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Bi-amping the AR-3a cheaply and non-invasively – WOW!!!


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For the last 4 hours I have been listening to my bi-amped AR-3a’s and I can’t believe the difference. Bass that just GROWLS through the 12 inch woofers, high frequencies are clearer than my TSW’s 610’s and stereo imaging that is just unbelievable. It’s hard to believe I’m listening to the same speakers.

What I particularly noticed is the punch at low power levels. I’m talking about just terrific sound at 1 watt or less! I’m hearing instruments I never heard in the music before. Individual people clapping! That’s right, I can pick our individual people clapping as opposed to audience clapping.

Who knows, I might just be incredibly lucky and everything fell into place, but I’d strongly recommend that you at least experiment.

The only down side is my favorite FM station that I’d listen to for hours on end (jazz only station) now sounds like crap. The 3a’s are so clear, I now hear the crude I never heard before. Oh well … I’m NOT going back.

Here is what I did:

1. I always listen to my 3a’s on an old HeathKit AR1500 and I still do! Only now the Heathkit just powers the woofers, terminals 1 and 2 on the 3a’s. Further, the tremble control is turned completely off. In short, the Heathkit is only producing low frequencies. (AR1500 is rated at 100 watts output at 4 ohms)

2. I take the audio signals from Tape Output jacks. This tap is before the tone controls so it has the complete audio signal.

3. The Tape Output goes into an old Pioneer audio/video amplifier (rated at 30 watts that was in my basement collecting dust) at the VCR Audio Input. Now this amp has the bass tone control turned completely off. In short, the Pioneer is only producing higher frequencies and it is powering the tweeter and mid-range via terminals T and 1 on the 3a’s.

4. So that leaves me with two independent volume controls. One on each amp and by adjusting these two controls I control the mix of high and low frequencies. It took me no more than 3 minutes to figure out how these two volume controls work together.

5. Now before you attempt this, you must make absolutely certain that both amps have common grounds on the speaker outputs AND those grounds MUST be connected to terminal 1 on the 3a’s. The “hot” or “red” lines go to 2 and T. Notice that the shielded audio cables from Tape Output to the VCR Input insures that ground on both amps is pegged to the approximately the same level.

6. Next, that the old 30 watt amp has more than sufficient to power to drive the mid-range and tweeter. In fact, it probably has too much power, so we must be careful NOT to over drive.

7. Lastly, I did NOT open the 3a’s! The crossovers are still there, but doing little since the amps are only producing frequencies consistent with the speakers they are driving. If I ever do anything with the crossovers, I think what I’d try is putting a shunt across the coil in series with the woofer. I’d probably leave the cap in place just to insure no stray high frequencies got to the woofer. Now whether there would be any difference with the coil out is hard to say. The base is so much improved; it’s hard to believe it can get much better.

Has anyone tried shunting the coil? If so, can you tell any difference?

Let me repeat the benefits:

1. Bass that just GROWLS

2. Clear/clean high frequencies

3. Great imaging

4. Lots more volume at 1 watt output (and I have absolutely no clue why this should be the case)

5. Both amps are running very cool - they are NOT being stressed at all! Before I retired the Pioneer it was my home theater amp and it normally ran so hot you could fry an egg on it. After 4 hours of bi-amping it’s just barely warm.

If you get a chance, here is an explanation of why and how bi-amping works:


In closing, you’ve just got to try this to see whether you can get similar results.

Good luck!


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Excellent news. Bi-amping can make a difference but it depends on the speaker and amps involved. My speakers displayed almost no change when I bi-amped without an active crossover but with one, the change was absolutely stunning.

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"Bi-amping the AR-3a cheaply and non-invasively – WOW!!!"

