mboxler
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Everything posted by mboxler

I think this is the document describing the issue. I don't remember anyone figuring out how to fix it. If you run differential inputs to the amp and bypass the input op amps, I believe you circumvent the issue. http://www.ti.com/lit/an/slaa719/slaa719.pdf Mike

About threequarters down this page...maybe? https://community.klipsch.com/index.php?/topic/113804klipschcrossovers/page/8/ Looks like it was pulled from here... https://audiokarma.org/forums/index.php?threads/crossoverupgradeonrf83s.588494/

Another way to look at it... The two rooms are the two capacitor plates. The wall between them is the dielectric. Ideally, the door between the rooms is so small that everyone (the current) will need to go through the hallway (the circuit) to get to the other room (the other plate). In reality, some people do get through the small door (leakage current). Sorry...only door analogy I could come up with.

I use this for capacitors http://www.pronine.ca/capimp.htm and this for inductors http://www.pronine.ca/indimp.htm Just enter the "resistor" value in the impedance field and it will calculate the 3db frequency.

If you are like me, you understand what capacitors are doing in a crossover, but may not know how they are doing it. I attached two videos that helped me. The first describes the capacitor itself. It helped me understand how an open circuit (the capacitor) can allow current to flow. The second places a capacitor in an AC circuit. It describes inductor as well, but that's another topic. If you replace the resistor with a speaker driver, or taps 0  5 in a heritage crossover, you will see why the current flows through them 90 degrees before the voltage across the capacitor changes. You will also see why more current flows at higher frequencies. I realize this is 20 minutes of your life that you will never get back, but I hope you find them educational. Mike https://www.youtube.com/watch?v=f_MZNsEqyQw https://www.youtube.com/watch?v=zO7RZZW0wSQ&list=PLkyBCj4JhHt4PnnwpbGZKV_EjX03DX8&index=15

Yes. Actually, I believe Bob Crites measured a K55 driver in a K400 horn and came up with closer to 14.5 ohms, but you get the point. If you mean the frequency at which the impedance of the capacitor is equal to the impedance of taps 0  5, yes. Using 14.5 ohms across taps 0 4 as an example, the load across taps 0  5 would be double that, or 29 ohms. A 13 uf capacitor reaches 29 ohms around 422 hz. A 14.5 ohm resistor in parallel with the 14.5 ohm driver gets you a 7.25 ohm load. I realize the driver is not a pure resistive load, but... By moving these to taps 0  3, the reflected load across taps 0  5 is 4 times that load, or 29 ohms, right back to stock. No apology needed. You had me questioning myself. I'm not saying that the series resistor won't work, it just works differently. In my example, adding a 14.5 ohm resistor in series with 29 ohm impedance of taps 0  5 results in a 43.5 ohm load on the 13 uf cap. As mentioned before, this load is in parallel with the k77 circuit, so that will change some as well. Again, if it sounds good, it is good. Mike

By across the squawker, we mean in parallel anywhere between taps 0  3 and the K55. Placing the resistor across the + and  terminal block screws going to the K55 is a convenient spot. A parallel resistor in and of itself will not change the voltage across the squawker. What it will do is draw more current from the amplifier. If the resistor is equal to the squawker impedance, the current drawn will double. Since the extra current passes "through" the 13uf capacitor, it charges twice as fast. This, in turn, doubles the corner frequency from 400 hz to 800 hz. We haven't reduced the voltage to the squawker, it just takes an octave longer to reach maximum voltage. By dropping the output taps to 0  3, we cut the current across taps 0  5 in half. Now the current through the 13uf capacitor is equal to the stock setup, and it's corner frequency is back to 400 hz. The maximum voltage across the squawker, however, is down 3 db at all frequencies. I assume a 14  16 ohm resistor was used??? Lpads work well because they drop the voltage across the squawker without changing the current drawn from the amplifier. The 13 uf cap charges at the same rate. Now let's place the socalled swamping resistor (usually 10 ohms) across taps 0  5. It has no effect on the voltage across taps 0  5, but it will draw a significant amount of current, and that current stays pretty much the same no matter what output taps are used. A 13 uf capacitor will charge way too fast. It needs to be replaced with, say, a 48 uf cap that will take longer to charge. I don't understand option two above. It would drop the voltage throughout the circuit, but it would also lower the corner frequency of the 13 uf capacitor because less current is "flowing" through it. At least I think that's right. No matter what, if the change sounds better to you, it is better! Mike

