Using Mcintosh Mc7106 with 4ohm speakers in bridged mode?

[Andons27]

Hello there! I was thinking about buying an old MC 7106 ($1150, like new condition) to power my LCR channels in bridged mode. It's a six-channel at 100 watts @ 8 ohms, 160 watts @ 4 ohms and can be bridged into 3 channels, effectively doubling the power. Anyway, the issue I'm running into is I was reading the amplifier doesn't like driving 4-ohm speakers in bridged mode, and I'm trying to drive Kef R7 meta & R6 meta, which are 4-ohm speakers. Can anyone verify if this is a terrible idea? Is there something I'm missing? Also, I could run all my speakers single channel, but that would be way less watts than I'm using now with the Emotivas, which is XPA 2 & 5 500+ watts each. The speakers are rated 15-250 watts recommended. I'm having a hard time deciding what to-do, so any input is welcome, thanks!

 

[TLS Guy]

Hello there! I was thinking about buying an old MC 7106 ($1150, like new condition) to power my LCR channels in bridged mode. It's a six-channel at 100 watts @ 8 ohms, 160 watts @ 4 ohms and can be bridged into 3 channels, effectively doubling the power. Anyway, the issue I'm running into is I was reading the amplifier doesn't like driving 4-ohm speakers in bridged mode, and I'm trying to drive Kef R7 meta & R6 meta, which are 4-ohm speakers. Can anyone verify if this is a terrible idea? Is there something I'm missing? Also, I could run all my speakers single channel, but that would be way less watts than I'm using now with the Emotivas, which is XPA 2 & 5 500+ watts each. The speakers are rated 15-250 watts recommended. I'm having a hard time deciding what to-do, so any input is welcome, thanks!

I have just checked the spec. You can not drive those speakers in bridged mode. If you do you will blow the amp fast.

Since this unit has autotransformers, I thought this might be possible. I checked the manual and it clearly states that the amp will only drive 8 ohm loads in bridged mode.

Your speakers actually drop lower than 4 ohms.

So, absolutely do NOT drive those speakers bridged.

I would not buy that amp. Like everything else amps have improved and by a decent modern amp. Class D amps are now excellent and I would recommend buying one.

Bridging is generally a very bad idea, especially these days when speaker impedances are lower than they used to be.

When it comes down to it, you really don't increase the power in real terms. If you bridge to an 8 ohm speaker, you will get the same power as bridging a four ohm speaker unbridged. So if you bridge to a four ohm speaker, it would be like driving a 2 ohm speaker unbridged and blow up the amp just the same.

There is only one amp ever made that would handle this and it is the Quad 303, which was guaranteed unconditionally stable under all loads. With that amp, you can even parallel the outputs!

The only bullet proof and long lasting vintage amps are the Quad 606 and Quad 909, but you would need two of them to drive your speakers and those amps fetch high prices on the used market, as many know of their great reputation. If you buy Quad gear make sure it is from the era when Peter Walker was alive and running the show. He was obsessed with making high quality gear that did not blow up. His current dumping circuits were pure genius.

 

[highfigh]

Hello there! I was thinking about buying an old MC 7106 ($1150, like new condition) to power my LCR channels in bridged mode. It's a six-channel at 100 watts @ 8 ohms, 160 watts @ 4 ohms and can be bridged into 3 channels, effectively doubling the power. Anyway, the issue I'm running into is I was reading the amplifier doesn't like driving 4-ohm speakers in bridged mode, and I'm trying to drive Kef R7 meta & R6 meta, which are 4-ohm speakers. Can anyone verify if this is a terrible idea? Is there something I'm missing? Also, I could run all my speakers single channel, but that would be way less watts than I'm using now with the Emotivas, which is XPA 2 & 5 500+ watts each. The speakers are rated 15-250 watts recommended. I'm having a hard time deciding what to-do, so any input is welcome, thanks!

