Fosi Audio P4 Preamplifier Review

[mike70]

what about this?
View attachment 468034

wow!
surely it sounds awesome, that amps are "oldies but goldies" (and we know decent ss amps are indistinguishable)

 

[gizmo90]

Am I the only one thinking of something like this ?

View attachment 467965

Nope. I was thinking the same thing. I still think my Yamaha AS1100 class AB sounds better than my TPA3255 amps. I'm convinced I like a little distortion.
After using the TPA3255 stuff for a while I miss the Yamaha. When I plug it back in it's noticeable to me. I actually don’t like the look as much as the smaller class D amps. I wish I liked them as much because the Yamaha pulls 90w in idle lol.

I should have someone help me with a blind test...

 

[mike70]

Nope. I was thinking the same thing. I still think my Yamaha AS1100 class AB sounds better than my TPA3255 amps. I'm convinced I like a little distortion.
After using the TPA3255 stuff for a while I miss the Yamaha. When I plug it back in it's noticeable to me. I actually don’t like the look as much as the smaller class D amps. I wish I liked them as much because the Yamaha pulls 90w in idle lol.

I should have someone help me with a blind test...

well, your brain is convinced, but maybe that's not the truth.
now you need to choose the red or the blue pill ... if you're happy now and don't want to change that, leave it that way
if you want to know the truth, please, do a right blind test ... i assure you it will be shocking (as happened with me and usually with everyone)
you can check the myriad of tests in the internet, and (with properly done tests) the results are always the same.

 

[norman bates]

Hooked up the P4 today.

Why ?

My 3 cherished 40 year old nakamichi ta-2a receivers are constantly acting up.
They are a nelson pass stasis design, no global feedback, regulated front end, tuner works well, and sounds like 85% of a threshold amplifier for 10% the cost.

The tone control defeat button goes open (muting the front end), so I bypass that.
The balance knob is a pot around the volume pot, that goes bad to the point de-oxit doesn't help and you adjust the balance every couple of nights.
The speaker selector can go bad (deoxit works well here).
But lastly, the front panel selector goes bad, either not switching or switching to nothing..............

But darn they sound great otherwise, lol.

So, since the receiver has a pre-out / in, I removed the jumpers and used the fosi as the front end.

Does it "sound" better" ?

Don't know, will hook up more revealing dynaudio speakers tonight or tomorrow.

I do know that I'd like the bass tone knob moved down an octave.
Most receivers / preamps spec their tone control at 50hz.
My 12" 2-way speakers have qts = .32 and Fs of 50hz, so the speaker is naturally (probably) 9db down near 50hz (if was tuned at 50hz anyway).
But the 12" cone area takes eq nicely.

So, a little less grunt than I had before (under 100hz), but now I have a headache free system, and basically 2 more back up amplifiers.

And I'm not looking at spending $300 - $1,000 for something new (fosi v3 monos / rotel a8 / rotel a11 mkii / yamaha as701).

But, perhaps a regulated 12v linear supply for the p4 would be an improvement........................



Norman

 

[norman bates]

Nakamichi ta2a output stage

 

[gizmo90]

View attachment 468094

View attachment 468220

Hooked up the P4 today.

Why ?

My 3 cherished 40 year old nakamichi ta-2a receivers are constantly acting up.
They are a nelson pass stasis design, no global feedback, regulated front end, tuner works well, and sounds like 85% of a threshold amplifier for 10% the cost.

The tone control defeat button goes open (muting the front end), so I bypass that.
The balance knob is a pot around the volume pot, that goes bad to the point de-oxit doesn't help and you adjust the balance every couple of nights.
The speaker selector can go bad (deoxit works well here).
But lastly, the front panel selector goes bad, either not switching or switching to nothing..............

But darn they sound great otherwise, lol.

So, since the receiver has a pre-out / in, I removed the jumpers and used the fosi as the front end.

Does it "sound" better" ?

Don't know, will hook up more revealing dynaudio speakers tonight or tomorrow.

I do know that I'd like the bass tone knob moved down an octave.
Most receivers / preamps spec their tone control at 50hz.
My 12" 2-way speakers have qts = .32 and Fs of 50hz, so the speaker is naturally (probably) 9db down near 50hz (if was tuned at 50hz anyway).
But the 12" cone area takes eq nicely.

So, a little less grunt than I had before (under 100hz), but now I have a headache free system, and basically 2 more back up amplifiers.