Whoa, not so fast. Customarily, a speaker such as the AR-3a should *not* be bi-amped because the AR-3a crossover-ground circuit for the woofer and midrange/tweeter is common. It is not isolated through two sets of input connectors by a strap to separate crossover circuits, as in some speakers designed to accommodate bi-amping. Connecting two different amplifiers (even with common-ground output circuits) to each other might cause either or both amplifiers to become unstable, oscillate, run hot and possibly cause excessive distortion under certain circumstances. Crossover components might also be damaged. Therefore, discretion should be exercised before connecting two amplifiers to a common-ground speaker. The strap on the back of the AR-3a was there to allow “woofer-only” operation, not to separate the crossover sections for bi-amping. If the two amplifiers became unstable due to this common connection, problems might arise with respect to dc offset, high-frequency oscillation or other serious issues. Any of a number of issues such as those could seriously damage the speakers.

It is not impossible to bi-amp the AR-3a, but the rewards for doing it are debatable. If you simply must do it, you should isolate the woofer circuit by disconnecting the blue woofer ground wire from terminal No. 1 and by running a *separate* ground for the woofer circuit out through the back of the crossover board to make this the woofer’s ground connection; connect the positive woofer connection to the No. 2 input connection on the back of the speaker in the normal fashion. For the midrange/tweeter make the connection of ground to the No. 1 input terminal and the “T” connection. In this manner, you have at least isolated the woofer from the midrange/tweeter. You should not disconnect the crossover network (nothing to do with preventing "stray high-frequency from getting to the woofer," as the woofer will roll off mechanically long before you notice any stray high frequency); moreover, you cannot control the output of the individual drivers simply with amplifier tone controls.

--Tom Tyson

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Tom, I agree we need to be careful.

Fortunately, I have the circuit diagram for the HeathKit AR1500, so I know everything in it is referenced to ground, including the shields on the audio cables. Then on the Pioneer I did a visual trace AND measured to verify that it also had a common ground referenced to the chassis AND the shields on the input cables.

Only after I checked these out did I attempt the 3 wire connection on the 3a's.

After many hours of listening, it's clear that the amps are NOT stressed in the least. They are both running cooler than before and the sound volume for the same output power (approx .5 to 1 watt - I have watt meters on the AR1500 output) is significantly HIGHER. I can offer no explanation for this, but it's really dramatic!

I further understand your concern about interactions between the amps and the crossover networks. To a certain extent common ground systems face this problem every day when they allow users to drive both A and B speaker systems simultaneously. The HeathKit has a tuned circuit in the output stage to prevent oscillations from back feeding.

My bigger concern was the phase of the signal at output on the two amps. I don’t have a dual trace scope so there is no way for me to know the phase relationship between these two signals. My guess is it’s impossible for them to be in phase, given that we have two different manufacturers. Complicating this is the phase difference between the two amps can vary over the audio spectrum.

For whatever reason, it seems to make little difference and I can’t explain that either.

I’m wondering if another way to think about this bi-amping, is that what I’ve really done is convert the 12 inch drivers into two very, very good subwoofers. Then the mid-range/tweeter combos become very high quality satellites (far, far superior to those little Bose satellites).

In any event, the sound difference is dramatic … at both ends. Stereo imaging is light years better and so is transient response. On jazz trios with double base, the woofers just GROWL.

There is a downside, however, and that is that poor audio tracks/sources sound much worse. I learned this on my favorite FM jazz station.

The one issue unresolved is the coil in series with the woofer. My question is what would happen if we shunted it? The base is sooo good now, I really can’t believe that it would make a significant difference. Further, that coil may block oscillations. As for the capacitor across the woofer, I’d leave it alone.

Purpose of adjusting the tone controls is NOT to control the drivers, but to send to the drivers the frequencies they were intended to handle and NOTHING more. Hmmmm that may explain why the amps are running cooler and the sound output is higher. Very little energy is wasted or discarded by the crossover network! Now, I’m really guessing here.

Hope this helps …


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It seems that you could have achieved the same result with an equalizer and one amp. Your use of tone controls (or, for that matter, the use of an electronic crossover with two amps) is simply changing the crossover slopes and associated sonic character of the original design. I suspect you have dropped a good deal of midrange information with your arrangement.

This may sound pleasing at first, but can become tiresome.

...just my 2 cents.


