I know I need an active crossover to do correctly but.... I have a tube power amp with attenuator . And i also have a crown xls 1502. I just rebuilt the crossovers on my Klipsch kg-4 .In the research i did I saw the induction wire gauge and the direction of the coils etc. I separated the hi and low on wooden boards and used 14 and 15 gauge air coil inductors with no ferrous metals and better cabinet wires and biding posts. I just want to try my tube amp on the tweeter (Crites titanium diaphragm installed today ) and the crown on the woofers . I know it's a dumb question . I just can't afford to do it right at this time I just don't know if the arrangement could hurt the tube amp. I know i won't get the advantages of active but can't help but think it would be fun to play with . I'm sure my hurt question is dumb too. I put this Dynaco VTA ST-120 tube amp kit in 2011. I am not a tech I have had to make alot of mistakes to get this far. When I built the amp I was far better off. I had a 24 x3o listening room with a ceiling that was like a horn it went from 8 to 12 then too 14 ft high Altec Votts thorens 125 watt kt 88 mono blocks . All sold . now its a 12' x12' x 92" ht. And It has a mode around 300 cycles that's bad.The kg4 sound nice in this dreaded cube . I'm a member of the dynaco forum . But I am tired of the snarky answers I get . I just want to know it won't be a risk to try this . Last time I asked if I could use a 6sn7 to 12au7 tube adaptor safely and I get a Why Not? from a guy that has way more knowledge than I will ever have . I don't think It's stupid to be carefull with something I couldn't replace. Hell I was running my tubes KT-120's @ .5v when the forum said .55=.6 and the kt 88's at.45v. the new tubes ... enough said. And now the forum advises the same . and have always had fans cooling it. So is tha-is ok to do . I separated the coils because of all the reading I did about it so the separation of high and low frequencies was more of a function over form . I already have the two binding posts .Thank you . Scott .
You don't need active to do it right, but you must know what the filters need to achieve.
I have made successful crossing and equalisation RC networks at line level. I've also incorporated them into the amp, but it's worth looking for opportunities to reduce the signal the amp sees.
Take care that inductors can be difficult to select for use at low frequencies and high impedances.
I have made successful crossing and equalisation RC networks at line level. I've also incorporated them into the amp, but it's worth looking for opportunities to reduce the signal the amp sees.
Take care that inductors can be difficult to select for use at low frequencies and high impedances.
You can make a 6db per octave hi pass with just a capacitor. You just need to know the input impedance and frequency you want. 1 divided by 2*3.14*input impedance*freq for the capacitor you will need. You’ll end up with a value in farads so it will look like 0.0000004000F or 4000pf for example.
Passive bi-amping can be worthwhile with modest improvements. It's probably not worth spending a lot of money doing but if you have the necessary bits why not try it?
The main benefits are more linear behaviour (lower distortion) in the high frequency amplifier because it is no longer producing the large currents required for the bass driver, and lower intermodulation introduced by the common speaker cable and crossover wiring in a typical non-biampable crossover implementation. In your case the character of the valve amplifier might better suit the horn as well.
You need to completely seperate the low pass (woofer) and high pass (horn) parts of the crossover so they have no common connections their own sets of input terminals.
You need to make sure the gain of the two amplifiers is the same to balance the lows and highs.
There's some good advice above about using a small coupling capacitor in front of the horn amplifier to reduce very low bass frequencies getting to the amplifier, which will preserve headroom in the amplifier.
You need to make sure that both amplifiers are either non-inverting or inverting, so that the two speakers sum correctly at the crossover frequency, otherwise there will be a narrow band of frequencies that cancel out centred on the crossover frequency.
If one amplifier inverts the signal, but the other does not, you can simply reverse the connections between the inverting amplifier and its driver by crossing over red and black wires are the speaker input terminals for that section only.
The main benefits are more linear behaviour (lower distortion) in the high frequency amplifier because it is no longer producing the large currents required for the bass driver, and lower intermodulation introduced by the common speaker cable and crossover wiring in a typical non-biampable crossover implementation. In your case the character of the valve amplifier might better suit the horn as well.
You need to completely seperate the low pass (woofer) and high pass (horn) parts of the crossover so they have no common connections their own sets of input terminals.
You need to make sure the gain of the two amplifiers is the same to balance the lows and highs.
There's some good advice above about using a small coupling capacitor in front of the horn amplifier to reduce very low bass frequencies getting to the amplifier, which will preserve headroom in the amplifier.
You need to make sure that both amplifiers are either non-inverting or inverting, so that the two speakers sum correctly at the crossover frequency, otherwise there will be a narrow band of frequencies that cancel out centred on the crossover frequency.
