Can I modify this High-Pass Filter from 100 Hz to 75 Hz ?

[Sonance'84]

It's labeled exactly like the PCB is laid out. I'll take pics.

And I think the switch is always connected to the treble out...it's a bypass switch that let's full range through to the monitors and it CUTS the sub out , so NO signal goes to the sub.

 

[Sonance'84]

Here's the top of the PCB with markings and you can see the wires going to their respective "out" terminals.

 

[Alan0354]

Yes, I corrected it already. Read post #20 again, you are right, I read the switch wrong originally. Everything is OK.

I gave you the suggestion, the new frequency is only an approximate as your inductor cannot be changed, I just calculate the capacitor only. But it should be close.

 

[Sonance'84]

Yes, you are right, I read the switch wrong. But the filter part is still correct.

I gave you the suggestion, the new frequency is only an approximate as your inductor cannot be changed, I just calculate the capacitor only. But it should be close.

Thank you, I really appreciate it!

I'll experiment with those cap values. You didn't change the resistor value, did you? I noticed that your re-draw has them labeled "100K", where the original were 200K.

 

[Alan0354]

Thank you, I really appreciate it!

I'l experiment with those cap values. You didn't change the resistor value, did you? I noticed that your re-draw has them labeled "100F", where the original were 200K.

I don't think the resistor is part of the filter, it's just to establish a DC path for the input. A lot of preamp has AC couple at the output, without the resistor, you have two capacitor in series and the junction between the two caps is floating and can charge up to high voltage and give people a shock.

I read from your picture, looks like the bands on the resistor is 100K. But you have the unit, you can measure it, a lot of times the red band looks like brown. Best to measure with meter. You can measure across the resistor with no input connected.

 

[Alan0354]

Wait, WHAT AM I THINKING!!!

You don't have to pull the C1 and C2 out, just put small caps across the original caps.

C2 is 0.1uF, you want 0.13uF, just put a 0.033uF across C2.

C1 is 0.047uF, you want 0.063uF, you need 0.016uF, so just get a 0.015uF and solder across C1.


What am I thinking!!!! Must be old age!!!!!

 

[Sonance'84]

Yeah, I couldn't tell if they're brown or red. Either way, I guess it doesn't matter if they're just a DC path.

The published -3 dB point on my monitors is 65 Hz, so I think anywhere between 65 and 75 Hz would be fine for the HPF. I usually have the sub's LPF at 75 Hz and the blend is nice...although, I've never tried anything lower.

 

[Alan0354]

Yeah, I couldn't tell if they're brown or red. Either way, I guess it doesn't matter if they're just a DC path.

The published -3 dB point on my monitors is 65 Hz, so I think anywhere between 65 and 75 Hz would be fine for the HPF. I usually have the sub's LPF at 75 Hz and the blend is nice...although, I've never tried anything lower.

You just have to try, I have no idea how it affect the sound, I just did the verification that you can up the values of the caps and find the values.

I think the best is you buy a few values and try it. Talk is cheap, use your ears to choose.

 

[Sonance'84]

I have a couple caps on hand to try out. If these get me down around 70 Hz, then I'll order more specific values to fine tune it.

add to C1: Vishay 0.01 uF (+/-1%) poly = 0.057 uF
replace C2: 0.15uF = Nitsuka 0.15 uF (+/-10%) poly = 0.15 uF

EDIT:
I also found some TI 0.068 uF poly caps, salvaged from some old JBL x-overs. So, another option would be:

replace C1 with TI 0.068 uF = 0.068 uF
add Vishay 0.01 uF to C2 = 0.11 uF

Would one option be better than the other here?

 

[Alan0354]

Nop, just try the easiest way.

 

[BinaryMike]

Either way, I guess it doesn't matter if they're just a DC path.

As I stated previously, the resistors are critical because they control damping, which has a profound effect on frequency response and transient response characteristics near cutoff.

 

[Sonance'84]

Wait a second...am I'm only adding to the C1 and C2 caps? Or would I add to all 4 caps?

Would C1 and C2 be for the Right channel and C3 and C4 for the Left?

 

[Sonance'84]

As I stated previously, the resistors are critical because they control damping, which has a profound effect on frequency response and transient response characteristics near cutoff.

I guess I didn't mean to make it sound like they aren't important, more that I don't need to mess with their values. Is that a correct assumption, or should those values be played with as well?

 

[UncleBingo]

If you aren't sure, you can use alligator clips to hold the new caps in. I do this with bypass caps on crossovers. Keeps you from soldering and making a mess if things are not copacetic.

 

[gadget73]

As I stated previously, the resistors are critical because they control damping, which has a profound effect on frequency response and transient response characteristics near cutoff.

testing would involve what, square wave check for ringing?

 

[BinaryMike]

I guess I didn't mean to make it sound like they aren't important, more that I don't need to mess with their values. Is that a correct assumption, or should those values be played with as well?

I've built a number of line level L/C crossover circuits, so I can confirm that the damping resistors are critically important. If you don't get this right, then the high-range woofer will likely overshoot or undershoot instead of reproducing transients correctly.

 

[BinaryMike]

testing would involve what, square wave check for ringing?

That should work, but I've seen some bizarre inductor behavior that forced me to go with frequency response analysis instead. It might be possible to avoid this problem by band-limiting the stimulus signal. Usually you're looking for the steepest cutoff slope consistent with zero peaking in the frequency domain, but a gentler slope (Bessel) is often necessary to achieve excellent squarewave response. I have no clue about the designer's preference in this case.

 

[gadget73]

sounds like it would be a good idea to do some testing on the stock design to see how it responds, and then make sure it works the same after altering the crossover points.

 

[keilau]

Need a meter that reads inductance. Resistance readings will not give you a useful measurement. What is printed on the inductors? Might give an idea of the value depending on what's there.

LRC meter are very affordable this day and the accuracy is more than adequate for crossover design. I got this and is very happy with it for under $40.
https://www.ebay.com/sch/i.html?_fr...LCR+meter.TRS5&_nkw=DM4070+LCR+meter&_sacat=0

Just remember that you need to isolate the component from the rest of the circuit when measuring its value. I used it to fine tune the inductor coil and select better matched capacitors. It works wonderful for the money.