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Old 19th January 2010, 09:38 AM   #141
njepitt is offline njepitt  United Kingdom
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Originally Posted by cviller View Post
Ok, I have done a quick sketch and I would like to hear what you guys think - is this completely insane or something that could end up being really cool?

There is a volume control for each channel - I would probably use double pots for stereo.

The filters are going to have dip switches so that the cross frequency can be set without too much trouble.

The headers J1-J6 are intended to be expansion slots where additional filters can be added (to get more than 12db slopes). I thought I would use jumpers to short them out when not in use.

As you can probably see, I have been very much inspired by B4 and XVR1...
Hi cviller,

I took a look at your schematic and I'm a little confused.

1. I can't see the filter caps and resistors.

2. Jacques' original circuit has one more buffer in each branch of the filters, with volume pot only *after* the filters. This appears quite different from your proposal, which has them before the filters.

3. Can I point out posts #24 and #74 , which have an important adjustment inthe original schematic (and addition of another buffer in the LP section). Does your plan include this and I misunderstood? Or have you found another way around the problem?

4. I like the idea of making the board enough to do a three-way, but how much does the discussion above on the LP section affect the band-pass section in your design?

5. (Dumb question, maybe) What do you mean by a dip switch?

Cheers

Nigel
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Old 19th January 2010, 10:33 AM   #142
AndrewT is offline AndrewT  Scotland
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I would not put a 6channel volume pot after the input buffer when a 2channel volume pot can do the job just as well.

Adjustments in the 6channels to balance out gain and sensitivity variations should be done at the output of the filters, but before the final line driving buffers. Some of this (fixed) adjustment can be built into the power amps if the gain required in one frequency band is much different from all the others.
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Old 19th January 2010, 02:08 PM   #143
cviller is offline cviller  Denmark
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Originally Posted by njepitt View Post
Hi cviller,

I took a look at your schematic and I'm a little confused.

Nigel
I can see that - the blocks of filter sections need to be drawn, but what I have made is just the "conceptual framework".
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Old 19th January 2010, 02:29 PM   #144
cviller is offline cviller  Denmark
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Originally Posted by AndrewT View Post
I would not put a 6channel volume pot after the input buffer when a 2channel volume pot can do the job just as well.

Adjustments in the 6channels to balance out gain and sensitivity variations should be done at the output of the filters, but before the final line driving buffers. Some of this (fixed) adjustment can be built into the power amps if the gain required in one frequency band is much different from all the others.
Thanks for you comments Andrew! I know you don't like too many pots.
I see it this way (for a two way full range with woofer): Normally, I would have higher efficiency on the fullrange, so I'd need to attenuate the highs - ok no need for pot on LP. This would also work if I decide to use an F4 as driver for the woofer. But right now I use a chipamp for the woofer, which has more gain than the power amps I build - in I case I would also need a pot on the woofer. But I can't take the pot away from the HP. I know I can adjust the gain on amps, but I would most likely use this XO on both home-brewed and borrowed amps, so I would lose a lot of friends this way...

Your other point about the placement of the pots is interesting. I expect your rationale is: "why throw away gain before filtering - this will hurt SNR". This is a good point, but I just copied what I saw (and heard) here:

DIY progress report

But if I did move the pots in the end, I would have to add yet another buffer stage.
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Old 20th January 2010, 05:25 PM   #145
dviswa is offline dviswa  United States
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cviller,
I would love to see what you will cook up. BTW, have we dropped 2sk170 in favor of BF862?

Dinesh
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Old 20th January 2010, 05:36 PM   #146
cviller is offline cviller  Denmark
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The bf862's are really tempting. You can get 100 for $22 and if they perform as good as 2sk170 I think they are worth some design effort.

I probably have to start a new thread soon...
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Old 20th January 2010, 06:02 PM   #147
njepitt is offline njepitt  United Kingdom
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Originally Posted by cviller View Post
The bf862's are really tempting. You can get 100 for $22 and if they perform as good as 2sk170 I think they are worth some design effort.

I probably have to start a new thread soon...
I'm using the BF862s, and the buffers that are up and running sound great. YMMV, of course... It may be worth remembering that juma used the BF862's on little adaptor boards, which could be used on a PCB designed for 2SK170 if you wanted to.

Cheers

Nigel
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Old 20th January 2010, 06:52 PM   #148
AndrewT is offline AndrewT  Scotland
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Originally Posted by cviller View Post
The bf862's are really tempting. You can get 100 for $22 and if they perform as good as 2sk170 I think they are worth some design effort.

I probably have to start a new thread soon...
I got 200 off 2sk170 for $34 and delivered to the door.
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Old 20th January 2010, 09:00 PM   #149
udailey is offline udailey  United States
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Andrew,
Cheapest I can find in the states is Mouser at 22 for a hundred.
Where did you find yours?
Uriah
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Old 21st January 2010, 11:03 AM   #150
AndrewT is offline AndrewT  Scotland
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Spencer has a thread offering 2sk170bl in swap meet.
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