2. speakers
  3. 167293-162421

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
likklegerry
imhififan's avatar
imhififan
2,180 posts
 
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-

LEFT SPEAKER / RIGHT SPEAKER
speaker terminals with everything connected on both speakers

MID/HIGH 0.0 ohms /
MID/HIGH 0.0 ohms
BASS 7.9 Ohms /
bass 6.8 Ohms
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
TWEETER 8 OHMS / 7.9 OHMS
MID 6.3 OHMS / 6.2 OHMS
BASS 6.1 OHMS / 6.0 OHMS

CONTINUITY TEST ON X-OVER WITH DRIVERS REMOVED USING DIODE FUNCTION
between positive and negative on x over
HF 000.2 {dead short} / 000.2 {dead short}
MF 000.5 / 000.5
LF OL. / OL.
MID HIGH INPUT IP OL. / OL.
BASS INPUT OL. / OL.

OL. BEING NO CONTINUITY

The above measurement of MID HIGH INPUT IP looks OK,

TEST TESTED AT/ON X-OVER SPEAKERS CONNECTED OHMS
HF 0.0002 OHMS / 0.002 OHMS
MF 0.0001 OHMS / 2.0 OHMS
LF 6.4 OHMS / 6.3 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.

pragmasi
212 posts
 
fiesta75 and imhififan are on the money with their advice... but I'd hold fire with the soldering iron until you've got a little more to go on.
IP+ and IP- should be open circuit at DC (OL), although you may need to leave the probes in place a few seconds while the caps charge.
If you're still getting 0Ω across IP+ & IP- then it's most likely a short somewhere between the input terminals and the copper pours that sit directly under IP+ & IP- on the PCB, you should be able to check this visually.
If that doesn't turn up anything then it might be time to reach for the iron.
fiesta75
1,378 posts
 
pragmasi - I agree, rule out the simplest possible problems first. That's why asked about cables and connectors. Did we ever get an answer about that? I'm going to look at the schematic now. Good luck!
imhififan's avatar
imhififan
2,180 posts
 
@fiesta75 and pragmasi,
IMO, the layout of components is not ideal, especially those capacitors that seat on top of resistors! since he is at it, I think it's time to fix that...
fiesta75
1,378 posts
 
I just looked at the crossover too, not good. Would be very easy to create a disastrous mistake, not to mention the EMI and RFI problems. Heat is not a friend of caps as you know.
More to discover