Alexander Posted February 21, 2020 Share Posted February 21, 2020 Has anyone taken the time to have measured say a 3636 autotransformer for mH & DCR at each tap combination? I mean with a lab like level of accuracy and not an eBay $20 type meter. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 21, 2020 Share Posted February 21, 2020 Maybe @BEC, ALK Engineering or how about the manufacturer? 1 Quote Link to comment Share on other sites More sharing options...
Alexander Posted February 21, 2020 Author Share Posted February 21, 2020 20 minutes ago, babadono said: Maybe @BEC, ALK Engineering or how about the manufacturer? All I have been able to find from either supplier has been the product of those combos in db's . But when I want to make up a circuit say in LTSplice I would like to “recreate” a T2A,T5A or T7A as needed. Quote Link to comment Share on other sites More sharing options...
Alexander Posted February 21, 2020 Author Share Posted February 21, 2020 I should add: I do have basic rudimentary means to measure this stuff but feel the actual accuracy would be very much in question Quote Link to comment Share on other sites More sharing options...
babadono Posted February 21, 2020 Share Posted February 21, 2020 @Deang Deanno, do you know where any of this is available? Quote Link to comment Share on other sites More sharing options...
mboxler Posted February 21, 2020 Share Posted February 21, 2020 2 hours ago, Alexander said: Has anyone taken the time to have measured say a 3636 autotransformer for mH & DCR at each tap combination? I mean with a lab like level of accuracy and not an eBay $20 type meter. I tried, but I seemed to get weird results on my DE-5000. 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 1 Quote Link to comment Share on other sites More sharing options...
Alexander Posted February 22, 2020 Author Share Posted February 22, 2020 4 hours ago, mboxler said: I can try to post my Type AA if you would like. Mike Hey Mike, I would love to see your example. Quote Link to comment Share on other sites More sharing options...
glens Posted February 22, 2020 Share Posted February 22, 2020 I don't think it's all that complicated. Sure, a transformer coil is going to have some inductance when measured singly for such, but I don't believe it's acting like an inductor (i.e. a filter element) while being used as a transformer. 2 Quote Link to comment Share on other sites More sharing options...
mboxler Posted February 22, 2020 Share Posted February 22, 2020 1 hour ago, Alexander said: Hey Mike, I would love to see your example. This may be hard to see. I'd be happy to send you the .asc file if you want. Mike Quote Link to comment Share on other sites More sharing options...
pzannucci Posted February 22, 2020 Share Posted February 22, 2020 10 hours ago, glens said: I don't think it's all that complicated. Sure, a transformer coil is going to have some inductance when measured singly for such, but I don't believe it's acting like an inductor (i.e. a filter element) while being used as a transformer. Yes they are over thinking it for audio frequencies. 1 Quote Link to comment Share on other sites More sharing options...
pzannucci Posted February 22, 2020 Share Posted February 22, 2020 If I was trying to guess and wanted real numbers, I would put a good 8ohm inductive load resistor on the taps and measure with something like woofer tester or DATS. You can extrapolate the numbers at each tap based on the change in impedance. Quote Link to comment Share on other sites More sharing options...
mboxler Posted February 22, 2020 Share Posted February 22, 2020 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 K-77. Quote Link to comment Share on other sites More sharing options...
Alexander Posted February 22, 2020 Author Share Posted February 22, 2020 18 hours ago, mboxler said: This may be hard to see. I'd be happy to send you the .asc file if you want. Mike . OK. I see what you have done here, not sure how you got there but if it works I will follow your example, thank you for sharing this. Quote Link to comment Share on other sites More sharing options...
Alexander Posted February 22, 2020 Author Share Posted February 22, 2020 glens and pzannucci, the problem is in the LTSplice program there are no elements (that I can find anyway) to represent an autotransformer when making even a simple Klipsch OEM crossover. To just have a cap in series with the mid drive makes a mess of things so I am looking for a way to find a work around. Quote Link to comment Share on other sites More sharing options...
mboxler Posted February 22, 2020 Share Posted February 22, 2020 1 hour ago, Alexander said: glens and pzannucci, the problem is in the LTSplice program there are no elements (that I can find anyway) to represent an autotransformer when making even a simple Klipsch OEM crossover. To just have a cap in series with the mid drive makes a mess of things so I am looking for a way to find a work around. 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 3619-ET 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 Quote Link to comment Share on other sites More sharing options...
glens Posted February 23, 2020 Share Posted February 23, 2020 Why not simply derive the impedance as seen from the high side of the transformer and use that in your calculations, treating the transformer and driver as a single entity? Quote Link to comment Share on other sites More sharing options...
Wirrunna Posted February 23, 2020 Share Posted February 23, 2020 This thread may be relevant - http://www.northreadingeng.com/Audio/group/viewtopic.php?f=12&t=10&p=38#p38 Quote Link to comment Share on other sites More sharing options...
mboxler Posted February 23, 2020 Share Posted February 23, 2020 1 hour ago, Wirrunna said: This thread may be relevant - http://www.northreadingeng.com/Audio/group/viewtopic.php?f=12&t=10&p=38#p38 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. Quote Link to comment Share on other sites More sharing options...
Deang Posted February 23, 2020 Share Posted February 23, 2020 On 2/21/2020 at 8:38 PM, glens said: ...I don't believe it's acting like an inductor (i.e. a filter element) while being used as a transformer. Right. The inductance is so high it’s not doing anything. Well, it is introducing phase shift. Quote Link to comment Share on other sites More sharing options...
Wirrunna Posted February 23, 2020 Share Posted February 23, 2020 (edited) On 2/22/2020 at 12:38 PM, glens said: I don't think it's all that complicated. Sure, a transformer coil is going to have some inductance when measured singly for such, but I don't believe it's acting like an inductor (i.e. a filter element) while being used as a transformer. I agree. I have always ignored the autotransformer in LTspice x-over models Here is the LTspice run plot of my home brew ES networks and the REW measurement of the network at the speaker terminals with the autotransformer in circuit with the mid. I may add a T2A autotransformer and the resistor attenuator to the LTspice model and compare the run prediction but don't hold your breath. Edited February 23, 2020 by Wirrunna Changed LTspice plot to white background 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.