Feb 072016
 

Yazaki-san, Ron-san, and I, buoyed by our dramatic success with our Real Sound adventure with my vintage McIntosh MC30 monaural amplifiers (below), embarked on another Real Sound adventure with my vintage McIntosh MX110 tuner-preamplifier, as I have reported on earlier in several posts.

The superb sounding vintage McIntosh MC30 monaural amplifiers after the our Real Sound adventure.

Well how do I say this? Things haven’t gone so well with our Real Sound MX110 adventure, and as of yet we haven’t figured out quite why, but we’re working on it, and moving forward in small steps.

Vintage McIntosh MX110Z tuner-preamplifier.

My vintage McIntosh MX110Z tuner-preamplifier.

One of the things about real-time blogging on the internet is that it is very transparent. When something works well and I really like it, you’ll see me wax enthusiastically about the results as soon as it happens, like I did with the amazing Duelund CAST crossovers project that Frederik & I did for my Westminsters, or the remarkable Western Electric WE16GA wire from Yazaki-san, to cite a couple of examples.

When things don’t work out so well you can also expect the same sort of transparency from me. That can be a bit more awkward for those involved, but I think it’s equally important, as it keeps things ‘real’ with respect to results, and you don’t have to wonder if you’re getting a candy-coated version of what’s happening here at Jeff’s Place.

A case in point: After Ron, Leo, and I had listened to the three modified vintage McIntosh MX110 tuner preamplifiers, it was clear that while there were some real positive sonic aspects to the modifications we had performed, overall the experiment was not a success, and all three of the modified MX110s sounded much worse than my ‘stock’ restored MX110Z that I had bought from the vintage McIntosh specialist team of Tom Manley & Terry DeWick at McIntosh Home Audio & DeWick Repairs.

My vintage McIntosh MX110Z.

My vintage McIntosh MX110Z.

In fact, the modified MX110s sounded so much worse than my stock unit they were almost unlistenable. This was particularly true on female vocals, which sounded very forward, edgy, and shouty, and listening for more than a few moments was quite unpleasant. My MX110 was the worst sounding of the three, Georges’s was a little better sounding, and Leo’s was a little better still, but still you wouldn’t have wanted to listen to any of them for very long.

As a reminder, here’s the modifications we implemented for the MX110s:

Modification A: We replaced the stock 56KΩ phono stage input resistors at R88 & R90 (left inputs) and R89 & R91 (right inputs), for phono input #1 and phono input #2 with Tepro RA 47KΩ metal film resistors. The phono stage’s sound quality depends mainly on these resistors.

MX110Z Modification A to the phono inputs.

MX110Z Modification A to the phono inputs.

Modification B: We modified the first stage cathode follower of the high level input by replacing two key pairs of 0.1uF capacitors at C93 & C95 and C94 & C96 with a pair of 0.22 uF Arizona Capacitors.

MX110Z Modification B & C to C93 & C95 and C94 & C96 (mod B) and R116 & R117 (first part of mod C).

Modification C: We did four modifications to the power supply. First we replaced the stock 47KΩ cathode resistors at R116 & R117 with Tepro RA 47KΩ metal film resistors (above). These cathode resistors have a large influence on the the sound quality because the signal current flows through them.

Next we added in the C1, C2, and C3 modifications (below).

MX110Z Modification C1, C2, and C3.

MX110Z modification C1, C2, and C3.

In the C1 modification we added a SPEC Ruby-Mica capacitor (MC103DA, 0.01μF / 500VDC ) to the circuit. Yazaki-san said, “Bridge rectifier circuit has good efficiency but diode’s switching noise level and distribution might be higher or wider than half-wave or full-wave rectification. And mica capacitor’s outstanding performance for high frequency could allow these noise to be able to terminate to the ground. I hope some effects would be promising. By the way, the Marantz Model 7’s plate power supply adopted half wave rectification. I imagine it would be one of the secrets of the sound of the Model 7.”

In C2 & C3 we added 0.22μF / 600VDC Arizona Capacitor capacitors to strengthen the power supply. Yazaki-san said this modification was to “strengthen or lower impedance of the plate power supply. Please select by Jeff-san’s inspiration . Because that each color cap could improve the sound, but If you like Red 0.22 for C93-C96, I would like to suggest you to use Blue or Green. Red with Blue or Red with Green could compensate the character of Red.”

Ok, so that’s what we did for modifications to the MX110. So what went wrong?