As mentioned, that amp isn't designed for 4 Ohm speakers in Bridged mode- the manual shows "OUTPUT LOAD IMPEDANCE 8 or 4 ohms, for all six separate channels 8 ohrns, Bridged operation" om page 14 of the pdf.

https://www.mcintoshlabs.com/-/media/Files/mcintoshlabs/DocumentMaster/us/Legacy/MC7106-HE-OWNERS.pdf?rev=e9d4786452984bf5af10b211223b1697&revision=e9d47864-5298-4bf5-af10-b211223b1697

 

[PENG]

Hello there! I was thinking about buying an old MC 7106 ($1150, like new condition) to power my LCR channels in bridged mode. It's a six-channel at 100 watts @ 8 ohms, 160 watts @ 4 ohms and can be bridged into 3 channels, effectively doubling the power. Anyway, the issue I'm running into is I was reading the amplifier doesn't like driving 4-ohm speakers in bridged mode, and I'm trying to drive Kef R7 meta & R6 meta, which are 4-ohm speakers. Can anyone verify if this is a terrible idea? Is there something I'm missing? Also, I could run all my speakers single channel, but that would be way less watts than I'm using now with the Emotivas, which is XPA 2 & 5 500+ watts each. The speakers are rated 15-250 watts recommended. I'm having a hard time deciding what to-do, so any input is welcome, thanks!

I am sure you will get the typically kind of response, that likely would tell you that MC 7106 should not be bridge to drive 4 ohm nominal speakers. The only thing I would add is the following additional caveat, that is, you can in fact do it, but whether it would be a "terrible idea" or not, would depend on:

- your listening habit (such as max spl you listen to)
- seating distance

Basically, that tiny 52 lbs class AB MC 7106 amp is rated 320 W bridged, 8 ohms, 2 channel driven, so it should be able to do 160 W bridged 4 ohms, 2 channel driven.

If unbridged, it is rated 160 W 4 ohms, or 80 W 2 ohms

That's based on simple math and derived from Mc's specifications.

So, if Emotiva amps will give you more raw output, but if again, it is you actual need of voltage and current vs the Mc's specs, if it has more than enough V and I, then I would think it is the better choice.

 

[carlosmiguez75]

Bridging the MC 7106 on 4-ohm speakers means the amp sees 2 ohms, too risky. Don’t do it unless the manual says it’s safe. Use single channels or get a better amp. Otherwise, you’ll damage the amp.

 

[TLS Guy]

I am sure you will get the typically kind of response, that likely would tell you that MC 7106 should not be bridge to drive 4 ohm nominal speakers. The only thing I would add is the following additional caveat, that is, you can in fact do it, but whether it would be a "terrible idea" or not, would depend on:

- your listening habit (such as max spl you listen to)
- seating distance

Basically, that tiny 52 lbs class AB MC 7106 amp is rated 320 W bridged, 8 ohms, 2 channel driven, so it should be able to do 160 W bridged 4 ohms, 2 channel driven.

If unbridged, it is rated 160 W 4 ohms, or 80 W 2 ohms

That's based on simple math and derived from Mc's specifications.

So, if Emotiva amps will give you more raw output, but if again, it is you actual need of voltage and current vs the Mc's specs, if it has more than enough V and I, then I would think it is the better choice.

I agree with your math, but not your advice. Making an old amp see a 2 ohm load is asking for trouble. And as you all know we all get carried away at time and advance the "throttle". First time the OP does that he is out a thousand bucks or more.

The R6 in particular is a very nasty load, going to 2 ohms at 180 Hz right in the power band. That speaker looks like a real amp buster. So bridged the amp will see 1 ohm in part of the power band. The R7 is not much better dropping actually below 4 ohms in the most power hungry region of the audio band. In other respects they seem very decent speakers, but I bet they have blown a lot of receivers and amps.

My strong advice is to get a better amp.

I just fail to understand why speaker designers pull these stunts. It really is not necessary, especially when you have control of the driver design, the crossover and cabinet.

You don't have to create these problems and the amp manufacturer will get the blame when it blows up!

We just don't call out this poor design enough. Poor design is what it is.

 

[PENG]

I agree with your math, but not your advice. Making an old amp see a 2 ohm load is asking for trouble. And as you all know we all get carried away at time and advance the "throttle". First time the OP does that he is out a thousand bucks or more.

That is valid point but there are at least two counter points to that:

1) We don't know what kind of Preamp/AVR/AVP he is using with the MC7106, so there is a good chance he can set a maximum volume, if he has something like your AV10, or even one of the Denon, Marantz, and likely Onkyo or Yamaha AVRs as well.

