Fosi Audio BT20A Pro Amplifier Review

[Fosi Audio]

Hi Fosi
Another area of interest for you maybe the multi channel AV amp market with this level of output. Then a higher output model. The design basis for a high power design could be argued considering the impending release of Dirac's new ART version of room correction which will potentially move Home theatre design towards more full range higher power speakers In all bed layer locations. This will mean some traditional small surrounds will likely be retired and replaced with larger speakers needing higher power to effectively contribute to the overall ART requirements. So a Multi channel higher power amp could be a design option to consider in the future:
low heat output;
stable design;
Switchable balanced/unbalanced inputs;
Option for volume control ;
12v trigger;
Soft start;
Low profile - Rack mount option;
Start with existing output design
Add a high power - designed for larger floorstanding or larger in wall speakers

For context - Storm Audio will launch ART first this year then followed by other manufacturers after October ( according to current press releases) so main stream options by the end of the year.
There has been a few opinions sofar that claim it has significant improvements over current offerings but will benefit from full range larger higher powered speakers for the co- optimisation duties rather than smaller surround speakers.

This may lead home theatre owners to consider replacing small surround / effects speakers and upgrade amps for these channel's power requirements as well.

Could be done with seperate amps but a neater solution would be a single unit.

Hi, thank you for your great suggestions.

Yes, we will consider the multi channel AV amp, in fact we are trying to develop such amps, usually it is 5.1 channel for home theatres, so our amp need to support Dolby so that we can decode the 5 channels, but we are encountering the Dolby certification right now.

Regarding your Switchable balanced/unbalanced inputs, I have one question, why not HDMI inputs for home theatre setups? Who will decode Dolby?

 

[Fosi Audio]

Hi Fosi
Another area of interest for you maybe the multi channel AV amp market with this level of output. Then a higher output model. The design basis for a high power design could be argued considering the impending release of Dirac's new ART version of room correction which will potentially move Home theatre design towards more full range higher power speakers In all bed layer locations. This will mean some traditional small surrounds will likely be retired and replaced with larger speakers needing higher power to effectively contribute to the overall ART requirements. So a Multi channel higher power amp could be a design option to consider in the future:
low heat output;
stable design;
Switchable balanced/unbalanced inputs;
Option for volume control ;
12v trigger;
Soft start;
Low profile - Rack mount option;
Start with existing output design
Add a high power - designed for larger floorstanding or larger in wall speakers

For context - Storm Audio will launch ART first this year then followed by other manufacturers after October ( according to current press releases) so main stream options by the end of the year.
There has been a few opinions sofar that claim it has significant improvements over current offerings but will benefit from full range larger higher powered speakers for the co- optimisation duties rather than smaller surround speakers.

This may lead home theatre owners to consider replacing small surround / effects speakers and upgrade amps for these channel's power requirements as well.

Could be done with seperate amps but a neater solution would be a single unit.

I understand how important that my amp will be on and off along with TV, and I think the eARC HDMI can do this thing and yes, the 12V trigger also serves that purpose, right?

By the way, can I know your setups for your home theatre now?

 

[Talisman]

Hi, thank you for your great suggestions.

Yes, we will consider the multi channel AV amp, in fact we are trying to develop such amps, usually it is 5.1 channel for home theatres, so our amp need to support Dolby so that we can decode the 5 channels, but we are encountering the Dolby certification right now.

Regarding your Switchable balanced/unbalanced inputs, I have one question, why not HDMI inputs for home theatre setups? Who will deode Dolby?

If you continue to be so quick to adapt to consumer demands, you could very quickly become my favorite producer.
HDMI input would be great, but with preouts

 

[webmst007]

Ok so background first- I have had numerous avrs over many years and currently run an Emotiva rmc1 with a. Marantz 7703 backup with a 7.4.4 system - I have built large panel electrostatics for fun over many years ( EE and Computer engineering trained) although PA and live mixing were my first love. Plus digital editing along the way .
So back to the design -
If you plan on a preprocessor or an avr design - I am sure you are aware of the large scale integration work, testing, and licensing required. Or simply buy/ co-develop with an existing provider as a partner for all the DAC/ processing/switching etc etc.
The additional piece is the multi channel amp to service the "seperated" market whereby users divide duties of an avr to preprocessor and various amp configurations. So we now have 2,3,4,5,7,9 and 11 channel amps all available at various price points.

So if you design an avr as an "all in one" device you will need to consider the HDMI as well as other input channels ( USB, optical, analogue, XLR etc etc). So the AVR follows typical offerings from Sound United ( Denon/Marantz etc) plus amplifier modules plus pre outs for the additional channels people may want to add.
Perhaps your main domestic Chinese/Asian market is 5.1 AVR's.
Most AVR's in the EU/US/AUS/Japan markets carry 7 bed layer channels plus more add-on channel options for larger setups (Dolby Atmos,DTS etc).
In larger home theatres, splitting the preprocessor and amp sections allows seperate upgrade paths and more flexibility in overall home theatre designs.
Historically AVR design has been a minefield for small scale manufacturers due to integration and fabrication/production challenges, and still is for some.

