Some say yes others no!
What is your take?
Please state the reason for your answer.
I'd like to know the precondition for a successful PLLXO, like:
Pre-amp output impedance.
Power-amp input impedance.
Complexity of the x-over.
Etc etc.
Please jump into the fray. I'm listening.
My goal is to drive a combo of midbass/midrange woofer and horn with my Radford STA25 tube-amp and the 15" bass section with solid state or tube.
Sincerely
Kris
What is your take?
Please state the reason for your answer.
I'd like to know the precondition for a successful PLLXO, like:
Pre-amp output impedance.
Power-amp input impedance.
Complexity of the x-over.
Etc etc.
Please jump into the fray. I'm listening.
My goal is to drive a combo of midbass/midrange woofer and horn with my Radford STA25 tube-amp and the 15" bass section with solid state or tube.
Sincerely
Kris
hasselbaink said:
I've not done it myself, but at a guess
Pre-amp output impedance - <100ohms
Power-amp input impedance - around 100k
Complexity of the x-over - 12db filters for 2 way should be achieveable quite readily.
Matching of levels will be harder with PLLXO than full active as impedance must always be considered. Also, features like notch filters will be much harder to implement
You can do some simple stuff well.
See here:
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html
See here:
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html
A PLLXO composed of resitors & caps works pretty well everywhere if 1st order. One has to adjust the R values to suit the impedances of your devices (ideally you use the input impedance of the amp as part of your PLLXO). 2nd order is possible, the slopes are quite droopy. That the second section requires Rs that are on the order of 10x as large as the 1st section, a 2nd order is much more restrictive. Your preamp needs to have the grunt to drive the 2 series R in the low pass, and sufficiently low output impeedance to not be loaded down by the load provided by the 1st section of the HP. and the input impedance of the amp needs to be high enuff to help satisfy the 10x requirement (again best to use the input R of the HP as part of the circuit). In my experience, an input impedance of less than 50k on the HP will reqiuire a buffer (as long as you have enuff gain in the LP section, a single buffer on the output of the HP covers off most situations.
The Marchand uses caps & chokes. This allows higher orders (4th is probably practical max) I beleive that the load built--in is 5k. That makes for a requirement of quite low output impedance of the pre-amp. The chokes in these have to be very large values, and it is hard to get them small physcially & large valued without compromises in their characteristics. (ie the Marchand is probably well priced given the challenge of sourcing those chokes)
dave
The Marchand uses caps & chokes. This allows higher orders (4th is probably practical max) I beleive that the load built--in is 5k. That makes for a requirement of quite low output impedance of the pre-amp. The chokes in these have to be very large values, and it is hard to get them small physcially & large valued without compromises in their characteristics. (ie the Marchand is probably well priced given the challenge of sourcing those chokes)
dave
I am using passive line level signal splitter at 150 Hz buffered on the outputs. The line level splitter was from Dan Hildebrands page, which is long gone. I do feel that RC filters present quite a signal loss, therefore would like to try merchangs LC one day. They claim only -1dB loss!
dave, do you know what is signal attenuation with 1st order RC crossover?
ed
dave, do you know what is signal attenuation with 1st order RC crossover?
ed
I have built into a BOSOZ pre-amp a line level passive crossover. the BOSOZ drives the filter, and the filter drives the amps directly with out a buffer. I used those panasonic polypropylene capacitors and some air core inductors. values are small enough that capacitors and inductors were not a problem. I used a CAD electronics simulator to get the rough values, then I swept the filters with a signal generator and measured the results to get the frequencies right on. (I had to make adjustments in the inductance and capacitance to get the frequencies just right.) I'm careful to do the sweeping with the filters between the BOSOZ and the Aleph 3 amps so that impedences are correct. I was even able to do some shaping of the response curves by experimenting.
Loss isn't too much and you can compensate for levels using the internal gain adjustments on the BOSOZ...which does not effect output impendance of the pre-amp.
Loss isn't too much and you can compensate for levels using the internal gain adjustments on the BOSOZ...which does not effect output impendance of the pre-amp.
I made the filters on a plug in board so I could try different capacitor values, inductance values and experimenting with more than one stage.
The results are very good...much better than the active crossovers I had been using which I thought killed the highly musical nature of the BOSOZ pre-amp and the Aleph 3 amps.
