Fosi Audio BT30D PRO TPA3255 "Subjective review"

[grogi.giant]

SBC is the most basic codec with the lowest bitrate and, therefore, the lowest sound quality. AAC and AptX are both steps up from SBC and are generally mainstream, though different devices might support either or both (AAC is most common on Apple phones and tablets, while AptX is the preferred standard for Android).

SBC - Android users get stuck with the lowest quality?
Bit depth:16-bit
Sampling Rate: Up to 48kHz
Bitrate: 328Kbps

AAC - Pretty much just Apple products?
Bit depth: Up to 24-bit
Sampling Rate: 44.1kHz
Bitrate: Up to 320Kbps

And they call it a Pro unit... I'm not convinced.

The biggest advantage of aptX over SBC is latency and lower power usage. There also is a slight quality improvement, but it is not obvious and majority will not hear a difference.

 

[grogi.giant]

Shame there's no bypass mode for the tone controls or any +/-dB Hz specs for them.

Assume sample TI implementation. https://www.ti.com/lit/an/sloa042/sloa042.pdf?ts=1676605234086.

Hopefully Amir can get his AP hands on them.

There isn't much variance between various TPA325x implementations. You can predict many things here.

• SINAD around 75dB (TPA3255@32V will give ~94dB @ 5W. -12dB for resistor network, -5dB for tone controls and additional -3dB for subwoofer branch and BT signal relay).
• There isn't PFFB - frequency response depends on load, with 4Ohm -0.5dB at 20kHz, with 8Ohm +1dB at 20kHz.

• Power with included power supply
  • ~80W into 4Ohm - current limited
  • ~50W into 8Ohm - voltage limited

Overall very good product. Three positional switch (the type used in Fosi DAC Q4) would be welcomed to disable BT, as well as stronger Power Supply (this device needs to drive at least twice the load).

 

[TSK]

First time poster and audio newbie here. I plan to use a non-powered 12 channel mixer (considering the Yamaha MG12XU) and want to use it to control powered speakers and subs for TV and karaoke at home. I also want to run a vintage turntable and a pair of passive ESS speakers through the mixer if possible. The speakers are 6 ohm rated at 275w. Is it possible to use the Fosi or some other amp to drive those passive speakers through the mixer, and do it in a way that bypasses the powered speakers?

 

[grogi.giant]

First time poster and audio newbie here. I plan to use a non-powered 12 channel mixer (considering the Yamaha MG12XU) and want to use it to control powered speakers and subs for TV and karaoke at home. I also want to run a vintage turntable and a pair of passive ESS speakers through the mixer if possible. The speakers are 6 ohm rated at 275w. Is it possible to use the Fosi or some other amp to drive those passive speakers through the mixer, and do it in a way that bypasses the powered speakers?

You connect the amplifier after the mixer, and to it the paid of passive speakers.

Active speakers don't require amplifier, you connect them directly to the mixer.

 

[TSK]

Thanks Grogi. So does that mean I can run the turntable through the mixer first, and then send that signal to the Fosi and then to the passives?

 

[grogi.giant]

Thanks Grogi. So does that mean I can run the turntable through the mixer first, and then send that signal to the Fosi and then to the passives?

Turntable -} Phono Preamp -} Mixer
Mixer -} Powered Speakers
Mixer -} Amp -} Passive speakers

 

[SWSL]

As I noted in the objective review page, this BT30D PRO is NOT shipping with TPA3255. Best we can tell, it's shipping with the lower voltage TPA3251 chips. Same family but lower output.

 

[Bohnster]

I've got a weird question. (3-Channel Setup)

I'm sure someone knows the answer to this. Could you make a three channel set up with this? Right channel goes to right speaker. Left channel goes to left speaker. And then the positive of left and right go to positive of a center channel positive, while you select either the left or right channel negative for the negative? I know in some amplifiers, connecting the positives of the amplifier can like, blow them up. I'm just curious if this could be done and have it not blow, up assuming you keep it within its volume limits.

