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ISO Realistic Mach One & Minimus-7 Makeovers/Remakes

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  • ISO Realistic Mach One & Minimus-7 Makeovers/Remakes

    Love to hear from anyone who's either done one of the few Minimus-7 crossover mods out there (I did the one from Speaker Builder Mag in '89?) - or woofer replacements - which is almost impossible. Also Mach One projects - either using the 290-184 replacement woofer (especially 2 of them in a tower or just re-worked the original system. Most DIY systems today with a good sub easliy match or beat them, it's a nostalgia thing, I owned 3 pairs at one point, drove them with an SX-1980. I did mod my best pair by adding 2 of the Audax TW-51 tweets per cabinet, crossed real high at 6dB as "supertweeters" as I was never happy with the high frequency performance of the original horns. That sweetened them up nicely without being too much. I'll try to get a photo from the current owner and post it, I think they look cool as well.

  • #2
    Wolf did a remake of the Minimus-7 I think. Sounded Really good... I think it got an ovation at MWAF a few years ago if I'm not mistaken.

    Zarbo Audio Projects Youtube Channel: * 320-641 Amp Review Youtube: *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
    *Part 2 *Gluing multiple curved laminations of HDF


    • #3
      Mach One recent project:

      That design is lacking some of the more advanced measurement and crossover design techniques of some other speakers around here, but Stash digs them and they likely outperform the originals.

      Would have loved to hear the Minimus 7 mod. I'm bringing my Nova 15 rebuilds to MWAF if it happens, they were well received at pre-COVID InDIYana.
      Electronics engineer, woofer enthusiast, and musician.
      Wogg Music
      Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus


      • #4
        They were called the Synchaetas.

        They do sound really good!
        "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
        "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
        "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
        "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

        *InDIYana event website*

        Photobucket pages:

        My blog/writeups/thoughts here at PE:


        • #5
          Thanks tomzarbo, I was amazed that he found a woofer that fit that hole perfectly, I have searched many times over the years before giving up. I have a pair of Silver cabs laying around, I may just give it a go. I have 1 pair of all 4 colors: black, white, silver and walnut veneer wood.


          • #6
            Since wogg mentioned me, I'll throw in my 2 cents.

            I bought the original Mach Ones back around 1976 or 1977. I recently built a pair of 'upgraded' Mach Ones based on those originals. I can attest to the replacement Mach One woofers sold at PE. They look exactly like the originals. Their sound quality is spot on. In a similar sized cabinet with similar crossover, their sound is just as warm and smooth as I remember from the originals.

            As far as loading dual replacement Mach One woofers per cabinet, you have to realize the sound may change substantially. This woofer needs a smaller internal volume to control its movement and provide its intended sound. Increasing the cab vol to fit two woofers will allow the woofers to move much more easily which may cause distortion or physical VC damage. Also, the sound will change. Bass will most likely be deeper. But mid bass boom may increase. And lower midrange will suffer, depending on crossover point. IMO, these woofers function best in smaller sealed internal volumes. I don't know if these woofers will make great subwoofers, as subwoofer parameters are a bit different

            For the super tweeter, I used the Pyramid TW18BK at PE, $15.48/pair! They are well built and their response is similar to the claimed response of the Mach One original super tweeter horn, with treble extending to 25Khz. These are 4 ohm drivers. I used the ERSE CROSSOVER CALCULATOR to determine an 8Khz 12dB crossover at 8 ohms (installing a 4 ohm power resistor in series between crossover and driver).
            IMO, the original Mach One tweeters always sounded a bit dull, even with the L-pad turned completely clockwise. In contrast, these Pyramid super tweeters sound amazingly smooth. Actually, much smoother and cleaner than I had expected. No harshness whatsoever. Very silky treble. Never overbearing.

            Good luck with Minimus-7 redo. I loved the Minimus-7's. I had owned several sets, both die cast and wood veneer. Back then, these speakers were groundbreakers, well ahead of their time.

            Their woofers are the old 'pincushion' style. Difficult to find ones which will drop in, nowadays. Many woofers may appear similar. However, acoustically, most similar woofers fall far to the wayside and disappoint. The originals could be purchased as a raw driver. They were 8 ohms. Their claimed resonant frequency was around 50 Hz. Their response was something like 50-5Khz. Around 85dB SPL.

            do not confuse those original 7's with later Radio Shack versions which appear similar but were made by RCA and are far inferior.

            When placed in corners, on the floor, those original 7's could fool people into believing much larger speakers were playing. The acoustic trick of playing bass harmonics was quite remarkable. Mid-bass accuracy was extreme as was point-source identification.

