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McIntosh MC2105 tap settings question

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Greetings,

 

I am running a pair of Cornwall I speakers with a McIntosh MC2105.  I am currently using the 8 ohm taps on the back of the amplifier.  What would be the expected effect on the sound if I used the 4 ohm taps versus the 8 ohm taps versus the 16 ohm taps? 

 

Thanks for your insight,

 

Andy

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I wouldn't suggest using the 16ohm tap  due to the large impedance mismatch for the loudspeaker..

 

I would expect the tonal balance between the bass and midrange to shift slightly between the 4ohm versus the 8ohm taps and I would use whichever sounds best in your unique system/room.

 

miketn

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Not sure of the benefits of an impedance mismatch

I have good luck with equalizers for changing the sound.

The c-32 is a studio in reverse, expander, loudness, high and low pass filters

parametric equalizer.

I still prefer a standalone equalizer

YMMV

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OK, when in doubt, read the manual. McIntosh recommends the 4 ohm tap for 3.2 to 6.5 ohm speakers, the 8 ohm tap for 6.5 to 13, and lastly, the 16 ohm tap for 13 to 26 ohms. 
 

Therefore, I measured the resistance of my Cornwalls at the inputs to give a value of about 3.9 ohms. Assuming a speaker’s resistance is about 70% of the impedance, we get a calculated speaker impedance value of about 5.6 ohms. 
 

So, I hooked up my Cornwalls to the 4 ohm tap for the first time ever AFTER listening to the same song critically 4x when using the 8 ohm tap (with and without the sub). Listening to the same song again leads me to conclude the 4 ohm tap seems to have moderately more bass*. I actually had to turn my subwoofer down a bit and I will have to adjust it a little more after I get home from work today to get it properly dialed in again (subtle, not dramatic). I could not tell a difference in the output. The volume seems to be about the same; I guess I should have checked with a dB meter.

 

The skeptic in me would not think changing the tap setting would have as much impact as what I am perceiving. I am still entertaining the possibility I am hearing what I want to hear; we will see how it shakes out over the next couple days. So far, I prefer the sound of the 4 ohm tap.

Andy

 

*Please note that perceived increases in bass does not seem to come at the expense of the mids or the highs; it just seems to give a little boost where it was lacking. 

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48 minutes ago, Klipschguy said:

OK, when in doubt, read the manual. McIntosh recommends the 4 ohm tap for 3.2 to 6.5 ohm speakers, the 8 ohm tap for 6.5 to 13, and lastly, the 16 ohm tap for 13 to 26 ohms. 
 

Therefore, I measured the resistance of my Cornwalls at the inputs to give a value of about 3.9 ohms. Assuming a speaker’s resistance is about 70% of the impedance, we get a calculated speaker impedance value of about 5.6 ohms. 
 

So, I hooked up my Cornwalls to the 4 ohm tap for the first time ever AFTER listening to the same song critically 4x when using the 8 ohm tap (with and without the sub). Listening to the same song again leads to conclusion that the 4 ohm tap seems to have moderately more bass*. I actually had to turn my subwoofer down a bit and I will have to adjust it a little more after I get home from work today to get it properly dialed in again (subtle, not dramatic). I could not tell a difference in the output. The volume seems to be about the same; I guess I should have checked with a dB meter.

 

The skeptic in me would not think changing the tap setting would have as much impact as what I am perceiving. I am still entertaining the possibility that I am hearing what I want to hear; we will see how it shakes out over the next couple days. So far, I prefer the sound of the 4 ohm tab.

Andy

 

*Please note that perceived increases in bass does not seem to come at the expense of the mids or the highs; it just seems to give a little boost where it was lacking. 

I just want to say that I love this thread. This is the kind of discussion that filled this forum back in the day. I'm really curious to hear from other folks who use the 4 ohm taps on their Mac solid state gear. 

 

Jeff

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Nothing wrong with experimenting changing taps and listen to what you like best. What you like is all that really matters. Use ears instead of brain. 

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The MC105 manual also lists the damping factor* for the various tap settings:

 

18 at 4 ohms output

 

13 at 8 ohms output

 

10 at 16 ohms output

 

*The damping factor is not very high versus modern solid state amplifiers, but it is very hard to complain about the sound.  (I seem to remember McIntosh was more into the slew rate spec rather than the damping factor spec; maybe someone would want to comment on "slew rate"?)

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Damping factor determines how the amp controls the bass speaker. After a certain amount any more will not be be noticeable. 

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Here is a graph of the Cornwall input electrical impedance.   Putting a single value on the impedance is not possible because it varies with frequency.  This is from the Belgian Audio Society test and I suspect it is on what we know as a "Cornwall" rather than a Cornwall II.  I have not seen any factory equivalent.  It is important that this goes down very low and probably to 4 ohms.  The Heyser review of the Klipschorn is at least consistent.  And likely the K-33 has a voice coil resistance of 3.8 ohms or so.  

 

Klipsch's notation that their speakers are "8 ohm compatible"  seems to only be saying that the owner can hook them up to an amp which says it is fit for 8 ohm loads.

 

Very generally the output impedance of a transistor is lower than 1 ohm despite what the autotransformer taps say.   This is not widely stated by manufacturers but at least in some instances the damping factor is given and ouput impedance can be calculated from this.

 

Also, it is true that Jacobi's lww is good in some circumstances but IMHO it is at best difficult to apply here.   For exaple, if your amp does have a 0.1 ohm output impedance we'd be looking for 0.1 ohm speakers.

