Anyone here familiar with speaker Crossovers?

ThisIsWeird

If so, I'll post. If not, I won't bovv

Ta.

SurferDan

What's the problem?

ThisIsWeird

Hi Dan.

Recently bought a pair of Mission M66i speakers. Found that one tweeter isn't tweeting as loudly as the other - a dire lacks of highs from one cabinet - so removed both tweeters, and wired them directly to my amp's speaker (both are rated at 4 ohm).

Played some mono music and some tweeterish sounds, such as an off-station FM signal. Both tweeters sound identical, so both are ok.

Replaced them in t'cabinets, and the same; one is nicely crisp - good ol' Wishbone Ash cymbals crashing - but the other is barely audible - you can just hear it when you put your ear next to the dome. Fed the amp's output direct to the speakers' HF inputs only, and the same.

Then I took the amp's speaker cable and touched it directly to the crossover PCB's output terminals to the tweeter, and loud and crisp sound. So it looks as tho' my crossover is faulty.

No visible signs of damage or dry joints. R1 is reading correct at just under 2ohm (it's a 1R8), and caps look ok, but I have no way to test them. L1 is a fraction of one ohm, which I presume is correct.

Worked out the schematic, which strikes me as weird (Qs on this coming too )

So, what do I do? Replace all the caps? What would/could be the most likely cause of this heavy attenuation?

Oh, and why the strange pairs of caps? C1 and C3 could, for example, surely be replaced by a single 905J jobbie? And why the use of an electrolytic in the other pairing? In essence, how does it work?!

Thanks for any thoughts.

Tassie_Devil

Maybe try asking on a forum like audiokarma?

https://audiokarma.org/forums/index.php#audiokarma-audio-forums.1

ThisIsWeird

Tassie_Devil said:

Maybe try asking on a forum like audiokarma?

https://audiokarma.org/forums/index.php#audiokarma-audio-forums.1

Thanks.

I have tried a couple of other forums, and I'm getting some decent advice on there. Hadn't heard of that one tho' :-)

Heedtheadvice

Your diagnosis of a crossover problem is probably good ( I am assuming  there is no wiring from speaker terminals to crossover that might just cause an issue.

Probably, because there could still be a tweeter problem  if somehow it had changed impedance. Maybe not likely but change over which speakers they are in ( or the crossovers ) and hear if the fault follows the tweeter. - supplying from the amp directly ( is a very low impedance source) would not act the same, as the crossover impedance in circuit is acting as a frequency dependant potential divider and the o direct is not.

If that logic shows that it is crossover then really you ought to do diagnostic measurements. Signsl generator and scope is best or measuring each component individually put of circuit. There could still be a dry joint problem so if youare good with a soldering iron add a small amount of flux or multiform dolder to every joint by resoldering. Problems with components and joints are not always visibly obvious.

The capacitors in parallel add their capacitance values and (as with series conections) that can be used to get specific values that are not readily available where critical in such circuits.

Also Electrolytic capacitors often have values that do not apply at higher frequencies so small value other types are added to correct.

If you make no progress do post again or p.m. me.

ThisIsWeird

Thanks HtA.

I think it's unlikely the tweeters themselves are faulty or altered - they outputted identically when tested from the amp; the mono hiss was inside my head. I'm reluctant to remove them again to do swapsies, are they are back in place and connected.

The biggie for me was when I connected the amp's output directly to the tweeter's output terminal on the PCB - the jump in volume was dramatic. There's just far too much attenuation in the crossover.

It's been suggested that C2 - the 32uF Electrolytic - is the most likely culprit, as the Poly caps very rarely fail? So, I'll do that first, and also wet all the pads.

Thanks.

Oh, and surf for 9uF 250V Poly Caps comes up with a Panasonic make for less than a squid from RS, so still confused by the use of two in parallel. There must be a reason Perhaps they weren't common at the time of these speakers - prob late-90's?

Heedtheadvice

Just had a look at your post on DIY audio and the suggestion to replace the electrolytic is good. A bit of a stab in the dark but the type can be problematic with age and will be cheap to replace. Should be easy to source but if difficult for you I probably have one I can send.

prowla

What happens if you swap the speakers to opposite sides of the room.

ThisIsWeird

Heedtheadvice said:

Just had a look at your post on DIY audio and the suggestion to replace the electrolytic is good. A bit of a stab in the dark but the type can be problematic with age and will be cheap to replace. Should be easy to source but if difficult for you I probably have one I can send.

Very kind. Fair chance I have one, but easy to get if not.

I'm actually considering going full-poly, as I see no reason to have an elec there except for its value size. A couple of 18uF polys, for example.

ThisIsWeird

prowla said:

What happens if you swap the speakers to opposite sides of the room.

The faulty one always has significantly less treble.