            I've thought about building Minimus-7's from scratch, as my Mach Ones. Their internal volume was around 99 cubic inches.
            There's a Dayton Audio woofer I'd use. TCP115-8. 8 ohms. 55-6Khz. 59Hz resonance. 82dB SPL. 4mm XMAX. Paper cone. Rubber surround.
            IMO, this woofer might provide the amazingly accurate bass harmonics of the originals, in a similar sized cab, as well as similar mids.

            I'd use the Dayton Audio 1.125 inch silk dome tweeters. DC28FT-8. Similar rectangular frame. 89dB SPL.

            I'd use a 6Khz 12dB crossover. I'd add a 4 ohm power resister in series between the crossover and the driver. Your tweeter crossover should be calculated at 6Khz 12 ohms.

            I loved the sound of the 7's, although I always found the treble a bit bright. I would design my new 7's to be somewhat more balanced.

            For myself, I'd build the above 7's to use as surrounds with my custom built Mach Ones. I think that would be cool. A retro surround sound system. I could fashion a pair of brackets to hang and angle the 7's, just as the originals.

            As wogg mentioned, I don't get into the complicated speaker building calculations. I go by my ear. It either sounds right, or it does not.

            Sorry as to the lengthy response. I miss the old days and all the speaker and component choices. Good luck!


            • #7
              Hey Stash, yeah I looked at your Mach One project thread, right on man! I owned (up to) 3 - pairs at one time of the original 40-4024A's around 1988. I got my first set in 1982. I hope to post a pic of a very minor tweak I did to my originals (a friend owns them now) - adding "super-tweeters" as I was never happy with their response above about 10k-12k. But you are totally right - there is no sound like those 15's, especially outside! On the Mini-7's, I used the original woofer you could buy off the shelf in 1984 as a midrange in my very first "real" car audio setup - a large box with all RS drivers - the 8" poly woofers, the Mini-7 woofer as a mid and the round "dome" piezo tweets.Did you ever look at Wolf's Mini-7 remake? I have a pair of silver cabinets that are missing woofers that I may try it on. I also have 1 set each of black, white and wood original 7's. And yes, the "Minimus 77's" are not the same. I also owned the Optimus 10's before I bought the Mach's. And I still own a set of Optimus 27's - the super-slim 6" 2-way with 8" PR. And I have a pair of Mini-11 cabinets also waiting to find pincushion 5" woofers for those. Actually my very first "real" speaker was a set of Nova-6's on special at Christmas in 1980 or 1981 I believe. Did you ever see the slim wall-mount Minimus-7? I never had a pair but I found one that I installed at a church on the back of a pew for a specific congregant who had trouble hearing (it was like $5 at a garage sale, put an l-pad on it just to be safe).


              • #8
                I will have to look at wolf's 7 design when I have time to really look it over.

                No, the Minimus-77s are not the same at all. I don't remember ever seeing the flatter wall mountable 7's.

                I did like the original mini amplifier made for the Minimus-7's. It was rated only around 10 Watts per channel. But its special bass equalization really made the 7s sound nice at lower volumes.

                I never liked the 11's. I bought them. Took them apart. They appeared to be good quality. But the sound was never right, to my ear. Bass seemed boomy. Overall sound was not balanced.

                There was also a more expensive version of the 11's ( but a different model), which featured a 5 inch woofer and a sophisticated top-mounted ribbon type tweeter, which was supposed to throw treble 360°. Also, disappointing. Just did not sound balanced to me.

                I' m not a fan of bass-reflex. I prefer acoustic suspension sound characteristics. Back in the 80's, many builders, including RS, tried to make every speaker, regardless of how small, bass-reflex, or, more appropriately, tuned, with a tiny port/duct configuration. Sound quality standards changed. Speakers were designed to be loud, more than accurate, IMO. Mid-bass boom became popular. Treble was harsh and shrill and in-your-face. Disgusting!

                There was another speaker, made by Braun, I believe, which was supposedly very similar to the original Minimus-7's. They were released around the same time. I' ve always wondered if the Braun and the RS models were made by the same factory. I was never able to find a pair to audition. They were said to be as good, or better, than the original 7's.

                In the 80's, Kenwood, which was a higher end brand back then, came out with a semi-portable mini-micro system. I bought it to try, and then returned it. It featured a higher powered clean mini amplifier and a pair of mini wooden speaker systems. The speakers reminded me of the original Minimus-7's. Each Kenwood speaker had dual 4 inch rubber rolled woofers and a 1 inch soft dome tweeter. I think in a MTM configuration. Their sound was impressive. Reminiscent of the old Minimus-7's.

                I can't tell you how many copy-cat mini speakers I tried back then. They all mimicked the 7's. And they almost always sounded like crap! Looks were very deceiving.


                • #9
                  About 6 years ago, I bought a cheap junk Innovative Technology stereo system from Walmart. The reason: the sound was unbelievably good. This $99 system featured a mini retro styled receiver and a pair of mini wood speakers.

