)
Just looked up the Lotoo Paw and holy moly that thing is small!
I have experience with EarMen and I like their performance. I think somebody over at Head-Fi had the Sparrow (200 bucks) and it was better than both iFi, Fiio, and even the Dragonfly.
Eagle is the cheaper option, instead of the flagship ES2981Pro chip, it uses the ES2981. You will notice that it looks like a USB stick, but you also have a female USB to USB C adapter, this makes it possible to hook it up to your phone.
They are European made, but I think Eagle is the one that may be using some Chinese parts. Both Eagle and Sparrow are CNC-machined from a solid block of aluminum. They use tempered glass on the front and back - and they are tiny. I found the dimensions on the site: 55 mm x 22 mm x 8 mm / 2.16” x 0.86 ”x 0.31”
Sparrow is 10mm shorter in length (45 mm)
Here is a gif of how the Sparrow is made… don’t know if I am allowed to share this, but here ya go:
this is exactly the reason why i am after dac/amp , the bass is way softer and there is no punch to it without one .