Fosi Audio P4 Preamplifier Review

[DACsNoMore]

Pre-amp with 3 RCA inputs and no input impedance specified anywhere. Hey - it is not important, right? Same is going on in similar cheap amps; most likely 10 kOhm - the lowest, so they could claim 1000 mega watts power output. Anything below 47 kOhm would result in [over]load the output stage in most tape decks causing upto -4 dB signal drop. Look for gears with 47 kOhm input impedance designed by OEM who cares about sound quality, not mega claims. If there is no input impedance in specs - it is probably junk. As for P4 - it will not cause drop on active input, but it will load all not active inputs and cause -4 dB signal drop on those. So if you have deck connected to this pre-amp and not listening to it - when you make recording the VU levels in many decks would show wrong signal levels due to line out [over]load (voltage drop). Fosi BT20pro - will not load line out and BT300 PRO - will cause -2dB drop.

 

[Ropeburn]

Pre-amp with 3 RCA inputs and no input impedance specified anywhere. Hey - it is not important, right? Same is going on in similar cheap amps; most likely 10 kOhm - the lowest, so they could claim 1000 mega watts power output. 10 kOhm will [over]load the output stage in most tape decks causing upto -4 dB signal drop. Look for gears with 47 kOhm input impedance designed by OEM who cares about sound quality, not mega claims. If there is no input impedance in specs - it is probably junk.

Please explain how a load of 10kOhm would "overload" any output, and result in a 4dB drop, compared to a 47kOhm load.

I'll wait for you to explain the difference a few dozen microamperes the output would have to deliver more would make.

 

[DACsNoMore]

Please explain how a load of 10kOhm would "overload" any output, and result in a 4dB drop, compared to a 47kOhm load.

I'll wait for you to explain the difference a few dozen microamperes the output would have to deliver more would make.

If you have no deck - there is no point to explain anything. In short, most decks have VU connected to line out internally, so are the headphones amp stage and calibrated with 47 kOhm load. When the standard load changes -> the voltage drops -> lower level on VU meters -> you will compensate to 0 dB (that would result in +2dB or +4dB of max levels) and mess up the recording. Fosi advertise P4 for tape decks - Thanks, but no thanks! Some decks with separate line out stage (Nak) would not be affected, but most midrange decks do not have such luxury. I never said "overload" - [over]load. [Over] is because of not standard load impedance. Not sure why P4 was designed to short inactive inputs to the ground. I am sure it is not good for your audio source output stage that is still playing.

 

[gino1961]

Hi found this on the issue

A tape deck's output impedance varies but typically aims for a low value (under 1kΩ, often around 100-600Ω) to drive connected gear without signal loss, though some older consumer decks might use a series resistor, making their effective output impedance higher (like 2.2kΩ for some Nakamichis) or requiring specific loads (e.g., 47kΩ for some Tascams) for best results, ensuring good frequency response when connected to amps or recorders

therefore if you can remove that series resistor with a smaller value one the effective output impedance will be about the value of the new resistor
Usually a 100 ohm resistor should be fine You could need a service manual

 

[DACsNoMore]

Deck with VU meters connected to the line out actually helps to visualize the results of low input impedance mismatch. In case of P4, if you listening to input #1 - it works perfectly fine for audio source connected to input #1 (pretty sure it is > 47kΩ, opamps have very high impedance in gΩ range). The audio sources connected to input #2 and #3 would be "loaded" with way lower impedance. No other amp or pre-amp with multiple inputs I have does this. Why not just disconnect from inputs #2 and #3, or load those with the same/matching impedance when input is in selected state? Possibly the easiest/safest for your audio source would be find in P4 those "inactive" load resistors and replace with 47kΩ. Replacing the P4 is more cost effective though.

 

[birkbott]

What about sticking this thing in a new enclosure and upgrading the volume control to something from Khozmo?

