[grainjar]

From reading around, the SMSL SU-9 Pro seems to have my preferred neutral sound signature with airy soundstage, whereas the Ultra model has a warm sound signature with a limited soundstage.

However, there's one review of the Ultra model that references its uniquely black background, which I'd love to try.

The spacing between instruments and vocals is not just spacious; it’s a void painted in obsidian, offering a blackness that lets each note emerge with crystalline precision. This DAC is the maestro of silence, where the absence of sound becomes as defining as the notes themselves.

source: https://primeaudio.org/smsl-su-9-ultra-review/

And so I was wondering if the SU-9 Pro model also shares this same black background, or if it's unique to the SU-9 Ultra. The Pro model is advertised as featuring the ES9039MPRO dac chip with 11 OPA-1612A op-amps, whereas the Ultra model has the AK4191 + AK4499EX combo.

I'm trying to get a desktop DAC with no audible noise floor for sensitive iems. I plan to pair it with the Topping L70.

 

[dunring]

For a DAC it's the connection that determines noise floor, like if you have noisy USB ports. I always go on Audisciencereview to choose from a DAC with no jitter penalty for optical connections. The other for amplifiers is check the 50mv test which determines noise floor. The most silent noise floor I've ever (not) heard is on the Topping E50 on optical feeding a Topping L30 II and with 10ohm IEMs it just magical. Never heard a noise floor so black that every whisper jumps out. The other standout is the Topping A70Pro and D70 Octo sound which is the best stack I've heard or ever will.
The L70 scores 93 on the 50mv test, so you'll have a terrific time with IEMs with it. If your using USB then a phone app to scan for EMI on your USB ports will tell you which has the least interference by waving it in front of them. It uses the magnetometer in your phone to detect it. The most quiet noise floor you can get is with Corning optical USB cables. Archimago did a big article and measurements how they affect noise floor. A 5 volt DAC like the SMSL DL200 or I use a D-6s will help also, my favorite is the 5.2 volt SMSL DO300EX which I would put into a blind test with any high end DAC regardless of price. The thing is amazing.

 

[grainjar]

For a DAC it's the connection that determines noise floor, like if you have noisy USB ports. I always go on Audisciencereview to choose from a DAC with no jitter penalty for optical connections. The other for amplifiers is check the 50mv test which determines noise floor. The most silent noise floor I've ever (not) heard is on the Topping E50 on optical feeding a Topping L30 II and with 10ohm IEMs it just magical. Never heard a noise floor so black that every whisper jumps out. The other standout is the Topping A70Pro and D70 Octo sound which is the best stack I've heard or ever will.
The L70 scores 93 on the 50mv test, so you'll have a terrific time with IEMs with it. If your using USB then a phone app to scan for EMI on your USB ports will tell you which has the least interference by waving it in front of them. It uses the magnetometer in your phone to detect it. The most quiet noise floor you can get is with Corning optical USB cables. Archimago did a big article and measurements how they affect noise floor. A 5 volt DAC like the SMSL DL200 or I use a D-6s will help also, my favorite is the 5.2 volt SMSL DO300EX which I would put into a blind test with any high end DAC regardless of price. The thing is amazing.

Ah, thanks for sharing. Do you use the A70 Pro for iems? It's very powerful, and so I remember watching a review that cautioned against it. I also read from a user review that the gain level is too high for sensitive iems.

Note that there's no very low gain mode of 0 dB let alone negative values, so the A70 Pro is not ideal for very sensitive, low impedance headphones like IEMs.

https://www.head-fi.org/showcase/topping-a70-pro.26956/reviews

By "optical," do you mean the port used to connect to televisions? I just use the standard USB port to connect it to my phone. I'm very basic, and so I just listen to music.

Also, can you elaborate on your recommendation for "5 volt" DACs? Is there a particular correlation between 5 volt DACs and low noise floor? In terms of tech specs, I haven't been paying attention to the voltage of DACs.