LC 600ohm xover
Posted: Sun Jan 13, 2008 12:05 pm
Ciao!
First post here but I have been looking at Dave's forum since ages.
I prototypied a 600Ohm LCL xover I am driving with my 801A preamp and I currently use it for my biamped system. Having a line xover allows me to run my horns and onkens free and it is a huge improvement over the "traditional" caps/inductors nets we attach in front of the drivers. Pultec made it in the golden years, why shouldn't I do it now?
Selectable freqs 600, 750, 900 and 1100Hz, 18db/oct and I am waiting for some NOS langevin 600Ohm stepped attenuator to replace the linear pots I am using to balance the low/high.
The basic schematic is pretty simple (the value you see in the attached file are NOT updated ... that was an old spice sim). An input 600:600 tranny, a R to offer the pre a flatter load, and the LCL - CLC network. The last 600R is a tapped resistor or pot. And an output 600:600 tranny.
At the scope I found the -3dB points are pretty close to the theoretical. The low freq filter cuts a at a freq a bit higher than theoretical while the hi freqs a bit lower. That's fine. The pendence is not exactly 18dB but that is not really an issue. Please refer to the xls graph for experimental values. The components values and the theoretical cutting freqs follow
High Pass 1100Hz
C 0.32uF
L 33mH
Freq 1095Hz
Impedance 454Ohm
Low Pass 1100Hz
C 0.626uF
L 68mH
Freq 1090Hz
Impedance 466Ohm
High Pass 900Hz
C 0.47uF
L 33mH
Freq 903Hz
Impedance 375Ohm
Low Pass 900Hz
C 0.94uF
L 68mH
Freq 890Hz
Impedance 380Ohm
High Pass 750Hz
C 0.47uF
L 47mH
Freq 757Hz
Impedance 447Ohm
Low Pass 750Hz
C 1.096uF
L 82mH
Freq 751Hz
Impedance 386Ohm
High Pass 600Hz
C 0.47uF
L 82mH
Freq 573Hz
Impedance 590Ohm
Low Pass 600Hz
C 0.94uF
L 150mH
Freq theo 564Hz
Impedance 466Ohm
As you see the impedance of the filter is lower than 600Ohm. Actually I found that the lower is the better using the ear as measurint instruments. The drawback is that the preamp will suffer because of the lower load. 400-600Ohm seems to be a good compromise here. Going up with the impedance was not giving good results, the driver will be happier but the overall results was not as good as a 400Ohm filter. Don't ask me why.
Does anyone care to share his experience on the subject?
Ok, a compulsory pic of the prototype is attached. I am using tapped inductors from cinemag and teflon caps from CCCP (line trannies are from cinemag too). It sounds right but I am considering an upgrade to nickel cored inductors.
Values of the inductors are 33, 47, 68, 82, 150mH with a signal in the 5Vrms range.
Dave, is there any chance you can mix some copper and nickel for this project? I need to see if other values may be of interest (thinking to go down to 300Hz or so).
Gianluca
First post here but I have been looking at Dave's forum since ages.
I prototypied a 600Ohm LCL xover I am driving with my 801A preamp and I currently use it for my biamped system. Having a line xover allows me to run my horns and onkens free and it is a huge improvement over the "traditional" caps/inductors nets we attach in front of the drivers. Pultec made it in the golden years, why shouldn't I do it now?
Selectable freqs 600, 750, 900 and 1100Hz, 18db/oct and I am waiting for some NOS langevin 600Ohm stepped attenuator to replace the linear pots I am using to balance the low/high.
The basic schematic is pretty simple (the value you see in the attached file are NOT updated ... that was an old spice sim). An input 600:600 tranny, a R to offer the pre a flatter load, and the LCL - CLC network. The last 600R is a tapped resistor or pot. And an output 600:600 tranny.
At the scope I found the -3dB points are pretty close to the theoretical. The low freq filter cuts a at a freq a bit higher than theoretical while the hi freqs a bit lower. That's fine. The pendence is not exactly 18dB but that is not really an issue. Please refer to the xls graph for experimental values. The components values and the theoretical cutting freqs follow
High Pass 1100Hz
C 0.32uF
L 33mH
Freq 1095Hz
Impedance 454Ohm
Low Pass 1100Hz
C 0.626uF
L 68mH
Freq 1090Hz
Impedance 466Ohm
High Pass 900Hz
C 0.47uF
L 33mH
Freq 903Hz
Impedance 375Ohm
Low Pass 900Hz
C 0.94uF
L 68mH
Freq 890Hz
Impedance 380Ohm
High Pass 750Hz
C 0.47uF
L 47mH
Freq 757Hz
Impedance 447Ohm
Low Pass 750Hz
C 1.096uF
L 82mH
Freq 751Hz
Impedance 386Ohm
High Pass 600Hz
C 0.47uF
L 82mH
Freq 573Hz
Impedance 590Ohm
Low Pass 600Hz
C 0.94uF
L 150mH
Freq theo 564Hz
Impedance 466Ohm
As you see the impedance of the filter is lower than 600Ohm. Actually I found that the lower is the better using the ear as measurint instruments. The drawback is that the preamp will suffer because of the lower load. 400-600Ohm seems to be a good compromise here. Going up with the impedance was not giving good results, the driver will be happier but the overall results was not as good as a 400Ohm filter. Don't ask me why.
Does anyone care to share his experience on the subject?
Ok, a compulsory pic of the prototype is attached. I am using tapped inductors from cinemag and teflon caps from CCCP (line trannies are from cinemag too). It sounds right but I am considering an upgrade to nickel cored inductors.
Values of the inductors are 33, 47, 68, 82, 150mH with a signal in the 5Vrms range.
Dave, is there any chance you can mix some copper and nickel for this project? I need to see if other values may be of interest (thinking to go down to 300Hz or so).
Gianluca