 

One this which is generally recognized is that audio amps put out less distortion when driving a load which is high in impedance.  Distortion is lower when you attach an 8 ohm load to a 4 ohm tap.  

 

Another matter is that background hum and noise is lower in magnitude when the transformer is not stepping up their level by the use of e.g. the 16 ohm tap.  

 

WMcD

 

 

Cornwall II.jpg

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I just looked around the Internet and see that the MC2105 has a damping factor of 13.  I don't see any info on what tap was used or what load was assumed.  Assuming an 8 ohm load this equates to an output impedance of 0.62 ohms.  = 8/13.

 

This does not mean that you should put a load on it of 0.62 ohms.

 

In conclusion though, if you have a speaker which varies between 4 ohms and up, you should use the 4 ohm tap.

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As always, thank you for your insight, Gil; I have always found your posts quite informative over the years. 

 

It would seem the Cornwall is well within McIntosh's recommendation to "use the 4 ohm tap when using 3.2 ohm to 6.5 ohm impedance loudspeakers."  As stated earlier: I like what I hear with my Mac. 

 

I certainly appreciate all the replies on this topic.

 

Andy

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I have a McIntosh MC352 that I run my CF-4’s and 1st gen RF-7’s off the 4 ohm taps when ever I rotate between the two sets, it sounds more balanced on both speakers compared to the 8ohm taps.

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On 2/9/2021 at 12:22 PM, Klipschguy said:

As always, thank you for your insight, Gil; I have always found your posts quite informative over the years. 

 

It would seem the Cornwall is well within McIntosh's recommendation to "use the 4 ohm tap when using 3.2 ohm to 6.5 ohm impedance loudspeakers."  As stated earlier: I like what I hear with my Mac. 

 

To be on the safe side , I would have stayed on the 8 ohms tap --being that the amplifier is not working as hard , and the amplifier is 50 years old -

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My understanding is my McIntosh amplifier will run cooler with less distortion and hum when using the 4 ohm tap setting (when powering  my Cornwalls). It would seem the 4 ohm tap not only sounds better (actually a lot better), but it is also easier on the amplifier.  However, the lesser hum and distortion is at some expense of power output (but it still has waaaaaay more than I need or use). 


The following quote is from the McIntosh owner’s manual:
 

“If a load impedance is used that is lower than the output impedance tap, then reduced power and possible distortion will result. If a load impedance is used that is higher than the output impedance tap, then neither the signal nor the amplifier will be harmed but the voltage available is limited to that stated at that tap.”

 

The Cornwall 1’s impedance curve is well within Mac’s spec for the 4 ohm tap, so it appears to be a good impedance match.  (For those using Klipschorns with McIntosh, there are different considerations compared to the Cornwalls. My understanding is Klipschorn’s impedance curve has a higher average value compared to the Cornwall due to the bass horn’s throat affecting the impedance seen by the amplifier (it raises it). So, the Khorn may share the same drivers as the Cornwalls, but is a different animal when impedance matching with amplifiers.)  I would be interested in what tap Klipschorn users find most pleasing to the ear. 

 

Andy

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Hi @Klipschguy,

 

I have an MC2125 with CWIII. I use my MC2125 only on the K33E, higher on the midrange / treble I run a Cary SLI50. At home I tested the 8ohms and 4ohms terminals of the MC2125, and well I prefer the 8ohms terminals, because the sound is better, the bass is fuller and with more firmness and authority. Take the test at home and tell us which terminals you preferred. 

 

😎

 

edit: I just read that you prefer 4 ohms at home, like what according to the installation and the tastes the opinions and the settings change 😋

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1 hour ago, mustang_flht said:

Hi @Klipschguy,

 

I have an MC2125 with CWIII. I use my MC2125 only on the K33E, higher on the midrange / treble I run a Cary SLI50. At home I tested the 8ohms and 4ohms terminals of the MC2125, and well I prefer the 8ohms terminals, because the sound is better, the bass is fuller and with more firmness and authority. Take the test at home and tell us which terminals you preferred.

 

😋

Interesting; I would like to see an impedance curve for the Cornwall III. The bass is significantly fuller when using the 4 ohm tap with my Cornwall 1 speakers. I think it is all about impedance matching. Numbers and theory are quite useful but only tell us so much; the ears are the final authority, as you know. 

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On 2/9/2021 at 8:54 AM, henry4841 said:

Damping factor determines how the amp controls the bass speaker. After a certain amount any more will not be be noticeable. 

So what is considered a high dampening factor?

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Thanks for posting, Mustang.
 

My Italian is not what it used to be, but it looks like plot number 4 is the impedance curve.
 

When comparing the Cornwall III impedance curve to the Cornwall 1’s, the impedance appears to be higher on average for the III; I would say the Cornwall III is solidly an 8 ohm speaker, while the Cornwall 1 is closer to 4 ohms. 
 

Interestingly, our ears seem to like the tap setting that most closely approximates the impedance of our speakers. I like it when numbers line up with what I hear. 
 

Andy 

 

P.S.  The Cornwall III response curves look impressive. 

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1 hour ago, rockhound said:

So what is considered a high dampening factor?

It depends on the speaker being used and does vary from one to another. What I meant is you make an amplifier with a damping factor of 100 when the woofer is well controlled with 20 the extra 80 will not be noticed. 

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