Passive line-level xover, will these caps work?

[cgallery]

Hi, I'm moving ahead a bit with my passive line level crossover.

I'm using these instructions:
TLS.org | Passive Line-Level Crossover

Target high pass frequency: 300-Hz, 2nd order.

Target low pass frequency: 300-Hz, 2nd order.

Amplifier input impedance of my two amplifiers: 69k.

I'm using the spreadsheet to compute values, and I'm a little confused.

The low pass seems simple enough, but the high-pass is a little less clear.

I have to specify an R1. If I leave the default of 10k, with a 69k input impedance and 300-Hz xover, I get an R2' "not possible" (cell E18).

If I change the R1 values to 5k, I get 181.6(k).

But what I don't understand is the Ramp and the difference between "R2" and "R2'" (note the apostrophe). What does "Use Ramp as R2 in HP" mean exactly?

Also, the spreadsheet has an E19 cell with another capacitor value and a note "(no R2")," what does that mean?

Also, I'm getting capacitor values ranging from .011uf to .11uf. In those sorts of values, Digi-Key has a good selection of Panasonic metallized film with 3% tolerances for fairly low bucks, those should work I assume?

Like these:
ECW-F6113HL Panasonic Electronic Components | Capacitors | DigiKey

If anyone can provide any inside on the 2nd order high pass I'd be very grateful.

At least I have the RCA jacks mounted on the little enclosure, so there is that.

 

[planet10]

In the HP filter you need 2 C(series)R(shunt) sections. In the 2nd one it makes sense to use the input impedance of the amp as the second R (Ramp). R1 should be at least 1/10th Ramp.

R2 prime (R2’) is the net impedance of Ramp and R2, This is for the theory part. Leave R2 out and just use Ramp.

Those caps should be fine.

Do note that a 2nd order PLLXO is “droopy”.

dave

 

[cgallery]

In the HP filter you need 2 C(series)R(shunt) sections. In the 2nd one it makes sense to use the input impedance of the amp as the second R (Ramp). R1 should be at least 1/10th Ramp.

R2 prime (R2’) is the net impedance of Ramp and R2, This is for the theory part. Leave R2 out and just use Ramp.

Those caps should be fine.

Do note that a 2nd order PLLXO is “droopy”.

dave

Thanks for your help.


By "droopy," do you mean the slops are more shallow than expected?

 

[planet10]

By "droopy," do you mean the slops are more shallow than expected?

Sort of. The roll-off is as expected, but it is not as steep a slope as a 2nd order active which either has feedback or 2 1st order buffered stages to keep the curve up at the corner.

dave

 

[cgallery]

In the HP filter you need 2 C(series)R(shunt) sections. In the 2nd one it makes sense to use the input impedance of the amp as the second R (Ramp). R1 should be at least 1/10th Ramp.

R2 prime (R2’) is the net impedance of Ramp and R2, This is for the theory part. Leave R2 out and just use Ramp.

Those caps should be fine.

Do note that a 2nd order PLLXO is “droopy”.

dave

Okay I'm sorry for the follow-up Q.

So for the high pass, I'm using three components. A capacitor in series, followed by a shunt resister, followed by a capacitor in series, and then no final resister because I'm using the impedance of the amp?

And if R1 has to be 1/10 of Ramp, and Ramp is 69k, then R1 has to be 6.9k or greater. Is 6.9k or 7k a commonly available resister? Have any recommendations for a value to pick here for R1 with a 69k amp?

I'm sorry, I very much appreciate the help.

 

[planet10]

...three components. A capacitor in series, followed by a shunt resister, followed by a capacitor in series, and then no final resister because I'm using the impedance of the amp?

Yes

then R1 has to be 6.9k or ...

or less. 5k is convenient.

dave

 

[cgallery]

Thank you, again.

In terms of the slopes, I had tried the FMOD product. I was using the 200-Hz models, but it appears their target amp impedance is 22k. I was surprised to see how little they claim the frequency will vary when used with amps of different impedances, it sure doesn't seem to match the calculators I've found.

I was getting tons of LF energy to my full-range satellite drivers, when compared to my Rolls 12db/octave electronic crossover.

So I figured I'd make a purpose-built unit intended for 69k amps. I just feel like this will work a lot better than the FMOD.

The Rolls is kinda noisy sometimes. I tap the top of it and the noise clears up, I think there might be a bad solder joint. I figured I'd try this passive crossover and then maybe give the Rolls a once-over.

Again, thanks for all the help!

 

[planet10]

The F-Mods are a poor implementation of a PLLXO. It uses R2 and has to guess what Ramp may be. The load for the preamp becomes small so the pre-amp has to have a really low output impedance.

dave

 

[cgallery]

I've included a screenshot, I'm hoping to order my parts this evening.

For low-pass, I should use a 5k series resister, then a .11uf shunt cap, then a 50k series resister, and finally a .011uf shunt cap.

For high-pass, I should use a .11uf series cap, then 5k shunt resister, then .018uf series cap, and that is it.

I know I'm belaboring this but it is because the spreadsheet has 7.6886 nf in E19 and I'm making sure I'm not supposed to substitute that for the 2nd cap. in the high pass?

 

[cgallery]

Oh, also anything special in terms of wattage on the resisters?


Also, metal film, thin film, thick film, wire-wound any suggestions?

 

[cbdb]

Those caps from digikey are 630volt way over kill. That makes them larger and more expensive . Find some 30v or so caps instead.

 

[cgallery]

Those caps from digikey are 630volt way over kill. That makes them larger and more expensive . Find some 50v or so caps instead.

Suggestions? I don't see they carry much else in the values needed, except for maybe surface mount.

They don't seem that expensive to me, but what do I know?

 

[cgallery]

Checked Mouser and they have smaller/less expensive Panasonic parts.

Less expensive options for 5k/50k resisters as well.

Guess I'll be ordering from Mouser.

 

[DUG]

Oh, also anything special in terms of wattage on the resisters?


Also, metal film, thin film, thick film, wire-wound any suggestions?

Not thick film.

 

[cgallery]

Can anyone confirm my values in post #9?

 

[planet10]

That looks like it will work.

Forth watt should be fine, pick your poison for the Rs. I used what was in the drawer.

dave

 

[cgallery]

Okay got it, once again thanks for all the help.