@George Ab: Waooo! That's spectacular! I'm looking forward to hear comments on the sound. I was in the process of considering the Marchand but now that I see this...
I was thinking to build the ESP P09 xover but this one is tempting.
I hope somebody can help with the following:
1. What's the input impedance? I have a tube line stage that doesn't like anything below 50K, 100K would be much better.
2. How much the PSU is critical? Would a classical LM317/LM337 regulator be enough to ensure low noise?
3. And now a final curiosity. In the past I've been really impressed with the Nelson's B1 buffer. If I had a different phono stage I would used it as my main preamp. How these buffers relate to the wonderful B1's circuit?
I was thinking to build the ESP P09 xover but this one is tempting.
I hope somebody can help with the following:
1. What's the input impedance? I have a tube line stage that doesn't like anything below 50K, 100K would be much better.
2. How much the PSU is critical? Would a classical LM317/LM337 regulator be enough to ensure low noise?
3. And now a final curiosity. In the past I've been really impressed with the Nelson's B1 buffer. If I had a different phono stage I would used it as my main preamp. How these buffers relate to the wonderful B1's circuit?
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No joy as of yet. Chasing hum, which is usually a challenge. Look at it with a scope and it adds another ground loop. Isolation xformer removes from high pass, but not band pass.... grrr... its like wack a mole. I am going to step away from this for a few day and go to my happy place of listening to music.
@piecor The Marchand is quality. I really like it. I have a balance input and output which I assume helps with hum. I am pretty sure Phil has a balanced input stage to single ended for XO and then single back to balanced for output. Even with that I still need a quality isolation transformer for the subwoofer outputs.
I will atempt to answer your questions and if I am off base someone will surely correct. For input impedence I am seeing a 50K ohm variable resistor for both low and high pass so the input Z would be 25K as they are in parrallel. If you need higher Z should be fine with a larger variable resistor. WRT the PSU with bias being 10mA for each set of FETs looks like 120ma for the entire XO. So any quality regulator should work fine as this does not draw much current. Sorry not familiar with the B1 buffer.
@piecor The Marchand is quality. I really like it. I have a balance input and output which I assume helps with hum. I am pretty sure Phil has a balanced input stage to single ended for XO and then single back to balanced for output. Even with that I still need a quality isolation transformer for the subwoofer outputs.
I will atempt to answer your questions and if I am off base someone will surely correct. For input impedence I am seeing a 50K ohm variable resistor for both low and high pass so the input Z would be 25K as they are in parrallel. If you need higher Z should be fine with a larger variable resistor. WRT the PSU with bias being 10mA for each set of FETs looks like 120ma for the entire XO. So any quality regulator should work fine as this does not draw much current. Sorry not familiar with the B1 buffer.
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I need two of these boards to make a 3-way design
https://diyaudiostore.com/products/diy-biamp-6-24-crossover
I suppose
https://diyaudiostore.com/products/diy-biamp-6-24-crossover
I suppose
Yes, you will need two boards. One board for the low pass, same board's high pass filter feeds into the next low pass filter section which is set at higher frequency creating a bandpass, last section is the high pass.
If you create a bandpass using the high pass feeding into a low pass section, you can avoid some circuitry by taking the output from the drain of last stage FET (leading into output 10uF cap shown on schematic) and jumper to the 10K resistor that leads into the first stage low pass filter. This reduces an output capacitor and input capacitor and buffer section. Someone drew this on the schematic in some posts back.
If you create a bandpass using the high pass feeding into a low pass section, you can avoid some circuitry by taking the output from the drain of last stage FET (leading into output 10uF cap shown on schematic) and jumper to the 10K resistor that leads into the first stage low pass filter. This reduces an output capacitor and input capacitor and buffer section. Someone drew this on the schematic in some posts back.
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One other consideration with three bands is input impedence. With schematic having 50K variable resistor for attenuating input signal, with three bands that is 50K in parrallel with 50K in parrallel with 50K so input impedence of 16.7K ohms. May consider a 150K variable resistor to get a more standard load of 50K as input Z. Until you brought up input Z I didn't give it a thought. I have a switched ladder network to attentuate the signal so I need to remove 7 resistors and replace with higher values on six rotary switches. There goes a day, should of thought about that going in, oh well.
So the input impedance is determined by the input potentiometer. Am I correct?
Last question before buying(?): Is there any formula to calculate the resistors to produce a precise xover frequency? I mean, in my case, I need 24db/oct filters at 90Hz and 600Hz. I know these variable resistors add flexibility, but I don't want the temptation of another toy for playing night and day instead of listening to music!
Last question before buying(?): Is there any formula to calculate the resistors to produce a precise xover frequency? I mean, in my case, I need 24db/oct filters at 90Hz and 600Hz. I know these variable resistors add flexibility, but I don't want the temptation of another toy for playing night and day instead of listening to music!
