Dual Voice Coil Speaker For Crate CA112D

[TomCarlos]

Friends...

I was given a Crate CA112D amp case with the speaker. This was an Acoustic Guitar amp. The amp chassis was gutted. So... the speaker. It is a 12", Dual Voice Coil, 8 ohms each. The amp had (2) Fifty watt outputs and another 25 watt output for the Piezo Tweeter.

So... Options ??

Use one coil only for a low power amp?

I assume you would run these in parallel or series? I never understood the dual voice coil thing anyway.

Tom

[Jazz P Bass]

Are you sure that the dual VC is stock?

In car audio, the dual VC is good for setting specific loads.

Series/ parallel.

[TomCarlos]

Yes... The owner manual and specs verify. The CA112D is a dual coil. The CA125D uses the same chassis but has two 8" speakers plus the piezo.

[Enzo]

Agree,I looked it up. The schematic doesn;t say,it just shows two 8 ohm speakers on the two channels. But the product description elsewhere proudly proclaims the special dual speaker. They wanted it to fit in a 1x12, but wanted to retain at least some of the stereo-ness of the original.

[g1]

Verify the phasing of the 2 coils with a battery and watching which way the cone moves.
Then you are free to use with coils in series, or parallel. Or one coil only at low power.

[J M Fahey]

Ouch!!!
*Terrible* solution to a probably self created problem.
Maybe Marketing Dept found that single 12"combos would outsell 4:1 dual 8 ones or some other equally stupid decision and tried to go that way.

Technically and Musically ridiculous.

Absolute worst case, they could have bridged those amps.
Even if you are stuck with 2000 "unusable" PCBs, you need only to cut a couple tracks and add a couple resistors and use, say, a single 12" 16 ohms speaker matching the new bridged impedance.
And if stereo amps had required 4 ohms each, new bridged would need an 8 ohms one, even easier.

Just curious, can anybody post the actual schematic?

Thanks.

[TomCarlos]

Thanks for the replies... I found this schematic for the CA112A and CA112Da. I believe it is the same as the CA125 model.

You can see two separate 50 watt amps and the 25 Watt Piezo Amp.

I agree Juan... a nutty configuration for a guitar amp. Oh those marketing people.....

[J M Fahey]

Thanks TomCarlos.

Now that I see it, an even nuttier design

They use a total of 5 (five) TDA2050 power amps.
* One for the tweeter ... check.
* two bridged for one 8"speaker ... check.
* another two for the other 8" speaker ... check ; so far so good.

BUT I'm more certain that they decided for a single 12" but use the ton half finished n2 x 8" chassis so they came with the brilliant idea of bridging both channels to get full power output on a single speaker ... only problem is you can't "bridge bridges" so they had to use the kludgy voice coil.

Before some say you actually *can* bridge bridges, I agree you can ... sort of ... IF they are monoblocs , each has itys own power supply, do not share ground, and in fact one of them has grounded output rail (á la QSC) ... so compared with this mess a dual coil must have looked sensible ... by comparison of course.

The proper solution would have been to use a single LM3886 or at worst a bridged pair .

[tedmich]

Gee with a name like Crate you'd expect better design...

[J M Fahey]

Oh, the electronics design is excellent, like all Crate amps, plus the best schematics in the Industry, including scope waveforms and lots of very detailed test points, I'm not aware of any other doing it to such a degree.

But the original design was for a very good 2 x 8" combo; probably didn't sell well or some competitor cleaned the table with their single 12" one so they kludged this monstrosity.

People at Eminence must still be chuckling at this OEM order

That said, the dual coil speaker must have cost between $1 and $2 extra, at most, and that because of the "customness" , and gap must have been enlarged by a few thousandths to accomodate the extra 2 layers , most probably AWG34 wire so extra .0125" .

That kills highs and efficiency because of weaker magnetism (wider gap) and doubled wire weight, that speaker must be noticeably duller than, say, a standard Legend type.

*Hope* the tweeter makes up for it; is it a piezo or a coil one?

Not necessary, only if you have some free time, but it would be interesting to have a speaker picture and see how they manage wiring.
Does it have an extra terminal set for the second set of wires?
Funny.

Of course, the end user should pray his speaker never dies, I bet in a couple years that weird speaker will be impossible to find, even at Crate.

Worst case, can the speaker panel be removed and a new 2x8" one be placed there?

[rjb]

Worst case, can the speaker panel be removed and a new 2x8" one be placed there?

OP said the chassis is gutted- question is how to best re-purpose the wacky speaker.

[Mike Sulzer]

OP said the chassis is gutted- question is how to best re-purpose the wacky speaker.

I think the question that needs to be answered is what is the impedance of the speaker if you connect the two voice coils in parallel or series. You can think a lot, or just measure the dc resistance and take the next standard value higher. Unless Crate screwed up their speaker specs, that ought to work.

[g1]

How about wiring the 2 coils out of phase for a super low efficiency speaker so you can crank the amp more with less loudness?
I guess the tone wouldn't be very good though, and maybe the coil would overheat?

[J M Fahey]

No mystery with the impedance, it's either 4 or 16 ohms, it's done every day with car subwoofers.
Speaker will be somewhat dull but usable.

As of using it as an attenuator, both coils are exact same number of turns and wound on the same former, so sound output should be 0 .

[Leo_Gnardo]

How about wiring the 2 coils out of phase for a super low efficiency speaker so you can crank the amp more with less loudness?
I guess the tone wouldn't be very good though, and maybe the coil would overheat?

I figure that would result in roasted voice coils in short order. Then you discard the speaker, and what you have left - - - is a very small dog house.