Fosi v3 Mono | TPA3255 PFFB | Balanced | [First Look from Fosi FB]

[sejarzo]

I notice that with the volume knob turned higher, the tweeter hiss is also higher, if I don't need the output, I'd prefer less hiss during silence. Does the removal of the volume knob mean that I will not be able to do this small trick and it will always be hissy? Will the higher sinad reduce the hiss?

If tweeter hiss is due to the output stage of a power amp, it should be consistent and not affected by the position of the volume control.

 

[Guddu]

I don't understand this reasoning.
If we ask (and obtain) from the producers greater engineering efforts, greater attention to materials, better performance, greater reliability, etc., then it will also be right for the producers to ask for an increase in the premium for their work. I don't think there is anything strange or absurd in this.

Deserving effort for sure, as long as it’s reasonable.
Hard to say anything about budget aspect, as we all might have slightly different take on it.

 

[surroundman]

I don't understand this reasoning.
If we ask (and obtain) from the producers greater engineering efforts, greater attention to materials, better performance, greater reliability, etc., then it will also be right for the producers to ask for an increase in the premium for their work. I don't think there is anything strange or absurd in this.

I see little need to explain in length about the reasoning, for it should be fairly coherent already. What is more absurd is your attempt for an argument that puts words in my mouth. Where have I denied the right of a manufacturer to ask more for improvements made? I have never made such claim. It is the amount of price increase that I am worried about, not price increase itself as a principle. And if I find that worrying, it doesn't mean you or anyone else must agree. It is how I alone see it.

 

[ban25]

Jeez I literally just ordered a ZA3 and now they release this?!?! Want!

 

[YesChickenNuggets]

Will sinad over rca be much lower?

 

[charlielaub]

Jeez I literally just ordered a ZA3 and now they release this?!?! Want!

The PFFB mono amp is not "released". It is not clear when they will actually be available for purchase, or at least I have not seen anything reported about that. Consider the news just a teaser at this point.

 

[sejarzo]

Someone on the Fosi Facebook page wondered about the power output into 8 ohms. My reply...

Based on the TI spec sheet, in PBTL mode as a mono amp, the chip can put out 495W at 2 ohms and 315W at 4 ohms at 1% THD. That suggests it would put out about 200W at 8 ohms, but those figures are based on a 53.5V supply. With a 48V supply, that would likely end up at about 160W at 1% THD, which is the point where distortion rises drastically with increased distortion.

Neither the spec table nor the graph for PBTL THD vs power cover 8 ohm loads.

Does 160W seem reasonable to expect for the high end of power available into 8 ohms, and perhaps more like 120W in the actual end product?

 

[Doodski]

Someone on the Fosi Facebook page wondered about the power output into 8 ohms. My reply...

Based on the TI spec sheet, in PBTL mode as a mono amp, the chip can put out 495W at 2 ohms and 315W at 4 ohms at 1% THD. That suggests it would put out about 200W at 8 ohms, but those figures are based on a 53.5V supply. With a 48V supply, that would likely end up at about 160W at 1% THD, which is the point where distortion rises drastically with increased distortion.

Neither the spec table nor the graph for PBTL THD vs power cover 8 ohm loads.

Does 160W seem reasonable to expect for the high end of power available into 8 ohms?

Hmmmz.. I like your question because it really needs answering and we face this question often when dealing with these TPA amps and the like. Firstly we need to decide if we are going to use a 3 variable power formula from Ohms law or if we are going to the the RMS power version formula. [Watts RMS = (Vpeak * 0.707) ^2 / R load] It doesn't matter all that much to me and some others as I have read here but the end result varies substantially. The things that limits us and the calculations is the amplifier power output linearity or what is actually occurring is the lack of linearity with these TPA amp power supplies and amp circuitry capability. So to guesstimate or estimate the amplifier power output in varying loads(Z) is a real crapshoot. It's hit and miss. It's fantasyland numbers that pop out of our noggins based on no facts. It would be so much fun if somebody would setup a ammeter to meter the total current draw @ varying Zs of say 8 Ohms, 6 Ohms, 4 Ohms and 2 Ohms and maybe even go all out and take a risk and see if the TPA amp can not burn up when driving a 1 Ohm load and how the protection circuit functions if it does. Then graph the results so we have that information right there easily seen and understood. If I had a lab I would love to do that but I do not have a lab at home anymore. Somebody could take this on as ASR project.

 

[Guddu]

Does 160W seem reasonable to expect for the high end of power available into 8 ohms, and perhaps more like 120W in the actual end product?

Seems like it, other mono mode testing are around those numbers @48v 5a psu.

PE. I don’t think PFFB improves power output capabilities.

 

[Guddu]

Jeez I literally just ordered a ZA3 and now they release this?!?! Want!

We may be months away from formal purchase/release date at this point.

If you don’t mind me asking, aren’t you happy with ZA3?

 

[sejarzo]

Hmmmz.. I like your question because it really needs answering and we face this question often when dealing with these TPA amps and the like. Firstly we need to decide if we are going to use a 3 variable power formula from Ohms law or if we are going to the the RMS power version formula. [Watts RMS = (Vpeak * 0.707) ^2 / R load] It doesn't matter all that much to me and some others as I have read here but the end result varies substantially. ....

I realized as soon as I hit the post button that I forgot to add the part about 120W in the final product, which didn't post until after you replied.

