Help! Need help with this crossover schematic

[milosz]

HELP!!

I have a Boston Acoustics T1000 crossover but I do not know how to wire it to the drivers or to the input from the driving amplifier. (I also have all the drivers)

This late 1980's 3-way speaker system has two 8 inch woofers, a 6.5 inch mid and 1 inch dome tweeter. Obviously they all have to be wired to the crossover and the whole business needs to have a + and a - terminal for connection to a driving amplifier.

I wrote Boston Acoustics and they could offer no guidance.

Can someone help me figure out how to wire this up?

I've drawn the schematic and taken a photo of the crossover. Some wires were still connected to the crossover - these wires lead to drivers and to the speaker systems's pair of input terminals, one + and one -. I've indicated these connection points on the schematic, and the labeled points' letter correspond between schematic and photo.

 

[mike66]

A 3 red wires, two woofer +, one to speaker in + terminal
B 2 black wires woofer -, brown/white to midrange -
C yellow to tweeter -, black to - input terminal
D white wire to midrange +
E brown to tweeter +
I think that covers it. Good luck!

 

[mike66]

Ferrite inductor is 2.75mH, yellow inductor is 0.42, and the red is 0.51.

 

[milosz]

GREAT! THANKS!!

That's just FANTASTIC!

 

[teal'c]

GREAT! THANKS!!

That's just FANTASTIC!

Maybe you can put that gun down now.

 

[daveyh]

Maybe now you can put that gun down now.

LOL. Please.

 

[Pete B]

I never heard these but always wanted to after reading the excellent review
of them in Audio. I redrew the schematic in SPICE.
The woofer to mid crossover is a series type that employs a fairly low parts count
and is first order. I first saw it used in the DQ-10, it is also used in some AR speakers such
as the AR-48s as I documented here: http://baselaudiolab.com/AR48s.html
Starting with the woofers it can be seen that the positive inputs are wired directly to the
main system input. Low frequency signals including DC pass through the 2.75 mH inductor
L2 and 80 uF C2 acts to shunt highs away from the woofer rolling it off and providing a path for
highs to the midrange. R3 and C3 appear to be roughly a Zobel for the woofer.
R5 provides attenuation for the midrange and L3 is a low pass to the mid rolling off the
high end to it. 16 uF C4 makes the low pass XO to the mid 2nd order. R4 and C5 provide
a Zoble for the midrange. C1 and L1 form a 2nd order highpass to the tweeter with the
total attenuation to the tweeter controlled by the total resistance of R1 plus R2 and the
ratio controlling the Q or shape the that rolloff.

 

[Pete B]

Just noticed, the 2uF cap, C3 in my schematic looks too small, it is in the bottom left corner of
the picture and is large, is that actually 42 uF? Anyone?

Edit: Fixed schematic and edited post with new diagram.

 

[toxcrusadr]

Looks like it says 42 in the pic, to me.

I've also seen this arrangement (the mid coming off the woofer circuit) in the Harley Concertmasters that I worked on for another AKer.

 

[mike66]

So, any opinions on if this net, considering its age, would benefit from new electrolytic caps? I've read what Ken Kantor has to say about keeping the same style, but maybe upgrading to 1% or 5% in the process might have positive results? Don't want to know about one brand being more "musical" than another.

 

[teal'c]

Maybe. You certainly won't hurt it but there's no way to tell if it will change your audio until it's been done. Plenty of people have replaced still good caps with new with no discernible change.
The tolerance rating would have minimal effect.

 

[Pete B]

NPEs more than 10 years old should always be replaced.

 

[Pete B]

The 8 ohm resistor connected to C in the schematic should be 4 ohms per the picture.

 

[Rajen1962]

The 8 ohm resistor connected to C in the schematic should be 4 ohms per the picture.

This thread may be too old to update but just in case… I took my T1000’s apart today and checked the cross overs (thinking about replacing the caps and coils) and noticed that R5 is two resistors stacked and wired in series. The top one on mine is stamped 4.5 ohms. Did manufacturers sometimes stack resistors and then stamp the total resistance on the top one? I’m hoping to order all the parts and build my new crossovers before taking the original ones out. But it seems like I will need to take a measurement of R5 to know what the value actual is. Thanks for you thoughts.

 

[Rajen1962]

This thread may be too old to update but just in case… I took my T1000’s apart today and checked the cross overs (thinking about replacing the caps and coils) and noticed that R5 is two resistors stacked and wired in series. The top one on mine is stamped 4.5 ohms. Did manufacturers sometimes stack resistors and then stamp the total resistance on the top one? I’m hoping to order all the parts and build my new crossovers before taking the original ones out. But it seems like I will need to take a measurement of R5 to know what the value actual is. Thanks for you thoughts.

I made a rookie mistake and didn’t actually separate the two resistors to see what the bottom one was! Did manufacturers actually stack resistors and then stamp the top one with the value? The cross over is glued in place so removing it to measure the resistance isn’t straight forward. I’m hoping to build the new cross overs before removing the originals. Thanks for your help.

 

[Pete B]

I made a rookie mistake and didn’t actually separate the two resistors to see what the bottom one was! Did manufacturers actually stack resistors and then stamp the top one with the value? The cross over is glued in place so removing it to measure the resistance isn’t straight forward. I’m hoping to build the new cross overs before removing the originals. Thanks for your help.

I'm late here and you are correct, now I can see the lower resistor in the picture.
I have no idea what the value is, but this means that the schematic is incorrect.
The resistors were stamped during manufacture and therefore we need to
know what the lower resistor value is. Those resistors are 10W each so it is
possible that they felt a 20W resistor was needed and they made one up by stacking.

It would be great if someone could check the value of that lower resistor.