Premier 88 crossover

[pontiacpete]

This 88 has only the coils left over from the crossover. There are 3 speakers, 2 are 3" speakers 16 ohms each and the other is a 15" speaker at about 8 ohms.
I have been looking at some of the calcutators on the site.
The first question is, if I use these coils how do I figure out their inductance?
Can I build the crossover with 2 coils?
Never done this before. Any help would be greatly appreciated

Thanks
pete

[pontiacpete]

Followed one of the youtube demos of measuring inductance. Applied a sinewave across the coil on the left in series with a 47R resistor.
Then increased the frequency until the AC was equal across the resistor and the coil at about 320mv. That frequency was 5.6k.
Then I divided 47 by 2X Pi x 5.6k equaling 1.2uH. Does this sound right?
The other coil is doing something different, will get to it tomorrow.

[Enzo]

If you cannot find a schematic for the crossover, making a new one is not difficult, but you need to determine what crossover points to use.

Frankly, if it were me, I'd not even worry about using the old coils, I'd just make a new one from scratch.

Actually I wouldn;t even do that, I;'d buy a bare crossover board from Parts Express, and use their charts to select coils and caps to stuff the board with.

[pontiacpete]

Thanks Enzo for your input.
I spent some time reading on Parts express site about crossovers. They have a lot of info there.
I am wondering if going this route would be overkill since this is a guitar amplifier. I have worked on some old gibsons like the GA50 which had 2 different sized speakers and there was only a cap to do the crossover. Is this a possibility?

Also, after all my research I'm discovering that I need the frequency range of the speakers which I don't know. The 15" had just been re-coned so I'm asking the re-coning guy what he thinks.

[pontiacpete]

If you cannot find a schematic for the crossover, making a new one is not difficult, but you need to determine what crossover points to use.

How is this not difficult?

Here's the amp schematic. This really isn't any help, I know, but the drawing shows 2 identified caps. But this amp has the coils too and what looks like clamps that hold some big capacitors.

So far every thing I've read says I need information that I don't have.
I have a scope and function generator and fluke meters. Is there a method using these instruments that will give me a rough idea of the crossover points?

Keep hoping a Premier 88 owner/enthusiast might chime in and give me values for the caps.

[52 Bill]

That schematic hurts my head.

The problem that you face is that the drawings that you have are for one specific amp and that amp doesn't match yours.

You have two coils and clamps for two large caps. There aren't that many crossover designs that use that combination of parts for a 2-way speaker system.

Look at the 12db 2-way crossovers here.
Crossover Design Chart and Inductance vs. Frequency Calculator(Low-pass)

[pontiacpete]

Thanks 52 Bill for posting this calculator.
I had been messing around the 12dB/octave crossover, already, putting in some random large caps that I have. This calculator helps, although I'm still having the guessing issue of the 'frequency'. But if I put in about 1000 -1500 Hz in this calculator, with 8 ohms for both low and high pass impedance(the 2 small speakers in parallel) it derives an inductor close in value to the one I measured at 1.2mH(not uH, I think I made a mistake in the post above). I'm not confident in my measurement of these, though. Perhaps I will do it over.
But with this crossover, the impedance being equal, it looks like the inductors and capacitors are equal, as well.
Am I on the right track here?

[52 Bill]

This calculator helps, although I'm still having the guessing issue of the 'frequency'. But if I put in about 1000 -1500 Hz in this calculator...

I really don't know the correct answer, but I would think that 1k-1.5k would be too low of a crossover point. That would really be more in the midrange area.

I would have expected the crossover point to be at least around 3k, maybe higher.

[pontiacpete]

Plugging the 3000Hz gives me .8mH coils, kinda close to what I measured, and 3.3uf caps.
I have a very limited supply of non polarized caps in stock but I do have the 3.3uf, so I tried them out.
The amp sounds really good. I am very tempted to leave it with this set up unless some one has anything else to add. ??

[g1]

Don't un-good it. Sounds like you're good.