Active filter power supply problems

[rayma]

I'll use a crossover from the same page: I'll still have some questions regarding single supply operation.

That will be more complicated, so finish designing the other board first to avoid confusion.

 

[rayma]

I'll use a crossover from the same page:

Here is a schematic for one channel. Op amp power supply connections not shown.

 

[Xappys]

Already made the modified subsonic filter board. Works as charm. Contacted Rod Elliott to consult a bit about filter's resistors (47K and 220K). Changed 47K to 23K for a 3.5dB boost at 80Hz and 220K to 270K for slighly lower -3dB point. All is fine except that I didn't take into account before that 3.5dB boost is more than double the power, so my woofer distorts earlier and I don't even wanna look to the tweeter . I guess I'll go back to 47K resistors or replace tda8932 with something beefier and make the active crossovers in late summer. Thanks again .

 

[Rick PA Stadel]

Hi Xappys,

All excellent tips and recommendations so far, but I would hope you might reconsider the choice of LM358:
- the input current is too high for 220K/270K bias, and is Sourcing, not Sinking
- should really be JFET input at these impedances
- the change to frequency response may be minimal, but you may not want it
- the LM358 is an older design - newer designs sound better

The usual reason for selecting an op amp 'designed for single supply operation' is to allow input common mode range to include one rail or the other -- but that is rarely useful for audio since the signal centers around some reference level.

Your work so far is excellent otherwise. I hope it continues to go well for you.

Regards,
-Rick

 

[Xappys]

Hi Xappys,

All excellent tips and recommendations so far, but I would hope you might reconsider the choice of LM358:
- the input current is too high for 220K/270K bias, and is Sourcing, not Sinking
- should really be JFET input at these impedances
- the change to frequency response may be minimal, but you may not want it
- the LM358 is an older design - newer designs sound better

The usual reason for selecting an op amp 'designed for single supply operation' is to allow input common mode range to include one rail or the other -- but that is rarely useful for audio since the signal centers around some reference level.

Your work so far is excellent otherwise. I hope it continues to go well for you.

Regards,
-Rick

Thank you for the tips. I would have most likely chosen a better op-amp, but only after getting all the parts ready I realised that single supply op-amp made more work than a simple dual supply op-amp would. I don't completely understand the concept of the modifications I did by following the tips of diyAudio community, but I guess it's a virtual ground to operate from DC supply and it would have been easier to make using dual supply op-amp? Would I need some alterations if I'd change to dual supply op-amp (still powering using DC supply) in the board as it is now (apart from pinout of legs obviously)? Also, is there anyway to reduce op-amp (subsonic filter) turn on thump?