Eagle-eyed reader, Gareth, had postulated that it was switching from 56KΩ to 47KΩ resistors on the phono inputs that was the culprit, and I had wondered about that myself. The difficulty we faced was that there were no Tepro RA 56KΩ resistors to be had for now, so we would have to wait a couple of months before we could get our hands on some to try. Clearly waiting for a couple of months for 56KΩ Tepro resistors was not an option for me, as I couldn’t just mothball my main reference system for a couple of months.

I conferred with Yazaki-san about what we were hearing and what we might do about it. He told me, “I checked the circuit diagram of the first stage of phono EQ of Marantz Model 7 and also McIntosh C22. They use the phono input resistor, 47kΩ and the grid resistor, 1MΩ for 12AX7. And the combined resistance is around 44.9kΩ. But MX110, the phono input resistor, 56kΩ and grid resistor, 220kΩ. And also the resistance is 44.6kΩ. When we installed 47kΩ into MX110, the combined resistance is 38.7kΩ. I suppose you have been using MC transformer and the combination of your MC transformer and the input resistor, 47kΩ would be some harmful effect on the tonal character. And so, I have a idea that, how would be changing the resistor R94 & R95 from 220kΩ to 1MΩ … And I suppose there would not be any negative effects about this changing.”

The black wire is pointing to the R94 220kΩ resistor.

The black wire is pointing to the R95 220kΩ resistor.

The black wire is pointing to the R95 220kΩ resistor.

Ron-san had a couple of suitable 1MΩ resistors, so he changed R94 & R95 from 220kΩ to 1MΩ resistors as Yazaki-san suggested.

You can see the blue R94 & R95

You can see the blue 1MΩ resistors Ron installed at R94 & R95 . The red pointer is on one towards the middle of the photo, and you can see the other in the lower left of the photo.

There was some small improvement by going to 1MΩ resistors at R94 & R95, but unfortunately the MX110s were still essentially unlistenable.

Ron-san to the rescue: Ron had a number of NOS ¼ watt 9KΩ Roederstein resistors manufactured prior to 1993 when Vishay had purchased the company, and so he installed a pair of those in series with the Tepro RA 47KΩ resistors on phono input 1, bringing the total resistance on input 1 back to 56KΩ, while leaving phono input 2 at 47KΩ as a control.

Going back to 56KΩ resulted in significantly better performance, so clearly the MX110 is very sensitive to the resistance used on the phono inputs. While there was a significant improvement by going back to 56KΩ input resistance, there was still some edginess in the region of female voice (and brass) that was not present in my stock MX110, and overall the modifications resulted in musical quality that was not as good as it was before we modified it, even though in some aspects there were improvements in sound quality.

Ok, I’ve told you what went wrong in our MX110 adventure, but now let me tell you what went right. Now that I have one phono input back up to 56KΩ on my MX110, I can say the modifications produced a much more resolving & transparent sound, more presence & body to images, and a much greater sense of space. The soundstage also expanded in width & depth. The sound also got darker & richer than with my stock MX110, and darker & richer is something I normally like, but in this case we overshot the mark just a bit I think. The timbral textures are very good, as is tone color. Macro-dynamic ability has increased, and bass resolution & impact has increased. I haven’t quite decided if there’s an improvement to the way harmonies & melodies are presented, and I haven’t assessed yet if portrayal of tempos is better or not.

These are my initial impressions, so I’ve got quite a lot more focused listening to do before I have the full measure of what is really going on with the modifications, and I suppose the components used in the modifications also need some more time on them to develop their full sound quality.

The next step is to bring the other phono input up to 56KΩ so I can listen to both mono and stereo recordings with their dedicated phono cartridges, which will tell me more about performance related to the modifications. Then our challenge will be to refine the modifications until we get better performance than we were getting from the stock MX110s, and that may not be all that easy, as a stock MX110 is a really good sounding preamplifier, but I do believe we can do it.

What we don’t know at this point is if the Tepro RA resistors on the phono inputs are responsible for the remaining edginess or not, but we should probably try some other resistors like the Roedersteins to make sure.

The good news is that while my MX110 does not sound as good as I believe it can, it now sounds good enough that I can enjoy listening to music with it again, and so my primary Westminster & vintage McIntosh reference system is now back up and running and ready for some more audio adventures.

While we haven’t yet achieved the desired results with the MX110s, I will continue to keep you posted as we try new things with the MX110s to get things sorted out a little better.

