RS 2.5 Single Amp/Bi-Amp switch issue

Several weeks after the successful repair of my RS 2.5 ECU and everything working and sounding fine as documented in the thread at the link below:

http://www.audiokarma.org/forums/showthread.php?t=630055&page=2

I suddenly noticed a strange anomaly with my right speaker wherein the sound coming from it was distinctly muffled when compared to the left speaker. I first swapped left and right channel cables on the ECU followed by the same procedure on both amplifiers driving the mid/tweeters and woofers and the problem persisted in the right speaker. I even swapped out the ECU with the spare that I had acquired while waiting for the parts to repair my original with no apparent change in the condition. If I remove the ECU from the signal stream, flip the Single Amp/Bi-Amp switch to Single Amp as per Infinity's instructions and passively bi-amp the speakers, the right speaker sounds fine. After checking the impedance of both EMIT's and EMIM's with them out of the circuit and discovering that they all check out as expected, the obvious conclusion is that there is something wrong in the passive crossover that only comes into play with the switch in the bi-amp position.

I am attaching a copy of the crossover schematic from the Infinity Classics website, the only one I know to be available, with the caveat that the crossovers in my 2.5's have significantly fewer components than are shown, likely an earlier iteration that predates the schematic. Without going into what components are not present in my crossovers when compared to the schematic which at this point would just muddy the discussion, can one of the RS 2.5 crossover gurus out there explain to me what changes when the switch is placed in the bi-amp position when compared to the single amp position, and in particular with regards to the attached schematic:



Is the switch shown in the biamp or single amp position?

Relative to the yellow highlighted dotted line - what does it indicate?

Does the dotted line that goes to the points adjacent to the 2.5/5mH choke indicate a third pole on the switch? Otherwise I don't see a circuit to the positive side of VC1 on the woofer.

I have a spare upper panel with the crossover intact that essentially matches the one's in my RS 2.5's and have been trying to match it to the schematic but because of the missing components, to include a double pole switch in my crossovers as well as the spare, in place of what appears to be a three pole switch on the schematic, I am just getting more and more confused. I will attach a photo of the passive crossover in my right 2.5 just for informational purposes.

So I basically need to know how the switch works - what it pulls in or removes from the passive components when it is in the bi-amp position.

Thanks for whatever help anyone can provide.

In the midrange circuit...
In Single-Amp mode, there is 125uf in series with the EMIMs. Flip the switch to Bi-Amp mode, and it brings in the 50uf cap in parallel, giving you 175uf. The schematic is drawn in the Single-Amp position. So, in the Bi-Amp position, the EMIMs are playing lower frequencies (larger cap value = lower frequencies being passed). The point is to allow the active crossover to set the 'actual' crossover value and contour the sound. The 'actual' crossover value should be higher than what 175 in the passive network would pass to the EMIMs. This is where a lot of damaged EMIMs came from: Set the switch to Bi-Amp without using the active crossover, and you are passing lower-than-normal frequencies to only two EMIMs to handle it without strain or failure. Well, a lot of them eventually failed after someone (or their curious child) "accidentally" set the switch to Bi-Amp and cranked the volume, not knowing that the EMIMs were playing lower frequencies and reaching excursion limits.

In VC1 circuit...
In Single-Amp mode, you have a 5mH series inductance in the circuit (the diagram is really bad here). Flip the switch to Bi-Amp mode and it taps the inductor at half of its windings, yielding 2.5mH. This makes the woofer play higher (less inductance = higher frequencies being played). Again, the point is that the active crossover will set the 'actual' crossover value and contour between the woofer and the EMIMs.

If you use a single amp with the switch set to Bi-Amp, there will be a larger overlap in frequency response between the EMIMs and the woofer. This won't hurt anything, but, as said before, start turning the volume up just a hair and those two EMIMs really start to feel the pain of playing lower frequencies. Again, this resulted in a lot of failures and severely messed up EMIM diaphragms.

The hard one to get is this...
In Single-Amp mode, they use 1100uf of capacitance in series with VC1. Flip the switch to Bi-Amp, and it's now 1800uf because of the paralleled 700uf cap. So, the infrasonic filter for the woofer is now allowing much lower frequencies to go to VC1. Frankly, I never could quite see the point of this. Maybe they were trying to yield a low passive assist function into VC1, I don't know. Even if that's the case, I still never could understand why. But, it is what it is. Out of curiosity, I've run the circuit configurations through a circuit simulator which gives dbV (decibels referenced to voltage) and phase, and I still couldn't glean any insight into the idea behind it after studying the curves.

G~

Here's another one, but again, they didn't draw the switch in the woofer series inductor.

Crossover problem

Great information. Thank you.

So it would appear that the dotted line only indicates that the switch contacts shown are simply part of the same device and not electrically connected in any way.

Here is where it gets tricky. My crossover does not have the 50ųfd or the 125ųfd caps in the EMIM circuit, just a single 75ųfd, nor does it have the 125ųfd cap in the woofer circuit but does of necessity have a number of differences in the wiring and as I mentioned only has a dual pole switch so I am really flummoxed as to why flipping that switch to bi-amp mode is causing this significant, almost complete muting of the EMIM's and EMIT's and also the woofers to a lesser degree unless something is causing a partial short to the inputs although the amplifiers, which are the two Soundcrafsmen in my avatar, show no signs of distress or overload.

I guess I have to try to cobble together some sort of schematic from the spare crossover that I have since I can just hold it in my lap as I trace wires, and try to sort out which pole in the switch I am missing and which component that comes into play when the switch is flipped into bi-amp mode could possibly be causing this very strange problem.