2) Without setting a limit, one can still advance the "throttle", such as any many of the AVRs to maximum volume and then the OP could still be out a thousand bucks or more, so I would say your valid point is sort of moot, though again still a good and valid point.

The R6 in particular is a very nasty load, going to 2 ohms at 180 Hz right in the power band. That speaker looks like a real amp buster. So bridged the amp will see 1 ohm in part of the power band. The R7 is not much better dropping actually below 4 ohms in the most power hungry region of the audio band. In other respects they seem very decent speakers, but I bet they have blown a lot of receivers and amps.

I don't know about R6, but the OP has the R6 meta, and that we have the official data from KEF, as follow:

R6 Meta | KEF Canada
NOMINAL IMPEDANCE
4 Ω (min. 3.2 Ω)

The actual measured value was a little better, minimum was about 3.4 ohm, that's a lot better than 2 ohms that you might have mistakenly read or assumed?

The R7 meta has very similar characteristics, and the non meta series typically would do better based on what I remember.

Now look at the facts on the MC7106:

MC7106 OWNERS

POWER OUTPUT, SIX CHANNELS 100 watts per channel into 8 ohm loads, or 160 watts per channel into 4 ohm loads minimum sine wave continuous average power output per channel, all channels operating.

So we both know worse case scenario, 100 W 8 ohms, 160 W 4 ohms, would mean at least 80 W 2 ohms, and that's with 6 channels operating, and the numbers are for continuous sine wave signal, we also both know full well that music signal is not "continuous" sine wave, not even close, so for practical use, the MC7106 will have no trouble doing 80 W into 2 ohms, 40 W into 1 ohm and likely much more as I am using worst case scenario here.

So, now that you know the above facts, you might agree with my advice too, though you obviously have to know my "advice" is based on the OP's obvious preference of the Mc amp to his Emotiva amp so I don't want to give him an unqualified "No" answer, because factually speaking, if you happen to someone who can't stand reference level and 15 to even 20 dB below reference is good enough for him, and that he seat no further than 3-4 meters, the MC 7106 will have enough juice for those 4 ohm nominal speakers that dip below 4 ohms, to 3.3 to 3.5 ohm minimum briefly in the range 100 to about 260 Hz (that's not even 2 octaves).

My strong advice is to get a better amp.

That would be my strong advice too, without knowing the OP's listening habit and seating distance, but he already of a reasonably powerful power amp, i.e. the Emo XPA-2, and under the right use conditions, the MC 7106 could be completely adequate.

I just fail to understand why speaker designers pull these stunts. It really is not necessary, especially when you have control of the driver design, the crossover and cabinet.

I think so too.

By the way, on page 14 of the MC7106's owner's manual, there's some specs related to bridged mode:

TWO CHANNELS BRIDGED 320 watts into an 8 ohm load, minimum sine wave continuous average power output. The output RMS voltage is: 50.6V across 8 ohms, that means the output voltage could reasonably be assumed to able to do 12.65 V into a 2 ohm load, based on the same current output for the 50.6 V across 8 ohms.

In case the OP is more comfortable with watts than V and I, power = V^2/R = 12.65^2/2 = 80 W as I estimated earlier, that would increase if we use the actual KEF specs for the minimum 3.5 ohm and can be estimated as follow:

Based on the same current for the 8 ohm example, when the voltage was 50.6 V, current, I = V/R = 50.6/8 = 6.325 A.

P = I^2*R = 6.325*6.325*3.5 = 140 W.

That means, when bridged into 3.5 ohm, the MC7106 could deliver 140 W without issues.
All these, obviously are based on resistive load, and this is fine because in this case, the phase angle at that minimum impedance point was nearly 0 degree. Even if is reasonably reactive/inductive, it wouldn't affect the current calculation, because the so called EPDR impedance value that Stereophile started using was based on heat dissipation, not the actual current output.

 

[TLS Guy]

That is valid point but there are at least two counter points to that:

1) We don't know what kind of Preamp/AVR/AVP he is using with the MC7106, so there is a good chance he can set a maximum volume, if he has something like your AV10, or even one of the Denon, Marantz, and likely Onkyo or Yamaha AVRs as well.

2) Without setting a limit, one can still advance the "throttle", such as any many of the AVRs to maximum volume and then the OP could still be out a thousand bucks or more, so I would say your valid point is sort of moot, though again still a good and valid point.



I don't know about R6, but the OP has the R6 meta, and that we have the official data from KEF, as follow:

R6 Meta | KEF Canada
NOMINAL IMPEDANCE
4 Ω (min. 3.2 Ω)

The actual measured value was a little better, minimum was about 3.4 ohm, that's a lot better than 2 ohms that you might have mistakenly read or assumed?

View attachment 74198

The R7 meta has very similar characteristics, and the non meta series typically would do better based on what I remember.

Now look at the facts on the MC7106:

MC7106 OWNERS


So we both know worse case scenario, 100 W 8 ohms, 160 W 4 ohms, would mean at least 80 W 2 ohms, and that's with 6 channels operating, and the numbers are for continuous sine wave signal, we also both know full well that music signal is not "continuous" sine wave, not even close, so for practical use, the MC7106 will have no trouble doing 80 W into 2 ohms, 40 W into 1 ohm and likely much more as I am using worst case scenario here.

So, now that you know the above facts, you might agree with my advice too, though you obviously have to know my "advice" is based on the OP's obvious preference of the Mc amp to his Emotiva amp so I don't want to give him an unqualified "No" answer, because factually speaking, if you happen to someone who can't stand reference level and 15 to even 20 dB below reference is good enough for him, and that he seat no further than 3-4 meters, the MC 7106 will have enough juice for those 4 ohm nominal speakers that dip below 4 ohms, to 3.3 to 3.5 ohm minimum briefly in the range 100 to about 260 Hz (that's not even 2 octaves).



That would be my strong advice too, without knowing the OP's listening habit and seating distance, but he already of a reasonably powerful power amp, i.e. the Emo XPA-2, and under the right use conditions, the MC 7106 could be completely adequate.



I think so too.

By the way, on page 14 of the MC7106's owner's manual, there's some specs related to bridged mode:

TWO CHANNELS BRIDGED 320 watts into an 8 ohm load, minimum sine wave continuous average power output. The output RMS voltage is: 50.6V across 8 ohms, that means the output voltage could reasonably be assumed to able to do 12.65 V into a 2 ohm load, based on the same current output for the 50.6 V across 8 ohms.

In case the OP is more comfortable with watts than V and I, power = V^2/R = 12.65^2/2 = 80 W as I estimated earlier, that would increase if we use the actual KEF specs for the minimum 3.5 ohm and can be estimated as follow:

Based on the same current for the 8 ohm example, when the voltage was 50.6 V, current, I = V/R = 50.6/8 = 6.325 A.

P = I^2*R = 6.325*6.325*3.5 = 140 W.

That means, when bridged into 3.5 ohm, the MC7106 could deliver 140 W without issues.
All these, obviously are based on resistive load, and this is fine because in this case, the phase angle at that minimum impedance point was nearly 0 degree. Even if is reasonably reactive/inductive, it wouldn't affect the current calculation, because the so called EPDR impedance value that Stereophile started using was based on heat dissipation, not the actual current output.

I am more risk averse than you and like to leave plenty of margin.

So, doing what you suggest leaves no margin, and I think you always need 100% margin at least for good design practice.

On the other issue, KEF should know better. Their founder Raymond Cooke led the way in how to limit adverse impedance swings and published a number of ways of going about it. I have used in methods on some of my designs over the years and they are effective.

Peter Walker strove to make his designs as stable as he could and not blow up when confronted with difficult loads.

Neither of these men would give time of day to any marketers or idiots telling them what price point that had to meet. The only thing they were concerned about, was if it was any good.

The harm done by these no nothing MBAs and marketing types is immense.

My suspicion is strong they had a hand in the premature failures of my 7705 and even more disgraceful the 7706. I don't believe for one minute it was chance that two units of similar design failed prematurely.

On that note, I see the NET is now lighting up for poor warranty service from Denon/Marantz. Warranty service is reported as slow at two months of more. it is now 2 months to the day my 7706 was shipped to them and I have heard nothing, despite a good letter in the box with all my contact details.

Also there are credible reports of them denying warranty claims on the basis of corrosion even when customers have had the units a very short time. They had better not pull that one on me, as this house has very tight environmental control with continuous monitoring and recording of humidity, temperature etc, and even radon.

I just hope my AV 10 is well designed and built and will have long legs.

These sorts of debacles will kill AV stone dead except for sound bars. Customers spend a lot of cash on equipment and in a lot of cases installation. They have a right to expect well designed and built gear and taken care of when things don't go right, and that should be very rare occasions.

By the same token, I think the owners have a responsibility to plan and design their systems reliably and carefully, with great attention to robust installation. I will say straight up that bridging an amp to half the impedance or less, the recommended by the manufacturer does not meet that criterion.

 

[PENG]

I am more risk averse than you and like to leave plenty of margin.

So, doing what you suggest leaves no margin, and I think you always need 100% margin at least for good design practice.

Not at all, it is not about risk, I probably am willing to accept lower risk than you, or the other way around, we don't really know that..... The fact is, you got your facts wrong about the R6 Meta's minimum impedance, KEF specs say 3.5 ohm, you thought it was 3 ohms, that's a big difference.

Also, we do not know the OP's requirement.

I have my facts and you are only summing things so far. I said it depends on the OP's listening habit and seating distance, that are still unknow at this point.

What if he sits only 2 meters, or even 3 meters and he never listen to with 10 dB of reference level, then what's risk you are talking about, as far advancing the "throttle", that won't by deliberately I hope because he will hear nasty distortions well before any damage can happen. If it is by accident, then it is a matter of limiting the volume maximum, I stated all these in my last post, there is no risk. You must know by know I don't typically make blanket statements, most things are not black and white. I usually state my assumptions if there are unknowns, and for the knowns, I always try to link information from reliable sources.

I think we have been on Audioholics.com long enough to know that we should try our best to avoid making blanket statements. I have never said any amps can drive 4 ohms or 2 ohm loads, without stating the use conditions/applications. Someone who has a 200 WPC power amp sitting from 5 meters listening to reference level will have higher risk than someone who has a 100 W AVR amp sitting from2.5 meters listening to 15 dB below reference. That's just facts, you cannot ignore listening habit, seating distance, speaker sensitivity, all else being equal. It is sad to see senior members responding to such questions without asking the OPs for more information that are often required to determine what kind of advice we can give.

It is like 4 wheel drive vehicles, not everyone needs the likes of the Grand Cherokee, Range Rovers, or Toyota 4 runners, many can get by with a Subaru Outback, or even a Honda CRV. It depends a lot of the potential buyers intended use.

 

[TLS Guy]

Not at all, it is not about risk, I probably am willing to accept lower risk than you, or the other way around, we don't really know that..... The fact is, you got your facts wrong about the R6 Meta's minimum impedance, KEF specs say 3.5 ohm, you thought it was 3 ohms, that's a big difference.

Also, we do not know the OP's requirement.

I have my facts and you are only summing things so far. I said it depends on the OP's listening habit and seating distance, that are still unknow at this point.

What if he sits only 2 meters, or even 3 meters and he never listen to with 10 dB of reference level, then what's risk you are talking about, as far advancing the "throttle", that won't by deliberately I hope because he will hear nasty distortions well before any damage can happen. If it is by accident, then it is a matter of limiting the volume maximum, I stated all these in my last post, there is no risk. You must know by know I don't typically make blanket statements, most things are not black and white. I usually state my assumptions if there are unknowns, and for the knowns, I always try to link information from reliable sources.

I think we have been on Audioholics.com long enough to know that we should try our best to avoid making blanket statements. I have never said any amps can drive 4 ohms or 2 ohm loads, without stating the use conditions/applications. Someone who has a 200 WPC power amp sitting from 5 meters listening to reference level will have higher risk than someone who has a 100 W AVR amp sitting from2.5 meters listening to 15 dB below reference. That's just facts, you cannot ignore listening habit, seating distance, speaker sensitivity, all else being equal. It is sad to see senior members responding to such questions without asking the OPs for more information that are often required to determine what kind of advice we can give.