Next up are listening comparisons with the new 6.8uF Duelund CAST hybrid silver-copper capacitors from Frederik, which I’ll compare to the 6.8uF Duelund CAST copper capacitors & 6.8uF Duelund CAST pure silver capacitors in the crossovers of my Westminsters.

Duelund CAST capacitor comparisons are next!

Duelund CAST capacitor comparisons are next!

As always, thanks for stopping by!

 Posted by at 8:22 pm

  13 Responses to “The Vintage McIntosh MX110 Tuner-Preamplifier Adventure: In Pursuit of Real Sound.”

  1. Hi Jeff

    Thanks for your update I had been eagerly awaiting this one. Not totally surprised by your findings as I have found trying to mod a lot of older equipment very difficult indeed to improve upon their coherence and musicality as originally intended by their designer.

    I have been modifying my Playstation PS1 over the past month or so that culminated in some success after a lot of frustration this weekend. Lets say that this unit and the McIntosh have a ‘vintage’ type sound.? Like your findings the unit was so well designed in the first place that any slight mod will throw it off from its wonderfully musical and timbrally accurate sound. e.g, changing the main power filter cap with anyone of the highly recognized caps completely destroyed its sound.

    In the end I simply just separated the power supply into a separate unit and copper shielded it. That made a significant difference to the sound without destroying it original character, especially the copper shielding. The DC blocking caps were removed and because i found it interfered with other preamp operations regardless of what protection they may have had in them, I had no choice but to add a DC blocking cap. I tried numerous ones, oil filled Jensens, my favouite PTFE caps, brand new oil filled M caps, NOS etc etc. The decapped PS1 however, iwas still a little bright and edgy sounding compared to the original if somewhat more transparent. Some of the DC blocking cap replacements (especially the NOS oil ones) completely destroyed the PRAT but helped greatly improve the PS1 further with natural timbral and tonal colors.I did try them in combination as well to no avail. In the end what made the difference?? Changing the power supply leads from the IEC to the power supply board with WE16GA and using Belden 1035 hook up wire between the dc blocking caps and main mother board and the output from the motherboard to the new chassis phono plugs. I noted a tremendous increase in musicality and timbral information. However I still needed a dc blocking cap, and in the end I found my old MHDT Paradisea DAC output caps in the loft, I know how much you liked the Havanna, so i used those. Bang the restoration was complete ,these caps did not destroy the sound and together with the Belden and WE cables I am now able to listen to the worse jazz recordings from the 40’s and 50’s and still gain great pleasure (thats a big smile on my face) from being able to follow every strand of the musical structure with such ease as it was so coherent and O so fluid musically in its presentation. I need to listen more but I have made a major breakthrough.

    The moral of this story, ??? are there any cabling changes that can be made in the Mcintosh? e.g use the Beldon internal hook up wire. Would it be worth removing the original mains lead for the WE or is that a step too far in taking a risk in terms of resale value. Are MHDT caps any good? in DIY projects and do they manufacture it themselves or is it re branded. Of course the PS1 and Mcintosh are of different era’s and design technologies and what worked in my CD player may not translate into a valve based unit, but food for thought nonetheless. I will go back and make more comparisons with the original.

    Look forward to your next installment. I have ordered a restored MX110 so i will remove the power cord and do some mods to the internal cabling with the old one I have in due course which did not cost me much but works very well.

    Kind regards Luke

  2. Jeff, sounds like one must take a deep breath before diving into mods/updates of some classic older gear. My experience was of a far more modest nature but there were some similar results.

    My first stereo included a Dyna PAS-3 I built from a kit. Some years later I became curious about several modifications touted by magazines and a few dealers. Fortunately I had access to my original unit (sold it to friends as part of a system) and used PAS-3s were cheap so I picked up a couple more. This allowed for an interesting comparison. In one I installed an “upgrade” kit from Audio Dimensions, in another a different “upgrade” kit. I was excited to see which upgrade proved best and how much both improved on the original. So imagine my surprise when, after some careful auditioning, I was forced to admit that overall I preferred the stock unit! All this was so many years ago I don’t remember details, but the result stayed with me. I can only say the two mods did involve part/circuit changes, not simply upgraded parts of original values.

    None of this is to suggest you will not have success with your MX110Z. Rather it is to caution that sometimes what looks good on paper will not please the ear.

    I do wish you well.

    • I’ll tell you what, I have renewed respect for what a truly great job McIntosh did with their design and voicing of the MX110. It’s a heck of a good preamp & phono stage that is not at all easy to improve upon.

