• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Fosi Audio V3 Mono Amplifier Review

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 8 1.5%
  • 2. Not terrible (postman panther)

    Votes: 15 2.8%
  • 3. Fine (happy panther)

    Votes: 108 19.9%
  • 4. Great (golfing panther)

    Votes: 413 75.9%

  • Total voters
    544
This scheme is valid only if there is an active crossover in the preamplifier, if there is a passive crossover in the speakers, then this scheme cannot be applied.
Why not?
 
Because the crossover for the speakers would be in two places.
Wdym?

Bi-amping a pair of bi-amp-able speakers is perfectly fine, even without an external, active crossover.

The passive crossover built into the speakers is designed specifically for this purpose.
 
Can you help me check if this diagram shows the right connection of bi-amping using 4 sets of V3 Monos? We're going to make a video to introduce it.:)
View attachment 374697
Please don’t create this HOW to video Fosi without first articulating WHY one might do this. I believe that anyone who owns the distinctly exotic equipment necessary for bi amping to provide ANY real benefits does not need such a howto video. Likewise, anyone who needs the howto does NOT own gear that would benefit.
 
This scheme is valid only if there is an active crossover in the preamplifier, if there is a passive crossover in the speakers, then this scheme cannot be applied.
Just how do you work that out? I've never heard of a x/over, active or passive ever built into a pre-amp.

I suggest you visit Elliott Sound Products where he explains the whole point of bi-amping. He recs. active x/overs for maximum benefit. I think the guy from Fosi using 4 x Monos is a bit OTT since it is the bass that uses by far the most energy. Rod also debunks bi-wiring. His site is well worth a visit.
 
Wdym?

Bi-amping a pair of bi-amp-able speakers is perfectly fine, even without an external, active crossover.

The passive crossover built into the speakers is designed specifically for this purpose.

I think the reason for external crossover (normally digital) is to bypass the passive crossover components and their power and sound quality losses.
 
I think the reason for external crossover (normally digital) is to bypass the passive crossover components and their power and sound quality losses.
Sure sure, I'm not arguing against that.

Just stating that bi-amping is possible, safe, and ok even without external crossover, even if it's not smart.
 
Because the crossover for the speakers would be in two places.
Wdym?

Bi-amping a pair of bi-amp-able speakers is perfectly fine, even without an external, active crossover.

The passive crossover built into the speakers is designed specifically for this purpose.
To give a bit more explanation to Zek's concern, the external cross-over in the preamp will introduce different phase shifts in the signal feeding the LF and HF inputs of the loudspeaker (as proposed in Fosi Audio's post #2055), which can screw up the phase alignment of the summed speaker output.

Below are some possible effects on adding Butterworth LPF and HPF to the 2 amplifiers, the intents of which is to filter out HF for the LF amplifier and LF for the HF amplifier. The phase shifts caused by these additional cross-over filters resulted in a cancellation notch at the cross-over point when these filters are combined with the cross-over filters in the loudspeaker. The top graphs (left - magnitude, right - phase) show the outputs of a 2-way LR4 cross-overs with cross-over frequency of 400 Hz. The bottom graph shows the outputs with the additional Butterworth LPF or HPF is cascaded to the LPF and HPF of the LR4 cross-over -- notice the cancellation notch at cross-over.

Cascade External Filters to Existing XO.png
 
Can you help me check if this diagram shows the right connection of bi-amping using 4 sets of V3 Monos? We're going to make a video to introduce it.:)
View attachment 374697
What exactly do you mean by bi-amping? To me it it involves speakers with passive crossovers, but separate terminals for HF and LF. In this case there is no crossover before the amps - the input to the amps is full range. I don't see how this is supposed to improve anything, but you can do it with commonly available hifi speakers.

Speakers designed to be used with an active crossover before the amps are rather uncommon in hifi, but do at least make sense.
 
Please don’t create this HOW to video Fosi without first articulating WHY one might do this. I believe that anyone who owns the distinctly exotic equipment necessary for bi amping to provide ANY real benefits does not need such a howto video. Likewise, anyone who needs the howto does NOT own gear that would benefit
 
If active wire/somebodyelse/NTK/mike70 would actually read Rod Elliot's explanation for bi-amping before posting they may then decide not to post.

Check out his ESP Philosophy (simplified) section and then if you think you can add anything do so.
 
If active wire/somebodyelse/NTK/mike70 would actually read Rod Elliot's explanation for bi-amping before posting they may then decide not to post.

Check out his ESP Philosophy (simplified) section and then if you think you can add anything do so.
Elliott's article is about the advantages of full active speakers (with active cross-overs feeding line level signals to the power amplifiers). It does not address the (problems of the) proposal by Fosi and is therefore irrelevant to this discussion.
 
If active wire/somebodyelse/NTK/mike70 would actually read Rod Elliot's explanation for bi-amping before posting they may then decide not to post.

Check out his ESP Philosophy (simplified) section and then if you think you can add anything do so.

Well according to Rod Elliot:
The most common question I get is "Do I need to disconnect the passive crossover in my speakers?"
The answer is ... Yes, otherwise you are not really biamping at all.
I stand by my statement
anyone who owns the distinctly exotic equipment necessary for bi amping to provide ANY real benefits does not need such a howto video. Likewise, anyone who needs the howto does NOT own gear that would benefit.
 
Fosi Audio’s diagram does not indicate speakers with passive crossovers built-in. It appears to show active crossovers feeding amplifiers which feed a woofer and a tweeter per channel.
 
Last edited:
Just think of the energy bouncing around inside the bass enclosure.
I think you'll find it's a rare speaker cabinet that uses materials that will contain any EM field within it, let alone bounce it around.
 
To give a bit more explanation to Zek's concern, the external cross-over in the preamp will introduce different phase shifts in the signal feeding the LF and HF inputs of the loudspeaker (as proposed in Fosi Audio's post #2055), which can screw up the phase alignment of the summed speaker output.

Below are some possible effects on adding Butterworth LPF and HPF to the 2 amplifiers, the intents of which is to filter out HF for the LF amplifier and LF for the HF amplifier. The phase shifts caused by these additional cross-over filters resulted in a cancellation notch at the cross-over point when these filters are combined with the cross-over filters in the loudspeaker. The top graphs (left - magnitude, right - phase) show the outputs of a 2-way LR4 cross-overs with cross-over frequency of 400 Hz. The bottom graph shows the outputs with the additional Butterworth LPF or HPF is cascaded to the LPF and HPF of the LR4 cross-over -- notice the cancellation notch at cross-over.

View attachment 374775
I think every preamplifier has a way to adjust the crossover frequency or switch it off. Even if you don't pay attention, when you reverse the polarity of the tweeter, for example, a small error of -3dB occurs, but the load capacity increases by 12dB. Biamping brings with it the ingenious possibility of adjusting the high frequency range depending on the age of the person.
 

Attachments

  • LR4 plus BU2 f 400Hz mit gegenphase.jpg
    LR4 plus BU2 f 400Hz mit gegenphase.jpg
    297.2 KB · Views: 28
Back
Top Bottom