 

[webmst007]

To your question regarding switching XLR/ RCA in a multi amp design. Some pre processors and AVRs offer all balanced or both ( XLR/RCA) audio outputs for use with outboard amps.

 

[Guddu]

Hi, thank you for your great suggestions.

Yes, we will consider the multi channel AV amp, in fact we are trying to develop such amps, usually it is 5.1 channel for home theatres, so our amp need to support Dolby so that we can decode the 5 channels, but we are encountering the Dolby certification right now.

Regarding your Switchable balanced/unbalanced inputs, I have one question, why not HDMI inputs for home theatre setups? Who will decode Dolby?

Seems like it goes into AVR or audio receiver category if you look to have HDMI input and more.
There are a few devices like nVidia Shield, apple TV, a PC with multichannel out etc. that could decode DD/DTS and output PCM on HDMI/Optical.
keeping bells and whistles aside, A multichannel TPA325x power amplifier could be a cost effective solution for many to use with multichannel DACs or pre-out from AVR.
If you add Optical input with DD/DTS decode then could be a simpler alternative to entry level AVRs provided performance is close to your TPA325x amps.

 

[ClosDeLaRoche]

@Fosi Audio
I'm glad to see that you're responding to our suggestions. If I may offer two suggestions for power amps and one for DACs:

Power Amps:
Please offer a High Pass Filter for the main speakers and a sub-out (pre-out that adjusts with the volume knob works too, but line-out that is independent of the volume knob is not good for connecting to a sub). Multiple settings for the crossover frequency and slope is great, but if you had to offer just one setting I'd recommend 80hz at a -24db per octave slope. I have a powered subwoofer with its own low pass filter, but finding a stereo speaker amp with a high pass filter seems nearly impossible!

Second, if you're offering a display on the amp then please allow the user to turn off the screen. A feature where the screen turns itself off after 5 seconds is best. I will not buy anything with a screen that is always on, it's so distracting when watching movies. Also, bright blue LEDs are the worst.

DACs:
If your DAC uses an ESS chip then please give the user the option to adjust the DPLL setting. If the DPLL setting is too strict, then the DAC will be unusable with certain TVs with high-jitter optical outputs.

 

[Joey]

@Fosi Audio
I'm glad to see that you're responding to our suggestions. If I may offer two suggestions for power amps and one for DACs:

Power Amps:
Please offer a High Pass Filter for the main speakers and a sub-out (pre-out that adjusts with the volume knob works too, but line-out that is independent of the volume knob is not good for connecting to a sub). Multiple settings for the crossover frequency and slope is great, but if you had to offer just one setting I'd recommend 80hz at a -24db per octave slope. I have a powered subwoofer with its own low pass filter, but finding a stereo speaker amp with a high pass filter seems nearly impossible!

Second, if you're offering a display on the amp then please allow the user to turn off the screen. A feature where the screen turns itself off after 5 seconds is best. I will not buy anything with a screen that is always on, it's so distracting when watching movies. Also, bright blue LEDs are the worst.

DACs:
If your DAC uses an ESS chip then please give the user the option to adjust the DPLL setting. If the DPLL setting is too strict, then the DAC will be unusable with certain TVs with high-jitter optical outputs.

hi bro, DPLL setting? what's mean

 

[Joey]

If you continue to be so quick to adapt to consumer demands, you could very quickly become my favorite producer.
HDMI input would be great, but with preouts

preout? what's the mean

 

[Graham849]

hi bro, DPLL setting? what's mean

Hope this helps https://erg.abdn.ac.uk/users/gorry/course/phy-pages/dpll.html

 

[Graham849]

preout? what's the mean

Hope this helps

What is a Pre-Out on an A/V Receiver and When Would You Use It?

Receiver’s can be complicated devices, and it’s easy to lose track of what specs and ports you need. One feature some receivers have–a Pre-Out–can be …

thehometheaterdiy.com

 

[DavidM1]

hi bro, DPLL setting? what's mean

Check out the SMSL C200 and probably a few other SMSL DACs.

 

[ClosDeLaRoche]

Check out the SMSL C200 and probably a few other SMSL DACs.

Yeah I own a C200. My Cambridge CXA61 has one too, although theirs is a simple "high" or "low".

@Joey It's jitter-reducing tech on ESS chips. If it's set high the DAC will have trouble locking onto signals from high-jitter sources, resulting in audio drop-outs. Many TVs quality as a high-jitter source.

Basically, if DPLL is set too high the DAC will be incompatible with some TVs.

