Fosi Audio P4 Preamplifier Review

[telemike]

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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.

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So the EQ is meh?

 

[Count Dacula]

So the EQ is meh?

It was better than no EQ on those modest KEF 2x6" towers. The new unit really sparkles, and really would still be worth the $100 even without the great bench specs. I know that sounds weird, but it's a nice unit, regardless of crazy performance.

I bought that Behringer EQ for a PA system I was given. It'll again, work better than no EQ. i have a few mini mixers with tone, they would work ok too, but are nothing special. None are worth mentioning in this thread, just that I was adrift in the Pre department. I relied on a few vintage and new receivers to simplify TV audio, but yeah....pretty happy with the Fosi.

 

[Count Dacula]

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

In a sense, yes...but it took the Vidar to deliver it.

 

[Northa40]

It would be great if this had a meter!

I purchased one of these and it works great, I don't want to sound stupid but what value is there in a meter on a pre-amp? Or is everything better with a meter? I personally think a clipping indicator on a power amp is much more useful.

 

[Count Dacula]

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

Bass modulation is not bad, but it takes the Vidar to make it happen. I'm coming from a mostly Adcom background.

 

[Johannesen]

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.

I might try a 5.5mm x 2.1mm F to 5.5mm x 2.5mm male battery adapter to check to see if a different PSU makes a difference. Amazon has an unregulated jameco linear 12v dc 1.5a psu for under $13.

 

[olds1959special]

I'm glad to see this got a 'great' rating. I am trying one out in my system. I plan to roll the op-amp.

 

[olds1959special]

Will I have to lower the volume of my DAC to use this without distortion? Can it handle 2.5 volts? This was a problem with the ZA3 amplifier.

 

[teched58]

I'm glad to see this got a 'great' rating. I am trying one out in my system. I plan to roll the op-amp.

Why? Why on Earth? I'm genuinely curious, even though this is coming over as rude.

What do you hope to accomplish that outweighs the risk that you will fry something on the circuit board?

It has a SINAD of 108 dB. Is a different op amp going to enable you to hear the angels sing?

 

[olds1959special]

Why? Why on Earth? I'm genuinely curious, even though this is coming over as rude.

What do you hope to accomplish that outweighs the risk that you will fry something on the circuit board?

It has a SINAD of 108 dB. Is a different op amp going to enable you to hear the angels sing?

I'm not planning on doing it, but there no reason to believe it will do anything harmful, if it can be put back together.

 

[olds1959special]

I got my Fosi P4 today. It works perfectly and completes my system! No need to roll op-amps or change power supplies!

 

[olds1959special]

Will I have to lower the volume of my DAC to use this without distortion? Can it handle 2.5 volts? This was a problem with the ZA3 amplifier.

It can handle up to 4V if you use the low gain setting, according to the manual.

 

[t4t3r]

Would this be a good option for a preamp/volume control for a pair of V3 monos? I want to try something a little newer in a 2-channel only setup. The gain setting switch is a little confusing as something I’m not used to.

 

[Joe Smith]

Would this be a good option for a preamp/volume control for a pair of V3 monos? I want to try something a little newer in a 2-channel only setup. The gain setting switch is a little confusing as something I’m not used to.

Yes, I think it would. The gain setting just gives you added flexibility re what you need for source levels etc. I keep mine at the lowest setting and it works fine for all of my sources.

 

[MLFan]

Interesting site....was lurking...now member..
I've currently (2) Fosi ZA3's, running in mono mode, fed by a Fiio M11Plus LTD, feeding (2) Martin Logan Aeon i's. Streaming Qobuz directly into the amps and using the Fiio vol control (headphone out) works very well. Limitation is no inputs for SACD, etc. Now have a Fosi P4 arriving today....will report on subjective results in a day or two.

 

[JeffGB]

I just recieved my P4, which I use to drive a Crown XLS 1500. I've always had trouble with RF noise when using the Crown with single ended devices so I ended up building a correctly wired RCA to XLR cable. This helped a great deal with my Schiit Heresy being used as a preamp. The RF still exists but is much reduced.

Now comes the Fosi P4 and noise appears again but this time a buzzing. I unhooked the DAC and the noise remained but slightly different so the problem was the P4 driving the Crown. I was disappointed but thought "I'll see if I can mod it, perhaps" but, before going down that path I dug out some cheap standard RCA cables and tried them. The noise is completely gone, including RF noise. I didn't expect that because the Schiit had been even noisier with standard RCA cables.

I'm going to go out on a limb and say I believe the difference is the power supply of the Fosi vs the Schiit. The Schiit just has a remote transformer that provides 16v AC, while the Fosi has an smps DC wall wort. I didn't expect the result, but I'm completely happy with the outcome.

 

[Karlaka]

I just recieved my P4, which I use to drive a Crown XLS 1500. I've always had trouble with RF noise when using the Crown with single ended devices so I ended up building a correctly wired RCA to XLR cable. This helped a great deal with my Schiit Heresy being used as a preamp. The RF still exists but is much reduced.

Now comes the Fosi P4 and noise appears again but this time a buzzing. I unhooked the DAC and the noise remained but slightly different so the problem was the P4 driving the Crown. I was disappointed but thought "I'll see if I can mod it, perhaps" but, before going down that path I dug out some cheap standard RCA cables and tried them. The noise is completely gone, including RF noise. I didn't expect that because the Schiit had been even noisier with standard RCA cables.

I'm going to go out on a limb and say I believe the difference is the power supply of the Fosi vs the Schiit. The Schiit just has a remote transformer that provides 16v AC, while the Fosi has an smps DC wall wort. I didn't expect the result, but I'm completely happy with the outcome.

Hi, Jeff.
The important thing here is that the problem was solved.
And once again, there's plenty of evidence that expensive cables aren't the solution to anything and often even cause problems. From the minimum standard up, it's all the same.
Some photos of all the cables used would be greatly appreciated.

 

[JeffGB]

I made a cable the same as the second one in this image from an earlier thread. I used a commercial pro xlr cable with one end changed to RCA and wired as the diagram shows. It worked much better with my Schiit Heresy, with greatly reduced RF noise but now, with the P4 it's more noisy than a plain RCA connection by a lot. I've tried several cheap RCA cables and they all work fine. It must be the difference between the P4 and the Heresy's power supply and/or grounding (also the grounding of the Crown XLS amp).

 

[xanalog]

Treat every balanced interconnect suspiciously.
Using @JeffGB' lower diagram; pin-out ALL adapters and cables with an Ohmmeter (DMM).

Not just pinX-to-pinX for continuity but to ensure that the shields are not tied to lo or hi pins.
Such mis-wiring sometimes occur by mistake or poor workmanship and other times depending on

...pin 1 is a ground pin. The other two pins have different uses depending on which country you’re in. Europe considers pin 2 the hot pin and pin 3 the cold. In comparison, vintage US devices had swapped the hot and cold method. So, pin 3 is hot, and pin 2 is cold. This is an outdated practice; most US devices use the European style.

It is a simple 10minute insurance policy.

 

[teched58]

I made a cable the same as the second one in this image from an earlier thread. I used a commercial pro xlr cable with one end changed to RCA and wired as the diagram shows. It worked much better with my Schiit Heresy, with greatly reduced RF noise but now, with the P4 it's more noisy than a plain RCA connection by a lot. I've tried several cheap RCA cables and they all work fine. It must be the difference between the P4 and the Heresy's power supply and/or grounding (also the grounding of the Crown XLS amp).

Occam's razor would tell you something far simpler: That it must be the difference between the cheap cable that works and the more expensive cable which allows noise and hum to get through the signal path and be heard.