If one amplifier inverts the signal, but the other does not, you can simply reverse the connections between the inverting amplifier and its driver by crossing over red and black wires are the speaker input terminals for that section only.
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Thank you very much . Is there a calculator to get correct coupling cap ? The crown has gain controls .And I have put all the options on the St-120 tube amp pentode, triode, Bias all 4 power tubes so i don't have to have matched quads delay for power tubes and an attenuator . So yes everything kind of lent itself to the idea. I seam to see most of the actives have the balanced inputs and outputs . I want the Accuphase F25V but It's $80.00 shipping AND 4 K to purchase ! .But it does come with some type of plug in with 1800 cycle point . I thought it would be interesting to try my Magnapans with active also but it has a strange design low pass 12 db per at 300 cycles and high at 2500 cycles .I don't know if they can be bi amped or not I don't know why but it mentioned Needing to use the amps in a vertical bi amp I have two crowns but one is an xls 1000 and the other is an xls 1500 but they do have hi and low pass up to 3000 cycles but no 1st order second order options . In looking at diving ahead of the power amps the phase and resistance issues are the same as a passive design ? . Again I yield to your expertise .Thanx allot I really appreciate it. and I will look into the inverting issue .so do you think I should put a cap in front of the horn tweeter ?
You can calculate the capacitor value but you need to know other circuit details from the schematic. Let's say the input impedance to the amplifier is ~20kΩ and you decide to block everything from ~500Hz down (you want this corner frequency to be a couple of octaves below the true crossover so it does not alter the alignment). The capacitor needs to be ~15nF. If you want it to be 250Hz, double the value (e.g. 27nF or 33nF). If the input impedance of the amplifier is 100kΩ for 500 Hz then divide the value by 20/100 = 15nF ÷ 5 = 2.7nF or 3.3nF, for 250Hz double that value = 5.6nF or 6.8nF. The actual value isn't important for this application; ±20% is fine.
There's a high pass filter calculator with explanation here: High Pass Filter Calculator
Going to an active crossover from a passive one is not as simple as replicating the crossover frequency; to a greater or lesser degree the passive crossover is designed to take into account the actual responses of the drivers connected to the output of the crossover. These responses will be quite different when the drivers are connected directly to amplifier outputs with near zero impedance, which is quite unlike a passive crossover with its frequency dependant output impedance connected to the drivers. An active implementation may need offsets in the high and low pass frequencies and some equalisation to replicate the passive crossover it is replicating.
Putting a large bipolar capacitor in front of the horn driver will give the driver some protection from DC if an amplifier were to fail. However if you implement a bi-amp passive design there will already be a capacitor in series with the horn driver, so there is no benefit in adding another one.
There's a high pass filter calculator with explanation here: High Pass Filter Calculator
Going to an active crossover from a passive one is not as simple as replicating the crossover frequency; to a greater or lesser degree the passive crossover is designed to take into account the actual responses of the drivers connected to the output of the crossover. These responses will be quite different when the drivers are connected directly to amplifier outputs with near zero impedance, which is quite unlike a passive crossover with its frequency dependant output impedance connected to the drivers. An active implementation may need offsets in the high and low pass frequencies and some equalisation to replicate the passive crossover it is replicating.
Putting a large bipolar capacitor in front of the horn driver will give the driver some protection from DC if an amplifier were to fail. However if you implement a bi-amp passive design there will already be a capacitor in series with the horn driver, so there is no benefit in adding another one.
This discussion kinda gets close to what I've been chipping at...although my app isn't 'huge', perhaps my path will generate some thought along this topic-
Started Q thread several months ago regarding 'Bi-Coiling' single amp outputs so that dual output trafo coils could be assigned individually to treb/mid & bass/sub.
Multiple tap OT's??
Original thinking posted is / was reason for where I am now-
Hammond 1620's: 0-4, 0-8 outs... Currently 0-4 winding is 2nd order to 12" sub. 0-8 winding is 1st order to mid bass, mid, & treb...
Been listening to this PP amp every nite since Apr '20 w/multiple config's... and this is the best sound so far...particularly in the mid/mid bass transition...
Jim
Started Q thread several months ago regarding 'Bi-Coiling' single amp outputs so that dual output trafo coils could be assigned individually to treb/mid & bass/sub.
Multiple tap OT's??
Original thinking posted is / was reason for where I am now-
Hammond 1620's: 0-4, 0-8 outs... Currently 0-4 winding is 2nd order to 12" sub. 0-8 winding is 1st order to mid bass, mid, & treb...
Been listening to this PP amp every nite since Apr '20 w/multiple config's... and this is the best sound so far...particularly in the mid/mid bass transition...
Jim