      I have truly enjoyed the stellar results of my adventures with hot-rodding my Westminsters with Duelund components, and my Mac MC30s with Yazaki-san’s ‘real sound’ recommendations.

      I’ve really enjoyed learning about how powerful the art of applying select components can be, it’s amazing how each component can effect the performance in such a dramatic way.

      Hearing the performance differences by using either the Red, Blue, or Green Arizona Capacitors, has been fascinating.

      We’re moving in the right direction again with the MX110, and I think now that we’ve determined that straying from 56K Ohm phono input resistors caused a major issue with performance, we’re going to experiment with various 56K Ohm resistors on the phono inputs to see what effects that has.

      Gary at Tepro is going to send us some 56K Ohm Tepro RA resistors to try, but that will take quite a while, so in the meantime I’ve got some 56K Ohm Allen Bradley carbon comps, Vishay VAR ‘naked ladies’, and Shinkoh tantalum resistors to try, which should be illuminating. Many thanks to Andy & Ron for suggesting those resistors to check out.

      For a while we will be having a phono input ‘resistor adventure’ with the MX110, which should be a blast! Expect to hear all about it in the near future!

      Kind regards,

      Jeff

  3. Hi Jeff-san,

    You could also try removing the Mica snubber cap in one of the preamps to compare with the others.. Plus, make sure that the Mica caps on the other preamps are directly soldered onto the rectifiers (if you haven’t done so) instead of bypassing the first 10uF lytic input cap.. Also, since Ron-san has a ‘scope IIRC, maybe you could experiment with other Mica values to check the effects (of lesser ringing..) along with the listening tests..

    Good luck on the MX110Z Real Sound experiments!

    • Hi Rick,

      Thanks for your suggestions and well wishes, very much appreciated!

      I will confer with Ron about your comments as we move forward to sort things out.

      We hope to get a start this week on trying some ideas that will help get everything voiced better on the MX110.

      I’ve had such good results with my ‘hot-rodding’ adventures on the Duelund-ized WRSE crossovers and the vintage Mac MC30s that the results with the MX110 caught me by surprise.

      We’ll do our best to get the MX110 sorted out so we can make a recommendation on hot-rodding it for improved performance. It should be fun!

      I’ve been loving learning about how all these different components influence sound & musicality performance as we’ve been going along, and I’m really looking at our MX110 adventure as another lesson. Sometimes these unexpected results are better teachers than when it goes smoothly!

      Kind regards,

      Jeff

      • Hi Jeff-san,

        You’re welcome. =)

        The Vishay RN60’s metal films are an affordable alternative to try. It has non-magnetic leads and end caps. They sound good to me as a phono input load and as part of an RIAA Eq circuit. But I would definitely try those Tepro 56k’s..

        Does using the linestage only part of the preamp (with your DAC etc.) also impart that upper mid forwardness or glare? If that’s the case, that could be a symptom of HF oscillation or ringing.. You can experiment with different Mica values empirically (directly across the diodes’ lead terminals) if it proves that removing the Mica in one of the preamps resolves that harshness (a “wrong” value could excacerbate a relatively benign ringing AFAIK..)

        It gets tricky since these are complex interactions with the power transformer and the specific diodes in use.. The standard .01uF value works great in Yazaki-san’s Marantz, but another value might be more optimal for the Mcintosh.. Ideally you could make it an RC snubber across the power transformer secondary, but that requires more involved measurements and maths to get nearest preferred values.

        OTOH, I could be completely off-base, and the source of the issue is something completely different and unexpected.

        I’m pretty sure you’ll find the source of that aggressive upper mid. It’s a good thing that almost all if not all golden era hi-fi tube preamps use low transconductance tubes…

        Best regards,
        Rick

  4. Hola Jeff.

    Glad to see I wasn’t just blowing smoke with my previous comments. As I’ve said before, the designers of these products knew what they were doing. Changing values in circuits is very rarely a good idea without careful consideration of the resulting effects. In this case, I’d say that the change in operating point of the first 12AX7 pushed the valve out of it’s most linear operating zone, with the results you’ve heard…

    A further thought about the “edginess” (sibilance?) you’ve reported – that may be a result of using a metal-film resistor. This is an effect I’ve heard before when working on my own amps. I’ve found that high quality carbon-films are a good compromise, giving more detail than carbon-comps, but without the sibilance of metal-films. Worth a try perhaps…

    Cheers (& good luck)… G

    • Howdy Gareth,

      You were right on the money, replacing the 47K with 56K helped immensely. The ‘edginess’ does include exaggerated sibilance on female vocals, increased record surface noise, and I’m not quite sure how to fully articulate it yet, other than to call it edgy & forward, but an unpleasantness related to female vocals & brass in particular, that can make listening unpleasant.

