Cross over circuit upgrade question

[sanu83]

Hello guys,
I am upgrading the cross over circuit for my floor standing speakers ( 12 yrs old).

I have replaced the bi polar electrolytic capacitors with poly polypropylene audio grade in one of the Floor speakers.
After the upgrade, I noticed that the background mid/high music is clearer than before but the Low Freq side became less.

I found this by comparing music with the other FS speaker which is still with the original cross over.

Any body have faced this problem before?. Does this has anything to do with the Poly propylene capacitors.

The capacitor values I replaced are bipolar 22uF, 0.47uF, 12uF. Also replaced the 750uF electrolytic capacitors with new (750uF electrolytic type)
The floor standing speakers are Mirage Omni speakers

Please advise. Does the new capacitors need a break in period

 

[TLS Guy]

Hello guys,
I am upgrading the cross over circuit for my floor standing speakers ( 12 yrs old).

I have replaced the bi polar electrolytic capacitors with poly polypropylene audio grade in one of the Floor speakers.
After the upgrade, I noticed that the background mid/high music is clearer than before but the Low Freq side became less.

I found this by comparing music with the other FS speaker which is still with the original cross over.

Any body have faced this problem before?. Does this has anything to do with the Poly propylene capacitors.

The capacitor values I replaced are bipolar 22uF, 0.47uF, 12uF. Also replaced the 750uF electrolytic capacitors with new (750uF electrolytic type)
The floor standing speakers are Mirage Omni speakers

Please advise.

Unless you can post a circuit, I really can not help you. One thing that does strike me is that 750uF cap. That is a stange value for a small speaker, unless it is a DC blocker, in which case the specs may be different to the old. The actual rating of a caps storage capacity is not the only spect you need to look at. I suspect you have meddled without really knowing what you are doing.

 

[Swerd]

I am upgrading the cross over circuit for my floor standing speakers ( 12 yrs old). I have replaced the bi polar electrolytic capacitors with poly polypropylene audio grade in one of the Floor speakers.

The floor standing speakers are Mirage Omni speakers. The capacitor values I replaced are bipolar 22uF, 0.47uF, 12uF. Also replaced the 750uF electrolytic capacitors with new (750uF electrolytic type).

As TLS Guy asked above, please provide a circuit diagram of your speakers' crossover. What model are your speakers? If you don't have a diagram but know the model, it might be possible to find the circuit online.

I also find that a capacitor of 750 µF is exceptionally large for a speaker. I don't believe I have ever seen such a large capacitor in a speaker crossover. Are you sure that cap was 750 µF, and not 75 µF? Even 75 µF is very large for nearly all speakers.

After the upgrade, I noticed that the background mid/high music is clearer than before but the Low Freq side became less. I found this by comparing music with the other FS speaker which is still with the original cross over. Any body have faced this problem before? Does this has anything to do with the Poly propylene capacitors.

No, this does not have anything to do with the capacitor construction material. But, it might have something to do with your use of an extremely large 750 µF capacitor to replace a much smaller one. Again, without the manufacturer's original circuit diagram, we cannot answer your questions.

While I'm asking questions, please tell us why you took this project on. Was there something about your speakers that sounded wrong? Or were you just getting rid of the non-polar electrolytic capacitors in your 12-year-old speakers?

Please advise. Does the new capacitors need a break in period?

Despite what you may have read elsewhere online about crossover capacitors, the answer is No.

 

[TLS Guy]

As TLS Guy asked above, please provide a circuit diagram of your speakers' crossover. What model are your speakers? If you don't have a diagram but know the model, it might be possible to find the circuit online.

I also find that a capacitor of 750 µF is exceptionally large for a speaker. I don't believe I have ever seen such a large capacitor in a speaker crossover. Are you sure that cap was 750 µF, and not 75 µF? Even 75 µF is very large for nearly all speakers.
No, this does not have anything to do with the capacitor construction material. But, it might have something to do with your use of an extremely large 750 µF capacitor to replace a much smaller one. Again, without the manufacturer's original circuit diagram, we cannot answer your questions.

While I'm asking questions, please tell us why you took this project on. Was there something about your speakers that sounded wrong? Or were you just getting rid of the non-polar electrolytic capacitors in your 12-year-old speakers?
Despite what you may have read elsewhere online about crossover capacitors, the answer is No.

I have run into large caps in speakers once before.

My friend Phil had a set of B & W 801's for many years.

He asked me to look at his rig, as the right channel had failed. On investigation, the problem was the right speaker.

I found that it had a large high value electrolytic cap in series with the +ve input of the crossover.

This was obviously done to block huge DC offset. Back then many amps did not protect speakers from massive DC offset from power transistor failure.

So upon this discovery I removed the caps from both speakers. The cap in the right speaker had failed.

If the OP is correct about the value of cap, I suspect something similar. In which case he probably has replaced the cap with one with one that has a much higher internal resistance. If that is the case he should rid get of those caps in both speakers. That is why I need to see the circuit.

 

[sanu83]

My speakers have not failed, i thought of getting rid of the old electrolytic capacitors.

The board has two 750uF capacitors. the negative side of the capacitors are connected together.

positive side of one capacitors are connected to + input from amplifier.
second capacitor + side is connected to mid speaker + connection.

Please find attached the cross over board pictures.

I dont have a circuit diagram, the speaker is mirage omni 260 floor speakers. Please share if any body has a circuit diagram.

 

[TLS Guy]

My speakers have not failed, i thought of getting rid of the old electrolytic capacitors.

The board has two 750uF capacitors. the negative side of the capacitors are connected together.

positive side of one capacitors are connected to + input from amplifier.
second capacitor + side is connected to mid speaker + connection.

Please find attached the cross over board pictures.

I dont have a circuit diagram, the speaker is mirage omni 260 floor speakers. Please share if any body has a circuit diagram.

Pictures are of no help. You should be able to draw a circuit from the boards though. If you can't, then you should not have been attempting this.

 

[Swerd]

I haven't been able to find a schematic diagram of the Omni 260 crossover. I have learned that it's a two-and-a-half way design, with a front facing 6½" woofer that rolls off at 700 Hz, and an identical upward facing 6½" driver rolls off at 2 kHz to the upward facing 1" dome tweeter. Both 6½" woofers operate as low as the ported cabinet's F3 frequency, said to be 35 Hz.
http://www.soundstagenetwork.com/revequip/mirage_omni260.htm
https://hometheaterhifi.com/volume_10_2/mirage-omni-speakers-5-2003.html

Thanks for the photos, they show the very clearly marked capacitors. You must have had a tough time fitting those new metalized polypropylene (MPP) onto that board. MPP caps are generally larger than non-polar electrolytic (NPE) of the same capacitance value.

You certainly did not misread the labels on those 750 µF caps. I'm guessing that they might be part of the 700 Hz low-pass filter (high frequency roll off) for the front facing woofer. We would need to see a schematic diagram to know for sure. I wish I had to patience to see if I could carefully work the wiring pattern as you showed in photo #2 into a crossover schematic. At best, it would require some guess work.

What is important is that those two 750 µF caps are polar electrolytic (PE) instead of non-polar (or bi-polar), and that they were wired together (as you described below) to create one equivalent non-polar or NPE capacitor:

The board has two 750uF capacitors. the negative side of the capacitors are connected together.

positive side of one capacitors are connected to + input from amplifier.
second capacitor + side is connected to mid speaker + connection.

What exactly did you replace those two old 750 µF caps with? Two new 750 µF PE caps, or one new 750 µF NPE cap?

If you used two 750 µF NPE caps, that might explain the loss of lower frequency sound that you heard.

 

[sanu83]

Hi

I tried putting back the old 750 µF PE caps, but the low side is still missing.

Right now i have replaced the 750 µF PE caps with two capacitors in parallel (470+330).

 

[sanu83]

Hi guys,
I have made the circuit diagram of the cross over. it is attached.
Please have a look. I already tried to remove the 750UF capacitors, but does not improve the Low freq.

 

[TLS Guy]

Hi guys,
I have made the circuit diagram of the cross over. it is attached.
Please have a look. I already tried to remove the 750UF capacitors, but does not improve the Low freq.

Well, the crossover high pass to the tweeter and low pass to the mid/woofer are fairly standard half section circuits, but the circuit to the woofer is the craziest circuit I ever saw. There is an tuned acceptor circuit in the +ve feed and a tuned rejecter circuit in the -ve leg. those 750 mfd caps are part of the acceptor circuit, which is partially bypassed by two parallel resistors. I would suspect all values are critical and you need to rebuild it with the original components. I did audition those speakers once at a dealer in St. Paul. I thought they were awful and now I know some of the reasons why.

 

[sanu83]

Thanks for the reply,
By original components, do u mean from the same manufacturer.
because i am replacing with same value but different manufacturer.

1) The resistors reads the same as printed on them, do I have to still replace the resistors?
2) How to find the value of the inductors, there is nothing printed on them....
3) For capacitors only the uFarad rating should match or its resistance also.
please advise

 

[TLS Guy]

Thanks for the reply,
By original components, do u mean from the same manufacturer.
because i am replacing with same value but different manufacturer.

1) The resistors reads the same as printed on them, do I have to still replace the resistors?
2) How to find the value of the inductors, there is nothing printed on them....
3) For capacitors only the uFarad rating should match or its resistance also.
please advise

The resistors should be fine as long as you check the values with your meter. I would just put the old caps back if it was working fine. Tuned circuits like those in you circuit are very touchy and it takes little to upset them.

 

[sanu83]

Guys, I put back all the capacitors back ,except the 22uf(marked 10) in the drawings. Now the low freq is back. and music sounds good also.
For some reason the old eletrolytic capacitors sound better than the new polypropelyne ones....

Can some one throw little light on how the acceptor and rejector circuits in the cross over circuit works.

 

[TLS Guy]

Guys, I put back all the capacitors back ,except the 22uf(marked 10) in the drawings. Now the low freq is back. and music sounds good also.
For some reason the old eletrolytic capacitors sound better than the new polypropelyne ones....

Can some one throw little light on how the acceptor and rejector circuits in the cross over circuit works.

If you put an inductor and cap in series it becomes a rejecter circuit at the frequency you calculate. You also have to calculate Q with varies the base of the peak
If you put an inductor and capacitor in series you get an acceptor circuit with the same caveats.

I suspect you difficulties have arisen due to different forward resistances between the new and old caps.

You have learned a valuable lesson: - Don't fix what ain't broke!