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>It seems that you could have achieved the same result with an

>equalizer and one amp. Your use of tone controls (or, for that

>matter, the use of an electronic crossover with two amps) is

>simply changing the crossover slopes and associated sonic

>character of the original design. I suspect you have dropped a

>good deal of midrange information with your arrangement.

>This may sound pleasing at first, but can become tiresome.

>...just my 2 cents.




I need your help here, because I really don't understand how I could have achieved the same results with a single amp. My use of the tone controls was to limit the frequency spectrum processed by each amp. My ultimate goal is to reduce intermodulation distortion (see referenced article):

“Intermodulation distortion in an amplifier is a form of distortion created when two different frequencies are being amplified simultaneously. The effects of intermod are most noticeable when one of the frequencies is much lower than the other, and the high frequency signal is actually modulated by the low frequency. This is quite different from the signals simply adding as they are supposed to. The effect (musically speaking) is that the sound is muddied, and the highs lose their transparency. Individual instruments become difficult to separate as their harmonics all start to blend into a 'wall of sound' (have another look at Figure 3B - this is intermodulation distortion at its worst).

By separating the low and mid+high frequencies from each other prior to the power amplifiers, we reduce (to a large degree) one of the major sources of intermodulation. This is a great benefit to the music lover, since the sound instantly becomes more open and cleaner.”

The tone control circuits on the AR1500 attenuate the frequency band by 15 to 18 db according to Heath’s specifications and this reduction occurs prior to the power amplification stage.

So Roy, how can one achieve this same result with a single amp?



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Guest SherwoodFool


Is this the same method you described for me for the 2ax's? If it is so, It seems that the only concerns are common grounds for the amps which you solved by your familarity with both of your amps circuitry or by presumably using same brand,same era amps(I certainly have enough Sherwoods for that).

I would like to hear your thoughts about overpowering(especially the tweeters). If I remember correctly your Heathkit puts out 45-50Wts/ch; Pioneer(SX-737?) 35wts/ch. I was about to double that. Do think that would be a problem?

BTW, Play WBGO on your computer. It's bad in Brooklyn,the city and Westchester. Good only in Newark & south to about Princeton. Didn't realize til I got out of town.



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I've two comments. The first concerns something Tom mentioned.

Tom mentioned the DC offset in the amps. Whereas I'm not familiar with the Heathkit AR-1500, I'm very familiar with the Heathkit AA-1800. The AA-1800 has two adjustments per channel, bias set to 35 mv and DC offset whis is set to zero VDC without speakers connected. (I own two of these amps.) If the DC offset is to far off and in opposite polarities, theres the strong probability there will be a significant current flow thru the common ground between the amps contributing to heat buildup. It might not be a bad idea to check the offset on both amps just to be sure you aren't shortening their lives.

The second comment concerns using the tone controls.

Your method works, but there's a much more elegant method that should result in far superior results. Use an active crossover in front of your two amps. I chose the marchand tube crossover in kit form. A good place to start for the crossover setpoints is one octave over the speakers crossover point for the low pass and one octave under for the high pass. This overlap should reduce or eliminate the chance of messing up the mids.

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Ok, I now what you are talking about now and you are correct those old amps had a DC bias adjustment to insure the “hot” line was at zero potential with respect to the common ground. Now this is for the high quality amps with plus and minus rail voltages. (I have had several amps that had those adjustments.) On the cheap amps with only a single supply voltage, they are capacitively coupled with the speakers, so this is a non issue.

The AR1500 has no such adjustment and frankly, I don’t know how it keeps the hot output at zero potential. There is a fairly complex system of diodes that appears to handle the biasing, but I don’t know how it works. So I read the manual and I still don’t know how it works.

In any event, it’s still a non-issue. The common grounds of both amps are pegged together through the 4 shields on the coax cables that connect between the amps. So, the only problem is the potential that the bias voltages on the hot outputs of the two amps is way off … like you mentioned. It’s still not a problem!!

Reason for this is that the hot amp outputs are NOT DC connected through the speakers! Look at the xover schematic. The mid-range and tweeter are capacitively coupled. There simply exists no path for DC to flow between the two hot outputs. I checked this before I connected the amps and since it’s a non-issue, I never mentioned it.

No question that you have a far more elegant and superior solution by using an active crossover. My goal was to do this as CHEAPLY as possible and see whether I could hear a difference. The difference is simply UNBELIEVABLE.

Returning to the cheap solution, I’ll bet just about everyone (or their son) has a low power amp or receiver collecting dust somewhere. So trying this should be really cheap, a couple of audio patch cables and some speaker wire.



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Russ, regardless of the manufacturer, I’d still suggest that you double check two things on the amps (with the power off):

1. that the two “non-hot” outputs are common. Zero ohms when you connect an ohm meter to each output

2. then test one output against the shield connection on any audio input jack. Again you are looking for zero ohms.

These two tests insure that your amps will work OK on the 3 terminals on the AR’s.

Next thing you absolutely must do, Russ, is insure that the common grounds are connected to terminal 1 on the AR’s. Reversing this is a recipe for disaster!

As for power, my two amps are way different. The AR1500 is conservatively rated at 100 watts RMS per channel into 4 ohms. The Pioneer is 30 watts “music power” (pure BS) per channel. Point is, the Pioneer still has far more power than the mid-range and tweeter can safely handle. So we need to always reduce the volume level for the tweeters upon changing audio sources. Nobody wants blown tweeters, so better safe than sorry.

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YES, the shields are connected to the common ground. This is one of the things I measured BEFORE connecting everything together. The whole ideal is to prevent "floating grounds". We want both amps to have exactly the same grounds and the shielded cables will force everything to a common point.

Then the fact that we tie the common grounds on the speakers together is irrevalant. The two chassis are already tied together via the coax cables.

The only output bias that can leak is the one connected to the woofer and that's no different than before I connected the other amp.

There is no DC path from the output of the high frequeny amp to anything. The xover circuits block DC on the mid-range and tweeter.

Lastly, the final test is heat and both amps are running significantly "cooler".

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Running cooler is a good thing and an indication things are going well. Not meaning to flog a dead horse, but well, OK perhaps I am.

If you consider that the ground or neutral for both the low level inputs and the high level outputs are connected to the same ground plane, and the low level inputs are connected to a single input connecting their shields to the same plane, you have a path for current flow from the high level ground thru the low level input, to the preamp, out the other shield and into the high level ground of the other amp.

For the heck of it, what's the resistance reading between the two amps negative terminals with the speakers disconnected?

The fact your amps are running cooler is a strong indicator you have little or no circulating current in the ground loop, but was something I had to be concerned with, and actually caused an intermittent hum.

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Yes, that would be a good measurement to make.

Unfortunately the way I have the HeathKit set up it will take me a while to unhook the speakers at the receiver.

I did measure the speaker wires connected to the HeathKit and verified that the resistance between the non-hot lead and the shield on an input cable was zero.

Same for the Pioneer. Only there I measured the speaker output to the shield on an input jack and got zero.

So if I make the measurement you are asking the only resistance I'll be measuring is that of the 4 shielded audio cables. It's got to be very, very close to zero.

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Mid-Range has it disappeared as Roy suggests??

Well, anything is possible. According to the specs the tone control adjustments seem to be working on the extremes of the audio spectrum. If that is the case, then we'd expect the mid-range to remain intact.

Time for an experiment ...

This morning while listening to my favorite FM station (strictly jazz), there was a female DJ promoting an upcoming concert. Well, I turned all the tone controls on both amps to the totally off position. The female DJ came through clear as a bell.

I guess the mid-range is still there and wouldn't you know it. The one thing we'd like to NOT hear ... there is no way to eliminate. It's just like being married!

I'm back to listening to my favorite FM station. It turns out that right after I bi-amped the 3a, the DJ was playing some of his old vinyl records. That's why I was so turned off by the sound.

Now, all I do is turn down the tremble adjustment on the Pioneer and the station sounds decent again. Actually, it sounds better than before because there is so much "punch" in the base.



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Joe, I happen to be the proud owner of a Technics SL Dl-1 Direct Drive Automatic Turntable System. I rarely use it though. I have the same problem as that DJ.

The $%#@ kids got into my records!

The few that they didn't touch still sound OK, but the others are just about totalled. I guess that's the real problem with vinyl ... it's pretty delicate.



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I was simply suggesting that you have altered the tonal balance of your speakers, which is the same thing equalizers (of various types), and other effects devices do. I highly doubt the "dramatic" difference you hear is strictly due to the elimination of intermodulation distortion. You have simply changed the frequency response of your speakers.

What are the frequency center points of your tone controls? How quickly do they roll off or increase per octave? Why were you considering "shunting" the woofer coil, which is a very essential part of the speaker design?

I have bi-amped speakers (both home and PA) that are built for that purpose, and have never heard the dramatic differences you describe.

As Tom mentioned above, the 3a crossover was not built for that purpose, but I am glad that your experiment has proven interesting and satisfying to you.


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Thanks for the comments/suggestions, Roy.

As for the tone control specs I don’t have much. All Heath “promises” is a 15db cut at 20K Hz with the treble tone control fully counterclockwise. They “promise” a 15db cut at 20 Hz with the bass tone control fully counterclockwise.

Frankly, I really believe the differences I hear has more to do with the electronics than the speakers. I seriously doubt that bi-amping has changed the frequency response of the speakers.

Too many things are going on:

1. far better transient response

2. far better stereo imaging

3. far more volume at the same power output

4. amps running much cooler than before

Like I mentioned early in my original posting, it may all be dumb luck. It’s possible that the lowly Pioneer amp that is now “unburdened” with low frequencies is producing an exceptionally clear and clean audio output compared to the HeathKit when it had to produce the full audio spectrum. It’s possible that the HeathKit was putting out a ton of distortion because of the severe power drain caused by the “power hungry woofers”. Further, that distortion would have been heard more in the high frequencies tending to “muddy” everything.

Roy, I really don’t know what’s going on and encourage folks to give this a try. The cost is insignificant! I mean everyone has a low power amp/receiver collecting dust somewhere. Only thing else needed is some audio patch cords and some speaker wire.

Hopefully, by having a number of folks attempt exactly the same approach, we’ll be able to determine:

1. whether others experience significant differences

2. which of the characteristics I mentioned are most often experienced

By expanding the pool of experimenters, Roy, maybe we’ll be able to figure out what’s really going on.

As for the 3a NOT being designed for bi-amping, I couldn't agree more. So many things had to fall in place for this to work WITHOUT having to open the box. On the otherhand, the AR3a was a speaker way ahead of it's time.



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>> I highly doubt the "dramatic" difference you hear is strictly due >>to the elimination of intermodulation distortion. You have simply >>changed the frequency response of your speakers.


I can't disprove your claim but I can offer anecdotal evidence TIM might be at play.

Unlike Jerry, I opened my speakers and made a modification to the crossover while I was in the process of replacing the old caps. unlike the AR9, the AR90 was not designed to be bi-amped. But at the same time, both speakers use a similar design 4 way crossover with the bass crossover point at 200 hz. Modifying the crossover to break out the bass drivers was extremely easy as the bass section had its own wires running directly from the speaker terminals. A carefull layout job with masking tape, a good router bit and patience allowed me to install a 4 post terminal cup allowing the speaker to be bi-amped.

The initial results bi-amping with identical amps (Heathkit AA-1800) proved to be of value. There was an improvement, but not that much, and the sound stage was a bit disjointed. Each amp was still reproducing everything and both amps would still run hot with heavy bass. (Ray Montford; Shed your Skin)

The next step.

I ordered a Marchand XM24 crossover as a kit. The high freq crossover point at 100 hz, the bass at 400hz. This overlap (one ocateve over and under) the passive crossover prevents the active crossover from interfering with the passive crossover.

The result was absolutely stunning. Everything Jerry listed as an improvement and more was noted. Improved mid clarity, cleaner, better defined bass that actually sounded like it went lower. It doesn't, its just better defined. We hear faint high freq instruments that previously weren't audible, such as triangles. Add to the list an extremely high WAF and it was a winning idea.