Texas Instruments TPA3255EVM evaluation board

This link shows a TPA3255 evaluation board, and on page 18 they start showing schematics. May not be the exact same setup, but maybe this would show someone who knows what's going on, if that's possible.

 

[Fosi Audio]

I've got a weird question. (3-Channel Setup)

I'm sure someone knows the answer to this. Could you make a three channel set up with this? Right channel goes to right speaker. Left channel goes to left speaker. And then the positive of left and right go to positive of a center channel positive, while you select either the left or right channel negative for the negative? I know in some amplifiers, connecting the positives of the amplifier can like, blow them up. I'm just curious if this could be done and have it not blow, up assuming you keep it within its volume limits.

Texas Instruments TPA3255EVM evaluation board

This link shows a TPA3255 evaluation board, and on page 18 they start showing schematics. May not be the exact same setup, but maybe this would show someone who knows what's going on, if that's possible.

We have plans to make a three channel amplifier indeed, but it is not the same as your idea.

Yours have just two channels out, right? The right channel goes to the right speaker, and the left channel goes to the left speaker, and then you connect both right and left channel to your center speaker. Am I correct?

This can be done too, but I think it is not friendly to users, I may make three channels out, right channel for speaker, left channel for left speaker and a center channel for center speaker.

 

[SWSL]

@ Fosi. Could you respond to my comment that this is NOT a 3255 amplifier? Your own pdf manual (found on fosiaudioshop.com) for this amp lists it as a 3251, which makes sense with the 36 volt power input limit. 3255 amps CAN use up to 46 volts at least. They will put out more power. Why not describe this one accurately?

 

[Fosi Audio]

As I noted in the objective review page, this BT30D PRO is NOT shipping with TPA3255. Best we can tell, it's shipping with the lower voltage TPA3251 chips. Same family but lower output.

Could you please tell me where did you find the TPA3251? We may have made a mistake, the BT30D PRO adopts 2 pcs of TPA3255.

 

[Fosi Audio]

@ Fosi. Could you respond to my comment that this is NOT a 3255 amplifier? Your own pdf manual (found on fosiaudioshop.com) for this amp lists it as a 3251, which makes sense with the 36 volt power input limit. 3255 amps CAN use up to 46 volts at least. They will put out more power. Why not describe this one accurately?

Thank you for refering that, Fosi Audio BT30D PRO is a TPA3255 amplifier, it adopts 2 pcs of TPA3255, here is the lastest manual.

And thanks for our customers' suggestion, we are developping the 48V version of BT30D PRO now.

 

[SWSL]

Could you please tell me where did you find the TPA3251? We may have made a mistake, the BT30D PRO adopts 2 pcs of TPA3255.

Hi. Thanks for responding! I have never been able to get my browser to open fosiaudio.com. It is blocked ny malwarebytes saying "website blocked due to compromised" So I cannot see the document you linked to. BUT your other site fosiaudioshop.com works fine.

That is where I bought my amp - at Fosiaudioshop.com. The user guide Fosi offers for the BT30D is found here.

I want to clarify that I am not unhappy with the performance! It is probably the best 325x amp out there for under $100 and the input/ output options are just what we need.

IF the current item sold is truly a 3255, then it would be good to know why it is downrated to the 36V which is the 3251's limit. I have seen that it's capacitors are rated 50V.

Thanks so much for participating in this forum and supporting your excellent product.

 

[grogi.giant]

@ Fosi. Could you respond to my comment that this is NOT a 3255 amplifier? Your own pdf manual (found on fosiaudioshop.com) for this amp lists it as a 3251, which makes sense with the 36 volt power input limit. 3255 amps CAN use up to 46 volts at least. They will put out more power. Why not describe this one accurately?

Hi. Thanks for responding! I have never been able to get my browser to open fosiaudio.com. It is blocked ny malwarebytes saying "website blocked due to compromised" So I cannot see the document you linked to. BUT your other site fosiaudioshop.com works fine.

That is where I bought my amp - at Fosiaudioshop.com. The user guide Fosi offers for the BT30D is found here. View attachment 272554

I want to clarify that I am not unhappy with the performance! It is probably the best 325x amp out there for under $100 and the input/ output options are just what we need.