The results are very good...much better than the active crossovers I had been using which I thought killed the highly musical nature of the BOSOZ pre-amp and the Aleph 3 amps.
I'm using the a pair of Marchands, 24db per octave at 70hz highpass, being fed from Creek OBH-12 remote passive line level attenuator/switcher which is being fed from a Bryston BDA-1 for most of my sources. The Bryston has a 50 ohm output impedance. I had tried an other DAC that had a 560 ohm out. Details here
http://www.diyaudio.com/forums/showthread.php?s=&threadid=131541&highlight=
The sub has it's own, active, lowpass.
Because of the passive nature of my setup I need high gain amps. Currently they are 36db gain X-Amps from AV123. Amps are plugged in to the wall. Everything else is plugged into a Pure AV conditioner. No hum, noise, or hiss. Very satisfied with this system. I've used active Xovers in the past and they've always imposed themselves.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=131541&highlight=
The sub has it's own, active, lowpass.
Because of the passive nature of my setup I need high gain amps. Currently they are 36db gain X-Amps from AV123. Amps are plugged in to the wall. Everything else is plugged into a Pure AV conditioner. No hum, noise, or hiss. Very satisfied with this system. I've used active Xovers in the past and they've always imposed themselves.
passive llxo
Thank you Coloradosound, I didn't know Marchand made passive line-level filters, only that they made active tube based ones.
Pano - I already know the T-linespeakers.org article. Thanks anyway.
So a pre-amp with an output imp. of say 300 ohm would require what? Two power amps of 100 kOhm? Can anyone give me a ball park figure?
tnx
Thank you Coloradosound, I didn't know Marchand made passive line-level filters, only that they made active tube based ones.
Pano - I already know the T-linespeakers.org article. Thanks anyway.
So a pre-amp with an output imp. of say 300 ohm would require what? Two power amps of 100 kOhm? Can anyone give me a ball park figure?
tnx
just to revitalize this thread from a newbs perspective, if ok? I hope you don't mind!
I read Dave's,Planet10 site and Art Ludwig's info, um, but please is there a more comprehensive reference of the subject? I searched PLLXO, and I'm still wading through it all!
Some 'dumb' Q's please:
Line-Level, I assume is low volume signal from source to amp.. But, is a preamp really necessary then?
Can't I just split the signal from the CD and buy another integrated amp for the mid/tweet (or FRanger)? LPass to woofer amp and HP to FR amp. Can various xo methods be integrated?
I know parallel/series can, so I guess they can be used on the driver after pllxo.
My ancient amp has "TUNER, CD & VIDEO - 135mV/22k ohms" input. Is 22K too low?
I'm (still) trying to understand the plusses and minuses of so many xo methods, and which is the cheapest to implement. PLLXO seems a very cheap solution, albeit, with limitations. 12dB/O max and Impedance restrictions etc.
Good passive xo inductors can cost as much as a cheap Behringer, so otherwise I might as well try 'active'. Now I'm told a cheap CreativeLabs Audigy 4 soundcard has good xo capability as well!
Nah, that can't be true, can it? ...oops, I should re-write this, but the Tour de France just came on!
I read Dave's,Planet10 site and Art Ludwig's info, um, but please is there a more comprehensive reference of the subject? I searched PLLXO, and I'm still wading through it all!
Some 'dumb' Q's please:
Line-Level, I assume is low volume signal from source to amp.. But, is a preamp really necessary then?
Can't I just split the signal from the CD and buy another integrated amp for the mid/tweet (or FRanger)? LPass to woofer amp and HP to FR amp. Can various xo methods be integrated?
I know parallel/series can, so I guess they can be used on the driver after pllxo.
My ancient amp has "TUNER, CD & VIDEO - 135mV/22k ohms" input. Is 22K too low?
I'm (still) trying to understand the plusses and minuses of so many xo methods, and which is the cheapest to implement. PLLXO seems a very cheap solution, albeit, with limitations. 12dB/O max and Impedance restrictions etc.
Good passive xo inductors can cost as much as a cheap Behringer, so otherwise I might as well try 'active'. Now I'm told a cheap CreativeLabs Audigy 4 soundcard has good xo capability as well!
Nah, that can't be true, can it? ...oops, I should re-write this, but the Tour de France just came on!