And I'm not looking at spending $300 - $1,000 for something new (fosi v3 monos / rotel a8 / rotel a11 mkii / yamaha as701).

But, perhaps a regulated 12v linear supply for the p4 would be an improvement........................



Norman

I get it dude, that’s supposed to be a legendary receiver. Looks like fun. I got a P4 recently too. It’s nice with the class d stuff with one input. I don’t think the power supply will do anything you can hear from what I’ve learned here. But I don’t know sh*t from shampoo I'm coming to find out. I just like having fun with this stuff so mission accomplished.

 

[olds1959special]

The remote for volume control is so bad with this, I'm just going to set it to the highest level needed and control volume with my DAC remote instead.

 

[norman bates]

The Fosi p4 preamp.

The motorized volume control gives it a good manual feel turning it.
For me at very low volumes, it doesn’t take much turning for a big change in volume.


I'm just wishing that when increasing the bass knob that 50hz would be louder than 100hz, like 6db, but this is a me problem.


So, out of the system it goes.

I am keeping the p4, it sounds fine, works well, I enjoy the company, and people saying that they take a lot of input from users (here).
And I like helping a company that is making some inexpensive but competitive products, so everyone can experience better sound.
Like rooting for an underdog.

For me, I just need more bass boost below 100hz for the speakers I use 90% of the time.
With the fosi p4 on my other speakers, it sounds great, very clear, and goes deep.
That setup though just can't thump like my 12" 2-ways can.

Maybe I will get some (used) large cone area speakers that go flat to 40-50hz, then I can put the fosi p4 back in my system.

Either way, highly recommended

 

[gino1961]

Hi to Everyone ! Thank you very much for this very valuable review as always by the way
Looking for a remote controlled volume solution i ended up buying this little preamp ( It should arrive on monday )
Looking at the lab report i did not understand this graph below

the heading says output the graph input
Does this mean that the preamp is unhappy with signal above 1V ? with which gain setting ?
I really do not need much Vout using even some integrated with their own volume set to max This means that they usually will output the max power with signal below 500mV
As i said above i am getting mad to find a cheap but good remote controlled volume solution I cannot sleep at night Not kidding
I really need a remote ... but the signal must pass clean and nice
Thank you to Dr Amir for another excellent review
Kind regards gino

 

[solderdude]

You need to see the plot above combined with the picture below.

What is observed is that distortion starts to rise (gently, not hard limiting) above 0.7V input voltage.
This is a bit clearer to see in the plot you posted as the 'gain' is not in that plot, just IM distortion at the input.
We see that the input behaves exactly the same at all 3 gains (it starts to increase distortion a little above 0.7V)
Note that even with 3V input the performance is still excellent.
The gain stage does not add much in distortion but the input stage noise is, of course, higher when a higher gain is selected.

So perfectly usable in all gain settings and with input signals of at least 2V.
Alas... we don't know when the input stage starts to clip.

I really need a remote ... but the signal must pass clean and nice

No need to worry about signals passing clean and nice ... they certainly will. This device is guaranteed to be 'transparent' (and won't impart a 'sound signature').

Note that in the lower volume range the remote control will not allow 'fine adjustment'.
You may have to use it on low gain and perhaps with the amplifier turned down a bit so you reach the maximum required level at full volume of the P4.
In that case volume control will be great using the remote.

 

[gino1961]

You need to see the plot above combined with the picture below.
View attachment 468834

Hi ! thank you so much for your very kind and extremely reply
I will use it with gain=3 absolutely

What is observed is that distortion starts to rise (gently, not hard limiting) above 1V input voltage.

Note that even with 3V input the performance is still excellent.

It is this thing that i do not understand I have always seen graph of THD+noise vs. Hz and output level not input
It is the first time and i cannot understand
In any device and also speakers the output is what is measured Maybe i am missing something

The gain stage does not add much in distortion but the input stage noise is, of course, higher when a higher gain is selected.
So perfectly usable in all gain settings and with input signals of at least 3V.
Alas... we don't know when the input stage starts to clip.
No need to worry about signals passing clean and nice ... they certainly will. This device is guaranteed to be 'transparent' (and won't impart a 'sound signature').

Thank you sincerely again I should get one next Monday I am quite excited on the basis of the review
I was thinking to try some diy kit but with this kind of performance for such a low price
At the very max i am thinking to a bigger case to have more space for an internal power supply and more space for connections on the back A gutting project

Note that in the lower volume range the remote control will not allow 'fine adjustment'.

