Fosi Audio P4 Mini Preamp with 3 RCA Inputs, Home Audio Stereo Pre amp for Amplifier/Active Subwoofer/Speakers, Preamplifier with 3-Level Adjustable Gain 3/6/9 dB, Bass and Treble Control

Quality item
Really good quality in performance and build.

Sounds fine & good set of features for the price paid.
Sounds fine, no audible signal degradation I can pick up, it does have more drive vs my previous passive. Quality of item is good for price paid, enclosure has nice feel, rca sockets are robust. I’ve bypassed tone controls and use lowest gain, which should in theory give best audio quality, so your mileage may vary. Feature set is good, in particular the motorised volume control, which is the main reason I bought it. I’m also using the 3.5mm output to a Topping L30ii headphone amp and that sounds great. I cannot comment on reliability, but I’ve not had issues with FOSI in the past (V3 / V3 mono). Looking forward to the full set of measurements and teardown on ASR. I would recommend on basis of features, as it stands. Just some more info. Gain and tone controls do not appear to effect the preout signal, so applicable to rca only. Pre is controlled by the volume though. Not an issue for me personally.

Pleasantly Surprised
For what this thing costs it is surprisingly well featured to the point I was a bit surprised. When switching inputs it disconnects the output makes the input switch lets it settle and then enables the ouptut again. Changing the gain setting it does the same thing too. Turning on or off the tone controls same behavior. That is some attention to detail. On the tone controls, personally I think they have too much range, but the actual tone control sound plenty good. The motorised pot is actually pretty good, and I think the main issue with is that there really isn’t a good way to get exact fine control and have it move at a sensible rate. It works well enough. The preamp has enough headroom to take any reasonable line level signal and handle it. I was pleasantly surprised to see that the volume pot was AC coupled which was a nice thing to see.If you’re so inclined the output opamp can be “rolled” as it is called. How much of a difference this makes? Honestly, I don’t know nor do I really care that much. I happened to have some OPA2134s and I swapped it over to one of those because why not? The default one it comes with is a NE5532 and there is nothing inherently wrong about that choice in this application so do not feel like it needs to be swapped because it does not. This thing has very good performance out of the box. Overall there really isn’t much to complain about it. Its small, sounds good, and does exactly what it says for a more than reasonable price.

Value for money
Seems a wonderful device for the money given the price of other pre amplifiers

I got the Fosi P4 preamp to feed into my Fosi V3. Only use one of the three inputs from my Schitt Mode 3E which handles optical from my Wiim Pro and USB from my PC.Very impressed with the P4. Added something to the sound compared the DAC to V3 direct and didn’t introduce ant noise whatsoever. The remote is handy and the volume knob is motorised to my surprise at the low cost I paid.I was going to add it to the tv set-up where I run a SMSL P100 DAC via it’s HDMI but it’s too goo to waste on that project.Awesome little preamplifier. Well done Fosi.

Ho inserito questo preamplificatore nella mia catena hi-fi desktop. Al primo ingresso è collegato un giradischi Audio-Technica con testina Ortofon 2M Red, preamplificato da un pre-phono Pro-Ject; al secondo ingresso un DAC Topping D50 III. È inoltre presente un lettore CD SMSL PL100, collegato al DAC tramite cavo ottico.L’esperienza d’ascolto è estremamente soddisfacente: il pre Fosi è completamente privo di rumore di fondo, le commutazioni degli ingressi avvengono tramite micro-relè Omron, silenziosissimi, e il potenziometro del volume motorizzato risulta molto comodo da utilizzare tramite telecomando.La qualità audio è eccellente. Prodotto assolutamente consigliato.Caratteristiche Tecniche PrincipaliIngressi: 3 ingressi RCA stereo (ideale per gestire più sorgenti come DAC, CD o streamer).Potenziometro Motorizzato: Una rarità in questa fascia di prezzo; permette di regolare il volume con il telecomando mantenendo un percorso del segnale puramente analogico.Controlli di Tono: Bassi e Alti con tasto Bypass sul retro per chi desidera un segnale più lineare e puro.Guadagno Selezionabile: Switch a 3 livelli (+3dB, +6dB, +9dB) per adattarsi a diversi finali di potenza.Op-Amp Rolling: Monta chip NE5532P su zoccolo, quindi facilmente sostituibili da chi ama personalizzare il suono (es. con Sparkos o Muses).Rumore di fondo: Estremamente basso (SNR =>110dB). Anche con guadagno alzato, il fruscio è quasi inesistente.Gamma Media: È il punto di forza; le voci sono riprodotte con buona chiarezza.Gamma Alta: Molto aperta e dettagliataGamma Bassa: Veloce e controllata, ma non eccessivamente calda.