Benign Error - AR-90 (possibly 9 also) Schematic

[johnfalc]

About seven years ago I replaced the caps of my AR-90s and I'm about to do the same for a pair of AR-9s I bought last year.

In reviewing the schematics and wiring diagrams I found here, along with photos I took at the time of the AR-90's crossovers prior to working on them, I find an inconsistency. 

In the schematic diagram the lower midrange units are driven through the attenuator, then through an 80uF cap followed by a 2.63MH inductor with a 30uF cap in parallel with the driver.  Note that in this depiction, no direct connection exists between the two capacitors.

However, in the wiring diagram and in the photos I took before working on the AR-90 crossovers, the order of connections is different.  This diagram (and the reality of what I found) show the lower midrange units driven through the attenuator, then through the 2.63MH inductor followed by the 80uF cap to the driver which, again, is paralleled by the 30uF cap.  Note (for it makes it easy to see the discrepancy) that in this case the two capacitors are directly connected in series with the driver driven from their junction.

Simulating the circuit demonstrates that the frequency and phase response are the same either way ... it just seems we should correct the schematic to match the wiring diagram and what I found in the AR-90s to eliminate any confusion.  When I get to doing the AR-9s I'll take photos to see if this is a consistent discrepancy.

[johnfalc]

Note I attached the AR-9 schematic but the AR-90 is the same for the LMR/HMR/TWT.

[DavidR]

The tweeter, UMR and LMR in the AR90 are wired out of phase. The AR9 is wired in phase for those drivers. The AR90 does not have the tank circuit (2500uF cap) that the AR9 has on the woofers.

The 30uF on the LMR is a shunt cap. The 80uF is the series cap. Both look to be wired the same other than the phase. At least on the schematics I have.

Not sure if this is the difference you are seeing.

[DavidR]

Here's a pdf of an AR90 xover that someone did. Who ever made it did a great job. It makes the wiring much easier to understand.

ar90 xoverschematic.pdf

[johnfalc]

1 hour ago, DavidR said:

The tweeter, UMR and LMR in the AR90 are wired out of phase. The AR9 is wired in phase for those drivers. The AR90 does not have the tank circuit (2500uF cap) that the AR9 has on the woofers.

The 30uF on the LMR is a shunt cap. The 80uF is the series cap. Both look to be wired the same other than the phase. At least on the schematics I have.

Not sure if this is the difference you are seeing.

No.  The difference I'm noting is ONLY in the order of components in the LMR circuit.  What I'm drawing attention to is that the schematic and wiring diagram show different orders for the inductor and 80uF cap.  It doesn't matter electrically but I like agreement on such matters.  John

[johnfalc]

That's a nice diagram and it matches the factory wiring diagram and my photos. I understand the layout just fine. 

My post is just drawing attention to the fact that the schematic in our library doesn't match this diagram, the factory diagram, or my photos, that's all.  

Note that the LMR green white is connected to BOTH capacitors which is not how it appears in the schematic.

[r_laski]

This is an AR9 woofer and Lower Mid Range (LMR) crossover section picture and AR engineering drawing of same. in the picture, the 80uF capacitor (gray) is on the lower right corner. As you can see, the purple wire comes from the attenuation board to one pole on the 80uF cap. The 2.63mH (13) coil is attached to the other 80uF cap pole. The other end of the 2.63mH coil, one pole of the 30uF capacitor, and white wire are attached at a single point. White wire connects to the (+) terminal on the 8" LMR. The green and brown wires are connected to the other end of the 30uF capacitor. The green wire goes to the (-) terminal on the 8" LMR. The brown wire goes to the upper black (-) binding post.

The AR9 crossover schematic is correctly drawn in how the AR9 LMR crossover is wired. It is NOT wired the same as the your AR90 LMR crossover picture or drawing. Hope this helps clear up the difference between the AR9 and AR90 LMR wiring.

Edited December 4, 2020 by r_laski
Added engineering drawing

[ligs]

Reading schematics can be a little confusing. Here is the equivalent circuit for just the speaker without the crossover.  

[DavidR]

Here's a picture of my AR90 lower board.

 

[r_laski]

I've posted this AR9 crossover diagram here and in my post/threads of my AR9 recap/upgrade. I've added the second 1.37mH inductor coil to the UMR section. See https://community.classicspeakerpages.net/topic/11407-my-ar-9-capacitor-recapupgrade-project/

my 12/3/2020 post for picture and details. It looks like the AR90 UMR section drawings in earlier posts on this topic have the same second inductor coil wired the same way.