Fosi Audio P4 Preamplifier Review

[early rejecter]

There are very few preamps that have a fixed line level out anymore. Rogue and Parasound are some of them.

In terms of more budget-friendly pre-amps, the OSD Pre-1 includes a rec/line out, and even a tape monitor which is even more difficult to find these days (no idea how it tests though). Personally I use an older Adcom pre which I found at a charity shop for $40, but they’re pretty widely available secondhand (at least in my area) for $150 - $200.

 

[Mike Madigan]

In terms of more budget-friendly pre-amps, the OSD Pre-1 includes a rec/line out, and even a tape monitor which is even more difficult to find these days (no idea how it tests though). Personally I use an older Adcom pre which I found at a charity shop for $40, but they’re pretty widely available secondhand (at least in my area) for $150 - $200.

I have several systems. I use an Emotive USP-1 preamp, several older NAD integrated that I just use as Pre amps with separate poweramps. I even still have,my hafler101 preamp I built as a kit in 79. I am currently playing with that on my test bench. I just brought up the line level out as a point of discussion. Thanks.

 

[Njoy]

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.

I am using it with SMSL SU1.P4 is connected to Yamaha HS8.Volume in Windows is 100.Gain set at 6db.
Measured the voltage
3db 3V
6db 4.2V
9db 6V
The volume knob on P4 is at 9 0 clock position,it's about 75db(Measured with mobile phone).
Really pleased with P4.

 

[digitalhardcore]

I am using it with SMSL SU1.P4 is connected to Yamaha HS8.Volume in Windows is 100.Gain set at 6db.
Measured the voltage
3db 3V
6db 4.2V
9db 6V
The volume knob on P4 is at 9 0 clock position,it's about 75db(Measured with mobile phone).
Really pleased with P4.

I'm new to this so bear with me, but I'm considering buying the P4 so hoping someone could help clarify the numbers above. Aren't these voltages way, way above line level even on the lowest gain setting? I'd really like some basic tone control knobs in my system (for quick adjustments), is this device going to cause an issue if used as an input on a minidsp flex?

 

[Njoy]

https://sengpielaudio.com/calculatorVoltagePower.htm

Use the above link to calculate the voltage output.I used a multimeter to calculate output voltage.The input voltage is 2volt (SU1).

 

[Michou]

Hi everyone,
Does anyone know the correct DC barrel plug size for the Fosi P4 preamp? Is it 5.5mm x 2.5mm center pin positive, or something else? Also, would any 12V 2A switch-mode wall-wart style power supply with the right plug work fine with it?
Please advise. Thanks!

 

[redjr]

Hi everyone,
Does anyone know the correct DC barrel plug size for the Fosi P4 preamp? Is it 5.5mm x 2.5mm center pin positive, or something else? Also, would any 12V 2A switch-mode wall-wart style power supply with the right plug work fine with it?
Please advise. Thanks!

Yes. The P4 is not very demanding, so most 12VDC supplies will work just fine.

 

[Joe Smith]

Hey, just curious, I see the "production slowdown" notice is still up on the Fosi P4 page, but they say that this should have gotten better by mid-May. Does anyone know if they are starting to ship these again? I thought this product would do well for them, it's a shame that the supply chain issues are a bottleneck.

 

[Michou]

Yes. The P4 is not very demanding, so most 12VDC supplies will work just fine.

Thank you for your response. My main concern, however, is specifically with the dimensions of the DC barrel connector. I’ve tried several 12VDC power supplies I had on hand, and while they’re electrically suitable, none of their plugs physically fit the preamp — they’re all slightly too small.

It seems the preamp requires a 5.5mm x 2.5mm barrel connector, not the more common 5.5mm x 2.1mm. I was hoping to get confirmation on that point before purchasing a new power supply or adapter.

 

[Count Dacula]

I got one, w00t! Order won't arrive until mid-July. mfg offered me a good deal after I put it on my EBay Watchlist.

It's simply not possible to pass on such a good-testing Pre, for systems that need some tone control.

