Inside the Minimus 7: repair and restore

[kfa888]

I used some formula-2001 in the surrounds. This is similar to armaroll (sp?) but it is better suited for rubber parts.

Funny project, not sure I could bring myself to spend much time on these speakers. Luckily my free pair were good so I did not have to make that decision.

FYI, The formula 2001 stuff is polyurethane based and Armor all is silicon based. I like the 2001 much better. I'm surprised you could get the rubber cement to stick AFTER putting the 2001 on.

 

[240sx4u]

Wow to think I just passed on a free set... they were my parents and they lived outside for almost 10 years. Tweeters were shot and the woofer surrounds were gone.

I agree, great sounding speakers though. They also sold that speaker under the RCA label after that became the house name at ratshack.

The RCA ones are also magnetically shielded and great for an inexpensive center channel. I dunno if the others are or not.

Evan

 

[jpdylon]

JP, do you think this would work well along a tear in foam? I've got some speakers with a split along the foam where the lip attaches to the driver cone- otherwise the foam is good.

and I second your idea on the re-dying of the cones- one could also carefully mask off the driver parts not to receive ink, and use an airbrush to apply the ink.

I've used the GC cement for tears in form as well. As long as you go easy on the application and let it dry for a few hours before using it, its great. It gets tacky in about a minute and its dry in 5. Takes at least an hour ro fully cure, but I say more to be safe.

Paul: I'll definitely look into getting the glue for the grills. They still hold on by themselves, but I wouldn't mind a little more secure fit.

I had a pair of minimus 7w a few years ago along with the system seven receiver that was designed for them. it was a great bedroom setup for its size. I eventually sold it to a collage kid who was dorming and he was amazed by the sound the combo put out in his little room. The System Seven Receiver had a EQ circuit tuned for the 7s that made them sound much bigger than they were at the flip of a switch. If you can find a system seven receiver to go with your 7s Give it a try. its only 15wpc, but it goes very well with the speakers.

 

[dbwinger]

caps

Jordan,

If you want to switch the electrolytics to polypropylene I have 2 4.7uf GE Caps that I am not using that I could send you. Let me know.

DB

 

[thedelihaus]

...One thing that can happen on these speakers is the flexible wires that go to the voice coil can become intermittant or break. You can patch them or replace them with solder wick desoldering braid...

This is very interesting. have you any tips on how to do this proper? Or pics? I've never thought of this- a good approach to a problem...

 

[Grainger49]

Just wanted to throw this in. I have had 3 pair. All bought at the "sale price" of $29/pr.

I lost one pair when I sold my 66 Mustang, the rear speakers but the other two pair are still doing service for me.

A synergistic match for them is a Dynaco ST-70.

Nuff said!

 

[Paul C]

First, a picture of an Optimus 7 and a Realistic 77 to show the difference in size.

Next my five Optimus Pro-55AV's (same size as 77's)

Last, a photo of Optimus Pro-X88AV's. This is the one with the 5 1/4" woofer (like 77's) and horn type tweeter.

 

[Pickoid]

I'm using three of the 88's (front L, R, and center) and two 55's (rears) in my low-budget home theater setup. I think they sound nice for the size. Correct me if I'm wrong, but don't the 88's have some variant of a Linaeum tweeter? The tweeter looks like it's made out of a couple of pieces of 35mm film or something.

 

[soundmotor]

It is a later set, maybe the last generation of the M7. The tweeter faceplate w/ concentric rings is the giveaway. The early version was a plain metal. Armor-All is great on surrounds. IIRC, the M7 surrounds have a fair amount of vinyl in them and they stiffen up quite a bit with age.

I picked up some poor beat up minimus 7s today at a thrift for 14 bucks. They were calling to me. The cabinets were rusted and scratched and the grills were dented and smashed in places. One of the emblums was missing as well.

These were definitely used as outdoor speakers. The woofers were faded from black to almost white, and the surrounds were dry and stiff, and were developing cracks in places.

As you can see, these are fairly simple speakers. Why they sound so good is definitely a result of decent build quality and good parts.

Posted here will be pics of the restore progress as well as the demensions, x over specs, and any other information people might find useful

Cabinet demensions:
Exterrior
height = 7-1/16"
width = 4-7/16"
depth = 4-1/8"

Interrior
height = 6-7/8"
width = 4-1/4"
depth = 3-11/16"

 

[soundmotor]

Definitely 2nd generation. The early version used the 40-1022 woofer which was Korean made IIRC. There were many articles in Speaker Builder by Cockcroft using that woofer in DIY designs. You could buy them at RS for $9.95 or so new.

