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Old 19th April 2013, 04:29 PM   #1
mortron is offline mortron  Canada
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Default PLLXO - Am I doing this right?

So this morning I woke up with the intention of plugging in some numbers and heading to the electronics shop to get resistors and caps to build a PLLXO. After playing with the sheet in the past, I gave it little thought.

This morning I am more concerned

So after using the values with my amps and setting the XO points, I got my results. I am planning to use both second order filters. The impedance of my HP amp is only 25Kohm... and the bass amp is 10Kohm. I see the LP amp is okay, but the 25K is too low? So my can of worms goes like this:

-The stuff in the far right column confuses me and makes little sense.

-When it says use Ramp for R1 or R2 in HP, does that mean, no resistor at all, or that I need a resistor with the same value as my amps input?

-Can I make this with 1 input, 3 outputs: one with a full range output, one with HP and one with LP?

The sheet did not make clear what the drawbacks would be to the impedance of the HP amp, and am not sure how to compensate.
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Last edited by mortron; 19th April 2013 at 04:47 PM.
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Old 19th April 2013, 07:57 PM   #2
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2nd order PLLXO, particularily HP, can only be used in a much more restrictivw set of circumstances.

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Old 19th April 2013, 08:06 PM   #3
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Quote:
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-When it says use Ramp for R1 or R2 in HP, does that mean, no resistor at all, or that I need a resistor with the same value as my amps input?
In the HP circuit use Ramp as R1 (1st order) or R2 (2nd order) as the resistor needed in the circuit.

Unless your pre has a really low output impedance, and lots of drive, less than 50k amp input for a 2nd order filter is an issue.

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Old 19th April 2013, 09:22 PM   #4
mortron is offline mortron  Canada
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Thanks Dave...

My gain on the pre is 7db and output impedance about 2000ohm. Here are specs from a review:

Review: Bottlehead Quickie tube preamp | Sound and Vision Magazine

So if I am understanding, the ramp as R1 would mean if my amps input is 25kohm, I'd use a resistor with the same vale as R1?

And in my situation, what would my options be with a PLLXO? Could first order work? I am following xo points from a thread (mjk) using slightly different drivers than I have. Should I try for a first order? There is a rising response about 250-300hz on my driver in its baffle. (Visaton B200 and dual Goldwood 1858 Hframe per side.)

Im building the hframes Sunday, so have all day today and tomorrow to mull over a temporary option. Thanks.
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Old 19th April 2013, 11:15 PM   #5
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Quote:
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My gain on the pre is 7db and output impedance about 2000ohm.
We are interested in grunt, not gain. 2k output impedance is high.

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Old 20th April 2013, 01:09 AM   #6
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What spec correlates to grunt? And high output impedance is bad? It's closer to 1.88K.
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Old 20th April 2013, 03:55 PM   #7
mortron is offline mortron  Canada
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Dave,
Given my restrictions, could I use a 2nd order low pass as described in the spreadsheet, and a 1st order on the high pass, and add a first order passive speaker level xo (to the hp) to get the phase right?
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Old 20th April 2013, 06:15 PM   #8
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Dave,
Given my restrictions, could I use a 2nd order low pass as described in the spreadsheet, and a 1st order on the high pass, and add a first order passive speaker level xo (to the hp) to get the phase right?
You could.

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Old 20th April 2013, 06:17 PM   #9
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What spec correlates to grunt? And high output impedance is bad? It's closer to 1.88K.
grunt = power. Voltage & Current.

Low output impedance <100 ohms

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Old 20th April 2013, 08:51 PM   #10
mortron is offline mortron  Canada
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Voltage 36v

I got bits at the shop... They were cheap. Hopefully the caps I got will suffice until I can buy nicer ones.


If I am implementing the values in my original post above, R1 at 10k resistor, I have that, but I messed up and R2 for the 1st order HP I don't have the 16.6667k resistor required, but have two 25k resistors, which is rAmp. Can I use these in the R2 position of the hp? There is a note at bottom but not sure if that applies here.


As well, do I just run the input to a common point and each filter hp/lp branches off from there? Thanks
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