Questions about inductors!

[tubesaregood]

I'm new to the forums. Hi everyone!

I recently purchased a DBX db-SW15 from a guy on craigslist. It's part of the old Soundfield line, I think, back when they still made home audio stuff. I had buyer's remorse, but the more it sits there in my room, the more I love how weird and cool it is.

Anyway, I hooked it up when I got it home, and there was horrible distortion from the driver. I decided that the driver's coils (dual coil) were shot. Then, I started reading up on crossovers, and learned that crossover units can fail. SO, I decided to test the low-pass portion of the crossover with a pair of bookshelf speakers. Same terrible distortion. The driver, however, is in great shape.

The crossover unit has inputs for an amp and outputs to sattelites. There is a 5.6 mH iron or ferrite core inductor on the low pass to the sub, and 150+170 50V NP electrolytics going to the sattelites, per channel. The caps seem to be in good shape.

Upon visual inspection of the crossover while it had signal going through it, I heard the inductors making uh, high frequency noise to the beat of the music. My questions - 1) Is a microphonic inductor ALWAYS a bad inductor and 2) would a bad inductor cause that nasty distortion I was talking about?

Another question - Theoretically, why is using only one coil of a dual coil speaker a bad idea, and what would happen if the coils were connected out of phase with each other (I'm assuming no sound at all with equal signal from both channels).

Thanks!

-Mike

 

[Ampdog]

Inductors

Hi Mike,

As nobody seems to have replied, I will do so at least partially. No, a microphonic inductor is never really a bad inductor, depending on what causes the microphonics. If it is so heroically delapidated that half the windings are hanging loose there might be a problem, but then you would not be asking here.

An inductor itself is unlikely to cause the distortion you experience, yet the fault does seem to be in the cross-over. The capacitors "seem" to be in good shape. How certain are you of this? And when you connected to a pair of bookshelves, is this then a stereo cross-over? If so, are both channels giving the same distortion? Poor solder connections? I would suggest you go through that, re-solder if in doubt, and make sure of the caps.

I have no experience of dual coil drivers, and will not venture advice on that subject.

 

[alan monro]

Gooday Mike. Iron core inductors are a cheap no-no in the "hi-fi' world.What I suggest is that you go to a electronic shop like tandy (radio shack) ,I think It is called that over there.Purchace a air core inductor type cross-over network for your speakers. Just take your old cross-over board ,they will soon find something suitable.The duel voicecoil probably is for different impedances 4-8ohm use the 8 ohm as it is the standard ,for car audio4 ohm is the norm. Please let me know how you go.Kind regards alan.

 

[HowY]

I've had a DBX sw15 for many (17+) years. NICE!

The crossover is of a pass thru design and it does use iron core inductors.

I'll tell 'ya I loved it in the older systems but if wired in pass-thru mode
the sub steals way too much bottom end from the mains (fed by the xover)
I always used to use the B channel to run it.

So here's what you do....

Buy a plate amp.... rip out the x-over and install the amp.

Made my system! Can wire as LFE or as low-level (my preference)
since I dont run "sub" - my sub out (lfe) feeds my transducers.

I actually did a project log on the conversion - very simple.

You can find plate amps a-plenty these days

Suprisingly the driver is well designed with a vented pole
(vented thru the cap) and is a rather rugged 15" driver
(by late 70's / 80's standards) and still holds up well.
Got a 1k watt amp powering it works well but I do plan
on upgrading the driver in the future.

FWIW

There is NOTHING wrong with wiring a single coil up
just watch the impedance. I can go on and on about the
pro's and con's to the "phase" at which they are wired and
the good/bad of different wiring.

Your dealing with a very old driver and what you'll hear
-todays standards- does not apply. This is not a long throw
coil - just provides for "stereo" hookup. So both channels
are fed.

Sub's today are basically single channel affairs so one can
dissolve into esoteric details of parallel - series wiring of the
coil. In this case (were talkin one of the original 'subs' now)
both coils are expected to act as a single load per channel.

Best of luck!