LX-mini Crossover Article

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Nelson Pass

Nelson Pass

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Joined 2001
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If those resistors 13-16, 35-38 are 100 ohms then you're at 15 mA bias, which is
a little high but not a problem. If you want the 10 mA, then you can use 150 ohms
or so, but I wouldn't bother. The values for R17-20 are nominal, and only affect the
low frequency rolloff. The higher the value, the lower the rolloff. The stock values
were 22K, and I can't find reference to 4K in the article.

np
 
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mfeif

Member
Joined 2016
Hey friends; I've read through every single post on this thread, but perhaps because it goes back for so long, I'm not sure whether or not the phase of the high-pass outputs needs to be inverted or not with the ASP build for the LX mini. I've read Nelson's PDF and every post here, but there have been multiple versions of this board and I'm just not sure.

Can someone who has built the kit enlighten me? I've just ordered the kit, so I'll need to wire it up eventually :)

Thank you!
 
wwschaff

wwschaff

Member
Joined 2022
Quote from Nelson’s Article: “ reminds me to mention that there are no phase inversion circuits in this crossover, only unity gain discrete Jfet buffers without feedback. This means that with this crossover you have to invert the phase of the mid-tweeter, probably in the speaker wiring between the amp and the mid-tweeter, otherwise you will be listening to that big deep dip.” There is also a Graph displaying this in the article and burning-amp video. I’m going to be building this as well!
 
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mfeif

Member
Joined 2016
Hi Friends,

Yesterday I took delivery of an LX Mini ASP kit; I was going through the parts list in Nelson’s install instructions, and unfortunately I think some resistors are missing…

The parts list says that some resistors have been paired for the JFETS, and ship with them, and DOES list that the values may vary; got it.

There should be 14 resistors according to the instructions:

R13 - R16 supplied with Jfets typical value ~ 100 ohms
R17 - R20 supplied with Jfets typical value ~ 4 Kohms
R35 - R38 supplied with Jfets typical value ~ 100 ohms
R39, R42 supplied with Jfets typical value ~ 10 Kohms

In my bag where the Jfets were/are there are 8 resistors of ~150ohms; I presume that these are R13-R16 and R35-R38.

But I don’t have any in there for R17, R18, R19, R20, R39, R42.

HOWEVER, OUTSIDE of the bag there are 12@ 27.4Kohm resistors, and the plans only seem to call for 4@ of them.

But that’s not close to the “typical” values listed above?

If it were missing resistors that were spec’d I could just get some, but since they’re supposed to be paired with the Jfets, I don’t know what values I'm supposed to have or what to do.

Does anyone know if the instructions have changed or something like that? I don't understand how to match a resistor to a Jfet; perhaps the 27.4Kohm ones are appropriate now?

Thanks.
 
elwood625

elwood625

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Joined 2013
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audiorasp said:
17 jfets, and only 8 100 ohm resistors.
Click to expand...
8 of the JFETs use the 100 ohm resistors for the current source (the bottom JFET's in the schematic), the other 8 JFET's are for the unity gain buffers (the upper JFET's in the schematic). The lone JFET is a spare (Nelson is very generous with us DIY'ers). The rest of the resistors and capacitors are for the low and high filters & EQ circuits.
Since I built this as a ACN, I had to select my own values based on my drivers.
 
elwood625

elwood625

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WBS said:
The most recent batch of LX Mini kits shipped to the store included 27K for R17-R20
mfeif said:
HOWEVER, OUTSIDE of the bag there are 12@ 27.4Kohm resistors, and the plans only seem to call for 4@ of them.
Click to expand...

Wouldn't be surprised if Nelson/PASSDIY just through in 12 instead of 4. They only cost a couple of penny's each. Don't forget R39-R42 use them also.
Click to expand...
 
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mfeif

Member
Joined 2016
I just re-read a few back pages, and found this:
Nelson Pass said:
If those resistors 13-16, 35-38 are 100 ohms then you're at 15 mA bias, which is
a little high but not a problem. If you want the 10 mA, then you can use 150 ohms
or so, but I wouldn't bother. The values for R17-20 are nominal, and only affect the
low frequency rolloff. The higher the value, the lower the rolloff. The stock values
were 22K, and I can't find reference to 4K in the article.
Click to expand...

And, thanks, Nelson, THAT is very helpful. (The reference is on page 10, in the "PC Board Parts List" table.)

27.2K is certainly a lot closer to 22K; I'll be a little more comfortable soldering stuff up!

It'd be nice for future newbies like me if a note could be added to (perhaps) the build guide to clear this up. :)

Thanks friends
 
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mfeif

Member
Joined 2016
Hi Friends, a question about the phase inversion instructions:

From Nelson's PDF: " reminds me to mention that there are no phase inversion circuits in this crossover, only unity gain discrete Jfet buffers without feedback. This means that with this crossover you have to invert the phase of the mid-tweeter, probably in the speaker wiring between the amp and the mid-tweeter, otherwise you will be listening to that big deep dip.”
Click to expand...

Is there any reason that this flip can't be done inside the ASP box, between the board and the connectors? Is there some subtle reason it's proposed to do it AFTER THE AMP instead of before?

Thanks!
 
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audiorasp

Member
Joined 2001
Paid Member
Thanks elwood625.
To be clear, l purchased the basic kit which the store describes as: This Basic Kit contains the PCB, 16 matched JFETs and 16 matching resistors R13-20, R35-42, and I only got 8 100 ohm resistors. I have no idea what the values should be for the other 8 resistors. I just might have to buy another kit.
 
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