The drivers in the minimus 7s are very heafty and well built for their application. The woofer is a 4" and the tweeter is a 1" soft dome The crossover consists of a coil and a cap for the tweeter.

These are the pictures of the drivers when I got them . You can see the cone is very well sun faded.

Woofer: Radio shack no. 1218 (8 ohm)
Tweeter: Radio shack no SD-60 (8 ohm)

Crossover: 0.4mh coil for the woofer, 4.7@50 mf bi-polar cap for the tweeter.

 

[drspiff]

Another mod for the Minimus 7 is to replace the funky spring wire connectors with dual 5-way binding posts. The casting where the spring clips mount is perfect for binding posts. Here is a shot of one that I modified.

 

[shrinkboy]

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-372 this partsexpress woofer is a spot on replacement for the RS unit, if ya just gotta replace the woof. screw holes line up, the whole nine yards. i know, cuz i tried.

BTW, has anyone ever heard of the Minimus 12? i've had a pair for years. they have an 11" or so cab, use a 5 1/4" woof, and dome tweeter.

ah, hell, i'll go get em and shoot some pix. hang on.

 

[shrinkboy]

the rare and mysterious minimus 12

here's pix of the 12 alongside a 7 for scale. the 12's have replacement woofs from RS. the originals developed tears in the rubber surrounds and at the time i was not aware of a repair method, so i just hunted down replacements.


er, a cone tweeter, not dome

 

[blownsi]

Wow these little guys must be desirable if you are going to that much trouble. I found four white ones last week at a yard sale last week for $2 each guess that was a great deal. They are in near perfect condition except for some little stick on feet applied to them. Guess I'll have to hook them up and give a listen before they are hung in my garage.

 

[drspiff]

My guess is that they are impressive for their size and cost. In the dollars/cubic foot/unit of sound equation, these are right up at the top.

 

[Paul C]

"They are in near perfect condition except for some little stick on feet applied to them. "

Those were supplied with the speakers.

Krylon Semi Flat Black is a near perfect match to the original black used on these speakers.

4" Woofer replacements for the small Rat Shacks: Parts Express 290-372 but the fs is on the high side.

5 1/4" Woofer replacements for the larger Rat Shacks: Parts Express 295-300 or 290-376

For the tweeter: Parts Express 264-804 Use this with the original tweeter's faceplate glued on with E6000 craft glue as per this article

http://www.partsexpress.com/projectshowcase/kuzimus77/kuzimus77.html

 

[thedelihaus]

Wow these little guys must be desirable if you are going to that much trouble. I found four white ones last week at a yard sale last week for $2 each guess that was a great deal. They are in near perfect condition except for some little stick on feet applied to them. Guess I'll have to hook them up and give a listen before they are hung in my garage.

You could flip them on eBay for $20 to $30 a pair, $40 a pair if you're lucky, and I've seen 'em get bid up to rediculous numbers a few times ($80 to $125). Which, of course, is foolish- there's tons of them out there. As stated, they seem to sell on an average of $20 to $40 on eBay, and usually $5 to $10 at yard sales.

These are an excellent performing speaker for their size. With such a small woofer, however, there's not a lot of bass to them. I own 2 pair, by the way. I've mentioned elsewhere, that for $40 you could do a lot better in the speaker dept, such as the Boston Acoustics A-40s, Advent Baby 2s, ect, but for under $40 a pair, ideally $30 a pair or less, and if you need something real small, these are an excellent little speaker at that price.

Great for low-volume nighttime listening, and for rear surrounds in a HT setup. :thmbsp:

 

[Paul C]

Flip them on ebay, and look for 77's or Pro-X55AV's. Those have the larger 5 1/4" woofers. The X55's have poly cones and rubber surrounds, shielded magnets. The larger models have much better bass.

 

[shrinkboy]

i just looked at my mini 7's and found 4.7 uF @ 50v caps. can you replace w/similar values at 100v?

shrinkboy, the nascient DIY'er

 

[SpruceMoose]

i'm using 3 pairs of 7s in my home theater setup as the side and rear speakers. they voice very much like the double advents i built for l/c/r use. i have owned all the speakers since the late '70s, and they still rock!

for a while i was using 2 pairs of the 7s in a quad setup with a sub in the crawlspace under the living room. sounded great, but was volume limited in a large room. every now and then i would tweek the eq on the system. one day, after i was done tweeking, i was listening, and enjoying some music with lots of bass. afterwards i noticed the sub amp was off! i had eq'd the system with only the 7s! i couldnt believe how good they sounded, even without the sub. made them even more volume limited though. but they can put out the bass!