McIntosh ML-1C Speakers

Discussion in 'Speakers' started by W5HRO, Oct 29, 2017.

  1. W5HRO

    W5HRO Administrator

    I just bought a pair of ML-1C speakers on eBay (or won the bid). The cabinets are almost like new and that's why I bought them. I'll eventually go through and replace the woofers, midranges, tweeters along with the crossover networks to update them to modern standards, but for now they will work like they are. Most McIntosh guys don't like theses old speakers, but I wanted them because of the cabinets and they go with my 1700 receiver and the wood matches it's cabinet. They were made in 1970. Whoever had these really took care of them.

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    Response: 20Hz to 20,000Hz
    Power rating: 100 watts peak
    Output sensitivity: 89dB/watt/meter re: 8 ohms
    Impedance: 8 ohms
    Woofer: 12" McIntosh
    Lower mid-range: 8" McIntosh
    Upper mid-range: 1-1/2" soft dome
    Tweeter: 2-1/4" cone with 1/2" super radiator
    Crossover frequencies: 250Hz, 1500 and 7000Hz
    Overload protection: none
    Finish: walnut
    Dimensions: 26" high, 15" wide and 13-1/2" deep
    Weight: 64 lb.
    Sold from 1970 to 1976
    Last retail price: $399.00 each
  2. W5HRO

    W5HRO Administrator

    Looks like the crossovers in these speakers are a bit more complicated. I might just rebuild them with heavier components.


    Also found this information below...

    Restoration for the ML-1C


    After more than 40 years, the most common problem is the deterioration of the 12" woofer and some 8" lower-mid surrounds. Only the surrounds need to be replaced. New drivers or new cone assemblies are not needed or recommended. Surrounds can be replaced with new polyether ones that will not deteriorate like the original polyurethane surrounds. Some early 8" mids had coated cloth surrounds that don't need to be replaced.

    Be certain the new woofer surrounds are made of polyether and that they have a 3/4" diameter roll. Many speaker repair centers do not supply the larger 3/4" roll. A surround that has only a 1/2" roll will restrict the woofer excursion and cause distortion for deep bass notes. If you have new surrounds put on the woofer for you, be certain they are NOT the rubber types. These heavy surrounds reduce the efficiency of the woofer and it will no longer match the 8" lower mid-range output. The heavy surround will also alter the woofer response and it will no longer match the MQ101 or MQ102 equalizer compensation required for the system to provide flat response to 20 Hz.

    The new 8" surround must also be polyether and the roll must be 1/2" in diameter. The 12" and 8" surrounds can be replaced with do-it-yourself kits or you can have them replaced for you by a McIntosh dealer or a supplier.

    Also found the Service Information spec sheet attached below...

    Attached Files:

  3. W5HRO

    W5HRO Administrator

    Went through the service information and it won’t be hard to replace the components in the crossovers with heavier ones. I can get all of the parts, even the coil values from the same place I bought those big crossovers coils that I was thinking or trying to use for RF chokes. What I might do is build a piggy-back board for each one to mount on the existing boards with the parts removed using short standoffs.

    The good thing is the diagram and schematic below have all of the updated values per the service bulletins.

  4. W5HRO

    W5HRO Administrator

    I put the crossover network on the spice simulator and it's pretty interesting. The below is what it would produce to the speakers at 40W RMS. I think it's funny they have the lower 8" midrange speaker peaked for right at 1kHz. They also originally planned to just make it a 3-way speaker system using the red 1.5" dome for the tweeter, but the engineer didn't like it when he analyzed everything so he added the 4th 2.25" tweeter to catch the high-end harmonics instead. This is sort of a one of a kind arrangement. Most 4-way speaker systems today have dual woofers rolled off at different places with just one midrange and one tweeter instead, but the McIntosh receivers and amps have one of a kind bass response as well anyway.

    Anyway, I found all of the heavier parts I need to rebuild them exactly the way they are, but I will sweep them with a function generator to make sure all of the peaks are in the right place on each one.

    12" Woofer

    8" Lower Midrange

    1.5" Upper Midrange Dome

    2.25" Tweeter
  5. W5HRO

    W5HRO Administrator

    McIntosh :mrgreen:

  6. W5HRO

    W5HRO Administrator

    I found a used set of ML-1C crossovers on eBay along with an extra pair of upper-midranges and tweeters.

    Anyway, below are the crossovers and it looks like the furniture place McIntosh used just cut the press-board squares in random sizes and mounted them inside of the speakers with screws. I can just rebuild these using some solid wood or plywood of the same thickness and screw them in making new holes.


    Then the upper-midranges below. McIntosh had the company make these in a custom smaller size so you cannot find new ones that will fit in the recessed slots because the modern ones are larger. That’s why I bought this extra set for backup.


    Then here are the tweeters below. I would have never known these were 16-ohms either and I bought them for backup as well.

  7. W5HRO

    W5HRO Administrator

    Received the old crossovers today and I'm shocked at how large the coils are. Pretty thick gauge wire too.

    I actually found and ordered two more of these so I will take them apart and build up two news ones using the best coils, but with all new higher voltage caps and higher wattage resistors. It would probably be easier if I took my speakers apart and just replaced the caps and resistors on the ones already in there, but If I build up two new ones instead I can just pull the others out and put in the new ones in less than an hour and the speakers wont have any downtime by sitting around for a week or more until I get around to replacing all of the parts. Knowing how I am I'd take them apart and let them sit for almost a month or more. My idea is to just Remove and Replace (R&R).

  8. W5HRO

    W5HRO Administrator

    Did also receiver the extra pair of upper midranges and tweeters. Going to referb (clean and coat) them for backups.

  9. W5HRO

    W5HRO Administrator

    I received my other two crossovers and they are the old original ones without the later revisions where they added the 5th coil and other components. I think what I will do is just rebuild them instead since they are on plywood and the same size. I can just strip off all the caps and resistors and replace them with new ones then add the 5th coil.

    I'll use 20W resistors instead of the stock 10W ones and 200V caps instead of the stock 100V ones.

  10. W5HRO

    W5HRO Administrator

    Was doing some research and contrary to popular limited ham operator knowledge certain types of capacitors do make a difference when used in audio circuits. High Pulse, Low ESR Metallized Polypropylene Film and High Pulse, Low ESR Electrolytic capacitors work the best and they make them with up to 630V ratings now. In limited bandwidth applications, such a voice communications the improved difference when using them will be minor, but when trying to cover the whole audio spectrum in music applications, such in speaker crossover design, using them is defiantly necessary to obtain the lowest distortion and the best possible sound.


    Attached below is a good technical bulletin on the subject. I will update these ML-1C crossovers with a combination of 250V High Pulse, Low ESR Electrolytic and 250V Metallized Polypropylene Film Caps. They didn't make these newer type of capacitors back in the 1970's and they just used whatever they had available at the time in the ML-1C speaker design.

    Attached Files: