Question about input impedance and input sensitivity.

I would sooner trust period-written factory literature than what some young whippersnapper who probably never set eyes upon, let alone owned an MX110 nor experimented with a variety of McIntosh amplifiers from widely varying eras- on the strength he happens to work at McIntosh. I have.

When you see how high you have to crank up the volume - and the amount of hiss you will observe from the loudspeakers when you do, you will see what I am talking about. Maybe...just maybe you can get away with it if you use very high sensitivity speakers but why take the chance in the first place when there is a multitude of other McIntosh amplifiers whose suitability for use with the MX110 is beyond question?

If you already happen to own a 275 MK VI, then by all means hook it up and try for yourself. If not...well that's the risk you have to decide whether it's worth taking.
 
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What we don't have is actual test data. :) McIntosh is stating the MX110 output impedance is 250 ohms. Some are disputing McIntosh without providing any data measurements.

If someone with an MX110 has access to test equipment, it would be awesome to see a verified, measured spec to nail down the MX110 output impedance specifications.

If the MX110 output impedance is 4700 ohms or less, it meets the 10:1 ratio when mating with the 275 Mark VI. However, if the MX110 output impedance is higher than 4700 ohms, it doesn't meet the 10:1 ratio.

Hopefully, someone who has test equipment can post the data.
 
I would sooner trust period-written factory literature than what some young whippersnapper who probably never set eyes upon, let alone owned an MX110 nor experimented with a variety of McIntosh amplifiers from widely varying eras- on the strength he happens to work at McIntosh. I have.

The problem with McIntosh's 1960 owner's manual is that it doesn't list the output impedance specifications of the MX110. We don't know if the 100K or more amp input impedance recommendation in the owner's manual was based on achieving a minimum specific ratio of 100:1, 50:1 or 10:1 etc.
 
The problem with McIntosh's 1960 owner's manual is that it doesn't list the output impedance specifications of the MX110. We don't know if the 100K amp input impedance recommendation in the owner's manual was based on a specific ratio of 100:1, 50:1 or 10:1 etc.

Honestly, does it really matter?

They recommend 100,000 ohm amplifier input for the MX110; 50,000 ohm for the C22; 5,000 for the C32. For the MX113, it is given as 47,000 ohm.

Note how values differ for these various units as provided by those who designed and built this equipment. They didn't pull these figures out of a hat.
 
...They recommend 100,000 ohm amplifier input for the They didn't pull these figures out of a hat.

Probably not, but such a wide range does beg a few questions that are not technically challenging to answer by measurement.

Of course, even if measurments suggest it should be OK it still may not be for some other reason we don't know. But, considering the question has come up some number of times it's probably worth creating the knowlege for it.
 
By way of interest, the owner's manual lists another output impedance spec for the L+R output jack of 150,000 ohms- for both the C22 and the MX110.

Just seems silly to obsess over what the precise measurements are when the manufacturer has presumably done this in making the recommendations it does.
 
Just seems silly to obsess over what the precise measurements are when the manufacturer has presumably done this in making the recommendations it does.

Understanding actual MX110 output impedance specifications before making an amp purchase is not silly.

Steve Hoffman has nothing but praise for his MX110 which he has reported excellent results in a $100K system.

In this post, Steve Hoffman noted that the excellent results he achieved with the MX110 resulted from pairing the preamp with Tenor 350M monoblock OTL amps.

The specifications for the Tenor 350M monoblock OTL amps state that the unbalanced input impedance of these amps is 33K ohms.

33K is less than the 100K ohms recommended by McIntosh, yet Hoffman is reporting superb results.

If the MX110 actually delivers superb results with amps of less than 100K ohms input impedance, the takeaway is that the MX110 can be used with modern amps, not just vintage ones. Thus the MX110 could be even more versatile.
 
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I measured the output impedance of my MX110 at 100 & 1,000Hz with volume control at 12:00, 1:30 (where I try to set up gain structure of system) and max. Bal @12:00 for all meas.

Findings:
3,700 ohm @ 12:00
5,800 ohm @ 1:30
~500 ohm @ full

No sig diff between 100 & 1,000Hz.

My conclusions:
1. MX110 will probably meet Mac’s performance specs driving loads >= 60,000 ohms.
2. Mac’s recommendation of 100,000 ohms was typically conservative.
3. MX110 can drive impedances lower than 60,000 ohms but will probably not meet Mac’s performance specs due in part to increasing influence of volume & balance control positions on output impedance.
 
I don't have my MX-110 owners manual any more, But as I remember my C-22 manual says 150,000 ohms. Using that kind of load Mac recommended using amps with 2.5 volt sensitivity to get the best signal to noise with highly efficient speakers. So there is some rom for compromise. Driving a new 275 VI would be a real challenge just by reading. I would call Ryan at Audio Classics. I am sure one of the guys there have connected a MX 110 to a new 275 and can tell what they have experience pro or Con. Remember because of the higher output impedance of the MX-110 it is more easily influenced by the quality of the hook cable to the amplifier. I'm not saying you have to spend big money, but you can't go cheap either.
 
C22 manual claims 50,000 ohm for main outs; 150,000 ohm for the L+R output- which is the same for MX110 & C22.
 
I measured the output impedance of my MX110 at 100 & 1,000Hz with volume control at 12:00, 1:30 (where I try to set up gain structure of system) and max. Bal @12:00 for all meas.

Findings:
3,700 ohm @ 12:00
5,800 ohm @ 1:30
~500 ohm @ full

No sig diff between 100 & 1,000Hz.

My conclusions:
1. MX110 will probably meet Mac’s performance specs driving loads >= 60,000 ohms.
2. Mac’s recommendation of 100,000 ohms was typically conservative.
3. MX110 can drive impedances lower than 60,000 ohms but will probably not meet Mac’s performance specs due in part to increasing influence of volume & balance control positions on output impedance.

Thanks - this is excellent information! Your analysis indicates that using the MX110 with the MC275 VI (47K ohm) appears to not achieve the 10:1 ratio. It's interesting that your data does suggest that the MX110 can pair with amps that have a 58K ohm input impedance (significantly lower than the 100K MAC published) and still achieve a 10:1 ratio.

By the way, McIntosh expert Terry DeWick posted back in 2011 that the MX110 "can drive most any load over 10K with no ill effects." That suggests using it with the MC 275 VI would be fine.

Have never had any problems driving a SS amplifier with the MX110, it can drive most any load over 10K with no ill effects, at 600 ohms you will have some bottom end roll off.

And Steve Hoffman reported excellent results wedding the MX110 with Tenor amps that have a 33K ohm input impedance.

Steve Hoffman said:
I have a $190,000.00 playback system in my listening room (the gear is not mine, just a loan) and I've been listening a lot these past few days to all types of music.

I took my 1966 McIntosh MX-110 Z out of the cabinet in my vintage system downstairs and lugged it upstairs for a little test.

At any rate, in my system upstairs I am using the giant Venture Audio Grand Excellence III speakers, the amazing Tenor 350M monoblock OTL amps, the Concert Fidelity CF-080 linestage, the Modwright Sony 9100ES tubed Platinum Signature Truth digital player and the McIntosh MCD500 player, Kubala-Sosna bi-wire and FMS interconnects.

So, all I did was set the McIntosh MX-110, Panloc wood case and all on the top of my rack and carefully switched out the Concert Fidelity linestage and hooked the amps up to the MX-110 along with my Modwright disk player. I made no other changes to the system, just one preamp substituted for another preamp.

Holy cow, it sounded WONDERFUL on the MX-110. I mean spooky real. I was astounded at how good it sounded. The McIntosh was really holding it's own in the system.