 

[xanalog]

P4 Pre-Order Shipping Delay Announcement
Dear Fosi Audio Customers,
We are profoundly grateful for your enthusiastic support for our new P4 preamplifier. Since its launch, we have received an unprecedented volume of orders globally, far exceeding our expectations. We understand you are eager to enjoy the exceptional sound quality of our product at home, and we want to transparently share the reasons behind the shipping delays and our solutions.
Production Update:
Due to supply chain constraints, the high-quality motorized potentiometers used in our P4 preamplifiers are currently in limited supply. Despite our efforts to ramp up production, we anticipate that the delivery of the new batch of products will be delayed until around May 15th. （This order is limited to orders placed between March 10th and April 10th. Orders placed prior to this date have already begun to ship.）
Release Date: April 10th. For customers who originally ordered with a planned April delivery, we will provide the following compensation.
Compensation Plan
We sincerely appreciate your patience and understanding. To express our gratitude, we are offering the following compensation options for affected orders. You can select on of them:
1. 10USD Coupon - For future purchases.
2. Double Member Points - Accrued in your Fosi Audio account.
3. Free Accessory Choice - Select one from a knob, banana plug.
We will ship orders in the sequence customers placed them to ensure that every customer receives their product as soon as possible. Please contact us at [email protected] to select your compensation option.
This subsidy is only applicable to customers who purchase the P4 on the official website with March delivery. Orders with delivery information noted as April delivery will not be eligible for this subsidy.
We commit to continuously update you transparently about production progress and to improve on such issues in the future. Thank you for your support and trust in Fosi Audio.
https://fosiaudio.com/pages/fosi-audio-p4-preamplifier

 

[Count Dacula]

Waiting for my Fosi P4, I had a funny idea. You know how the good audio companies are always looking for new products....this is a biggie.

How about full size versions of the same equipment, for the people who like a big fat knob to grab onto? Even though the cost would be higher, a market exists for full sized versions....some people don't want to give it up or mix styles. I'm ok with a smaller form factor, but surely would pay $50 more for a full sized unit, if that's what I was into. Another plus is with the same exact products, the established reputation of the original smaller units still applies for the "new market" customers.

 

[DualTriode]

I received a Fosi P4 on my doorstep a couple of days ago.

Hooked it up to the analyzer but had issues with PS HD's in the noise floor. Put the cute little amp in a shielded steel box bonded to the analyzer ground connection, the PS HD's were removed.

Yet at 2 v RMS the SINAD was 104.2, 2nd and 3rd HD's were both near -112dB's.

I suspect that a OPA1656 Op-Amp could be lower.

 

[xanalog]

I suspect that a OPA1656 Op-Amp could be lower.

Stop it!

 

[Count Dacula]

Mine came today, and it's awesome. I have avoided preamps since my trusty NAD 1300 fried itself, instead going for a flat volume control scheme for the most part. My main system has only sub control, for instance. My Loki Mini Schiit the bed, so the Q4 came around at the right time for me. I was using a cheap Behringer EQ with light adjustment for a little loudness compensation, so hooking up the Fosi was night and day. It's crystal clear and smooth. I was using an Asguard 2 previously as well.

The wife was onboard, saying I should get another for the main system. I explained the Fosi specs out like a $900 preamp (from back in the day) for 1/10th the price.

I like the servo switches, kind of high end retro, imo. pic later...

 

[xanalog]

...I like the servo switches, kind of high end retro, imo. pic later...

+1 goes to FOSI for revisiting the design of a Remote Control.

The P4 remote can also control the ZD-3, as well as the ZP-3.
Replaceable AAA batteries (2x) also gives this remote some heft.

 

[joqueval]

Este fin de semana he podido jugar con el P4 y realmente he quedado muy satisfecho.

El control remoto es una ventaja si tienes el punto de escucha lejos.

Algo sencillo y sin complicaciones sobre todo si quieres cambiar entre dispositivos.

 

[Count Dacula]

I kept a nod to simplicity. It's the living room TV, so the wife is in charge. It is a legit system though.

The EQ was meh.

 

[DSJR]

View attachment 457329



I kept a nod to simplicity. It's the living room TV, so the wife is in charge. It is a legit system though.

The EQ was meh.

View attachment 457332

You've added BASS to those KEFs? Wow

I seem to remember that starting with this generation, KEF spiced up their tweeters a bit for effect. Not as much and rather flatter than B&W and PMC do, but I recall a couple of dB at least was added to tweeter level - I think the largest version with racetrack bass driver were pretty effective from memory. Having those KEFs shoved under the telly and in what looks to be an alcove may add mid-bass too, but obviously I'm only surmising from a long way away on the end of a keyboard

 

[xanalog]

You've added BASS to those KEFs? Wow

But hey, that 'added bass' was free of charge!