 

[gino1961]

What about sticking this thing in a new enclosure and upgrading the volume control to something from Khozmo?

you will lose the option of controlling the volume with a remote

 

[birkbott]

you will lose the option of controlling the volume with a remote

Khozmo has remote options

 

[gino1961]

Khozmo has remote options

Well then it could work very well Not that a remote control is mandatory Then any decent stepped attenuator could be an option
To be honest i am already quite satisfied by the P4 as it is I do not like completely the form factor I would much prefer a lets say 30cm wide unit series
I do not like mini components because the controls and the connectors can be too close each other

 

[Joe Smith]

I agree, a wider preamp is nice, the form factor of the Schiit Saga 2 is better (and I really like their stepped relay attenuator). I have older classic width preamps that still work fine (NAD, Nikko) and it would be great to see some new preamps on that form factor that don't cost an arm and a leg - I guess Emotiva does have some.

I had noted to Fosi as a beta tester that the controls are really tight on the P4, even for my medium size fingers, but they were already in production with it.

 

[gino1961]

I agree, a wider preamp is nice, the form factor of the Schiit Saga 2 is better

Hi i see a width of 9" ? i was thinking more to a 12" width actually What worries me is the spacing between connectors on the back
I also love external power supplies to keep the mains transformer away from circuitry

(and I really like their stepped relay attenuator).

Me too This is a fundamental issue Some cheap preamps have cheap pots I am very interested in volume control chip ... i am sure they can be technically transparent
I was thinking to gut a little but excellent headphone amp like the Topping L30 and replace the volume pot with one of those chips ... but i need a full working pcb for them

I have older classic width preamps that still work fine (NAD, Nikko) and it would be great to see some new preamps on that form factor that don't cost an arm and a leg - I guess Emotiva does have some.

imhe just replacing the pot with a stepped attenuator can transform a decent preamp to a very good one ... and also removing the transformer from the case
Listen what Mr McGowan had to say on this topic some years ago

I had noted to Fosi as a beta tester that the controls are really tight on the P4, even for my medium size fingers, but they were already in production with it.

Absolutely I have already two preamps the P4 and the GR40 and love both
But what intrigues me is the volume control solution ... i would like that Fosi Audio would adopt one ... pga or NJR units i mean
like the NJW 1195A
just look where it is used ... a 2400 euro unit

TONEWINNER AD-3PRO+ Integrated Amplifier

With the AD-3PRO+, Tonewinner offers a Class A integrated stereo amplifier rated at 2x165W at 8Ω.

www.audiophonics.fr

it must be very very good indeed I have another preamp the old Hegel P2A ... it uses a PGA something ... cristal clear
i tend to think that the days of very expensive stepped attenuators are close to the end
People who do not like chips is because they have not tried the best ones ... as usual prejudice is a bad beast

 

[Joe Smith]

Really, for the money, the Saga 2 is a pretty good thing. It uses a wall-wart, so power transformer is offloaded, there is 3-way adjustable gain (including fully passive mode), has a remote, has the great stepped relay attenuator, four RCA inputs, RCA and XLR out... I had been waiting on Fosi for the P4 and then the Saga 2 was announced right around the same time. The main nicety of the Fosi is the tone controls, useful for me when playing non-digital content at low levels...

I had hoped Schiit would do a preamp with an add-in card for phono, but alas, no go on that.

I had looked at the Emotiva but didn't love the build quality.

The Schiit Saga pairs nicely with the Gjallarhorn mini-amp for a compact system, or dual (monoblock) Gjallarhorns or a Vidar amp for more power.

 

[SnakeLord]

Really, for the money, the Saga 2 is a pretty good thing.

Schiits Saga 2 might be a fine product (which we actually dont know as it hasnt been measured on ASR or elsewhere independently. I wish we would see more of their products being tested on ASR).

But we are talking here about 3x the price of the Fosi P4. So the question is what does the Saga 2 three times better as the P4? Trigger? - nope, Fully Balanced? - nope, EQ? - nope, Better volume attenuation? - yes. Thats basically it.
Fosi P4 is simple, functional and affordable. It just does what its made for - hard to beat for around 80-100$.