I dropped this antique thing into the heart of a world class stereo system and the sound didn't go to hell, it stayed right up there in Groovyland. It will do the same for you if you have a modest system or a fancy shmancy system.
 
Having owned a number of MX110s over the years, I seem to be the only guy that thinks one can do much better for a preamp. The MX110 is firmly im my rearview. IMHO, it would be a real limiting factor in unlocking the performance an MC275 VI is capable of.
 
Having owned a number of MX110s over the years, I seem to be the only guy that thinks one can do much better for a preamp. The MX110 is firmly im my rearview. IMHO, it would be a real limiting factor in unlocking the performance an MC275 VI is capable of.

What aspects of the MX110 did you find subpar?
 
What aspects of the MX110 did you find subpar?

Obviously I’m not damacman but my $.02 regarding a few of MX110 weak points are:
1. Unbuffered outputs
2. Tone controls don’t produce flat response in 12:00 position and channels don’t track well
3. Volume control tracking is not so good ( meas unit has NOS control)
4. Not particularly quiet with many sources of extraneous noise injection. In my unit, the wire to “stereo” light was routed near volume control. This caused annoying low level buzz in output when tuner was in stereo mode and light was lit.

No question the 110 is a visually pretty unit with a nice feel to it. But it wasn’t TOTL when new and it certainly isn’t now. Just my opinion but a restored MC240 or other Mac amp of the era far outperforms the 110 relatively speaking.
 
My biggest beef with the MX110 is that it sounds lean with the Loudness switched OUT and boomy with the Loudness switched IN.

The loudness feature on vintage gear was never intended to be hi-fi. Boomy is normal. It was designed to boost low end for listening at low levels (for example during the evening in an apartment).

What amp did you mate the MX110 with?
 
My biggest beef with the MX110 is that it sounds lean with the Loudness switched OUT and boomy with the Loudness switched IN.

I found similar on my 110. On mine at least, most of the leanness was due to tone controls not flat @ 12:00. At 12:00 low end was down between 3.5 and 1 dB betw 20 and 200 Hz. I fiddled with tone controls to get +/- 1/2dB 20Hz-20KHz and marked pos on front panel. Overall tone control position is quite sensitive.

Loudness adds a pleasing boost with some of the speakers I use but the effect diminishes rapidly as volume is turned up due to loudness tap location on control: mostly gone by 12:00 so I tend to use bass controls more than loudness.
 
Obviously I’m not damacman but my $.02 regarding a few of MX110 weak points are:
1. Unbuffered outputs
2. Tone controls don’t produce flat response in 12:00 position and channels don’t track well
3. Volume control tracking is not so good ( meas unit has NOS control)
4. Not particularly quiet with many sources of extraneous noise injection. In my unit, the wire to “stereo” light was routed near volume control. This caused annoying low level buzz in output when tuner was in stereo mode and light was lit.

No question the 110 is a visually pretty unit with a nice feel to it. But it wasn’t TOTL when new and it certainly isn’t now. Just my opinion but a restored MC240 or other Mac amp of the era far outperforms the 110 relatively speaking.

That's interesting the points you raise #3 and #4 which my MX110 is exhibiting neither of those maladies. Volume control tracking in fact is excellent throughout the range as verified on the MPI 4, whereas on the MX113, tracking is only accurate in the 12:00 - 3:00 range. (Maybe I just got lucky - :dunno:)

- I've never observed any noises associated with the illumination of MPX Stereo on my example either. In fact I've always found the MX110 relatively free of crosstalk issues and interference in general.

- I cannot comment on the flatness of the tone controls except to say 12:00 seems to work fine to my ears..

Otherwise, I have no major criticism of the MX110's overall performance but I will also add that MX110s that are still essentially original which only received bare minimum servicing to keep operational over the years - it's unlikely to be performing to spec and won't be long before a full fledged restoration will be needed. I still appreciate the MX110 for its classic beauty but much like a classic car, it definitely needs a fair amount of attention! :)

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