caps for 4/8ohm with TA2020

sfasf

Member
2011-10-28 10:05 pm
TA2020 datasheet (7.1) says output caps Co and Cz should be 0.47uF for 4ohm speakers and 0.22uF for 8ohm speakers. What does this affect? and how important is it?

I ask as I am making a board that I want to be suitable for use with either 4 or 8 ohm speakers, and having to include 2x the output caps and switching won't be trivial. Should I just use the 4ohm values? (most boards seem to do this and I haven't heard of problems with anyone with 8 ohm speakers). Or use something inbetween? or ??

[As an aside; the datasheet actually says Cz should be 0.22uF for 4ohm, but changed to 0.22uF for 8ohm. I take it this is an error, and it should be 0.47uF for a 4ohm load?; this is also how it is shown on the evaluation board's datasheet (7.03). Are there any other areas where I should stray from the datasheets?]
 

sfasf

Member
2011-10-28 10:05 pm
right.. thanks.. so what would be the effect of using the 0.47uF caps with 8 ohm speakers be compared to the recommended settings; would it cut off the high frequencies or let higher frequencies pass through? (or am i misunderstanding?)

What would be the negative results from allowing higher-than-specced frequencies through?
 

sfasf

Member
2011-10-28 10:05 pm
Thanks. What would be the issue if more HF got through and radiated? Since it is presumably above the audible range? Might it cause damage to tweeters?

Do you have a opinion of what values to use? (it's hard to know where the default cutoff lies to know how much headroom exists.. would it be the gentle roll off that starts at 6kHz [around -0.5db @ 18kHz], or would the cutoff be much more immediate where it occurs?)
 
HF radiating could interfere with other equipment.

You could try using a capacitor in between the two values and compromise.

You really need audio to be cut off above 30KHz so you dont lose top to the tweeters.

My 2092 based class d amp has about 10 volts of carrier left to the speaker and that's using the app note circuit as a basis for my own design.