I mean if it comes down to some simple SE source switching or an EQ/Volume/gain control solution for your chain, you dont really need all the fancy higher priced stuff.

 

[Joe Smith]

Schiits Saga 2 might be a fine product (which we actually dont know as it hasnt been measured on ASR or elsewhere independently. I wish we would see more of their products being tested on ASR).

But we are talking here about 3x the price of the Fosi P4. So the question is what does the Saga 2 three times better as the P4? Trigger? - nope, Fully Balanced? - nope, EQ? - nope, Better volume attenuation? - yes. Thats basically it.
Fosi P4 is simple, functional and affordable. It just does what its made for - hard to beat for around 80-100$.

I mean if it comes down to some simple SE source switching or an EQ/Volume/gain control solution for your chain, you dont really need all the fancy higher priced stuff.

I agree, the Fosi is a great value. Value alone, it wins. For me, the Saga 2 is also worth the price uptick. For those of us who listen to a lot of music at quieter volumes, the perfect channel matching and volume control at lower levels is a vital preamp feature. It's nice to also have the fully passive option.

The volume pot on the P4 was what I liked least about it. It's nice that it's motorized and has a remote, but it is not great at playing soft volumes. You get far better low volume control from the pot on the V3 amp.

I think this middle tier/level stuff from Schiit is just a bit overpriced for what it is. I can't say that the Gjallarhorn + Saga 2 for $600 sounds a leap better than a Fosi V3 stereo amp and P4 preamp for about $190. But it is nicely designed, has U.S. service available, etc. Some of the money with Schiit goes for their image and branding, for sure.

 

[SnakeLord]

I agree, the Fosi is a great value. Value alone, it wins. For me, the Saga 2 is also worth the price uptick. For those of us who listen to a lot of music at quieter volumes, the perfect channel matching and volume control at lower levels is a vital preamp feature. It's nice to also have the fully passive option.

The volume pot on the P4 was what I liked least about it. It's nice that it's motorized and has a remote, but it is not great at playing soft volumes. You get far better low volume control from the pot on the V3 amp.

I think this middle tier/level stuff from Schiit is just a bit overpriced for what it is. I can't say that the Gjallarhorn + Saga 2 for $600 sounds a leap better than a Fosi V3 stereo amp and P4 preamp for about $190. But it is nicely designed, has U.S. service available, etc. Some of the money with Schiit goes for their image and branding, for sure.

After evaluating the 3 preamp options - Fosi P4, ZP3 and Schiit Saga 2. I ended up with the P4 and im happy with it so far.

The build is solid. The tone controls feels nice and have some nice resistence in movement. No problems whatsoever at low volume, no channel disbalance or anything, the control is precise. Altho i am currently using Fosi ZA3 amp which also has volume control set to around 70-75% and if i crank it up to 100% (basically bypassing the amp controls), then indeed even at the lowest P4 gain of -3db i need to turn it down quiet far leaving not much of space for farther lower volume attenuation. Its pretty loud at 10-12 oclock setting.

I also need to say, that the P4 is a compromise which i had to make out of those 3 devices, its not perfect. The lack of the 12v trigger is the biggest downside of it. Because of that i cant shut my ZA3 down when shutting down the P4. Would have been perfect solution with the P4 remote. Huge missed opportunities here.

The ZP3 actually suits my needs much better since it has the balanced and the 12v trigger in/out. Its like perfect preamp for me, bringing all the key feauters i need. But somehow Fosi managed to fuck it up badly while designing the volume controls.
Digital knob on an preamp without any feedback of what volume it is currently set to is just insane! Whoever at Fosi came up with that idea and thought it was a good one... boy oh boy.