      It’s time for a resistor adventure for the MX110s’ phono inputs, which should be fun and illuminating. Gary at Tepro is going to send us some 56K Ohm Tepro RA resistors to try in the next 3-4 weeks, so until those come I’m going to try some 56K Ohm Allen Bradley carbon comps, Vishay VAR ‘naked ladies’, and Shinkoh tantalum resistors, at the recommendation of Andy Moore and Ron. If you have any additional recommendations I’m all ears!

      Even though the outcome with the MX110 was unexpected, it is turning into a great learning experience, which I truly value.

      After our ‘resistor adventure’ with the MX110’s phone inputs, we’ll work our way through every modification to see if we can optimize further.

      Many thanks to Yazaki-san, Ron, Andy, Rick, and you, Gareth, for your suggestions, very much appreciated!

      Keep those ideas coming!

      Kind regards,

      Jeff

      • Hola Jeff.

        I’m just glad to help (or at least not hinder) a fellow seeker of audio nirvana…

        As to further suggestions, I’d suggest trying a wider range of brands & resistor technologies. High sensitivity valve inputs are a strangely counterintuitive area – a resistor which sounds great in a later stage of a circuit (with a higher voltage) can sound terrible on the (low voltage) input, and vice-versa. No idea why, but that’s my experience. Thankfully, resistors are pretty much the cheapest components in a circuit, so swapping them out isn’t financially expensive. Timewise, well that’s another matter. Find a local electronics supplier & drop a few bucks on a range of resistors – CC, CF, MF, what have you. Try them in circuit, and keep careful notes of how they respond in-circuit. Don’t be surprised if the expensive “Audiophile” types sound worse than cheap “no-name” types. Trust your ears, if it sounds right, it is right…

        Just be aware that this sort of thing is only guaranteed to take up time and lead to more questions…

        Oh, and as always when working on valve electronics, a couple of voltage discharge leads (clip leads with 100K resistors inserted, to discharge the power supply caps) are your friend…

        Cheers… G

  5. Dear Jeff
    i got my serviced version of the MX110 and was able to sample the tuner section for the first time.(the unserviced mx110 i already have needs a tuner realignment) Both me and my wife sat there mesmerized listening to it through a mini Denon system and some lovely full range single cone speakers. Beautifully, emotionally evocative to sum up. What a fantastic tuner. You sure you don’t want to explore any further upgrades to that section of the mx110?? I know the other areas take priority but the tuner is one beautiful music making part. I will shortly be able to sample the phono section for the first time with the Yves MC225 and am just waiting to get the MC30’s from Yves with his Arizona cap upgrade!!!

    PS I am also getting in as many West-caps as i can from EBAY (thats the hermetically sealed NOS PIO) as it seems to have simplified diy ing. It seems to improve anything i put it in to. In the PS1 it helped improve the sound by parallel union with the main filter caps in the SMPS power supply as well as the signal path dc filter cap on the main board. It seems to improve the sound no mater where i seem to add it. The PS1 is now beginning to blossom into one special cd player. As soon as the MHDT Havanna arrives i will be sure to add it it to the output caps i bet that will also work with little effort. thank you again for all your free advice.

    Kind regards Luke

    • Hi Luke,

      That’s great on the MX110! I really love my MX110, it’s so musical, magical, and so emotionally engaging in the way it plays music.

      I love the tuner too, and once having experienced how satisfying it is, I could never do without it.

      I haven’t really thought about modifications to the tuner section, as we’re still trying to figure out the line and phono sections. Once we do that … well, the tuner might not be safe! 😉

      That’s awesome on the MC225 & MC30s from Yves, I predict you’ll love them!

      Cool on the PS1. Keep me posted on your adventures with the Havana, I’m really curious as to how that comes out.

      Awesome comment, keep me posted on developments!

      Kind regards,

      Jeff

  6. Jeff hope to see you in the UK one day at a hifi show ????? Plus I can lend you one of my bikes 54cm so we could go out for a ride, plus my wife makes a gorgeous salmon oven cooked with herbs and veg!!!

    Kind regards Luke

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