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Old 4th December 2009, 03:22 PM   #41
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Quote:
Originally Posted by AndrewT View Post
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.
Another good site is Rod Elliot's. See esp. Project 9 and Project 81.

If you need gain, you could splice a JFET BOZ to the input (or output). Or maybe something like Juma's BF862 Preamp.
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Old 4th December 2009, 03:33 PM   #42
njepitt is offline njepitt  United Kingdom
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Quote:
Originally Posted by Jacques Merde View Post
...
If you need gain, you could splice a JFET BOZ to the input (or output). Or maybe something like Juma's BF862 Preamp.
I'm thinking about putting juma's BF862 preamp at the input, as you suggest. Since it has a gain of 2, would anything in the crossover circuit need altering to handle a higher input?

I quite like the idea of doing a preamp with switchable crossover, so it can be used with or without breaking into high and low freqs, with BF862 throughout. Still thinking it all through, though, and am interested in hearing any and all ideas....

Cheers

Nigel
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Old 5th December 2009, 12:10 AM   #43
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Originally Posted by njepitt View Post
I'm thinking about putting juma's BF862 preamp at the input, as you suggest. Since it has a gain of 2, would anything in the crossover circuit need altering to handle a higher input?

I quite like the idea of doing a preamp with switchable crossover, so it can be used with or without breaking into high and low freqs, with BF862 throughout. Still thinking it all through, though, and am interested in hearing any and all ideas....

Cheers

Nigel
Nigel,

I think that the BF862 will make a good choice. Its high gm makes it attractive, IMO. The circuit should handle larger input signals fine, though with some increased distortion . You might consider limiting the supply voltages to +/- 9 Volts with the BF862, just to avoid any possibility of exceeding the max Vds of the BF82.
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Old 5th December 2009, 12:39 AM   #44
njepitt is offline njepitt  United Kingdom
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Originally Posted by Jacques Merde View Post
Nigel,

I think that the BF862 will make a good choice. Its high gm makes it attractive, IMO. The circuit should handle larger input signals fine, though with some increased distortion . You might consider limiting the supply voltages to +/- 9 Volts with the BF862, just to avoid any possibility of exceeding the max Vds of the BF82.
Hi Jacques,

I certainly don't have enough understanding of these things to judge how much distortion would be increased, but it's definitely to be avoided if possible... The obvious alternative would be to use separate gain stages after splitting the frequencies; I mean put one in each of the LP and HP outputs. Is this likely to be better from the point of view of distortion? (Against doing it this way is the obvious increased complexity,which sort of goes against the elegant simplicity of the original idea... Still trying to think this through...)

Cheers

Nigel
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Old 5th December 2009, 01:20 PM   #45
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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
I think having multiply spaced holes for the caps is generally a good idea. I have to agree with Jaques that the Panasonic 1% are likely the baseline (see what Mr. Linkwitz himself has to say about this). On that note his site is fantastic reading when it comes to linelevel cross overs and the considerations going into their design. As regards more exotic caps, keep in mind that we are not trying to deal with 250V or higher parts as required in passive cross overs... Tolerance being tight on the caps is one of the main requirements here (again, see Linkwitz on the subject).

My 2cents.

Peter
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Old 5th December 2009, 01:30 PM   #46
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About caps:
I have read from various sources that polystyrene caps are to be preferred on this kind of filter. RS components has good ones but not many options on values...I will go for polyester then reevaluate for an upgrade.
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Old 5th December 2009, 02:57 PM   #47
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Peter,
Thanks for your input. I have them spaced at 5mm, 7.5mm, 10mm and 15mm and width is 9mm.
Uriah
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Old 6th December 2009, 08:52 PM   #48
udailey is offline udailey  United States
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Default PCB a few options

Guys what do you think?
The only difference between these two is the obvious absence of filled plane in the center. Ground on both encircles the board. In the one that is filled in the center - the fill is not connected to ground.
So let me know what you think about the layout. The board is right now 58mmX115mm.
Uriah
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Old 10th December 2009, 03:35 PM   #49
spencer is offline spencer  Hong Kong
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Yamaha F1030 (believe F1040) is using a buffer to do active crossover. Thus B1 can be used to replaced the buffer in F1030. Refer to HERE for F1030 circuit diagrams.
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Old 11th December 2009, 11:31 AM   #50
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Hi Jaques, I note that Rod Elliot included an inverting buffer in his 12db/octave crossover for the LP section (which seems a bit odd as I would have thought the tweeter would be the one you invert). Anyway I guess the question is, what were you planning on doing with respect to the 180 degree phase shift of low compared to high? reverse the polarity on the speakers for one (as would be done in a passive crossover)?

Tony.
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