The formula for parallel resistance is 1/Rt= 1/R1+1/R2+1/R3....If any one or more of the paralleled resistor is 0 ohm, it is a short circuit and the total resistance should be 0 ohm.
https://www.electronics-notes.com/articles/basic_concepts/resistance/resistors-in-series-parallel.ph...
Since he measured almost 8 ohms then the total resistance will be 1/8 ohm + 0 ohm or 0.125ohm.
testing a crossover
hi guys and girls i have a
problem with my 3 way wilmslow-audio mirrage speakers , I am hoping you can help me with the problem,.
Lately my power amp went pop and i sent it away for repair,when i
received it back {repaired} it went pop again,on sending it back to
the repair technician ,he has come back to me ,and asked me to take
some ohms readings on the speakers, on testing the speakers , i run
these speakers using 2 power amps{Arcam Alpha 10s,using one for low
pass{bass} and the other for MID/HIGH,this is the amp which keeps
blowing,on the high /mid,on testing the terminal the bass{low pass}
read {left speaker]7.9 ohms ,right speaker bass 6.8ohms, But on the
left and right speakers hi/mid ,both read 0.0 ohms,{which we all know
is wrong}
BUT the strange thing is,when the blown amp was away,i only used one
power amp to run both speakers in bi wire config,and they worked
ok,all being a bit lack of bass and tightness,but still sound great.
So i stripped both speakers and checked the drivers,all 6 drivers
where good no shorts reading approx correct ohms for age,{Speakers
disconnected from x over}.can any one help with this,i would be so much in debt.
kind regards Mark
problem with my 3 way wilmslow-audio mirrage speakers , I am hoping you can help me with the problem,.
Lately my power amp went pop and i sent it away for repair,when i
received it back {repaired} it went pop again,on sending it back to
the repair technician ,he has come back to me ,and asked me to take
some ohms readings on the speakers, on testing the speakers , i run
these speakers using 2 power amps{Arcam Alpha 10s,using one for low
pass{bass} and the other for MID/HIGH,this is the amp which keeps
blowing,on the high /mid,on testing the terminal the bass{low pass}
read {left speaker]7.9 ohms ,right speaker bass 6.8ohms, But on the
left and right speakers hi/mid ,both read 0.0 ohms,{which we all know
is wrong}
BUT the strange thing is,when the blown amp was away,i only used one
power amp to run both speakers in bi wire config,and they worked
ok,all being a bit lack of bass and tightness,but still sound great.
So i stripped both speakers and checked the drivers,all 6 drivers
where good no shorts reading approx correct ohms for age,{Speakers
disconnected from x over}.can any one help with this,i would be so much in debt.
kind regards Mark
Showing 11 responses by imhififan
i would also upload some photos, but as this is my first ever use on this site,im not sure how to do thisGo to Virtual Systems page, use the "Create System" to upload photos. https://systems.audiogon.com/ |
ill try draw a schem.but its difficult, but ill do my best@ likklegerry, If you can print-out the crossover pcb photo and add all the component position on it with wiring and post the picture, maybe we can figure out the schematic and go from there. https://www.wilmslowaudio.co.uk/ekmps/shops/wilmslow/images/crossover-pcb-452-p.jpg an example: https://ibb.co/3zyQRyG |
Hi Guys,thankyou so much for all your help,but i still dont see a solution to this problem,in my opinion there is shorts in both xos,please see below-Please disconnect the wires from binding post and measure the MID/HIGH resistance again across IP+ and IP- to rule out the short is not from the binding posts. DRIVER TEST DISCONNECTED FROM X OVER The above measurement of MID HIGH INPUT IP looks OK, TEST TESTED AT/ON X-OVER SPEAKERS CONNECTED OHMS The HF measurement should equal to the DC resistance of the 0.22mH inductor. The MF measurement should equal to the DC resistance of the 2.5mH inductor + 2.2Ω. My suggestion is desolder all components from PCB, clean up the PCB, measure all components before re-install to PCB, leave some gap between resistor and capacitor to avoid heat damage those capacitors. |
You can find all the photos here https://systems.audiogon.com/ Without drivers connected, The HF measurement should equal to the DC resistance of the 0.22mH inductor. The MF measurement should equal to the DC resistance of the 2.5mH inductor + 2.2Ω. |
I don’t know it’s can be of any help, you can find the xover schematic here: https://ucarecdn.audiogon.com/a89e98dd-d4a0-4acf-9f74-934683ea9b70/-/autorotate/yes/ |
Please look at this photo: https://ucarecdn.audiogon.com/32d4343f-f8e2-4de2-95f7-2e0766972c94/-/autorotate/yes/ If that is a short, for bi-amping, it will connect two amplifier output together through the 3.5mH inductor and the 3.3Ω resistor. There could be more similar problem spots on the PCB that we can’t see from those photos, that was the reason I suggest OP to clean up the PCB and reinstall components. |
Tell you what,you guys have put so much time and effort into this,this weekend i am going to clean everything up and start again,i will take variuos readings on crossovers,re-assemble the whole two speakers and do it all again and then i will come back with a list of readings,it seems thats all i can do,Something to consider: Put the LF xover ( the 3.5mH inductor and 51uF capacitor ) on a separate circuit board to eliminate shorts from HF/MF crossover components. Better yet, upgrade to air core inductor! https://images-na.ssl-images-amazon.com/images/I/71pf0GZOI1L._AC_SL1500_.jpg |
I just recently learned that iron core inductors are suppose to be better than air core for the bass driver due to the lower dc resistance in many cases.@fiesta75 If replace a cored inductor with air core, I think it is important to use the same inductance air core inductor with very close DCR to the cored inductor, it will be bigger, heavier and cost more. I’m still learning...I'm as well, learning is a lifelong process. He wouldn’t even need to make a PCB, he can just use point to point wiring for those 2 componentsAgree 100% |
Lower than expected dcr for 0.22uH inductor; from what I can tell, a nominal dc resistance for that inductor is about 0.21 ohms.Are you refer to the 0.22mH inductor across the tweeter? https://ucarecdn.audiogon.com/a89e98dd-d4a0-4acf-9f74-934683ea9b70/-/autorotate/yes/ DCR varies with wire gauge and core type, for example, DCR of an 0.22mH 18AWG air core inductor is about 0.2Ω, DCR of an 1mH 18AWG "I" core inductor ( about 4.5 times higher inductance than 0.22mH ) is only 0.17Ω. You can see from the photo that it is an cored inductor, I won't be surprised its DCR will be 0.05Ω or less. https://ucarecdn.audiogon.com/bfe5fcb3-3dd7-42ff-835d-9e69c47231fd/-/autorotate/yes/ |