Arfa Daily wrote:

------------------
Hi all. Long time no visit this group. Hope all the usual suspects are
well !

Question regarding the crossover boards fitted to Jamo D870 three-ways.
There are two, connected together. They carry Jamo type / part numbers
53581 and 53582.

Does anyone know the correct connections for certain ? They have been
brought to me on their own with various issues - broken off and missing
resistor etc - with a request to repair them and mark up the cables. One
of the boards has six connection points that fix directly to connector
posts on the back of the cab. These appear to allow for bi-wiring ,
bi-amping or single amp / wiring depending on the fitting of straps
between the terminals. The other twwo terminals are for 'HF tuning',
depending on the fitting or not of more straps.

This input board has three smallish air cored chokes on it plus a few Cs
and Rs, and three sets of 'output' cables. One of these is marked "T+"
and "T-" so that's pretty certainly the tweeter output. A second cable
is marked "+W" and "-W" which you might think would be to the woofer,
but I don't think it is. The third cable is just marked "+" and "-" and
this goes across to the second board to points marked "AMP" - and +.
This board has two large ferrite cored chokes and some biggish values of
C. It then has another output cable marked "W+" and "W-". So I think
that this is the actual woofer connection and the cable on the other
board also helpfully marked "+W" and "-W", is actually the connection to
the mid driver.

I've tried feeding an amp in and sweeping it from a sine generator, but
the results between mid and bass are pretty inconclusive. The biggest
choke wound with the heaviest gauge wire, is directly in series with one
of the "W" marked output connections on the second board, and I think
that is the clue that says this is the output to the woofer, which will
require the highest drive power of the three, and the highest value of L
in series.


Anybody familiar with these to confirm for sure what's connected to
where, or failing that, anyone have any issues with what I think I've
come up with or my thoughts on how I got there ?



** The first thing to get clear is that this speaker is an oddball combination of a two way PLUS sub woofer in the *same* enclosure. There is no dedicated mid driver.

The design looks dodgy to me as it simply adds a sub woofer in parallel with the two way pair at low ( under 100Hz) frequencies while having them share the same air volume allows air pressure from the sub woofer to pump the cone of the main woofer.

You have identified the connections to the second board correctly, though the make should have labelled the outputs SW rather than W.

Bench running with resistive dummy loads attached is not going to reveal how the real system performs, so no surprise your results look odd.


...... Phil