                  The receiver itself was crap. I opened it up. Sloppy wiring, soldering, etc.

                  But the speakers caught my attention. They featured a small 4 1/2 inch woofer and a cone tweeter and a FAKE cone midrange!

                  I brought it home. Took speakers apart. Cabinet was maybe 1/4 inch cheap light weight wood-like material. The woofer seemed to be a generic woofer, just slightly larger than the standard 4 inch size. A very cheap small cone tweeter. The fake midrange was a piece of plastic, not connected to anything, which looked ike a driver. The crossover consisted of a single tweeter cap. No polyfil. Just an empty cab with a fairly large ducted rear-port.

                  I connected these speakers to my home receiver. I could.not believe the bass. Very deep. Unbelievably deep for its size. Incredible, considering the quality. The treble didn't sound half bad either. Not shrill or annoying.

                  I wrote to Innovative Technology. I was told I could buy the woofers directly.

                  I don't know if those woofers are still available. But I would absolutely buy them to build Minimus-7 type speakers.

                  Over the years, I've auditioned many moderate to expensive speakers which did nothing for me. But, every now and then, I'd run across a speaker which sounded so good thst it stopped me in my tracks. A couple of those speakers defy all the rules of quality speaker design and construction. Just saying.

                  Here's a pic of a Innovative Technology system which looks the same as the one to which I refer. I don't know if it is exactly the same model. The price and features are the same.
                  Attached Files


                  • #10
                    The receiver was the STA-7. I had one for a little, never deployed it with the Mini-7's, sold it.

                    Click image for larger version

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                    • #11
                      Yep. That's it. For its time, it was a high end mini component.

                      The mini amps and boombox built-in amps of the 80's cannot compete with todays mini T-amps and such.

                      But there were exceptions. Sony came out with a series of mini component portable systems, beginning with FH, I believe. Some of those had nice quality lower powered amps, typically 20-30 watt/ ch range. Low distortion, wide bandwith. Decent speakers. Speaker drivers were square aluminum cones. I owned a couple. I'd fine tune the cabinets or add mass to the woofer cones. Then they sounded a bit better. Was never a fan of aluminum woofers. I have yet to hear one I like. They sound boomy, I don' t care who makes them or what their claimed response suggests. They are always boomy. .

                      Technics, which was the high end of Panasonic, came out with a nice component portable stereo. I think the SA-C07, or something like that. It featured a true high fidelity amp delivering 30 wstts/ ch at very low distortion over the full audio spectrum, per the old IHF specs. Plus, it featured a BASS control set at 50 Hz instead of the stupid 100Hz of most amps of that time. And the TREBLE control was set at 20Khz, I think. Not the typical 10Khz.
                      unfortunately, the detachable speakers consisted of ultra cheap boomy bass-reflex plastic cabinets (to reduce weight), and ultra cheap drivers. The cool thing about the speakers was the woofer and tweeter were time aligned, meaning their VCs were lined up, vertically. That was another trend, back then. The amp and deck are worth buying. That amp should power any speaker system.


                      • #12
                        Back then, there were some really nice equipment and some real junk. Specifications would be the tell-tale. A good amp, deck, etc would list impressive IHF specs. It's unfortunate that modern equip does not state many specs, mostly because their specs suck. And people no longer seem to care.

                        In some ways, high fidelity took a huge step backwards. Especially after the introduction of surround sound. Sound effects and DSPs took the place of high quality audio specs. IMO anyway lol


                        • #13
                          PE sells a few pincushion frame 4" drivers that will drop in the M7 cutout. PRV and GRS. The Dayton PC105 uses that frame, there is a Visaton as well.

                          Newark is still selling the excellent MCM 4" aluminum cone 4" driver with the pin cushion frame (MCM PN 55-1856 - $13). There are mods out in the wild to use that woofer in the M7, as well. I did one quite a while ago but in the Optimus Pro X7 (I think) cabinet. The crossover would likely work in the M7 design, although I had to do outboard crossovers due to the undersized cabinet. In my humble opinion, this woofer is the best choice for modding these speakers. Actually, the best choice is to ditch the cabinet and build one a little larger. The original Minimus woofer is actually very, very good and is capable of solid bass production in a larger cabinet. The "crossover" in the M7 is pretty pathetic, you may well be surprised at what a competent crossover can bring out of the drivers. The SD tweeter used in the M7 went through numerous iterations, the earlier Japan made are very nice crossed at 4K or higher.

                          You can find tons of 4" drivers on Ebay, as well.
                          Don't listen to me - I have not sold any $150,000 speakers.


                          • #14
                            All good information - not all new, but thorough, thanks!


                            • #15
                              Here's my resto-mod of the similar TEAC LS-X7: