Bi-wiring a pair of AR-2Ax

[thornev]

I searched the forum, but found nothing specific.

I've bi-wired my 2Ax's to simulate bi-amping. It was a challenge to figure out how to do it with only 3 terminals. Usually there are 4. So what I did was to wire one amp's COMmon (-) and HOT (+) to terminals 1 and 2 respectively which is the woofer. The other amp I wired the HOT (+) to terminal T and left COMmon (-) unattached. It seems to work fine, but I want to make sure I'm not causing the amps to draw too much power. I'm assuming the speakers are 8 ohm loads.

Does this hookup sound OK?  Please, no comments about the bi-wire versus bi-amp controversy, nor if bi-anything makes a difference. Thanks, Thorne

[frankmarsi]

I'm confused.

"other amp I wired the HOT (+) to terminal T and left COMmon (-)  unattached".

To clarify, you did not connect the 'second-amp's other side and left it "unattached""?  Is the other side of amp #2 operating as an open?

If this is so, no change was initiated and no results, no difference, second amp is doing nothing..

You should provide a simple diagram.

[thornev]

There are 4 wires per speaker coming from the amp. There are 3 terminals on the speaker. Yes, I left the COM, which is one of the 4 wires, unattached. I've attached 2 snapshots.  Thorne

terminal 1 (top, woofer) is COM (-) from amp.

terminal 2 (middle, woofer) is HOT (+) from amp.

terminal T (bottom, midrange and tweeter) is HOT (+) from amp.

I don't know what to do about the dangling COM (-). Connect it to other COM on top?

Thorne

[bfastr]

I think it depends more on the amp or amps you are using to do this.  are both outputs from the same physical amp?  if so it may share a common "common".  do you have a simple DVM? (volt/ohm meter) with the amp off check to see if there is continuity between the two outputs "common".  if you do then only one common wire will be needed.

If you are using two physically separate amps it will depend on the amp.  if its two diff amps and the second common is hanging in space then as Frank says , that amp is doing nothing for you.  maybe if they are the same brand amp they will play nice and allow you to stack the commons.  or maybe the common is shared thru the ground wire of the amp, although this is a poor way to return to the amp, but at least you could then stack common wires.

try pulling the woofer hot that is fed by the amp feeding the common. do you still hear the mids and highs? 

you may be able to stack the separate amp commons without a problem since the speakers are now isolated inside the cabinet , but I cant say that for sure. 

 

[thornev]

bfastr... I think what you say about the common being shared is what's going on in the AR 2Ax because I get good sound out of the highs and lows.  The 2 amps I'm using to drive the speakers are Fisher 500-C and Marantz 2265B. Both of them have outputs for 2 pair of speakers. I doubt they are 2 separate amps. They're probably the same single amp sending the same signal to both speaker outputs.  I was worried that I might be doing damage to the amps by wiring this way, but so far it looks like everything is fine. I'll try measuring at the speaker outputs to see what I get. If anything is different I would expect it would be the impedance in that I'm driving the speakers individually now instead of as the drivers tied together through the internal crossovers.  In other words I worry that I'm drawing twice the power from the amp because of sending the 2 sets of speaker outputs to a single pair of speakers that are setup to be bi-amped (they have the bar that connects the highs and lows).   Thorne

 

UPDATE: I checked the commons on all speaker outputs and there is continuity between them. Since they share a common, I apparently don't need that 22nd common that dangles on the back of the AR-2Ax. Is impedance perhaps a problem i.e. the hi and lo in each speaker may be drawing twice the power from the amp? Since they have an internal crossover, maybe each driver draws only what they need?

[RTally]

What you describe is bi-amping, not bi-wiring. Bi-wiring is when you run two sets of wires from the speaker to a single amp/receiver. With bi-amping you have one amp/receiver driving one set of drivers and a second amp/receiver driving the other set of drivers.  

It sounds like you have both the Fisher and the Marantz running at the same time using the passive crossover in the speakers. I assume you have the bass driver (terms 1 & 2) connected to one receiver with a pair of wires. Then you have a third wire connecting the tweeter (term T) to the plus speaker output of your other receiver. Because your receivers have a common ground and you are connecting them together by sharing the same input signal, your speakers work. But the negative speaker output from the receiver connected to the tweeter is flowing through something that does not normally see speaker power.

The idea behind bi-amping (and bi-wiring) is to have the speaker current carried by independent wires between the amps/receivers and the speaker drivers. In your case, the tweeter receiver has the current for the tweeter common flowing through a non-traditional path. That non-traditional path may be the chassis ground connected by your power cords or it may be the shields of your interconnect that ties the two receivers together. Don't do that. 

Your tweeter amp/receiver needs to have two wires for each channel connected to the tweeter circuit. You should connect a pair of wires for each channel to the tweeter (terms 1 and T).

PS: Wiring two amps/receivers to the AR this way will fry an amp/receiver that does not have a common ground. Fortunately for you, it worked out. 

[thornev]

RTally - What we don't know is how these 2 receivers are wired for each pair of speaker outputs. (or do you know the Fisher 500-C and Marantz 2265B?) I assume that each receiver sends the same amp output to each set of speaker outputs and therefore that would not classify as bi-amping. The Fisher 500-C has 4 power tubes if that helps.  The Marantz is solid state.  I know I made it sound like I am bi-amping, but the truth is I don't really know. I apologize if I was misleading.

Are you're saying that the 2Ax's only need one HOT wire to terminal 2 (the woofer) and the tweeter requires both a common and HOT at terminals 1 and T? Like I said, the 2Ax has only 3 terminals.

One other thing... I'm not running the 2 receivers at the same time. I have both of them hooked up to a speaker selector box so I can choose which amp powers which set of speakers. But I have only one of the receivers powered on at any one time.

[bfastr]

Thorne,

after looking at a Marantz schematic it seems to me you arent gaining anything by using the remote speaker output as a second amp to the speaker. the Marantz outputs share a common return at the connectors. and the hots, or outputs come from the same main amp. they are just run in parallel.  so from what I can see you are effectively just moving the jumper from the back of the speaker to the Marantz remote speaker switch.     but I could be wrong,  maybe a Marantz engineer will chime in.

I think your assumption that the output is shared is correct. So I don't see the advantage of breaking up the connections at the speaker ( in this case )

 

Bob

[thornev]

Thanks, Bob. You may be right. It might be placebo, but I could swear the highs are a tad more full with the bi-wiring.  Thorne

[onplane]

On 11/19/2018 at 5:50 AM, thornev said:

RTally - What we don't know is how these 2 receivers are wired for each pair of speaker outputs. (or do you know the Fisher 500-C and Marantz 2265B?) I assume that each receiver sends the same amp output to each set of speaker outputs and therefore that would not classify as bi-amping. The Fisher 500-C has 4 power tubes if that helps.  The Marantz is solid state.  I know I made it sound like I am bi-amping, but the truth is I don't really know. I apologize if I was misleading.

Are you're saying that the 2Ax's only need one HOT wire to terminal 2 (the woofer) and the tweeter requires both a common and HOT at terminals 1 and T? Like I said, the 2Ax has only 3 terminals.

One other thing... I'm not running the 2 receivers at the same time. I have both of them hooked up to a speaker selector box so I can choose which amp powers which set of speakers. But I have only one of the receivers powered on at any one time.

Thornev, for the past 9 years I have been bi-amping my AR-3a's using just the 3 terminals AR provided. Each of my amps has it's own volume control and thus I can vary "voice" by simply varying the power I send to each speaker half. Huge advantage to doing this is to flatten the response curve (see below).  This curve was provided by AR with both pots set to max. As you can see AR intended the higher frequencies to "roll off" and this yielded very acceptable results when playing back records produced at that time.  I found it way, way too laid back and somewhat "muffled" when playing back CD's and other digital recordings.  

Notice that with a single amp there is no way to "flatten" this curve unless you modify the xover.  With two amps (bi-amp) you can apply more power to the mids and tweeters. Since the tweeters in the AR3a lag the mid driver, you'd cut the mid back (via that mid control) to bring the mids and tweeters into balance. Now this makes a base heavy speaker even more bass heavy and muffled!  The key is to advance the mid tweeter amp volume control to bring everything back into balance.

Now for the differences between what I do and you do.  Both of my amps are of the common ground design. That is, I can connect the commons of the amps together and connect both to terminal 1.   YOU SHOULD NOT DO THIS.  Your Fisher is not a common ground amp and it is good that you left that "com" lead hanging.  

With my amps I can power just the woofers or just the mids tweeters.  The setup you have the return line for the Fisher is through the shielded cables from the Marantz. To prove this turn just the Fisher on and set the volume low. Then disconnect the audio cables going to the Marantz and you'll find the speakers going quiet. (Quickly plug the Marantz back in because it is usually not good to run tube amps totally unloaded.)

If you really want to run the tube amp on the mids and tweeters, the safest way to do this would be to modify the xover and bring out that 4th terminal. By doing this you isolate the power output stages of the amps from each other and can run any type of amp on each speaker half.

Hope this helps...

Regards,

Jerry 

 

 

 

 

[thornev]

Thanks very much, Jerry, for the lengthy explanation and for validating that I wired my AR-2Ax's correctly.  After a few weeks of bi-wiring my 2AX's, I'm not so sure I like them that way. I'm not sure, but it sounds like the speakers are holding back.  Then again, if I'm understanding what some have said above, there is no discernible difference between normal and bi-wiring the way I did it.  My Marantz 2265B is not a tube amp, but I do know that no amp likes to run for very long without a load.  Thorne

[onplane]

8 minutes ago, thornev said:

Thanks very much, Jerry, for the lengthy explanation and for validating that I wired my AR-2Ax's correctly.  After a few weeks of bi-wiring my 2AX's, I'm not so sure I like them that way. I'm not sure, but it sounds like the speakers are holding back.  Then again, if I'm understanding what some have said above, there is no discernible difference between normal and bi-wiring the way I did it.  My Marantz 2265B is not a tube amp, but I do know that no amp likes to run for very long without a load.  Thorne

Well, if you are running two amps EACH WITH ITS OWN VOLUME CONTROL, you are by definition bi-amping.  There is a huge difference between bi-amping and bi-wiring. With bi-amping you gain voice control, because you can vary power sent to each speaker half.

Bi-wiring has absolutely no provisions for doing this.

I am well aware that your Marantz is a solid state common ground amp. Remember I instructed you to turn on the Fisher and instructed you to disconnect the Marantz. Disconnecting a turned off amp would normally do nothing.  In your case, disconnecting the Marantz will cause the Fisher powered drivers to go... quiet.

Regards,

Jerry 

[thornev]

Without looking back through my posts I am guessing I omitted a very important device in my setup that has misled everyone...

I have 2 receivers/amps: a Fisher 500-C and a Marantz 2265B. And I have 2 pair of speakers.  Both amps and each pair of speakers are hooked up to a TEC TC-905B Speaker Distribution Center. The objective was to be able to listen to either pair of speakers playing media through either receiver.  I can actually have all 4 speakers playing whatever audio source is playing on either receiver.  Thorne

 

PS - TEC is Technolink Enterprise Co. in Taiwan.

[onplane]

37 minutes ago, thornev said:

Without looking back through my posts I am guessing I omitted a very important device in my setup that has misled everyone...

I have 2 receivers/amps: a Fisher 500-C and a Marantz 2265B. And I have 2 pair of speakers.  Both amps and each pair of speakers are hooked up to a JEC TC-905B Speaker Distribution Center. The objective was to be able to listen to either pair of speakers playing media through either receiver.  I can actually have all 4 speakers playing whatever audio source is playing on either receiver.  Thorne

Perhaps, Thorne, you should review your pics in your 2nd post in this thread.  (The pics with the dangling com lead.)  My comments were in reference to that post and those pics.

Now, as for your TC-905B, do you have a schematic for this thing? From what I can find, it has a headphone jack.  Headphone jacks (that is the standard 3 connector 1/4 inch plug) are designed for common ground amps.  Your Fisher is NOT a common ground amp and you could damage that old unit connecting to a switch not designed for it.

Regards,

Jerry

 

[thornev]

Jerry,  When you say "not a common ground amp", what exactly do you mean?  I've done restoration on the Fisher and I always used the chassis as ground, not that that has anything to do with the common of the speaker leads.   Thorne

 

PS - I do not have a schematic for the 905B.  I'll look.

[thornev]

Here's a description of the 905B:

The NEW TEC-905B speaker selector with volume control will allow you to use two stereos with up to 10 speakers (5 pairs) placed around the house, restaurant, office, warehouse etc.  You can turn each set of speakers on and off, and adjust the volume for each pair as well.  The input for the TEC-905B comes from your stereos, amps, receivers, etc.  This just means you take the speaker wires from the back of your stereo, amp, etc. and plug them into the either input terminals on the back of the TEC-905B.  Each speaker pair has independent rotary volume control. Volume adjustment and impedance matching is accomplished through internal heavy-duty multi-trapped transformers for each speaker. This allows complete, independent control of each pair with maximum efficiency and virtually no generation of heat. The built-in precision auto impedance correction and overload protection circuits will safe-guard your amplifiers and speakers from damage due to excessively low impedance when all 10 speakers are playing at the same time. Rear gold plated color coded professional grade banana socket connections accept up to 12AWG wires. Also has headphone input with individual volume control as well.

Features:

• Dual source inputs
• Five speaker pairs output
• Each pair of speakers can be alternatively switched to either amplifier A or B
• Accepts up to 12 gauge speaker wire via gold plated banana socket connections
• Frequency response: 20 Hz to 20 kHz
• High efficiency transformer based designed, fully automatic amplifier impedance protection
• Compatible impedance with 4 - 16 ohm speakers  
• 100W RMS, 200W peak per channel power handling
• Individual rotary volume controls
• Master ON/OFF switch connects and disconnects the signal distribution from the amplifiers to the speakers
• Dimensions: 2.25"H x 15.5"L x 8.5"W
• Weight : 12 lb
• Headphone input with volume control 
• Pre-printed zone and equipment list label included for easy speaker connection identification
• Sturdy metal enclosure
• Passive design, no power required

 

[onplane]

1 minute ago, thornev said:

Jerry,  When you say "not a common ground amp", what exactly do you mean?  I've done restoration on the Fisher and I always used the chassis as ground, not that that has anything to do with the common of the speaker leads.   Thorne

 

PS - I do not have a schematic for the 905B.  I'll look.

A common ground amp has the high level speaker output (red speaker output terminal)  referenced to a common ground that is consistent throughout the entire chassis of the unit. This means both black speaker output terminals are always at the same potential all of the time.

Your Fisher has output transformers (one for each channel) and neither of these outputs are connected to the output of the other channel. They are isolated from each other and should never be connected together.

 

Hope this helps..

Jerry

[thornev]

Aha !  Maybe that accounts for why lately the Fishers aren't sounding as good as they used to. I'll have to research this.  Thanks for pointing this out.

[onplane]

Thorne, the switch description means nothing.  Post the circuit diagram. Most of these devices are designed for modern amps.

[thornev]

The company that manufactures the 905B, TEC, is in Taiwan. I found their web site and sent an email requesting a schematic. We shall see.   Thorne

[thornev]

So, Jerry... Since I inferred from your post that the 2 output transformers do not share a common ground (did I get that right?), I wired each side of the Fisher to the AR-2Ax's.  That is, on the Fisher, there are 2 sets of speakers to select.  I wired "speaker 1" to the woofer lugs and "speaker 2" to the mid tweeter lugs.  And of course I still have the common leads not connected at the speaker side for the mid tweeter.  Is that OK?  I tried it and so far nothing has blown up.  

So I'm bi-wiring the 2AX's with just the Fisher.   It sounds damn good... much better than the setup I had with the speaker selector box.  Only thing I'm wondering about is impedances.  I'm setup such that the woofer is 8 ohms and the mid tweeter is 8 ohms.     I have 8 ohm L-pads connected to the mid and to the tweeter.  The speakers are 8 ohms when they are not bi-wired. I don't know the individual driver impedances and I don't know if the crossovers in the speakers affect the impedance numbers.  Thorne

 

PS... Uh oh. All of a sudden I was getting no signal from the woofers in the 2AX's.  Gulp.  Time to hook them up to something else to test.

[onplane]

21 hours ago, thornev said:

So, Jerry... Since I inferred from your post that the 2 output transformers do not share a common ground (did I get that right?), I wired each side of the Fisher to the AR-2Ax's.  That is, on the Fisher, there are 2 sets of speakers to select.  I wired "speaker 1" to the woofer lugs and "speaker 2" to the mid tweeter lugs.  And of course I still have the common leads not connected at the speaker side for the mid tweeter.  Is that OK?  I tried it and so far nothing has blown up.  

So I'm bi-wiring the 2AX's with just the Fisher.   It sounds damn good... much better than the setup I had with the speaker selector box.  Only thing I'm wondering about is impedances.  I'm setup such that the woofer is 8 ohms and the mid tweeter is 8 ohms.     I have 8 ohm L-pads connected to the mid and to the tweeter.  The speakers are 8 ohms when they are not bi-wired. I don't know the individual driver impedances and I don't know if the crossovers in the speakers affect the impedance numbers.  Thorne

 

PS... Uh oh. All of a sudden I was getting no signal from the woofers in the 2AX's.  Gulp.  Time to hook them up to something else to test.

Thorne, what you describe is bi-wiring and the "benefits" of doing this are frequently debated. When you select both sets of speakers on the Fisher, that selector switch inside the Fisher applies exactly the same signal to both of Fisher's speaker output terminals. 

In this case, you can connect the return speaker lines together at speaker terminal 1.  The advantage of doing this is you can select (via the Fisher selector switch) to listen to the woofers or the mids/tweeters or both. When you leave that lead dangling (not connected), you cannot select to listen  the mids/ tweeters alone.

Again, you may connect this way when bi-wiring (that is using a single amp). You should not connect this way when bi-amping unless both amps are of the common ground design.

Regards,

Jerry