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Fosi Audio BT30D Pro review

Our R&D responsed Taper A will go up exponentially, and taper B will go up slowly at first and faster in the middle and will go slowly again in the end.

So do you think it is better to go up exponentially?

When designing an audio amplifier, it is generally recommended to use a volume potentiometer with a logarithmic (also known as audio taper or type A) taper. This is because the human ear has a logarithmic response to sound pressure level, so using a logarithmic taper potentiometer allows the volume control to have a more linear response when adjusted.

On the other hand, a linear taper (also known as type B) potentiometer would have a linear change in resistance as the shaft is turned, which would not accurately mimic the response of the human ear to changes in volume. This can result in a volume control that feels uneven or non-linear to the user.

It is worth noting that some applications may require a linear taper potentiometer, such as when a precise, evenly spaced adjustment is needed, or when the potentiometer is being used for a purpose other than volume control. In these cases, a linear taper potentiometer may be more appropriate. However, for most audio amplifier applications, a logarithmic taper potentiometer is the preferred choice.

Again, all these need to be lab tested. The crossover frequency should be accurately marked on the product. Maybe the pot value isnt adapted correctly.
 
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Our R&D responsed Taper A will go up exponentially, and taper B will go up slowly at first and faster in the middle and will go slowly again in the end.

So do you think it is better to go up exponentially?
Human ear sensitivity has logarithmic characteristics. For this reason, the volume pot used to adjust the volume of audio equipment has long been used to have a tapered A characteristic that changes as shown in the figure A to match the characteristics of the human ear. As far as I know, all but the Chinese audio makers use taper A volume pots.
However, many Chinese audio manufacturers do not understand this, and most of their products use a volume pot with a linear characteristic taper B.
As a result, turning the volume knob slightly from zero will result in a very large change in volume. There is also the disadvantage that the R/L-ch gang error is greatly amplified.
Taper B volume pot is used in circuits that require linear characteristics such as voltage adjustment and tone control. Never used for volume control.
 

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A-taper is needed when using it for volume control.
B-taper could be preferred when it is going to be used as input level trimming or gain adjustment (so not volume control) when using various amps.
The sub_vol control for instance it would be logical to use a B-taper for that, assuming this is taken after the volume control.
There are 'tricks' to create a slightly more 'A taper alike' volume control using B taper potmeters but this trick leads to a varying input resistance.
To use this trick mount a resistor of 0.1x to 0.3x the track resistance between the wiper and cold side.
Maybe this has been done already... ?
An advantage of (cheap) linear potmeters is a better balance between L and R tracks.

picture from this website.

Schermafdruk van 2022-12-23 09-22-12.png



It is weird to see these basic design concepts are not known to the designers of these amps.
50k also is very high in value. 10kA to 20kA is high enough and when it is behind an input buffer 5kA is already fine.
 
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It is very disappointing to see that the volume pot for volume control still uses a taper B 50kΩ.
It is common sense in audio technology to use a taper A for the volume pot for volume control.
Manufacturers such as AIYIMA have gradually been modified to use Taper A.
a07 still using B50k :D
 
Human ear sensitivity has logarithmic characteristics. For this reason, the volume pot used to adjust the volume of audio equipment has long been used to have a tapered A characteristic that changes as shown in the figure A to match the characteristics of the human ear. As far as I know, all but the Chinese audio makers use taper A volume pots.
However, many Chinese audio manufacturers do not understand this, and most of their products use a volume pot with a linear characteristic taper B.
As a result, turning the volume knob slightly from zero will result in a very large change in volume. There is also the disadvantage that the R/L-ch gang error is greatly amplified.
Taper B volume pot is used in circuits that require linear characteristics such as voltage adjustment and tone control. Never used for volume control.
Thank you for your explanation, now I think all our products should turn to taper A.
 
Yes, that's right.
A07 Pro uses taper B like A07. Disappointing product.
If one primarily uses a remote control, does the volume control type still make a difference?
 