I used the spec sheet power numbers for 2 and 4 ohm loads to estimate power at 8 ohms.

There was no need for me to add that 0.707 factor because I compared two peak voltage values, as it would cancel out in the end. I used the ratio (48/53.5)^2, or ~0.80 to scale the 200W at 53.5V supply to 160W with a 48V supply.

My interest is mostly in the cost vs audible benefit vs wait time for these to arrive between running two of these versus one of the Audiophonics stereo units using the Hypex or 3e modules with PFFB and similar power output that would be around $440-450 delivered in the US.

 

[Doodski]

I realized as soon as I hit the post button that I forgot to add the part about 120W in the final product, which didn't post until after you replied.

I used the spec sheet power numbers for 2 and 4 ohm loads to estimate power at 8 ohms.

There was no need for me to add that 0.707 factor because I compared two peak voltage values, as it would cancel out in the end. I used the ratio (48/53.5)^2, or ~0.80 to scale the 200W at 53.5V supply to 160W with a 48V supply.

My interest is mostly in the cost vs audible benefit vs wait time for these to arrive between running two of these versus one of the Audiophonics stereo units using the Hypex or 3e modules with PFFB and similar power output that would be around $440-450 delivered in the US.

Why would you wait for delivery if you have other amplifier options that are suitable and that you like too? What is the hook that caught you attention to this specific amp?

 

[sejarzo]

Why would you wait for delivery if you have other amplifier options that are suitable and that you like too? What is the hook that caught you attention to this specific amp?

I don't need a new amp immediately, and if two of these cost under $350 with equal performance to the $440 or so alternatives, they are in the mix.

 

[charlielaub]

Someone on the Fosi Facebook page wondered about the power output into 8 ohms. My reply...

Based on the TI spec sheet, in PBTL mode as a mono amp, the chip can put out 495W at 2 ohms and 315W at 4 ohms at 1% THD. That suggests it would put out about 200W at 8 ohms, but those figures are based on a 53.5V supply. With a 48V supply, that would likely end up at about 160W at 1% THD, which is the point where distortion rises drastically with increased distortion.

Neither the spec table nor the graph for PBTL THD vs power cover 8 ohm loads.

Does 160W seem reasonable to expect for the high end of power available into 8 ohms, and perhaps more like 120W in the actual end product?

IF you want to just keep it simple, the "mono" mode does NOT put out any more power into 8 or 4 Ohms compared to a BTL (stereo mode) TPA3255 amplifier. Maybe a few more Watts but to the first order approximation it's the same.

Where the mono amp can deliver it's full power is into 2 Ohm loads. You need more current in order to do this, so the FOUR amplifier blocks within the TPA3255 are arranged in a bridge-parallel configuration (a parallel connection of the two sets of bridged/BTL channels). There is nothing is to be gained if your speaker impedance is not dipping down that low. Hardly anyone will be able to take advantage of this extra power because home audio speakers rarely have such low impedance levels.

 

[Doodski]

I don't need a new amp immediately, and if two of these cost under $350 with equal performance to the $440 or so alternatives, they are in the mix.

IC.. Makes sense now. I must admit monoblocks are cool. They just are..LoL...

 

[sejarzo]

IF you want to just keep it simple, the "mono" mode does NOT put out any more power into 8 or 4 Ohms compared to a BTL (stereo mode) TPA3255 amplifier. Maybe a few more Watts but to the first order approximation it's the same.

All I know is that TI specs the chip at 255W/ch in stereo into 4 ohms in BTL and 315W/ch at 4 ohms in PBTL, which I do agree is likely insignificant in actual use.

 

[sejarzo]

IC.. Makes sense now. I must admit monoblocks are cool. They just are..LoL...

I had a pair of IRD chip-based monoblocs years ago, followed by some early icePower monoblocks before I sold all my separates and bought the most powerful Onkyo AVR in 2010 or thereabouts.

 

[charlielaub]

Here's another analogy about the mono TPA3255 mode: It's like asking the question of whether you should put a big spoiler on your car. Sure, a spoiler will indeed help with downpressure and traction and will look COOL! But not really until you reach 100 mph, and since you can never really drive that fast (at least where I live) it's not going to actually provide much tangible benefit. In the same sort of way, the mono mode TPA3255 is not going to make a difference compared to the same (e.g. PFFB enabled) TPA3255 stereo amp for almost all conditions and most all home audio speakers.

 

[Doodski]

Here's another analogy about the mono TPA3255 mode: It's like asking the question of whether you should put a big spoiler on your car. Sure, a spoiler will indeed help with downpressure and traction and will look COOL! But not really until you reach 100 mph, and since you can never really drive that fast (at least where I live) it's not going to actually provide much tangible benefit. In the same sort of way, the mono mode TPA3255 is not going to make a difference compared to the same (e.g. PFFB enabled) TPA3255 stereo amp for almost all conditions and most all home audio speakers.

But.... but.. 2 Ohms stable with the mono block configuration!

 

[charlielaub]

But.... but.. 2 Ohms stable with the mono block configuration!

But... but... my car can go 180 MPH! (not really) That would be a capability that you cannot take advantage of. Cool to have, but useless.

Do you have a 2 Ohm load to drive with this amplifier? If the answer is YES, then buy it! If not, there seems to be no real good reason to do that...