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Pass Labs B4 crossover questions
Pass Labs B4 crossover questions
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Old 4th July 2016, 10:53 AM   #101
Zen Mod is offline Zen Mod  Serbia
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Pass Labs B4 crossover questions
you can always ask NP is it possible getting new one with 100K Rin
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Old 4th July 2016, 11:15 AM   #102
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you can always ask NP is it possible getting new one with 100K Rin
Oh, all right I'll do that, thanks. Am I correct in my assumption about the impedance consideration?
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Old 4th July 2016, 12:40 PM   #103
Zen Mod is offline Zen Mod  Serbia
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Pass Labs B4 crossover questions
with 600R for Rout,it is certainly better to feed 100k than 10k
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Old 5th July 2016, 12:30 AM   #104
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That was my thought. I'll email NP and see if he'll do a custom B4. Thanks.
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Old 5th July 2016, 08:15 PM   #105
Nelson Pass is offline Nelson Pass  United States
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Pass Labs B4 crossover questions
The answer will be no. The input impedance is governed by the
value of the pot used to adjust the relative levels in parallel with the
100K of the input buffer.

If you use a 100K pot, then at midpoint you would see 25K in series with
the input of the Jfet buffer and this would inhibit the high frequency response.

Better to let 600 ohms drive 10K.

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Old 5th July 2016, 08:37 PM   #106
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The answer will be no. The input impedance is governed by the
value of the pot used to adjust the relative levels in parallel with the
100K of the input buffer.

If you use a 100K pot, then at midpoint you would see 25K in series with
the input of the Jfet buffer and this would inhibit the high frequency response.

Better to let 600 ohms drive 10K.

Thanks Nelson. I took another look at the specs for the EAR 868, and they state not that it has an output impedance of 600 ohms, but that it puts out 5 volts into a 600 ohm load. EAR's Tim de Paravicini does a fair amount of work in the recording studio field, where I take it that 600 ohm figure is a standard. It doesn't seem like the specs would be given that way if the pre-amp couldn't drive a 600 ohm load, so 10k should be no problem. I'll just get me a revised B4 and give 'er a shot. Thanks again, the B4 looks like a beaut!
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Old 5th July 2016, 11:44 PM   #107
Nelson Pass is offline Nelson Pass  United States
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Pass Labs B4 crossover questions
It has a spec into 600?

Hahahahaha....

We won't worry about it then.

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Old 6th July 2016, 08:30 AM   #108
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Originally Posted by Nelson Pass View Post
It has a spec into 600?

Hahahahaha....

We won't worry about it then.


Yeah, EAR doesn't provide much technical info on their products, and my feeble memory latched onto that 600 ohm figure. But it's for the other side of the equation!
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Old 3rd October 2016, 02:27 PM   #109
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I have a few questions about the B4, this is probably the best place for them even though this is an old thread.

I have one (Thanks Mark at Reno HiFi), and am using it to cross a 2-way with an Altec 416 and a Heil AMT. Right now the Heil sounds best with a 1st order passive, but that may be because I haven't found the sweet spot on the B4 for it yet.
2A3 SET amp on the Heils, PPP EL34 on the Altecs.

1. On the 416 1000Hz @ 24db - What's the difference Sallen Key vs. Linkwitz Riley? I have all the DIPs the same (4 sets each channel).
2. On the Hi Pass, is the S-K vs L-R set by the setting on the Low Pass, or is there only one default type for the Hi Pass?

I have tried to mimic my passive but just doesn't sound quite right.
I also tried 1000Hz 24db on the Altecs and 1000Hz 24db on the Heils, and again not quite right.

(btw: Replacing a pro XO with the B4 only on the Altecs yields much improvement)

TIA
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Old 13th July 2017, 11:09 AM   #110
Studley is offline Studley  United Kingdom
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Back in January NP announced on the FW website that the B4 was to be discontinued. I'm wondering if there are any plans for a replacement?
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