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
fiesta75
1,378 posts
 
No NOT ac voltage, DC voltage. This is the offset voltage of the amp and I wanted to make sure they were low as THAT could be a cause of capacitor failure.
fiesta75
1,378 posts
 
Well if you have lifted one lead of each cap and they test good, I would say it's a short on the PCB. Check all the resistors just to be safe, most resistors open or go high when they fail. In one picture I saw a couple capacitor leads that looked very close together. On another note, you said the amp worked for about 3 hours when you first got it back. So I'm assuming they sounded good when bi-amped before it went pop? I'm thinking there could be physical contact between a couple components lead wires. Reason, it work for a while. Maybe vibration caused the components to get physically close enough to short. What is the value of the cap connected to the midranges in the bi-amp configuration?
fiesta75
1,378 posts
 
For some reason I can't access your crossover photos I saw yesterday. Anyone else have this problem?
likklegerry OP
30 posts
 
thankyou all again for this help,i uploaded a schematic of the crossover wilmslow have now sent me,i will test and check all readings and offset dc today,then i will get back to you all.
so many thanks
regards
mark
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.

More to discover