Hello piecor,
Michael Rothacher offered a simulation to play with the values of the capacitors and the resistors:
http://doublesecretlabs.com/apps/passxo
If you read the article of Mr. Pass about the 6-24 AXO you will find the important information.
https://www.firstwatt.com/pdf/art_diy biamp_6-24_ crossover.pdf
I have built one 6-24 AXO as a subwoofer crossover (adjustable below 60 Hz up to above 200 Hz crossover frequency) and then
'daisy-chained' with a second 6-24 AXO at a crossover frequency at 2500 Hz. Sounds excellent
Cheers
Dirk
Michael Rothacher offered a simulation to play with the values of the capacitors and the resistors:
http://doublesecretlabs.com/apps/passxo
If you read the article of Mr. Pass about the 6-24 AXO you will find the important information.
https://www.firstwatt.com/pdf/art_diy biamp_6-24_ crossover.pdf
I have built one 6-24 AXO as a subwoofer crossover (adjustable below 60 Hz up to above 200 Hz crossover frequency) and then
'daisy-chained' with a second 6-24 AXO at a crossover frequency at 2500 Hz. Sounds excellent
Cheers
Dirk
Declaring victory over hum. Iso-max Jensen isolation xformer on input and I have to use shielded interconnects. I had Kimber KCAG unshielded interconnects that were inputting noise. My grounding scheme at the board level is solid, but need to do some work on areas like hooking up shield to ground to shorten ground loops, but for now I’m good.
Listening impressions: I am over the moon with this DIY active XO! IMO for apples to apples comparison the biggest improvement is going to an active xo over passive xo whatever method you use. Caveat is it is not easy getting the crossover points and slopes right and anytime you de-integrate your system by adding amps you are increasing likelihood of hum etc. With that caveat out of the way, amps directly controlling bass and mid drivers and not having to go through inductors, capacitors and resistors work well… tight control, accurate phasing, etc. In my experience even using a digital solution like a Behringer active xo or Minidsp will garner improvement over a passive xo, but as much effort and expense as most have put into sorting our digital front end hard to justify an A/D converter and multiple D/A converters after the DAC. With the Pass Labs XVR1 being out of production the best commercial solution IMO is the Marchland active XO. I do love that piece of gear. This DIY solution of a handful of unity gain FETs and no feedback is next level. What I am hearing is its excellence at what it doesn’t do, no sonic signature or smearing that can be experienced even with well implemented op amps. It performs its function divided audio frequencies to amps without adding or subtracting information from signal. Just really happy with this xo.
Still work to do. The startup delay circuit that shunts output to ground until power stabilizes still dumps voltage into amps. It just delays it when the relay kicks in. Not bad, but it trips protection circuitry of my Moon Audio amp. Easy solution is turning on amps after active xo and turning off amps before turning off active xo. I likely will remove capacitor responsible for delay and add a capacitor to 12V trigger signal to delay turning on amps. Should not be an issue when I turn off, as at turnoff when 24 decreases to approximately 19V output is shunted to ground and amps are shut down from loss of 12V trigger voltage. Will have to test to find out. Shouldn’t be hard to engineer, but for now just going to enjoy the music.
This has been a fun and really worthwhile project.
Thank you Nelson for providing this to the DIY community.
Listening impressions: I am over the moon with this DIY active XO! IMO for apples to apples comparison the biggest improvement is going to an active xo over passive xo whatever method you use. Caveat is it is not easy getting the crossover points and slopes right and anytime you de-integrate your system by adding amps you are increasing likelihood of hum etc. With that caveat out of the way, amps directly controlling bass and mid drivers and not having to go through inductors, capacitors and resistors work well… tight control, accurate phasing, etc. In my experience even using a digital solution like a Behringer active xo or Minidsp will garner improvement over a passive xo, but as much effort and expense as most have put into sorting our digital front end hard to justify an A/D converter and multiple D/A converters after the DAC. With the Pass Labs XVR1 being out of production the best commercial solution IMO is the Marchland active XO. I do love that piece of gear. This DIY solution of a handful of unity gain FETs and no feedback is next level. What I am hearing is its excellence at what it doesn’t do, no sonic signature or smearing that can be experienced even with well implemented op amps. It performs its function divided audio frequencies to amps without adding or subtracting information from signal. Just really happy with this xo.
Still work to do. The startup delay circuit that shunts output to ground until power stabilizes still dumps voltage into amps. It just delays it when the relay kicks in. Not bad, but it trips protection circuitry of my Moon Audio amp. Easy solution is turning on amps after active xo and turning off amps before turning off active xo. I likely will remove capacitor responsible for delay and add a capacitor to 12V trigger signal to delay turning on amps. Should not be an issue when I turn off, as at turnoff when 24 decreases to approximately 19V output is shunted to ground and amps are shut down from loss of 12V trigger voltage. Will have to test to find out. Shouldn’t be hard to engineer, but for now just going to enjoy the music.
This has been a fun and really worthwhile project.
Thank you Nelson for providing this to the DIY community.
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I'm starting to make the crossover and I'm going up the... stream of the thread!
I hope I don't disturb you but, since I'm interested in doing an XOver with frequencies that are also the ones used by you (60-120 Hz), I would like to know what values you used in the Biamp 6-24 used by you, assuming that you also have used - as I would - a 24dB XOver.
Thanks!
I have used 10-turn precision pots -with linear taper- from Bourns and in the other AXO those have been Vishay/Spectrol.
Normally you use pots with a logarithmic taper- for volume control. But I like it that way. With 10-turn pots you can adjust very accurate.
I have to check if I used 25 kOhm or 50 kOhm pots. But both values will work fine. Recommended by Nelson Pass are the 50 kOhm -pots.
Greets
Dirk
Normally you use pots with a logarithmic taper- for volume control. But I like it that way. With 10-turn pots you can adjust very accurate.
I have to check if I used 25 kOhm or 50 kOhm pots. But both values will work fine. Recommended by Nelson Pass are the 50 kOhm -pots.
Greets
Dirk