This is a review and detailed measurements of the Fosi ZP3 balanced preamplifier. It was sent to me by the company and costs US $189 (coupons available for less).
Despite its low cost, the look of the unit is attractive to me. As is the functionality of having balance and tone controls. What is not is the volume control. It is a rotary, microprocessor controlled volume control which nicely allows remote control access (supplied). The problem is that there are no indications anywhere was to what you have set the volume to. You can easily turn on the unit with volume set to max and cause panic. Usually rotary controls have some kind of display or at least bar graph showing you level. Mechanical ones don't have this issue because they have minimum and maximum stops which we don't have here.
But there is plenty of good news in the back:
Despite the low cost, we have XLR (combo) balanced input in addition to dual RCA inputs. What's more, a couple of switches underneath let you invoke a high pass filter for main outputs, allowing the system to properly integrate with a subwoofer. I will show the response later. Trigger input is there as well in addition to built-in power supply. Let's see how it performs.
Fosi ZP3 Preamp Measurements
I started with balanced in and out, feeding the unit 4 volts:
I like to test amps in "unity gain" meaning same voltage out as what is put in. Alas, I could not do that here as the volume control digital steps are rather coarse, jumping from 3.8 volt to 4.4. I decided to give it the benefit of doubt and going with the latter. SINAD of 108 dB is excellent for a such a pre-amp, leaving plenty of headroom to play 16 bit content without much disturbance. As you can see, third harmonic sets the SINAD. Noise itself is quite a bit lower which is nice:
Switching tone control takes its toll though:
Unbalanced in/out shows fair bit of degradation over balanced due to added distortion:
Here are your choices for frequency response:
Note that if you enable tone controls but leave the switch at "20 to 20 kHz," you get some additional low frequency roll off. So I suggest selecting "bypass" if you don't want filtering.
Crosstalk is excellent for a product at any price level let alone what we have:
IMD response shows that higher performance (and more expensive) amps don't have to close shop, especially if you enable tone control:
We can see the same in our wideband distortion vs frequency test:
The preamp can produce lots of output voltage which is nice though optimal level is what I have tested:
This though, aggravates the issue with lack of volume level display as you could seriously overdrive your power amp and speakers. On the positive front, if your power amplifier is low gain, you can take advantage of that with better SNR by using the pre-amp to push it at higher voltages.
Recently, we have had a lot of discussions around "phase" measurements. I thought I give those people a nod by showing the phase response with and without tone control:
When integrating with a sub, this phase shift will interact with sub's own phase response, producing likely unexpected total output. This, then gets manipulated with room modes. Translation: you better measure your room and deal with it that way than try to compute/predict your way out of it using this kind of measurement.
Conclusions
Fosi continues to push the price/performance metric ZP3. It is feature rich and includes many things members ask for. But as they say, be careful what you ask for. Analog filtering of the output has a real cost. Lack of volume control indicator is a serious usability issue for me personally. For that reason, I can't recommend the ZP3. If that doesn't matter to you, and you are on a budget, the ZP3 can make for an excellent preamplifier.
------------
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/
Despite its low cost, the look of the unit is attractive to me. As is the functionality of having balance and tone controls. What is not is the volume control. It is a rotary, microprocessor controlled volume control which nicely allows remote control access (supplied). The problem is that there are no indications anywhere was to what you have set the volume to. You can easily turn on the unit with volume set to max and cause panic. Usually rotary controls have some kind of display or at least bar graph showing you level. Mechanical ones don't have this issue because they have minimum and maximum stops which we don't have here.
But there is plenty of good news in the back:
Despite the low cost, we have XLR (combo) balanced input in addition to dual RCA inputs. What's more, a couple of switches underneath let you invoke a high pass filter for main outputs, allowing the system to properly integrate with a subwoofer. I will show the response later. Trigger input is there as well in addition to built-in power supply. Let's see how it performs.
Fosi ZP3 Preamp Measurements
I started with balanced in and out, feeding the unit 4 volts:
I like to test amps in "unity gain" meaning same voltage out as what is put in. Alas, I could not do that here as the volume control digital steps are rather coarse, jumping from 3.8 volt to 4.4. I decided to give it the benefit of doubt and going with the latter. SINAD of 108 dB is excellent for a such a pre-amp, leaving plenty of headroom to play 16 bit content without much disturbance. As you can see, third harmonic sets the SINAD. Noise itself is quite a bit lower which is nice:
Switching tone control takes its toll though:
Unbalanced in/out shows fair bit of degradation over balanced due to added distortion:
Here are your choices for frequency response:
Note that if you enable tone controls but leave the switch at "20 to 20 kHz," you get some additional low frequency roll off. So I suggest selecting "bypass" if you don't want filtering.
Crosstalk is excellent for a product at any price level let alone what we have:
IMD response shows that higher performance (and more expensive) amps don't have to close shop, especially if you enable tone control:
We can see the same in our wideband distortion vs frequency test:
The preamp can produce lots of output voltage which is nice though optimal level is what I have tested:
This though, aggravates the issue with lack of volume level display as you could seriously overdrive your power amp and speakers. On the positive front, if your power amplifier is low gain, you can take advantage of that with better SNR by using the pre-amp to push it at higher voltages.
Recently, we have had a lot of discussions around "phase" measurements. I thought I give those people a nod by showing the phase response with and without tone control:
When integrating with a sub, this phase shift will interact with sub's own phase response, producing likely unexpected total output. This, then gets manipulated with room modes. Translation: you better measure your room and deal with it that way than try to compute/predict your way out of it using this kind of measurement.
Conclusions
Fosi continues to push the price/performance metric ZP3. It is feature rich and includes many things members ask for. But as they say, be careful what you ask for. Analog filtering of the output has a real cost. Lack of volume control indicator is a serious usability issue for me personally. For that reason, I can't recommend the ZP3. If that doesn't matter to you, and you are on a budget, the ZP3 can make for an excellent preamplifier.
------------
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/
, that indicator means nothing. The knob will rotate and rotate infinitely.
