S310II Schematic Question

[maabx]

http://manuals.harman.com/JBL/HOM/Te...310II%20ts.pdf

In looking at the schematic, I see three inductors:

L1 - 2.4mH
L2 - 300uH
L4 - .3uh <----should this be .3mH (or 300uH)?

Thanks in advance.
Mike Brown


Here is the crossover:

HPIM1241.JPG

I am going to to rebuild my crossovers with DC biasing.

[Earl K]

Hi Mike

Re the L2 & L4 values ; The only range of inductor value that makes any sense ( for a stated 3500 hz crossover point ) is the milliHenry , mH range . In this case , .3 mH .

- .3 mH is of course 300 uH but that's a cumbersome and confusing designation ( just look what happened to the author of the pdf file ). Micro Henrys also don't easily plug into a bunch of short-hand formulas, without a bunch of mental gymnastics .

- Glad to see you're going to DC bias the crossovers.

[maabx]

Thanks for the reply Earl. That is what I thought (.3 mH). But in looking at the crossover, I was even more confused. L2 and L4 are then assumably both .3mH, but the inductor coils are different dimensions. Can this be easily explained? I would like to rebuild the entire crossover with new inductors; but not with different values from the original. My other alternative is to just rebuild with new caps (and resistors for the 9vDC supply).

I will post pictures and impressions when I finish the work.

Thanks, Mike Brown

[Earl K]

Hi Mike

But in looking at the crossover, I was even more confused. L2 and L4 are then assumably both .3mH, but the inductor coils are different dimensions. Can this be easily explained?

Why two physical types of .3 mH coils ?

(a) They likely have different DCR values ( & I'm guessing ) with the coil that's in the midrange circuit having the lowest DCR ( DC Resistance ) .
(b) The cost of a coil can be directly connected to the gauge of the wire used ( which will determine the DCR value ) . Whether or not the coil is built as an aircore or ferrite core will also determine the effective DCR values .

- When you rebuild those crossovers , measure the DCR values of the original coils ( remembering to "Zero" your multimeter first ) and then buy replacements that are as close a match as possible.

[Zilch]

Agreed. To be certain, you'll need to measure both the inductance and DC resistance to choose substitues. JBL frequently uses the inherent resistance of inductors as part of the filter. You may have to use external resistance to precisely match the filter characteristics.

[maabx]

OK, thanks. I am going to purchase an LCR meter for this project.

Is inductor L1 a ferrite core inductor? Would it be OK to replace it with an air core?

Thanks, Mike Brown

[Zilch]

L1 and L2 both appear to be laminate core inductors on the schematic, but L2 is air core in the pic, looks like.

Air core is preferred, actually, providing you can match the DCR's....

[maabx]

At this point, as close as I can tell, the DCR for all three inductors is roughly .5ohms. Would lowering the DCR of all three to .36ohms be audible? Using Solen, that is as close as I can get to original. I'm just wondering if .14ohms would be audible. I know I can add resistance.

Thanks, Mike Brown

[duaneage]

If you lower the DCR of the inductors significantly, the Total Qts of the driver will go down. For woofers that means slightly weaker bass and the need for a slightly smaller cabinet. Midranges should be OK, might even help them sound better in a small enclosure. Tweeters should not be affected as they don't depend on an enclosure for dampening as much as a dynamic cone does.

Find the box tuning frequency before and after to see if it shifts. You might be OK. Shifts are more pronounced with very low Qts drivers because it behaves like a ratio to the driver electrical Q.

Rotate one inductor up off the board to prevent mutual coupling and give those cheap Asian electrolytic Caps a decent burial.

[maabx]

OK. I am going to add series resistance. Does it matter if the resistors are before the inductor or after, vis-a-vis the speaker input?

[maabx]

Is it OK to use 2.5ohm resistors in place of the 2.4ohm in my crossovers. I want to use mills and 2.5ohm is as close as I can get. Will the updated crossovers be functionally equivalent?


Thanks, Mike Brown

[Lancer]

Is it OK to use 2.5ohm resistors in place of the 2.4ohm in my crossovers.

Yes. 2.5 ohm was the original specification anyway, 2.4 ohm was substituted later when JBL changed vendors...

[maabx]

Thanks, Lancer.

Original specs.?? Do the original specs specify inductor DCR by any chance?

Thanks again, Mike Brown

[maabx]

Is the technical sheet linked at the top of this thread being fixed? It looks like it was removed for some reason.

[maabx]

Is the technical sheet linked at the top of this thread being fixed? It looks like it was taken down for some reason.