I think a passive line level XO will sound better than active.
use a capacitor and inductor for a second order filter that will have good roll off and not reduce gain too much. Capacitor/Resistor implementations like the one you are looking at in PLXXO web site will reduce the gain quite a bit.
capacitors will be in the order of .4uf and inductors will be on the order of 50mh.
Mock up your xo in an electronic simulator to get the approximate values and then put it in your system. Then get a signal generator...hook it up to your preamp and sweep the system to see where the roll off actually is. Then make adjustments in inductance and capacitance accordingly.
When done...it will sound great...
use a capacitor and inductor for a second order filter that will have good roll off and not reduce gain too much. Capacitor/Resistor implementations like the one you are looking at in PLXXO web site will reduce the gain quite a bit.
capacitors will be in the order of .4uf and inductors will be on the order of 50mh.
Mock up your xo in an electronic simulator to get the approximate values and then put it in your system. Then get a signal generator...hook it up to your preamp and sweep the system to see where the roll off actually is. Then make adjustments in inductance and capacitance accordingly.
When done...it will sound great...
I haven't done it but see no reason why you can't. The output impedance of the pre and the input impedance of the power amp don't matter, as long as they're flat with frequency. That's usually the case. You can design a passive network to give any response you want and drop it between, but the cost will always be gain. As long as you have enough excess gain to overcome the loss of the network (and sufficient headroom so it doesn't clip), it should work fine. There are various books on passive network design- if you search around you might find a copy of the old Sams Photofact book, Passive Audio Network Design by Howard M. Tremaine somewhere for cheap. IMO, and good text from Terman on up would be a good start on understanding this stuff.
audionut, great!
cap and coil topology will be the same as a 'normal' passive parallel xo?, (but lower values?)
I'm wondering why the R was introduced in the Ludwig article if it has a big insertion loss?
So, do I still need a preamp.... and can't I just use 2 integrated power amps?
Can I simulate pllxo in Speaker Workshop? I did some passive stuff in that prog.
Sig-generator, I think I have software to do that. I just bought a new WM-61A electret module from Gainphile and have just downloaded ARTA, so early days for measurement just yet.
BTW, please say G'day to Omni in Rossford Ohio for me! cheers mate and thanks.
Conrad, ...wow,
re: "I haven't done it but see no reason why you can't."
Thats very encouraging indeed. I need to read up further on your other comments before I can make a sensible reply! Your help is very much appreciated!
PS: Lance Armstrong is awesome! Go Lance!
cap and coil topology will be the same as a 'normal' passive parallel xo?, (but lower values?)
I'm wondering why the R was introduced in the Ludwig article if it has a big insertion loss?
So, do I still need a preamp.... and can't I just use 2 integrated power amps?
Can I simulate pllxo in Speaker Workshop? I did some passive stuff in that prog.
Sig-generator, I think I have software to do that. I just bought a new WM-61A electret module from Gainphile and have just downloaded ARTA, so early days for measurement just yet.
BTW, please say G'day to Omni in Rossford Ohio for me! cheers mate and thanks.
Conrad, ...wow,
re: "I haven't done it but see no reason why you can't."
Thats very encouraging indeed. I need to read up further on your other comments before I can make a sensible reply! Your help is very much appreciated!
PS: Lance Armstrong is awesome! Go Lance!
Yes ! if you use a loudspeaker with high impedance, the amplifier impedance and the loudspeaker response.
According to these formulas I made for the example, a crossover on SW with real speaker. Here the speakers are SEAS T25 and the old CA21.
I made a impedance file for the amplifier : 20K and 0 for the phase.
In the woofer section I compensate the baffle step, the crossover frequency (-3dB) is 500Hz !
The tweeter section have a crossover frequency (-3dB) of 2700Hz.
The tweeter have not resistor before the amplifier because it's the impedance the amplifier.
The real xover frequency of the system is 1800Hz. The phase of the system is good because the tweeter and the woofer have acoustic center physically align. You should align the tweeter by tilting the baffle.
An externally hosted image should be here but it was not working when we last tested it.
I've been looking at this page....I believe that the example laid out there assumes the turnover frequency is the same for high and low pass. That seems to introduce some dependency of R1 (in the LP filter) in calculating R2.
What I want to do is design a 1st order crossover that has a different turnover frequency for the LP than the HP (400 and 1600 Hz respectively)
Also, my HF and LF amps have different input impedances.
Anybody know of the calculations that would incorporate these variables?
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