It is like 4 wheel drive vehicles, not everyone needs the likes of the Grand Cherokee, Range Rovers, or Toyota 4 runners, many can get by with a Subaru Outback, or even a Honda CRV. It depends a lot of the potential buyers intended use.

OK, I read the impedance curve from the graph plot, but half and ohm is neither here nor there.

The issue is that the manual says not to do that. I think that is reasonable advice. On the whole I am against bridging, and consider it a risky endeavor. So the safest course is not to do it in this instance. I guess we will stand by our advice, and I stand by mine, which is don't do it.

 

[Andons27]

That is valid point but there are at least two counter points to that:

1) We don't know what kind of Preamp/AVR/AVP he is using with the MC7106, so there is a good chance he can set a maximum volume, if he has something like your AV10, or even one of the Denon, Marantz, and likely Onkyo or Yamaha AVRs as well.

2) Without setting a limit, one can still advance the "throttle", such as any many of the AVRs to maximum volume and then the OP could still be out a thousand bucks or more, so I would say your valid point is sort of moot, though again still a good and valid point.



I don't know about R6, but the OP has the R6 meta, and that we have the official data from KEF, as follow:

R6 Meta | KEF Canada
NOMINAL IMPEDANCE
4 Ω (min. 3.2 Ω)

The actual measured value was a little better, minimum was about 3.4 ohm, that's a lot better than 2 ohms that you might have mistakenly read or assumed?

View attachment 74198

The R7 meta has very similar characteristics, and the non meta series typically would do better based on what I remember.

Now look at the facts on the MC7106:

MC7106 OWNERS


So we both know worse case scenario, 100 W 8 ohms, 160 W 4 ohms, would mean at least 80 W 2 ohms, and that's with 6 channels operating, and the numbers are for continuous sine wave signal, we also both know full well that music signal is not "continuous" sine wave, not even close, so for practical use, the MC7106 will have no trouble doing 80 W into 2 ohms, 40 W into 1 ohm and likely much more as I am using worst case scenario here.

So, now that you know the above facts, you might agree with my advice too, though you obviously have to know my "advice" is based on the OP's obvious preference of the Mc amp to his Emotiva amp so I don't want to give him an unqualified "No" answer, because factually speaking, if you happen to someone who can't stand reference level and 15 to even 20 dB below reference is good enough for him, and that he seat no further than 3-4 meters, the MC 7106 will have enough juice for those 4 ohm nominal speakers that dip below 4 ohms, to 3.3 to 3.5 ohm minimum briefly in the range 100 to about 260 Hz (that's not even 2 octaves).



That would be my strong advice too, without knowing the OP's listening habit and seating distance, but he already of a reasonably powerful power amp, i.e. the Emo XPA-2, and under the right use conditions, the MC 7106 could be completely adequate.



I think so too.

By the way, on page 14 of the MC7106's owner's manual, there's some specs related to bridged mode:

TWO CHANNELS BRIDGED 320 watts into an 8 ohm load, minimum sine wave continuous average power output. The output RMS voltage is: 50.6V across 8 ohms, that means the output voltage could reasonably be assumed to able to do 12.65 V into a 2 ohm load, based on the same current output for the 50.6 V across 8 ohms.

In case the OP is more comfortable with watts than V and I, power = V^2/R = 12.65^2/2 = 80 W as I estimated earlier, that would increase if we use the actual KEF specs for the minimum 3.5 ohm and can be estimated as follow:

Based on the same current for the 8 ohm example, when the voltage was 50.6 V, current, I = V/R = 50.6/8 = 6.325 A.

P = I^2*R = 6.325*6.325*3.5 = 140 W.

That means, when bridged into 3.5 ohm, the MC7106 could deliver 140 W without issues.
All these, obviously are based on resistive load, and this is fine because in this case, the phase angle at that minimum impedance point was nearly 0 degree. Even if is reasonably reactive/inductive, it wouldn't affect the current calculation, because the so called EPDR impedance value that Stereophile started using was based on heat dissipation, not the actual current output.

 

[lovinthehd]

I'd just continue using your Emotiva amps. Bridging is generally not a great way to go vs just getting a more capable amp.