That's the easiest way to do it. This is an easy/inexpensive way to lower the voltage across the driver AND keep the current "through" the 13uf capacitor close to a stock AA crossover.

Did you end up soldering a 15  16 ohm resistor across the squawker and move the squawker to taps 0  3?

A55g and need for an HF crossover point mod?
mboxler replied to Alexander's topic in Technical/Modifications
Although the video describes a transformer instead of an autotransformer, it will still work. If your primary inductance is 105.3 mH, then set your secondary inductance to 10.53 mH. The 10 db turns ratio is 3.165. 3.165 squared is 10. Since this a step down transformer, you divide the primary inductance (105.3) by 10 to get the secondary inductance (10.53). I haven't tried this, but I think I got the math right. If you want to model an autoformer, the inductor values would be 49.2 mH and 10.53 mH. Mike 
A55g and need for an HF crossover point mod?
mboxler replied to Alexander's topic in Technical/Modifications
I would be happy to send you my version of a 12 tap auto transformer. It seems to work pretty well. It's currently part of a Type A simulated circuit. I assume I can attach an .asc file in a private message. Mike 
Looks good to me! You have now created two separate filter circuits. They will become one parallel circuit when the binding posts are strapped. They can also be paralleled when "strapped" at the amp...biwiring. They can also be run as separate circuits, each connected to its own amp...biamping. Mike

I like the colors! I believe you should move the common wire that connects to tap 0 from input L  to input H . The autoformer is part of the high pass filter. Mike

This won't be too difficult... Relabel the input terminals as input low. Use the two empty terminal barrier strips as input high + and . Move the wire going to the 13uf cap from the current input + to the new input high +. Cut the common wire between the output woofer  and the output mid . If you cut it close to the woofer out  screw you may have enough to shift the remaining wire to the left. In the end, one common wire from input low  to woofer out , one common wire from input high  to output tweeter  and output mid . Now, connect your top binding posts to input high, and the bottom binding posts to input low. For single wire from your amp, you will need to strap your + binding posts together and your  binding posts together. For biamp/biwire, remove the straps. Actually, you made your speaker a little more versatile! I hope I visualized that right. Mike

