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Old 6th April 2014, 10:42 AM   #11
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Default MC4s too bright

Hi all, my MC4s (V1) are overly bright but the tweeters sound fine with no distortion.

So where is this brightness coming from ?

Have the woofers become lazy ? or is this all down to the crossover (caps) ?

Took a look inside and all is original and untouched.

Only took a close up of the xover caps for the bass, but the highs have the same capacitors again.

Date stamp in the cab says Sept 1987
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File Type: jpg 20140323_173130.jpg (356.0 KB, 63 views)
File Type: jpg 20140323_173500.jpg (372.3 KB, 59 views)
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Old 6th April 2014, 11:00 AM   #12
system7 is offline system7  United Kingdom
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Possibly the metal tweeters are not set to your taste. There's a thing in the industry called showroom brightness that sells speakers, but they get on your nerves when you get home.

Looks like Musical Fidelity also used this similar common H0532-08 19TAFD/G tweeter.

I'd have to see the crossover schematic to say what you should do here precisely, but you'll probably add a tiny bit more resistance (maybe 2.2R) to the treble filter input and shunt a zobel (7.5R 7W wirewound resistor and 0.68uF polypropylene capacitor in series) across the tweeter to tame it. Very easy actually. You can get the bits at Maplin.

I take it you have the below model. Looks like polycone and metal tweet. It is common enough for ferrofluid, if applied here, to dry out and solidify. But that usually just stops the tweeters working at all.
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Well, there it is! Best regards from Steve in Portsmouth, UK.

Last edited by system7; 6th April 2014 at 11:13 AM.
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Old 6th April 2014, 12:26 PM   #13
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Hello Steve,

Yes that's the ones with the transparent woofer

From what I understand caps can go off tune with age. So replacing them might tame the treble or bring up the bass so they are even again.

Got no schematic, but there are 4 caps, 2x @3u and 2x @6u

That's the wrong tweeter, this one seems more like it:

Monacor DT-250
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Old 6th April 2014, 12:57 PM   #14
system7 is offline system7  United Kingdom
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It's some sort of minimalistic design by Martin Colloms as I understand it. Uses the Rogers 8" bass AFAIK. Bit like some Epos designs.

The schematic is something you work out from observation. I'd expect a coil on the bass and maybe an RC shunt, and a capacitor and resistor to the tweeter at least. Perhaps a coil on the tweeter too. Bit like this maybe, but not too interested in coil values anyway. Resistor and capacitor values are readable.

Click the image to open in full size.

Those plastic capacitors really shouldn't age. But some connectors and joints could be corroded or dry jointed. Crimp connectors to the drivers might be worth pulling off and reconnecting for fresh metal. It's worth noting polarity before you disassemble though. Otherwise you're scratching your head to get the phase right!

Bear in mind that frequency response IS slightly affected by amplification type too. Valves sound very different from solid state. They interact with speaker impedance more.
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Last edited by system7; 6th April 2014 at 01:05 PM.
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Old 6th April 2014, 01:03 PM   #15
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ah ok so the bass was made by Rogers, interesting not heard of them doing anything but radios for a long time.

Yes my amp is valve, but got 4 pairs of speakers here and the MC4s are by far the brightest. They are known as being rather bass heavy by design !

I imagine some new ClarityCaps would blow the pants off of those installed here near thirty years ago anyway
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Old 6th April 2014, 01:12 PM   #16
system7 is offline system7  United Kingdom
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I never spend too much on capacitors these days. Good 250V polys are quite adequate. Get 400V types if you've got room.

Capacitors

Now come on. Work out the schematic. I can then tell you why they sound bright and how to fix it. Soggy bass is a given with valves. They don't drive reflex too well. Something to do with damping factor, or lack of it!
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Old 6th April 2014, 01:23 PM   #17
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I will have to take them to bits again, not got the time at the moment, got the lawn to mow which not done since last august !
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Old 6th April 2014, 01:27 PM   #18
system7 is offline system7  United Kingdom
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Quote:
Originally Posted by Barbieboy View Post
I will have to take them to bits again, not got the time at the moment, got the lawn to mow which not done since last august !
At your leisure, my friend.

Ping me a PM when you do update here. Otherwise I might miss it.

FWIW, I think that bass was used in the Spendor BC1 too. Tweeters are tweeters though, IMO. All much the same.
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Old 6th April 2014, 01:33 PM   #19
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wonder if bass drivers loose their magnetism or something after a while which could explain the situ ?
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Old 6th April 2014, 01:45 PM   #20
system7 is offline system7  United Kingdom
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Quote:
Originally Posted by Barbieboy View Post
wonder if bass drivers loose their magnetism or something after a while which could explain the situ ?
Ferrite is perfectly stable. It's the old AlNiCo drivers that needed periodic remagnetising. No, that's not it...
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