Question: About BPA200 schematic

[Mrpong]

Refering to the schematic in the page 12th of the Bridge/Parallel Amplifier (BPA-200) documentation, I have some questions as follows:-

(1) At U1 and U2, the signal is sent to non-inverted input PIN, but at U3 and U4, the signal is sent to inverted input PIN. What is the purpose of this topology?

(2) Let's focus on feedback, U1 and U2 uses 20.5Kohms. However, the feedback of U3 and U4 uses 21.5Kohms. OK this may be just a little but why doesn't it use the same value?

(3) The circuit uses 4.7uf (Ci1, Ci2, Ci3, and Ci4) as coupling capacitors, doens't it? So we can change it to 2.2 or 3.3uf?

(4) Are there any ways to tweaking up this National's design?

(5) The document suggests using servo to eliminate DC offset. Can we neglect these servo stuffs?


Thank you !!

 

[SpittinLLama]

1 - This is Bridge/Parallel, one side of bridge is running non-inverting, other side is running inverting. This makes a bridge. The chips configured the same are in parallel.

2 - Gain for inverting, Av = -Rf/Ri, non-ionverting gain, Av = 1+ Rf/Ri, hence the difference to get equal gain on both sides of the bridge.

3- I don't see those on page 12.

4 - Yes, add more in parallel or add servos

5 - yes, see the circuit on page 15.

-SL

 

[Mrpong]

Thank you. Just another basic question: Can we apply this circuit to LM3875 instead of LM3886?

 

[sreten]

Thank you. Just another basic question: Can we apply this circuit to LM3875 instead of LM3886?

Hi,

yes you could but the limitations into lower impedance loads will be the
same as the limitations of a single LM3875 compared to a single LM3886.

In other words why would you ?

🙂/sreten.

 

[Mrpong]

Hi,

yes you could but the limitations into lower impedance loads will be the
same as the limitations of a single LM3875 compared to a single LM3886.

In other words why would you ?

🙂/sreten.

Hi...Thank you your comment. It's because I already have a lot of LM3875.

 

[sreten]

Hi...Thank you your comment. It's because I already have a lot of LM3875.

Then you could consider parralleling for 4ohm loads.

For bridging you should consider 3 or 4 in parrallel per side,
i.e. for a BP200-u-like use 6 or 8 LM3875s per channel.
Some advantages in the extra heatsink contact area.

🙂/sreten.