Moving sale (Colorado)  Cornwalls, crossovers, parts, etc
mboxler replied to Red's topic in Garage Sale
Which part of Colorado? 
Measuring autotransformer values....
mboxler replied to Alexander's topic in Technical/Modifications
Crap! I've seen that thread but never scrolled down far enough to see Mr. Warren's schematic of a T2A. Since the inductances of the various taps are listed on the T2A datasheet, he made it easier by replacing one four tap autoformer with four one tap autoformers. I, on the other hand, have been struggling with the one four tap math. The inductance of the T2A taps 0 and 5 must be 45.6 mH...4 times the 11.4 mH inductance between taps 0 and 3. 
Measuring autotransformer values....
mboxler replied to Alexander's topic in Technical/Modifications
Coupling series inductors using the K command is the only way. While having a few beers with my brothers, I got an idea. I disconnected my 3619ET from ALK crossover and measured the inductance from 0  5, 76 mH. Again I tried to measure the other taps, but the reading would always change each time I tried. I decided to calculate the inductances based on the turns ratios involved. I used 76 mH as my baseline inductance. I think it works. Maybe you can also try this and see if it's close. It's sure a lot cleaner. The response curve is similar, but the phase curve changed. The DCR values for inductors L1 thru L5 are .108 .076 .054 .038 and .093 ohms respectfully. Around .37 ohms total. Mike 
Measuring autotransformer values....
mboxler replied to Alexander's topic in Technical/Modifications
Here's the response curve of the 20 X 10 mH inductor (mutually coupled) T2A, using tap 4 (14 inductors). Green is voltage across taps 0 and 5, red across 0 and 4. Not sure how close it is the the voltage across a real K77. 
Measuring autotransformer values....
mboxler replied to Alexander's topic in Technical/Modifications
This may be hard to see. I'd be happy to send you the .asc file if you want. Mike 
Measuring autotransformer values....
mboxler replied to Alexander's topic in Technical/Modifications
I tried, but I seemed to get weird results on my DE5000. Seems like the numbers would fluctuate each time I measured. More importantly, It seems that the measurement between taps 0 and 3 would not always equal 1/4 the value between taps 0 and 5. The issue, however, is that the output voltage of an autoformer is based on the winding ratio, not the inductance ratio. Inductance is based on several variables, and windings is only one of them. LTSpice let's you specify the inductance and DCR only. All other variables being equal, a 40 mH inductor should have twice the windings as a 10 mH inductor. My T2A LTSpice autoformer equals twenty 10 mH inductors in series and coupled. Tap 4 equals 14 of the inductors. Tap 3 equals 10 of the inductors. Tap 2 equals 7 of the inductors. Taps 1 equals 5 of the inductors. It comes out pretty close. My reasoning was that each of the 10 mH inductors would have the same number of windings. I can try to post my Type AA if you would like. Mike 
Looking Good! I see the autoformers got a little roughed up. They were fine when I sent them. I should have mentioned that when I wrapped the common wire on the barrier strips, I intended them to be on the crossover side. It will work as you have it, but it will be easier to connect/disconnect the cables from the amp and to the drivers. If the amp is still on, as you connect/disconnect a + wire it will be too easy to touch it to the common wire below it. Mike

Type A Crossover  Capacitors in series?
mboxler replied to Robbie010's topic in Technical/Modifications
It wasn't pretty, but I got some numbers out of LTspice. I modified my test board and came up with 12.769uf and 2.077uf values. When I plugged these cap values into LTspice, I came up with voltages that were very close to what I measured with my Fluke meter. Back to LTspice... Again, 2.83 volts 400 hz, 14.2 ohm K55, and 8 ohm K77. Capacitors 13uf and 2uf. Classic Type A K55 1.276 volts K77 .074 volts 2uf cap moved to amplifier input K55 1.38 volts K77 .114 volts (3.6 db increase) 13uf and 2uf in series with K77, no connection to autoformer K77 .0985 volts My autoformer model is a work in progress. I'm curious what voltages others end up with. Mike 
Type A Crossover  Capacitors in series?
mboxler replied to Robbie010's topic in Technical/Modifications
My apologies @John Warren . I've never used LTspice, and didn't understand the schematic. I've been using iCircuit and XSim, but can't simulate transformers/autotransformers. This link is interesting. Inductors are used along the a Kstatement to mutually couple the inductors. Both transformers and auto transformers are discussed. I'm playing with LTspice now. Slow learner. https://www.analog.com/en/technicalarticles/usingtransformersinltspiceswitchercadiii.html 
Type A Crossover  Capacitors in series?
mboxler replied to Robbie010's topic in Technical/Modifications
Looks like that autoformer simulation creates an electrical band pass across the 13 ohm resistor. Was that your intent? An accurate simulation would result in the voltage across the K55 rising to 0db along with the K77. I did find this, but I'm not smart enough to determine if it works. https://www.quora.com/Whatistheequivalentcircuitforautotransformersimpedances 
Type A Crossover  Capacitors in series?
mboxler replied to Robbie010's topic in Technical/Modifications
Unless I'm doing something wrong, this comes very close to what I'm seeing if you assume the K55 is a 16 ohm load. 13uf cap impedance + ((double the K55 impedance // (2uf cap impedance + K77 impedance))