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Old 4th December 2009, 12:20 PM   #31
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by pheonix358 View Post
Could you post the formulae for the RC values for those of us that are challenged? Additionly I assume this is a unity gain. If so can the gain be increased.
go to Linkwitz site.
If you use gain stages then the gain controls the Q. It becomes a very different design if you adopt other than unity gain.
You can use ECV Sallen Key or MFB as your gain filter stages.
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Old 4th December 2009, 01:06 PM   #32
udailey is offline udailey  United States
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Originally Posted by Jacques Merde View Post
Uriah,
I also do not see a signal connection from the input buffer to the HP and LP sections.

Jacques
The other missing traces I dont know how I missed them last night. I had removed them and moved the power input and signal input around the board. Must have got caught up with family stuff and thought I fixed them. I think I found a good spot to get the signal from initial 2sk pair to the junction of 22nF and 10k2.
I think I still want to redo the entire layout in that ladder style.
So what kind of capacitors were you thinking of using? Are they regular Wima Box style or are these the big audio caps like Nelson had on the original B1?
Uriah
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Last edited by udailey; 4th December 2009 at 01:09 PM.
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Old 4th December 2009, 01:10 PM   #33
udailey is offline udailey  United States
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Default fixed .gif

Here is the GIF of the board
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File Type: gif B1.GIF (25.2 KB, 1548 views)
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Old 4th December 2009, 01:30 PM   #34
AndrewT is offline AndrewT  Scotland
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how about fitting the frequency setting Rs & Cs to dip headers and having dip sockets on the PCB?
When one has finalised all the adjustments then consider hard soldering the Rs & Cs permanently to the PCB pads.
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Old 4th December 2009, 01:48 PM   #35
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Jacques

I wonder if it won't be better to do the same on with the hi-pass section as you do with the low-pass section. (Please excuse the different labeling)

The green plot is at the input of R4, the blue plot is at the output of J3.

Johnny
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Last edited by yggdrasil; 4th December 2009 at 01:50 PM.
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Old 4th December 2009, 02:12 PM   #36
AndrewT is offline AndrewT  Scotland
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loading C2 with 10k2//22k completely upsets the filter.

The buffer MUST show near infinity input impedance for the filter to work properly.

Similarly the input buffer MUST present a near zero source impedance to the filter for it to work as expected.
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Old 4th December 2009, 02:30 PM   #37
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Quote:
Originally Posted by pheonix358 View Post
Hi all, this looks like just what I need as well. Could you post the formulae for the RC values for those of us that are challenged?
For the 2 pole LR use:

R = 1 / (2 * PI * f * C)
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Old 4th December 2009, 02:33 PM   #38
udailey is offline udailey  United States
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Andrew,
Using SIP... I found this one 310-13-120-41-001000 20P IC Socket Mouser 2.32 ea.
Hope they will do the job. It will take a 15-25mil lead.
I was thinking to make the board a lot bigger and single sided so people can etch it themselves. I can put room at each cap position for caps with 5mm, 7.5mm, 10mm and 15mm pin spacing. I am making the resistors bigger to so they can accomodate resistors up to 12mm long plus leads. I cant stand boards that only make room for 5-6mm resistors. Since I am making the components bigger I get to have a larger board, which does have its drawbacks, but it will probably allow me to do single sided. So I will work on it over the next few days.
If everyone thinks just WIMA box caps are fine here then I think I have all the info I need, but I wonder if people are going to want to use big caps like Axon, Mundorf, etc..
Uriah
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Last edited by udailey; 4th December 2009 at 02:35 PM. Reason: fixed lead diameter that SIP will take
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Old 4th December 2009, 02:39 PM   #39
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Quote:
Originally Posted by udailey View Post
So what kind of capacitors were you thinking of using? Are they regular Wima Box style or are these the big audio caps like Nelson had on the original B1?
Uriah
I'd like to avoid making specific part recommendations beyond good quality film types with tight tolerance.

I will probably establish a baseline for evaluating more exotic parts with the Panasonic 1% film caps available from Digi-Key.
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Old 4th December 2009, 03:06 PM   #40
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Quote:
Originally Posted by yggdrasil View Post
Jacques

I wonder if it won't be better to do the same on with the hi-pass section as you do with the low-pass section. (Please excuse the different labeling)

The green plot is at the input of R4, the blue plot is at the output of J3.

Johnny
Quote:
Originally Posted by AndrewT View Post
loading C2 with 10k2//22k completely upsets the filter.

The buffer MUST show near infinity input impedance for the filter to work properly.

Similarly the input buffer MUST present a near zero source impedance to the filter for it to work as expected.
Johhny,

There's no advantage to it that I can see. Also, AndrewT's advice is spot on. In your schematic, you need to remove U1/U2 and R6/R13.

The rationale for providing a separate buffer for the feedback cap is that at high frequencies, the input signal is shunted through the feedback cap and appears (attenuated) across the output impedance of the buffer, wrecking the stopband attenuation. That path doesn't exist in the high pass section.

You can refer to this article from EDN for additional information.
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