Fosi Audio P1 Tube Preamplifier Mini Hi-Fi Stereo Preamp 6K4 Valve Vacuum Pre-amp with Treble Bass Tone Control for Home Theater HiFi System(not for Turntable)

This little preamp provides a great introduction into tube amplification, both the benefits and drawbacks of using tubes.First of all, as this is a preamp, it is very easy to set up direct A/B comparisons with commodity recording equipment (namely USB recording interfaces). Run a line out recording through the preamp, and again direct, match the output levels, and you now have a better insight into what these tubes are actually doing to the sound with A/B testing (preferably blind ABX testing).The good news - this preamp is pretty quiet and does a good job amplifying the signal coming in. I've had zero issues with noise including this in my playback chain. For a component containing tubes it is surprisingly quiet.The bad news (depending on your point of view) - the EQ knobs on this device affect the sound output far more than the tubes themselves. This is not a knock on the quality of the EQ, no, in fact, the EQ knobs are actually very useful given there is only a treble and a bass knob. In fact, the preamp is almost worth the price of the device given how well these work.The tubes themselves work as advertised. Sending a sine wave through the preamp, I definitely see way more second-order harmonic distortion through the preamp than through a direct output without the preamp. For instance, with a 440 kHz sine wave, I see the expected bump of 880 kHz at -30dB from the main signal. And there is noticeable compression running high-volume sounds through the preamp, particularly when running into the preamp at higher outputs. In short the expected effects of the tube (even order harmonics and compression) are measurable with sufficiently juiced inputs using relatively inexpensive measuring equipment.The real question is whether these effects are noticeable by your ears. For me at least the answer is yes, but the effect is pretty subtle, nowhere near what I was anticipating. For better or worse the stock tubes actually perform very well and have a good amount of headroom available before you notice any obvious changes in the sound. You kind of have to go out of your way to hear obvious changes, though, whether that be with bass-heavy music (Sublime's 40oz to Freedom works great for this) or by deliberately overdriving the inputs.A fun quantification of how this preamp affects sounds is to do a null test. First capture a recording of music played through the preamp tube, and then do the same exact source without the preamp tube. Line up both recordings *exactly* to the sample and to the same level, then invert the phase of one of them. Play them together and you'll get an exact audio representation of the difference between both input modes. This is more difficult than it sounds but if you do it you will hear the obvious distortions being introduced by the tubes. The interesting part is that they are both almost inaudible (unless you are carefully listening for them), and that even though these distortions sound not so great by themselves, when mixed into the output they can actually improve the sound of the music.OK, enough navel-gazing for now. Is this worth purchasing if you want to understand what "magical" tubes do? Absolutely. Is the effect going to be obvious? Probably not, unless you swap in tubes that are either busted or have very low headroom.Oh, and if you want to get an easy check for whether the tubes are actually in the signal path, grab a pencil and (gently) tap on each tube. As long as you don't have a fake you should hear the taps through your output speaker/headphones. There shouldn't be any ringing from the taps - that would indicate the tubes have gone bad and are microphonic - but you should be able to hear something with the volume up high enough. And the sound volume should increase gradually after a cold start like any self-respecting tube would.Speaking of tubes, I wish the silly LEDs under the tubes were not included. Even though this is just a preamp there is enough voltage running through the tubes to emit a slight glow after the tubes have warmed up. The red LEDs that turn on when powered up are *sort* of useful to make sure the device is working, but ultimately silly as it looks super fake compared to a real tube glow.

So...let me tell you a story about a dude named Cheap Guy who was attempting to upgrade his PC sound system.See, Cheap Guy is...well... a cheap guy! Cheap Guy does not like\endorse\believe\deal with large Visa bills at the end of the month (he REALLY hates it!) BUT he was also was VERY tried of his PC sound system sounding like (poo icon).So, Cheap Guy went about looking at replacing his entire setup but at a budget of under 250.00.Cheap Guy thought he had it all figured out:- 10th Anniversary S.M.S.L DAC -- SMSL SP100 Headphone Amplifier Tube Hi-Res Audio Desktop Amplifier- ART HeadAMP 4 Four-Channel 8-Output Stereo Headphone Amp- Cables (2 new RCA cables and one RCA to 3.5MM cable which connects to the ART HeadAMP through the bypass on the SMSL SP100 which allows Cheap Guy to plug-in multiple headphones and speakers into one unit).Cheap Guy fired up the system and WOW! Way better than what he had before but the sound stage was not what he thought it would be. Something be a missing. **head scratch**. What could it be? **BING!*** Pre-Amp! Duh!So, Cheap Guy set out to find a good, solid, price competitive tube pre-amp and, after a lot of research, landed on the Fosi Audio amp.Why?- Terrific price- RCA connecters (a must)- Tube Amp (Cheap Guy is old and loves tube amps and tube pre-amps).- Bose Desktop Speakers - Bose Companion 20 Multimedia Speaker System (available here on Amazon. I already had them. B-Day gift from Cheap Guys wife about two years ago).- Terrific Price (I already said that but the price for what you get is so good I had to say it again!)Cheap Guy gets the unit, reads the instructions (tubes need to powered on for 30 minutes before running anything through them), waits, throws on some Zeppling and... WOW! I thought the first iteration of this new setup was good but after hooking-up the Fosi pre-amp, the sound stage expanded at least 50%. The sound difference is...amazing. Clean, clear, expansive, just dead on! Cheap Guy is blown (BLOWN AWAY) at what this little guy has brought to the table.Tubes: Yeah, yeah, buy new tubes...blah...blah...blah... but Cheap Guy is not interested. The design of the unit was around the tubes that came with the unit and to Cheap Guy, they sound really good. In the future, will Cheap Guy upgrade the tubes? Maybe. But the sound as it stands now is perfect for Cheap Guy.Fosi, you have outdone yourself. The description next to the product: "This pre-amp improves everything detail, transparency, immediacy, richness, tone associated with your music.: is DEAD ON!I mean....I'm outa words to describe it. It the perfect fit with the DAC and AMP's I already have in place. Amazing is all I can say.The Doors, Ridders in the Storm just came on Amazon HD Music. I think I am going to cry. **Deep Sigh**. Just get it.

Sound quality to price ratio = 5 Stars. Hardware = 4 stars.Sound quality is actually good. Enough bass, mids are just right, not too forward nor backward. Treble is sweet. I like that you can roll op amps to get the sound signature you want.The tube sockets are kind of loose fitting. If you roll tubes a lot, chances are the sockets will loosen further. Suca Audio and FX audio beats Fosi in this regard.The supplied power adapter is only rated for 1 amp. Fosi should have supplied a higher amperage like 1.5 or higher amps.Changing some capacitors in the power chain and in the audio chain improved the sound a lot and I mean a lot. Wider soundstage and I think even the frequency response - deeper lows and higher frequency extension. Sound quality changed from good to great.By the way, Fosi Audio's customer service is excellent. The first unit I received is faulty and Fosi Audio replaced it with a new unit.