And last but not least the Schiit Saga 2: Cut the freakin useless HPA down, put balanced + 12v trigger in/out and voila! Its perfect for 300$. But not as it is now, too many compromises for higher price. Also they use this "cool" type of marketing, selling you "lifestyle" similar like apple did and does which i dont like. "Buy our produts because we are cool, so you can be cool too".

Thats why P4 > Saga 2

 

[Joe Smith]

Yeah, the Schiit marketing stuff can get a little heavy-handed, but they make good things. I view them the same way I do Apple - I don't want to go down the depth of the rabbit hole, but I am happy to use a few good items and leave it at that. I do enjoy my iPhone 16, it's my third Apple phone, before that I was a Blackberry 10 guy. I dislike Android for the most part. Ditched Windows, now use Linux Mint 22 at home and a small Chromebook for traveling.

I agree with you on the ZP3, that volume control is a darn shame. I have not used one, but the descriptions fry my brain, don't know how that one got through product testing.

The P4 is a good little unit and you sure can't beat the price! I don't use triggers so that's not a big deal for me. I wish the volume control had more finesse for quiet listening levels.

 

[gino1961]

At the risk of sounding like a broken record, I still don't understand why the volume control ICs intended for this function aren't used, at least in budget devices.
They're incredibly cheap and have impressive performance.
If I'm not mistaken, I read that even high-end units use these chips.

Classé CP-800 D/A preamplifier | Stereophile.com

I was setting up for some musical demonstrations I was to present for a Music Matters evening at the ListenUp! store in Boulder, Colorado, in May 2011. For these events, an audio store invites manufacturers (and the occasional journalist) to demonstrate to local audiophiles the musical benefits...

www.stereophile.com

"The volume control is implemented with two two-channel Burr-Brown PGA2310 programmable-gain chips, one per channel used as a differential volume control."

The ZP3 has one similar IC .... very good design choice.
It is sad that the actual level is not displayed.
Maybe in a version 2.0, hopefully.
Also, I found it strange to see higher distortion in the ZP3 than in the P4.
strange

 

[KurtKlötentreter]

I have to express my gratitude to all these in depth, data backed reviews of affordable audio gear, @amirm

Hadn't been looking forward to black friday in years, but Fosi had lots of discounts going on recently and I was only able to pull the trigger on a few of them because you had measured all the gear living on my desk now.

Your write ups helped me grasp what matters in audio gear (for my use anyways) and saved me from potentially wasting money on meaningless, if not worse performing gadgets.

Current setup is a Fosi K7 into a P4 into dual V3 Monos, and I couldn't be happier tbh. Way overkill for my speakers, but probably future proof to some extent, and the pre out on the P4 allows me to drive dual subwoofers (1 for each channel) - only thing missing now is some way to high pass my speakers, but I'm undecided on whether I'll live with it until I can afford a MiniDSP Flex or if I'll try to get some inline RCA high pass filters first.

In any case, if it weren't for you, I'd probably still be listening to creators which swear by their ears to tell me that gear like the P4 lacks "depth" and "layering" and that only expensive OP amps might fix that. Kudos to you!

 

[letit08]

Bonjour à tous,

Peut on utiliser le sortie Jack 3.5mm pre-out comme sortie pour l'enregistrement. Je souhaite l'utiliser avec une interface audio ESI U22 XT pour numériser mes disques vinyle...


Hello everyone,

Can we use the 3.5mm pre-out jack as an output for recording? I want to use it with an ESI U22 XT audio interface to digitize my vinyl records...

 

[gino1961]

Bonjour à tous,

Peut on utiliser le sortie Jack 3.5mm pre-out comme sortie pour l'enregistrement. Je souhaite l'utiliser avec une interface audio ESI U22 XT pour numériser mes disques vinyle...


Hello everyone,

Can we use the 3.5mm pre-out jack as an output for recording? I want to use it with an ESI U22 XT audio interface to digitize my vinyl records...

hi ! i would use a separate phono preamp and send its outs directly to the audio interface inputs
i would try a battery powered one ... even very cheap even diy