Hope you figure it out.
I'd like to know which caps I can replace for single amping thus not having to replace all of them???

Coastsider said:

My crossover does not have the 50ųfd or the 125ųfd caps in the EMIM circuit, just a single 75ųfd, nor does it have the 125ųfd cap in the woofer circuit

Click to expand...

Hmmm, interesting. So you have a first-order low-pass on VC1 instead of 2nd-order, and a fixed crossover frequency on the high-pass for the EMIMs.

Didn't you recap these a few years ago, or am I thinking of someone else? I seem to remember a bunch of capacitors arranged in a circle. Were those yours?

Sometimes it's really tricky trying to diagnose this stuff when you don't have the speakers right there in front of you, and/or can't listen to exactly what they're doing.

I guess you could just do a re-wire, and make the switch take the high-pass cap out of the midrange circuit entirely (direct couple the EMIMs to the driving amplifier), and also have it remove the woofer's low-pass inductor out of the circuit (directly coupling VC1 to its driving amp), and let the external active network set the xover frequency that way. BUT.....that's just brainstorming. I don't remember enough about that Infinity crossover to say for sure that that's a viable option. I'd be much more comfortable running a 4th-order active network if I was going to do that.

G~

I did recap my RS 2.5's a few years ago but that only involved replacing the two smaller caps, the 3.83ųfd on the EMIT's and the 75ųfd on the EMIM's. I do remember that thread about replacing the big cans on the woofers with those big bunches of caps arranged in a circle, but that wasn't me. I left them all in place, and in my case they consist of an 1100ųfd and two 600ųfd electrolytic capacitors, simply because I could not source appropriate replacements.

I've already done some re-soldering and also pulled the toggle switch apart to make sure there was nothing wrong with it but as yet have not replaced anything that is replaceable. It certainly seems that something must have failed just because of the suddenness with which this problem occurred but the fact that so few additional components are introduced into the circuitry when the switch is toggled to the bi-amp position makes it all the more confusing since I've already eliminated the ECU as the potential source of the problem.

For now I can just continue to bi-amp the speakers passively until I come up with a solution but it's pretty frustrating, especially since I went to the trouble and expense of getting the ECU back in working condition after it's power supply transformer failed.

I do appreciate the information and suggestions nonetheless and will report any progress I make with this very strange problem.

Problem solved

I had the metaphorical "stupid" switch in the on position.

I'm too embarrassed to say anything beyond that but everything is once again back to working spectacularly well.

Metaphorically speaking, I'm red in the face asking which capacitors would be replaced for single amp only function????

tubed said:

Metaphorically speaking, I'm red in the face asking which capacitors would be replaced for single amp only function????

Click to expand...

If your crossover matches the schematic then based on what I see for single amp use you should replace the 3.83ųfd in the EMIT circuit, the 125ųfd in the EMIM circuit and the 125ųfd shunt capacitor in the Watkins VC1 circuit. I'm attaching a photo of RS 2.5 crossovers from a 2011 posting by AK member rdp91356 that shows the 125ųfd's as both radial lead electrolytic cans and 50ųfd and 75ųfd axial lead caps in parallel. If the 125ųfd caps in your crossovers are cans you should be able to replace them with axial lead film caps of appropriate voltage. It's been my experience that the large 700ųfd and 1100ųfd non-polar electrolytic cans are difficult if not impossible to source.

Here's a link to that 2011 thread that might be of interest since it has lots of RS 2.5 crossover information.

http://www.audiokarma.org/forums/showthread.php?t=408573

^^^^^
Thanks Coastsider!
I was basically a bit confused about the caps for the midrange since they seem to be the only caps affected by the single/bi amplifier circuitry.
So the 125uf it is.

When I have my 2.5's in the bi-amp position the emims are separated from the woofer completely or am I missing something here?

InAp said:

When I have my 2.5's in the bi-amp position the emims are separated from the woofer completely or am I missing something here?

Click to expand...

As it should be in bi-amplification.
From what I've read lately here, when the 2.5s are switched to biamp mode the crossover points change, perhaps lower on the EMIM???

Don't tale this as accurate, but I think in single amp mode the xo is at 200 hz, In bi-amp mode it's set by the active xo at users prefrence. At least thats how I use mine

InAp said:

Don't tale this as accurate, but I think in single amp mode the xo is at 200 hz, In bi-amp mode it's set by the active xo at users prefrence. At least thats how I use mine

Click to expand...

There you go.
I don't have the the control module so I'm only concerned with the single amp mode
FWIW, my RS 2.5s are finally sounding very good as I believe when I acuqired them they hadn't been used much and under my direction are breaking in nicely

Are you using the stock emim's or Graz re-mans

InAp said:

When I have my 2.5's in the bi-amp position the emims are separated from the woofer completely or am I missing something here?

Click to expand...

The EMIM's and EMIT's are always separate from the woofers unless you have the high and low inputs strapped together.

If you are passively bi-amping using two amps or actively bi-amping with an active crossover such as the Infinity ECU and two amps, the straps must be removed for obvious reasons. If you are using a single amp the inputs have to have the straps installed or if you don't have the factory straps, some other method like jumpers can be used to connect the high and low inputs together.

As far as the toggle switch goes, with a single amp or passive bi-amping it is in the single amp position. Only with active bi-amping is it placed in the bi-amp position which modifies the crossover frequencies. I know it's confusing but that's how it is explained in the user instructions.