Fosi Audio P4 Preamplifier Review

[Joe Smith]

Glad to see this nice preamp option getting some attention. It really does pack a lot of value in for a very low price. As I mentioned in earlier comments, the only larger issue I had was that using the remote, the volume jumps quickly at the low end of the pot's range. This can be tweaked with the knob as needed, or the knob on the V3 or similar amp if using with one of those. The price is even lower than I was expecting to see when I was using my preview device.

 

[AdamG]

just registered to "attack" me like this... amazing...
no comment..

He just asked you a simple question. I see no attack here. Slow your roll and show some respect and compassion.

I came to incorrect conclusion and I have withdrawn my comment in a follow up post below.

 

[morillon]

Sorry, my response isn't for this answer, but for this one (I'm just taking the last comment):
Publication dans le fil de discussion « Test du préamplificateur Fosi Audio P4 » : https://audiosciencereview.com/foru...dio-p4-preamplifier-review.61467/post-2260135
;-)
( look profil of him)
(My words and my questions were really nothing original...really nothing....)

 

[Sokel]

He just asked you a simple question. I see no attack here. Slow your roll and show some respect and compassion.

It sured looked like an attack (see Ant's quote above your post) on top of ignorance.
If @OG_Tiredofthe_BS was following ASR he would know that this is a known problem which Amir sometimes refers too.

If an analog pot is not of high quality, is susceptible to imbalance the more we attenuate.

 

[antcollinet]

He just asked you a simple question. I see no attack here. Slow your roll and show some respect and compassion.

Dunno. If this

You're just being an insufferable know-it-all looking for reasons to complain

Were directed at me, Id probably have interpreted it as an attack.

 

[AdamG]

It sured looked like an attack (see Ant's quote above your post) on top of ignorance.
If @OG_Tiredofthe_BS was following ASR he would know that this is a known problem which Amir sometimes refers too.

If an analog pot is not of high quality, is susceptible to imbalance the more we attenuate.

Dunno. If this



Were directed at me, Id probably have interpreted it as an attack.

I stand corrected. Missed this and you both are correct to point this out. My apologies to @morillon . The quoted post has been deleted and a Warning was issued. Thank you both for correcting my mistake. No excuses got this one wrong. Appreciate the correction.

 

[xNORgate]

Back at the ranch...

I am surprised that 9dB of gain is being so highly rated by ASR members.

 

[Carl-Fosi Audio]

Back at the ranch...
View attachment 438283
I am surprised that 9dB of gain is being so highly rated by ASR members.

What's the matter with 9dB?

 

[Joe Smith]

Back at the ranch...
View attachment 438283
I am surprised that 9dB of gain is being so highly rated by ASR members.

Three levels of gain, switchable. While 3/6/9 is perhaps modest, that's really all this little unit needs. Fosi is developing devices that "meet the middle." If one wants to play at 500 wpc in a huge room, you're probably going to purchase different equipment, aren't you?

 

[Daverz]

Back at the ranch...
View attachment 438283
I am surprised that 9dB of gain is being so highly rated by ASR members.

9 dB is actually a typical gain for a "line" preamplifier. And most people will never get above 0 dB.

 

[stupendousredman]

This is a review and detailed measurements of the Fosi Audio P4 budget RCA preamp. It was sent to me by the company and as of this writing, is on sale for US $80.

View attachment 436153
The look is attractive enough for the class. A momentary switch turns on the unit and cycles through inputs, with a reassuring relay click. There are tone controls with detents in the center. Finally and very surprisingly so, the volume control is motorized and activated through remote control (not shown)!!!

Back panel shows exactly what one would need in this class:
View attachment 436154
Three inputs are provided. A switch nicely bypasses the tone controls if needed. Gain settings are available from 3 to 6 and 9 dB. The only thing missing is trigger support.

Fosi Audio P4 Preamplifier Measurements
The preamp ships with the gain switch set to 6 dB so I ran the dashboard there:
View attachment 436156
This is excellent performance for the class with distortion at -114 dB or threshold of hearing. So we are noise bound:
View attachment 436157
We have a wide margin to clear 16 bit audio without impacting its noise floor. Moreover, performance is almost maintained even at highest gain.