IF the current item sold is truly a 3255, then it would be good to know why it is downrated to the 36V which is the 3251's limit. I have seen that it's capacitors are rated 50V.

Thanks so much for participating in this forum and supporting your excellent product.

Honestly - what difference does it make?! Do you really care if you have 2x300W capable chip?!

The chip itself might be rated to 51V, but if other elements, capacitors especially, are not capable to handle that voltage, it is not usable. The amp is rated to 36V.
At that voltage TPA3251 and TPA3255 will be identical, TPA3251 might be even so slightly better.

 

[SWSL]

Honestly - what difference does it make?! Do you really care if you have 2x300W capable chip?!

The chip itself might be rated to 51V, but if other elements, capacitors especially, are not capable to handle that voltage, it is not usable. The amp is rated to 36V.
At that voltage TPA3251 and TPA3255 will be identical, TPA3251 might be even so slightly better.

Yes, because this is a 2.1, I would prefer to have the full power of the 3255. While I am very satisfied with the performance and especially the price/performance ratio, we are using this amp for an ongoing outdoor dance and may upgrade our subwoofer to a better but less sensitive driver and could use all the watts available. I have already ventilated it and installed a fan. It would be nice to have the option to switch to a higher voltage power supply and approach the capacity of the 3255. AND I want to encourage Fosi to be clear about their products. They seem to be a good company. This is the only amp Fosi sells that claims to use a 3255 but limits voltage to 36V. On the ones that really can handle 48V, we can be fairly certain that it is a 3255.

But you are also correct - it's fantastic either way and simply (and more cheaply) upgrading to a 36V 10amp PS will still allow more for the sub.

 

[Fosi Audio]

Hi. Thanks for responding! I have never been able to get my browser to open fosiaudio.com. It is blocked ny malwarebytes saying "website blocked due to compromised" So I cannot see the document you linked to. BUT your other site fosiaudioshop.com works fine.

That is where I bought my amp - at Fosiaudioshop.com. The user guide Fosi offers for the BT30D is found here. View attachment 272554

I want to clarify that I am not unhappy with the performance! It is probably the best 325x amp out there for under $100 and the input/ output options are just what we need.

IF the current item sold is truly a 3255, then it would be good to know why it is downrated to the 36V which is the 3251's limit. I have seen that it's capacitors are rated 50V.

Thanks so much for participating in this forum and supporting your excellent product.

Hi, thank you for pointing out our mistakes, we have updated the user manual now, you can get the lastest manual from here.

 

[Fosi Audio]

Honestly - what difference does it make?! Do you really care if you have 2x300W capable chip?!

The chip itself might be rated to 51V, but if other elements, capacitors especially, are not capable to handle that voltage, it is not usable. The amp is rated to 36V.
At that voltage TPA3251 and TPA3255 will be identical, TPA3251 might be even so slightly better.

Yes, the limitation is from the capacitors we used, since so many people want to use 48V power supply to get the max power, I think I will ask our R&D to upgrade to 48V version.

 

[Soulsounds]

Yes, the limitation is from the capacitors we used, since so many people want to use 48V power supply to get the max power, I think I will ask our R&D to upgrade to 48V version.

The existent bt30d pro users how can we proceed?
Because since I got my bt30d pro version I always have the same question:

Why this amplifier cannot accept and use an 48v power supply if it was equipped with dual 3255 chip amp.

Just give us a solution.. thanks you in advanced.

 

[SWSL]

Oh well. In any case, for us existing owners, upgrading to a 36V 9- 10 amp power supply will still allow most of this amp's power and headroom, especially with the (usually) low impedence subwoofer where it matters.. LRS-350-36 does the job.

 

[Timmy89]

Yes, the limitation is from the capacitors we used, since so many people want to use 48V power supply to get the max power, I think I will ask our R&D to upgrade to 48V version.

Please don't tell me this, I just ordered the bt30d pro model these days, and the possible imminent release of an improved version is making me worry, maybe it was better to wait for the improved version... when is its release? I'm tempted to make a return and wait.