Two B1 and a crossover

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#21
that Pllxo article omits a few cases that need component value corrections.
Rs (the source output impedance) when feeding the High Pass and when feeding the Low Pass. The Low Pass is easy. R1+Rs = R'1

How does one correct the High Pass component values for a Rs<>0r0?

What does one do when the Low Pass has a resistance (Ramp) parallel to C1?
 
#22
Floric said:
But this is an active Sallen-Key filter...
Click to expand...

I think this is still relevant no matter what type of filter is used

"I strongly suggest that resistor values should be not lower than 2k2 and no higher than 20k - this is a reasonable compromise between opamp loading and noise. " Rod Elliott

Maybe you didn't read it carefully.
 
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#23
AndrewT said:
that Pllxo article omits a few cases that need component value corrections.
Rs (the source output impedance) when feeding the High Pass and when feeding the Low Pass. The Low Pass is easy. R1+Rs = R'1
Click to expand...

I measured my ones after tey were built, I think you may omit it.

AndrewT said:
How does one correct the High Pass component values for a Rs<>0r0?
Click to expand...

I think that is not necessary because Rs is in series with C1, so no voltage-divider is built.

AndrewT said:
What does one do when the Low Pass has a resistance (Ramp) parallel to C1?
Click to expand...

It is in my opinion in series with C1. Even if there is an output impedance, there is still a voltage source.


Edit: Had overseen the questions.
 
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#24
thanh1973 said:
I think this is still relevant no matter what type of filter is used

"I strongly suggest that resistor values should be not lower than 2k2 and no higher than 20k - this is a reasonable compromise between opamp loading and noise. " Rod Elliott

Maybe you didn't read it carefully.
Click to expand...

I read the article, some years ago. If you read Linkwitz, you will find anything around 10k.

Lower values are good for lower noise. But we are talking about a (kind of) b1 and not about an Opamp that would drive 600R without any problems.
 
#26
Ok sow if i use something between 10 and 20 kohm it should be fine.
And i dont need to calculate with the input and output of the B1.

I will calculate some and see if can get any good standard values for the components.

Thanks everyone for your help.
 
#29
there is a suggestion from the designer that the 1k was chosen to ensure stability into any load.
Some have suggested trying as low as 220r, conditional on checking stability.

Eliminating the output resistor and feeding into one or a pair of filters never entered the discussion.
 
#30
I am also interested in this XO

I just read this topic, as i was looking for an opamp less crossover for my Hiquphon+seas W15cy001 active setup. I will be using gainclone as amps and i had the same idea, with using PLLXO's between B1 or other buffers.
So more information please, who has build something like this? Can you post some pictures & shematics.
Could i also use this setup for balanced pre amp and power amp?
thanks.
 
#33
Hi,

regarding the input impedances of the filter networks, first approximation is R1. When driven by a B1 it should be higher than 5k (at least).

Regarding the output impedance, if you use a buffer after the filter, it is not of matter because the input impedance of a B1 with a gate stopper (and no R or an R>=1M to ground) is that high that it won't affect the filter characteristics.

Best regards
 
#34
So the buffer after filter should be the b1 without a pot (25k or 50k) am I right?

In addition after high pass there is no need to use the 10uf capacitor, lets say highpass is 1500hz which value for the cap is good enough?

Thanks
 
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#35
As I wrote above, I would use

Code: 
               input
          Volume-Pot (20k)
Input-Buffer 1           Input-Buffer 2
Lowpass-Filter           Hipass-Filter
Buffer                   Buffer
Lowpass Pot (20k)        Hipass Pot (20k)
Buffer                   Buffer
Cap (4.7-10u)            Cap (>470nF)
Low Out                  Hi Out

The Hi-and Lowpass Pots could be done as stepped attentuators (e.g. with 12 Steps from 0 to -11 dB). I used stereo 6x Switches to give a 20K stepped att with 6 steps per channel 0 to -5 dB and a switched resistor before the att to give another -6dB.

But I would highly recommend to use the symmetric-voltage supply version of the B1 for that. If not you would have to implement the B1 with caps (before and after), those would affect the filters.

Best regards
 
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#39
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#40
Harolda said:
Hello Floric,

you would leave out the pot for the buffer before and after the filter or only after the filter (if so what is the purpose of the pot in the buffer before the filter?)

regards
Click to expand...

Its a buffer (passive pre) with the filter, the first pot is the system volume control and the last pots are to balance your highs and lows.
 
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