This is as unfortunate as common I notice that the very best preamps use resistors networks to set the level
But honestly at this price I cannot expect what is impossible

You may have to use it on low gain and perhaps with the amplifier turned down a bit so you reach the maximum required level at full volume of the P4.
In that case volume control will be great using the remote.

Thanks again and absolutely I have already a decent cheap dac ... the Smsl su-1 that i like a lot
I am very curious to listen Very
Kindest regards gino

 

[solderdude]

In any device and also speakers the output is what is measured Maybe i am missing something

In this test the gain is subtracted so 1V in is 1V out, 2V in = 2V out.

This is as unfortunate as common I notice that the very best preamps use resistors networks to set the level
But honestly at this price I cannot expect what is impossible

Yes, its a value thing.
Much cheaper to use a motorized volpot.
This way there is no need for a memory circuit, lots of relays, and more complex circuitry/firmware and an indication for the volpot position.

 

[Steven Holt]

There are two outputs (the RCA’s marked “output” and the mini jack marked “pre out”) so one of them could be used with a subwoofer. You would use the subwoofer’s internal crossover as it would be fed a full range signal.

Sorry for the late reply, I just came upon this. Sorry to say, you cannot use the RCA out to connect the subwoofer, that one is for connecting to your AMPLIFIER, not subwoofer. As far as the mini jack goes....maybe, if your sub has a 'pre in'. Mine does not, and I've yet to see one that does...but I won't exclude the possibility.

 

[Ropeburn]

Sorry for the late reply, I just came upon this. Sorry to say, you cannot use the RCA out to connect the subwoofer, that one is for connecting to your AMPLIFIER, not subwoofer. As far as the mini jack goes....maybe, if your sub has a 'pre in'. Mine does not, and I've yet to see one that does...but I won't exclude the possibility.

Subwoofers and amplifiers are the exact same thing in this context. Many have stereo line inputs intended for full range signals, which then get internally summed and filtered etc. which is the same as "pre in".

 

[gino1961]

Hi this little unit is very clear indeed
I guess you all are using the humble stock wall wart?

 

[gino1961]

10.1kΩ at max volume and 60.1kΩ at minimum volume.

Hi I'm a happy customer and thank you very much for providing excellent sound at unbelievable prices
I just don't understand the variable input impedance
Why not a 10k constant vs Hz ?
Quite standard value for line preamps fwiu

 

[Ropeburn]

Hi I'm a happy customer and thank you very much for providing excellent sound at unbelievable prices
I just don't understand the variable input impedance
Why not a 10k constant vs Hz ?
Quite standard value for line preamps fwiu

I guess it's because the volume pot is before the input buffer, not after. Not exactly standard design, but it still works fine.

 

[gino1961]

I guess it's because the volume pot is before the input buffer, not after. Not exactly standard design, but it still works fine.

Thanks a lot very interesting
The result sounds spectacular
I am getting an impressive level of detail i thought were only possible with very expensive units

 

[gino1961]

I guess it's because the volume pot is before the input buffer, not after. Not exactly standard design, but it still works fine.

Hi good morning ! sorry to bother you again But fwiu usually input buffers are just down the rca inputs Maybe with a selector in between
Usually the chain is input buffers > potentiometer > output stage
I have to study very deeply the input buffers approach ... a powerful buffer followed by a very low impedance pot could work just fine
There should be a big DC blocking cap in between Something like this big 20uF PP cap

4.16.10.25.14 DUCATI ENERGIA - Condensatore: in polipropilene | per motori, in regime; 20uF | TME - Componenti elettronici Italia

DUCATI ENERGIA 4.16.10.25.14 | Condensatore: in polipropilene; per motori, in regime; 20uF - Prodotto dipsonibile nell'offerta della Transfer Multisort Elektronik. Verifica la nostra ampia offerta.

www.tme.eu

I have to calculate the low Hz cut But 20uF before a 5k pot could work
It is a change of approach for me Very interesting

 

[redjr]

Fosi continues to impress. Not just the performance and not just the price, but also their brand look and style.

I'd like to see them stick to a consistent form-factor (width primarily) - at least within a model line. As it is, every new item has just enough change to make it 'unmatchable' for stackablity with anything else. The gold knob is the only similarity carried across their recent products.