We can see the effect of gain on distortion+noise:
View attachment 436158

IMD test shows exemplary performance when compared to much more expensive reference up to 1 volt output:
View attachment 436159

Frequency with or without tone control bypass is excellent:
View attachment 436160

Crosstalk is very good:
View attachment 436161

As is wideband noise+distortion vs frequency:
View attachment 436162

Conclusions
The Fosi P4 surprises with incredibly low cost while providing features such as motorized volume control and excellent performance. It simply has no weak point, other than absence of trigger. This is what happens when a company is laser focused on customer needs and excellence in engineering.

I am happy to recommend the Fosi P4 to many of you who need to switch between multiple unbalanced/RCA sources.
------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Amirm has spoken...Phew! My order is already paid for and awaiting fulfilment at Fosi Audio. Thank you.

 

[holbob]

This is currently only £79.99 currently at Amazon UK

https://www.amazon.co.uk/gp/product/B0DQXPBNZD?smid=A27MPXN0R8YFPE&psc=1

 

[beaker152]

This is a fairly generic issue with motorized potentiometers -- at low levels, my 35+ year old Yamaha processor is pretty much useless for small volume increments when its seven-gang pot is turned via its remote.

mine arrived recently and i've been very pleased with it. same comment on the coarse volume adjustments, though, on my system, i reduced the output of the DAC input to give me more granularity when adjusting the volume on on the P4

 

[stadsbeplanner]

would it be suitable to use on a Leak Stereo 20 which has a very high input sensitivity of 125mV?

 

[Mike Madigan]

Sounds like a deal. I just wish Preamps included a line level "record output" for connecting to receivers/integrated amps. I have those independently driving outdoor speakers and etc. There are workarounds but I miss those outputs being standard. Old guy here.

 

[Bertran]

The start of the review says 'budget preamp' but unless you need more features or inputs there is no need for a better one. If ever need to add volume control or more RCA inputs to a system then this is what I will buy. I voted great and I would vote higher as I don't think I've seen a preamp this good at this price level.

I actually want preamp with a DAC, LDAC and DSP and more but then that's a different matter, another price level and maybe a almost different class of device and off topic.

Great product!

May I ask when BT is usually used?
What functions do DSPs usually want?

 

[DavidM1]

May I ask when BT is usually used?

I use Bluetooth several times a week from phone and iPad. I teach music and it is fuss free and instantaneous in lessons - YouTube, Apple Music, backing tracks, drum patterns, metronome, tuning notes etc.

 

[redjr]

I recently received my new P4. I was intrigued by its feature set, which was just what I was looking. However, what I've noticed is this thing is hot(gain). I have the gain set to 3dB and even at only 8:00 this thing is too loud for my near field listening use case. That doesn't allow me any room to fine tune the volume settings. I'd have wished that they would have included a setting for 0dB. My amp does not have the option of lower the gain either. Note; I am using an Ian Canada DAC build with transformer output.

Anyone else experiencing this gain issue?

My DAC link on DIYAudio;

Edit: BTW, the P4 sounds marvelous through my Modulus-86 amp. The Modulus is a little amp is the one to be reckoned with!

Edit 2: My Modulus build images here.

 

[JakeK]

May I ask when BT is usually used?

I use bluetooth all the time if I want to stream a podcast or something easily from my phone. Also when friends visit it's nice for them to be able to bluetooth something from their phone to the speakers.

What functions do DSPs usually want?

Mostly room mode corrections and speaker tuning. For example a speaker is close to a wall or corner or there is a room mode that makes some bass sounds too loud and you want to tune that out.

 

[Carl-Fosi Audio]

Sounds like a deal. I just wish Preamps included a line level "record output" for connecting to receivers/integrated amps. I have those independently driving outdoor speakers and etc. There are workarounds but I miss those outputs being standard. Old guy here.

Do you mean a line out?