 

[renaudrenaud]

Thank you @Fosi Audio for this amp. Bought yesterday and waiting for it. Gonna use it with a diy project. Cool to have something low price with respectable measurements!

 

[DavidM1]

Yeah I own a C200. My Cambridge CXA61 has one too, although theirs is a simple "high" or "low".

@Joey It's jitter-reducing tech on ESS chips. If it's set high the DAC will have trouble locking onto signals from high-jitter sources, resulting in audio drop-outs. Many TVs quality as a high-jitter source.

Basically, if DPLL is set too high the DAC will be incompatible with some TVs.

Yes, although it is actually a lower value in the C200 dac dpll setting for use with sources that have less jitter. The manual recommends a high dpll value for some problematic tvs.

 

[ClosDeLaRoche]

preout? what's the mean

It's an analog output, usually RCA or 3.5mm, with power output matching the volume knob on the device. This is best for hooking up to a subwoofer if the sub has its own crossover.

A 'line-out' is the same but its output is always at full power, independent of the volume knob. This is best for hooking up to another amp like a headphone amp.

 

[ClosDeLaRoche]

Yes, although it is actually a lower value in the C200 dac dpll setting for use with sources that have less jitter. The manual recommends a high dpll value for some problematic tvs.

Thanks for the correction

 

[Fosi Audio]

Ok so background first- I have had numerous avrs over many years and currently run an Emotiva rmc1 with a. Marantz 7703 backup with a 7.4.4 system - I have built large panel electrostatics for fun over many years ( EE and Computer engineering trained) although PA and live mixing were my first love. Plus digital editing along the way .
So back to the design -
If you plan on a preprocessor or an avr design - I am sure you are aware of the large scale integration work, testing, and licensing required. Or simply buy/ co-develop with an existing provider as a partner for all the DAC/ processing/switching etc etc.
The additional piece is the multi channel amp to service the "seperated" market whereby users divide duties of an avr to preprocessor and various amp configurations. So we now have 2,3,4,5,7,9 and 11 channel amps all available at various price points.

So if you design an avr as an "all in one" device you will need to consider the HDMI as well as other input channels ( USB, optical, analogue, XLR etc etc). So the AVR follows typical offerings from Sound United ( Denon/Marantz etc) plus amplifier modules plus pre outs for the additional channels people may want to add.
Perhaps your main domestic Chinese/Asian market is 5.1 AVR's.
Most AVR's in the EU/US/AUS/Japan markets carry 7 bed layer channels plus more add-on channel options for larger setups (Dolby Atmos,DTS etc).
In larger home theatres, splitting the preprocessor and amp sections allows seperate upgrade paths and more flexibility in overall home theatre designs.
Historically AVR design has been a minefield for small scale manufacturers due to integration and fabrication/production challenges, and still is for some.

Thank you for such a detailed explanation, yes, develop an "all in one" device is a big challenge, but it is much more convenient for home theatres, I mean just a multichannel amplifier without decoder can be a good solution for home theatres too and we indeed are considering to develop such amps. But still we think an "all in one" device is a must for us.

And if we want to develop an "all in one" device, do you think the ability to handle videos is important? Cause I find lots of AVRs that have HDMI Out.

 

[Fosi Audio]

Seems like it goes into AVR or audio receiver category if you look to have HDMI input and more.
There are a few devices like nVidia Shield, apple TV, a PC with multichannel out etc. that could decode DD/DTS and output PCM on HDMI/Optical.
keeping bells and whistles aside, A multichannel TPA325x power amplifier could be a cost effective solution for many to use with multichannel DACs or pre-out from AVR.
If you add Optical input with DD/DTS decode then could be a simpler alternative to entry level AVRs provided performance is close to your TPA325x amps.

Thank you, your advice has been written down.

 

[Fosi Audio]

@Fosi Audio
I'm glad to see that you're responding to our suggestions. If I may offer two suggestions for power amps and one for DACs:

Power Amps:
Please offer a High Pass Filter for the main speakers and a sub-out (pre-out that adjusts with the volume knob works too, but line-out that is independent of the volume knob is not good for connecting to a sub). Multiple settings for the crossover frequency and slope is great, but if you had to offer just one setting I'd recommend 80hz at a -24db per octave slope. I have a powered subwoofer with its own low pass filter, but finding a stereo speaker amp with a high pass filter seems nearly impossible!

Second, if you're offering a display on the amp then please allow the user to turn off the screen. A feature where the screen turns itself off after 5 seconds is best. I will not buy anything with a screen that is always on, it's so distracting when watching movies. Also, bright blue LEDs are the worst.

DACs:
If your DAC uses an ESS chip then please give the user the option to adjust the DPLL setting. If the DPLL setting is too strict, then the DAC will be unusable with certain TVs with high-jitter optical outputs.

Wow, HPF, sub-out, Multiple settings for the crossover frequency, got it.

How much power do you want?