Does a preamp impact sound quality?

[duffer5]

I welcome your input on why the improvement???

So I have been on the fence, do I or don't I get an external preamp. Well, I remembered that my Class A Oppo HA-1 headphone amp / preamplifier had a high quality preamp built in and decided to use my ACTIVE speakers via that HA-1. Well lo and behold when I set the Gustard R26 dac (bypassing it's built-in preamp) to fixed volume output and controlled the volume via the HA-1 (which has an analog control knob) with connected active speakers via xlr my sound jumped a level in the best way possible. I have attached a description of the HA-1 circuitry and the preamp specifications.

I welcome your input on why the improvement??? Kinda dumbfounded once again. How can this be and thank you in advance for educating a newbie.

Hifi Rose 150b streamer feeding Gustard U18 DDC via USB, Gustard U18 Feeding the Gustard R26 DAC via i2s, R26 feeding the Oppo HA-1 Class A discrete headphone amp / preamplifier via xlr analog in, HA-1 feeding Active speakers via XLR out.

 

[AnalogSteph]

I welcome your input on why the improvement???

It could be either of two things:
1. Without precise level matching and direct A/B switching, your comparison is anything but reliable. You may be fooling yourself.
2. The DAC may be operating in a more suitable level range now. Using digital attenuation on an R2R DAC arguably is not the smartest thing ever. I am a bit concerned about the IMD vs. level data:

That's not great, even by the standards of R2R DACs. Here's the A26 (AK4191 + AK4499EX based) for comparison:

This is basically noise-limited below -25 dBFS, while that is still not the case at -50 dBFS for the R26.

I would leave the setup as it is now, even if it is rather overcomplicated. (I presume you are using XLR cabling throughout?)

Should you ever tire of the excessive amount of boxes, you could still ditch the whole lot for a Topping DX7Pro+ or something.

 

[duffer5]

@AnalogSteph, thank you very much for the detailed reply. Extremely helpful and you are correct, XLR throughout. I suspect you are spot on with "The DAC may be operating in a more suitable level range now," as it is set to "fixed," so zero digital attenuation. And thank you for the suggestion of the DX7PRO+, also helpful.