LX-mini Crossover Article

[mworthin]

If you were like me, you will be thrilled with the results. No comparison.

According to the original First Watt article, those are among the resistors that are JFET-dependent.

 

[Nelson Pass]

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

 

[dgcoffee]

Thanks so much for the reassurance!

Yes r13-16, and 35-38 are 100ohm.

I found the 4Kohm reference in the The parts list in the article: R17-20 has a “typical value ~4Kohms. but my pack came with 10 Kohm

 

[dgcoffee]

She’s alive and sounds incredible. Somehow these little guys (lx minis) continue to impress. They share a room with some dusty klipshorns, the juxtaposition is a great conversation starter.

Very fun project, thanks to everyone involved!

 

[Nelson Pass]

The filter curves were SL's, I just replicated them in analog.

 

[mworthin]

She’s alive and sounds incredible. Somehow these little guys (lx minis) continue to impress. They share a room with some dusty klipshorns, the juxtaposition is a great conversation starter.

Very fun project, thanks to everyone involved!

My wife calls them the "Spy Camera Speakers!"

 

[WBS]

...R17-20 ... my pack came with 10 Kohm

The most recent batch of LX Mini kits shipped to the store included 27K for R17-R20.

 

[mfeif]

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]

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!

 

[mfeif]

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.

 

[audiorasp]

My situation is similar to mfeif"s. I received my kit in early January and it had the pcb, 17 jfets, and only 8 100 ohm resistors. I've been in touch with the diyAudio store but no resolution so far.
George

 

[elwood625]

17 jfets, and only 8 100 ohm resistors.

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]

The most recent batch of LX Mini kits shipped to the store included 27K for R17-R20

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

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.

 

[WBS]

Per NP, "There is an error on the schematic - 13-16 and 35-38 are chosen for jfets,
typical value is 100 ohms." The ~100 ohm resistors are included in the essentials kit with the JFETs.
The 27.4K resistors are for R6, R8 and R17-R20

 

[mfeif]

I just re-read a few back pages, and found this:

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.

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

 

[mfeif]

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.”

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!

 

[Davey]

@mfeif No, it can't be done inside the ASP box. This is an unbalanced architecture and doesn't support that.
You need to flip polarity of your speaker wire going to the mid-tweeter drivers.

Dave.

 

[wwschaff]

RCA cables always want the signal on the inside and the ground on the outside if that makes sense. Flip the + and - on the speaker cables instead.

 

[audiorasp]

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.

 

[Davey]

@audiorasp Eight 100 ohm resistors is correct. I'm not sure why you'd need to buy another kit?????
Look on Page 10 of your LXmini Pass ASP PDF.

Dave.