Explanation for "3. Pots in Slots" in my post #1,155.You can test the resistance in situ pretty accurately if you pull the various
jumpers off the board first, otherwise you will get wrong values on a
couple of the filters because other impedances are in parallel with the
thing you are trying to measure. Keep in mind that there are 10K
resistors in series with the pots, and you will have to find those spots
on the board that represent the nodes you want.
I find that I can eyeball it fairly well, after all these are linear pots and
I did mark the center resistive value on the board for reference.
I can get you high precision, but you will pay a steep price for it, but
high precision is not the point of this exercise - adjustability is.
What I want is the ability to get any values based on listening and
measurement so as to optimize the crossover for the vagaries of the
loudspeaker drivers and so on. This issue is not generally addressed
in analog products - they tend to offer only canned filter settings.
Maybe I can add some jumpers in strategic places to be able to measure what needs to be measured. If the need is there. Something for future revisions?
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https://www.diyaudio.com/community/threads/diy-biamp-6-24-crossover.357657/post-7099134
This does not look too complicated. I can pick four LSK170 with 8.5-9.5mA Idss and then adjust the 2K trimpot in place of R1 in this image from zero ohm up to whatever value that it needs to show 800mV across R2 in this image.
But this is on the PCB, right? Otherwise I have to build a copy of the pcb and hope everything turns out identical.
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I built my 6 -24 XO using 2SK170bl parts for the buffers, I used a jumper for the "bias" resistors and used matched pairs for left and right channels (thanks to cubicincher's excellent advise). Selecting the JFETS was easy, I used JFETS greater than 9mA because of what Nelson stated in the article:
The Jfets are J113 and we want them operating at about 8 mA current in the buffers. The
ones in the kit are selected along with Source resistors to give this with a matched
characteristic.
Since I bought the kit and used the J113's and resistors as CCS, Nelson already selected the CCS parts to give 8mA of current to the buffers. In Nelson I trust, so I just used 2SK170bl at 9mA and above. The hardest part of the build was soldering the 170's because the pin out is different, they look like the line dancers at Radio City Music Hall.
Did you do this for all Q1 on the board or just the four on the input buffer? Any photos?
From what I gathered, it is more complicated than to just use LSK170BL at 9mA at Q1 in the input buffer. The resistor for LSK170 can be jumpered, but the tricky part is to choose a resistor for the source of the J113 on Q2.
Yes, I selected 150Hz as the crossover point for the SLOB speakers I built. It's an integrated preamp using the BA2018 line stage and a separate power supply enclosure. The clear plexiglass cover is temporary until I have the pots adjusted to my liking.
Attachments
Nice, I am hoping to get a similar crossoverpoint if only I can lod my lowest horn that deep. What caps and resistor values did you choose?
You changed only four Q1 to LSK170BL?
No, I changed all of Q1's to 2SK170's, I used the Toshiba parts. I used the calculator in Nelson's article to determine cap and resistor values. I'll have to look and see what the values were, I remember having trouble finding the caps Nelson recommended in the BOM for the values I needed.
Ok, just curious as we have the same almost. I should probbaly use 180Hz.
How do you measure the pots and resistors? When soldered they won’t give the correct value.
The PCB from the DIYStore has arrows printed on the board to set the pot's initial starting point. I'm not an electrical engineer so I build everything according to the instructions and hints that the forum designers provide.
Every time I thought I was smart enough to change things, I ended up with disasters. No more.
Every time I thought I was smart enough to change things, I ended up with disasters. No more.
Hoe abou
How about a very finely tuned ear? Mine is very sensitive around 700-1000hz. Coincidentally the same frequency as an angry wife.I find that broadband response flaws are easy to hear and adjust. The real work happens at crossover points, and that's where a microphone is very handy. Fortunately it doesn't have to be an expensive one...
Hello Delineation,
I would answer your question like this: If capacitors are used in a circuit and there are resistances (resistors)
around it, then they can / will form a RC-filter.
Whether you have a cap at the output of an preamp (BA-3-preamp for example) and you will have a
resistor to ground at the input of your next stage (active crossover / poweramp) it will form a RC-filter.
In a single ended design (like the 6-24 AXO) you have caps before the buffer and after the buffer at the
output. There will be resistance around those caps to form a RC-filter.
This is how I think about it.
But there are more experienced persons on this forum who could chime in?
Cheers
Dirk
I would answer your question like this: If capacitors are used in a circuit and there are resistances (resistors)
around it, then they can / will form a RC-filter.
Whether you have a cap at the output of an preamp (BA-3-preamp for example) and you will have a
resistor to ground at the input of your next stage (active crossover / poweramp) it will form a RC-filter.
In a single ended design (like the 6-24 AXO) you have caps before the buffer and after the buffer at the
output. There will be resistance around those caps to form a RC-filter.
This is how I think about it.
But there are more experienced persons on this forum who could chime in?
Cheers
Dirk
The way I understand the circuit is the buffers set the impedance, from the article: "input impedance is 12 Kohms and output impedance is about 250 ohms"
With all those buffers I hope even that is not necessary. I hope it is plug and play with most DACs and amplifiers.
Hopefully it's as simple as measuring the input impedance of the device you are feeding!