Why the dramatic change? I can only guess it was a reduction in TIM.

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>The initial results bi-amping with identical amps (Heathkit

>AA-1800) proved to be of value. There was an improvement, but

>not that much

That has been my experience as well when using existing passive crossovers.

>I ordered a Marchand XM24 crossover as a kit. The high freq

>crossover point at 100 hz, the bass at 400hz.

Using an active/electronic crossover changes the rules of the game quite a bit. Among the more obvious things, the crossover slopes are different (probably much steeper than the gradual 6db/12db per octave design of the original 3a crossover). If you also change the original crossover points, significant differences are likely to be heard. Fortunately you have deemed the changes to be improvements.

>Why the dramatic change? I can only guess it was a reduction

>in TIM.

That is probably part of the result, but you essentially redesigned the speaker system when you replaced the original passive crossover. I believe, as I do with Jerry's approach, that the speaker system's frequency response curve has been altered as well.

In Jerry's arrangement, he has somehow achieved a significant difference utilizing the original passive crossover through the manipulation of the two amps' tone controls. The information he provided suggests that the controls operate at the extremes of the audio range, which would make them less likely to create a midrange problem, as I originally suggested. Some tone controls can affect a broad spectrum of frequencies however. Using them to modify crossover slopes is a crapshoot at best.

The original crossover of the AR-3a has some woofer to midrange issues. It is possible that you have both addressed that problem somewhat in your bi-amping adventures....and, hey, if it sounds good...........:-)!

Keep us posted.


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I need to clarify.

I did not redesign the crossover but rather replaced value for value with new caps. The old caps were so bad the tweeter was pretty much dead and the upper mids were useless. There was about a year span between the crossover rebuild and the addition of the active crossover giving more than adequate time for my ears and the new caps to settle in.

In addition to this, my first attempt at biamping the speakers was done with the original caps. I've heard the speakers single amped and biamped with the old caps as well as with the new. New caps with active crossover absolutely wins out.

As for changing the crossover points, thats why the active crossover points are one octave away from the passive crossover point. Very likely, the active crossover is attenuating the very end of the rolloff, but not hearing Shania Twain come thru the bass drivers is a plus I can live with. Fact is, with both the original caps and the new poly caps, womens voices did and do come thru the bass section unless I use the active crossover.

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Roy, please see my new thread.

It turns out that the tone controls are doing very little as far as sound quality. My guess, Roy, is that I would see more heat if I were to set them to max. (Remember everything is running cool right now)

That is, when I turn the treble control to max on the AR1500, which is only powering the woofers, I heard NO more high frequencies. I do sense a very, very slight reduction in clarity. In short, the passive xover within the AR3a is doing it's job perfectly!

I mean, I'm send the woofer a ton of high frequency signals and NOTHING is coming out of the woofer.

Then when I turn the bass tone control all the way up on the mid-range/tweeter amp, again I heard no more bass. Again if I listen very carefully, I can sense a very, very slight reduction in clarity.

Once again, the passive xovers are working perfectly!

In short, the passive xovers are only allowing the proper frequencies to get to the drivers.

My new theory is that the gain in clarify is due to three things:

1. reduced instability on the rail voltages on the mid-range/tweeter amp

2. NO counter EMF from the woofer feeding directly the to mid-range/tweeter - actually this is Richard's idea

3. slight reduction in IM by focusing the amps on a narrower audio range



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>YES, the shields are connected to the common ground. This is

>one of the things I measured BEFORE connecting everything

>together. The whole ideal is to prevent "floating

>grounds". We want both amps to have exactly the same

>grounds and the shielded cables will force everything to a

>common point.

But are the amplifiers tied to "earth" ground? Neither receiver has a 3-wire cable, does it? Therefore, the grounds are basically "floating" on a common chassis ground, which would permit some offset to occur. Any offset in one amplifier would be felt in the circuit of the other amp, potentially causing oscillation, and most likely increased distortion.

--Tom Tyson

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