Looking at these and similar units and their modest SNR specs (85 dB below 1.5 V is a whopping 84 µV of output noise after all), I would guess the answer is vacuum tubes + b0rked gain staging in this preamp. Nothing unusual in hybrid gear. Oh yeah, and the line stage has a massive 28 dB of gain, too, which would explain the very high noise if all of that goes after the volume pot.
This preamp basically needs a power amp with an input level control. (Typical tube power amps did, as do several solid-state ones.) Alternatively, make use of the headphone amp instead, which exhibits a significant 10 dB less noise, not to mention far lower distortion. Or both of these options at the same time, actually, which should enable entirely noise-free (yet still plenty loud when needed) listening.
The headphone output should also do a nice job driving the usual not-too-sensitive hi-fi cans - HD600, DT880, K701 and the like. Actually, you can probably fry an HE-6 or a K240M with this guy (10 W / 30 ohms!), or most anything else with a reputation for being notoriously hard to get going.
But as a regular preamp - FAIL.
Wrong forum section, btw - Analog Line Level would've been the correct one.
This preamp basically needs a power amp with an input level control. (Typical tube power amps did, as do several solid-state ones.) Alternatively, make use of the headphone amp instead, which exhibits a significant 10 dB less noise, not to mention far lower distortion. Or both of these options at the same time, actually, which should enable entirely noise-free (yet still plenty loud when needed) listening.
The headphone output should also do a nice job driving the usual not-too-sensitive hi-fi cans - HD600, DT880, K701 and the like. Actually, you can probably fry an HE-6 or a K240M with this guy (10 W / 30 ohms!), or most anything else with a reputation for being notoriously hard to get going.
But as a regular preamp - FAIL.
Wrong forum section, btw - Analog Line Level would've been the correct one.
Check the tubes...
This thread is well past it's "sell by" date, but for posterity's sake I would like to point out the following:
1. The hissing noise is not endemic to the design. At least not in the one I own. Check the tubes. If the preamp is noisy, try new tubes. It's only a pair of 6922s, so this would be my first step. AI recommends 6H23s. Keep in mind that the design keeps the heaters on all the time.
2. While this line stage does have 28 db of gain, the L-1 also has left and right volume controls that allow you to reduce the output to reasonable levels and use a wider range of the main volume control.
3. The SS headphone amp is quite powerful and I'm sure it measures well, but I'm not sure that I would prefer to listen to it over my speakers.
This thread is well past it's "sell by" date, but for posterity's sake I would like to point out the following:
1. The hissing noise is not endemic to the design. At least not in the one I own. Check the tubes. If the preamp is noisy, try new tubes. It's only a pair of 6922s, so this would be my first step. AI recommends 6H23s. Keep in mind that the design keeps the heaters on all the time.
2. While this line stage does have 28 db of gain, the L-1 also has left and right volume controls that allow you to reduce the output to reasonable levels and use a wider range of the main volume control.
3. The SS headphone amp is quite powerful and I'm sure it measures well, but I'm not sure that I would prefer to listen to it over my speakers.