KLH 17 & 20 crossover question

[Dchristie]

Hi folks, I have a question regarding the KLH 20 and 17 high pass crossover.

From the schematic, it looks like it is a 6 db crossover with frequency shaping as per the SPDT switch.

What I would like, is for someone to confirm exactly what components are in the signal path for the increase, normal, and decrease positions via the SPDT.

Here is what I think is applicable to each switch position:

1 - Increase position: 2.0 uf cap in parallel with a 3.0 ohm resistor in series with the 8.0 uf cap (the other 3.0 ohm resistor and 7.5 ohm resistor are bipassed).

2 - Normal position: 2.0 uf cap in parallel with 3.0 + 3.0 ohm resistors (6.0 ohms total) in series with the 8.0 uf cap ( only the 7.5 ohm resistor is bipassed).

3 - Decrease position: All 3 resitors ( 3.0 + 3.0 + 7.5 ohm = 13.5 ohms total) are in series with the 8 uf cap. The 2.0 uf caps are not part of the decrease position crossover.

Can anyone please confirm the above and if I am missing something ( highly likely) please provide the correct information.

Thanks,

Dean

[JKent]

Hi Dean

Don't know where I got this or I'd give proper credit, but here is the crossover.

Kent

[Dchristie]

Thanks Kent.

I am looking for some confirmation as to which of the crossover components are involved with each switch position. It is not often that I see extra caps in series in a simple circuit just to provide tweeter adjustment. Normally, level adjustment is provided with various resistors so I am curious as to understand what the 2.0 uf caps do as there must be some frequency shaping going on as well as level adjustment.

I guess another way to ask my question is IF I only wanted to use one of the switch positions for the tweeter in a modified 17 or 20 crossover, what would those components be if I wanted to eliminate the switch. I have made a stab at it with my earlier posting but I am not sure that I have it right and I hoped someone could either confirm or correct my assumptions.

Dean

[JKent]

OK, hold on. My sketch does not match the schematic. Will get back to you on this.

Kent

[dxho]

The switch only controls access to resistors. The caps aren't part of the switch circuitry; they're always 'on'. Or so it looks to me.

Decrease pulls all 3 resistors in; normal bypasses the 7.5 ohm resistor; and increase bypasses one of the 3 ohm resistors and the 7.5 ohm unit.

[RoyC]

Hi Dean and Kent,

I dug out out my notes, and they match the schematic Kent posted. As Kent mentioned above, the drawing was off (the 7.5 ohm resistor was in the wrong place). I see it was removed.

Understanding the (on/off/on) switch is the hard part.

Dean:

1- Increase position: 2uf cap and 3ohm resistor in parallel to each other followed by a series 8uf cap.

2- Normal position: 2uf cap and a 3ohm resistor in parallel to each other followed by a series 3ohm resistor. Here is the tricky part...The other 2uf cap is in parallel with this entire circuit. This is again followed by the series 8uf cap

3- Decrease position: Is the same as the normal position prior to the 8uf cap. A 7.5ohm series resistor is added before the series 8uf cap.

Roy

[JKent]

Thanks Roy.

Yes, I removed that sketch for fear someone may use it as a guide.

Kent

[Dchristie]

Thanks Roy.

So both 2.0 uf caps are part of the circuit for all switch positions except the increase position which is as I originally posted it :

Increase position: 2.0 uf cap in parallel with a 3.0 ohm resistor in series with the 8.0 uf cap (the other 3.0 ohm resistor and 7.5 ohm resistor are bipassed).

Thanks everyone for your assistance!

Dean

[RoyC]

Thanks Roy.

So both 2.0 uf caps are part of the circuit for all switch positions except the increase position which is as I originally posted it :

Dean

Dean,

You posted "The 2.0 uf caps are not part of the decrease position crossover." That statement is not true, as the "Decrease" configuration is the same as the "Normal" position with the exception of the additional 7.5ohm resistor before the 8uf cap.

Also, be aware a 6 ohm resistor cannot be used in these circuits due to the fact that 3 ohms of the 6 are in parallel with one of the 2uf caps.

I think you've got it now, but I'm just clarifying these things based on your first post.

Roy

[Dchristie]

Hi Roy, Yes,I think that I have got it.

My statement "So both 2.0 uf caps are part of the circuit for all switch positions except the increase position which is as I originally posted it" was only meant to be applicable to the increased switch position and not the other 2 positions - poor wording on my part now that I re-read my last post. It is rare to see caps paralleled with resistors in series with another cap for such a simple circuit, but it is nice to see that KLOSS was truly trying to provide some quality in his designs and not just making them as simple as possible just to save costs. I think the Smaller Advent also uses a cap in parallel with a resistor to provide some high frequency shaping as well.

I have a couple of model 17 woofers and also a couple of tweeters and I am thinking about putting together a system but would like to leave out the switch and just use the high pass circuit that sounds best which is what prompted my original question.

Thanks again !

Dean