Probably placebo, but I think BT30D Pro sounds fuller and less harsh than LM4562 Aiyima A07 on my Wharfies 12.2 and 210.
 
While looking at the schematics of the ATS2853 Bluetooth chip, I noticed an ONOFF pin. Could that be wired to a physical switch somehow?
 
Hi all,
I'm trying to see if it's easy to build a 5.1 A/V system with a BT30D and a TB10D
Using a 5.1 decoder like this one : (HD920PRO)
D-codeur-Audio-HD-HD920PRO-5-0-r-cepteur-Dolby-Atmos-DTS-AC3-4K-convertisseur-3D.jpg_Q90.jpg_[1].jpg

Directing 2 front channels to the BT30D => FR, FR and Sub (active or passive)
Directing 2 back channels to the TB10D => RR, RL

That would be a 75+60+110 = 245€ system.
 
i had a BT30D Pro to play with for a week, before installing it into a friend's sound system. It's a fantastic sounding amp, the best i've come across in that price range ... and i got it on sale. Could care less whether the pots are logarithmic or linear.
 
While looking at the schematics of the ATS2853 Bluetooth chip, I noticed an ONOFF pin. Could that be wired to a physical switch somehow?

Yes, it can be connected to external touch switch.
 
i had a BT30D Pro to play with for a week, before installing it into a friend's sound system. It's a fantastic sounding amp, the best i've come across in that price range ... and i got it on sale. Could care less whether the pots are logarithmic or linear.
So glad you like it, we have a BT20A PRO which uses taper A to achieve linear sound, and will send to @amirm to test
 
Hi all,
I'm trying to see if it's easy to build a 5.1 A/V system with a BT30D and a TB10D
Using a 5.1 decoder like this one : (HD920PRO)
View attachment 255565
Directing 2 front channels to the BT30D => FR, FR and Sub (active or passive)
Directing 2 back channels to the TB10D => RR, RL

That would be a 75+60+110 = 245€ system.
Have you tried this setup?
 
Human ear sensitivity has logarithmic characteristics. For this reason, the volume pot used to adjust the volume of audio equipment has long been used to have a tapered A characteristic that changes as shown in the figure A to match the characteristics of the human ear. As far as I know, all but the Chinese audio makers use taper A volume pots.
However, many Chinese audio manufacturers do not understand this, and most of their products use a volume pot with a linear characteristic taper B.
As a result, turning the volume knob slightly from zero will result in a very large change in volume. There is also the disadvantage that the R/L-ch gang error is greatly amplified.
Taper B volume pot is used in circuits that require linear characteristics such as voltage adjustment and tone control. Never used for volume control.

Hi, thank you for your explanation, now we are developing the BT20A PRO which adopts Taper A, and we will see the feedbacks of our customers.
Thank you again for your suggestion, and if you want a sample, just leave the delivery address and we will be so proud to invite you to test and give us some suggestions.
Kind regards,
 
So glad you like it, we have a BT20A PRO which uses taper A to achieve linear sound, and will send to @amirm to test
Good news, we like companies that are keen to improve their devices.
In case taper A give better results (which should) will you then sell taper A for TB30D Pro / TB10D or give us parts number to buy them ?
Thanks
 
Hi all,
I'm trying to see if it's easy to build a 5.1 A/V system with a BT30D and a TB10D
Using a 5.1 decoder like this one : (HD920PRO)
View attachment 255565
Directing 2 front channels to the BT30D => FR, FR and Sub (active or passive)
Directing 2 back channels to the TB10D => RR, RL

That would be a 75+60+110 = 245€ system.
What do you do for a centre channel? Or will you run it in 4.1 mode?
 
Hi all,
I'm trying to see if it's easy to build a 5.1 A/V system with a BT30D and a TB10D
Using a 5.1 decoder like this one : (HD920PRO)
View attachment 255565
Directing 2 front channels to the BT30D => FR, FR and Sub (active or passive)
Directing 2 back channels to the TB10D => RR, RL

That would be a 75+60+110 = 245€ system.
What's your centre speaker?
 
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