Inside the Minimus 7: repair and restore
- Thread starter jpdylon
- Start date
lukiedog
Super Member
Picked up a pair of 7w's with the early tweeter (non-ringed) and would like to update the crossover. There's alot of talk about it, but no one seems to have given the details. The ebay kit looks like it adds a resistor, cap, and inductor on the woofer and replaces the tweeter cap with a film cap, possibly of a different size. I'll put together and post a diagram of the upraded crossover if someone gives me the specifics.
Micropassatman
Swollen Member
whyaskit said:
I have a set of Minimus 4.5's that have no tweeter in them. They run fullrange. One speaker cuts in and out intermittently, and I have yet to figure out why. Might be the voice-coil wire separation? Should I just swap out the woofers? These are walnut colored wood speakers, with the metal mesh grilles. Anyone else have a set? They're in my bathroom next to the Pioneer A-X50 mini-integrated amp they're connected to. They don't sound too shabby either(especially when they're both working!).
Although I do have the schematic for the upgraded crossover (and I'll try to get it posted later for those of you that are interested) the easiest thing to do is just move the original coil from it's parallel connection on the tweeter to a series connection with the 'woofer', and then replace the original 4.7uf electrolytic on the tweeter with a decent film cap of the same value (still in series). That'll give you a simple 1st order filter on both drivers and a reasonable amount of protection for the tweeter. Moving the coil to the woofer and replacing the cap on the tweeter with a Dayton metalized film cap or similar will probably get you about 90% of the improvements that the upgrade crossover from the guy on eBay will, and you can do it for about $3.
I know some of you guys here really like the M7, and this may not be very popular, but you've basically got a couple of really cheap drivers in a too small enclosure and no amount of crossover fiddling is going to change that. If you absolutely have to have tiny speakers for low volume near field use they're OK, but IMO there are so many other good speakers around that it really isn't worth putting very much time, money, or effort into a pair of Minimus 7s. Having said that, I do have a pair with the simple crossover mod outlined above, and I don't plan on getting rid of them any time soon. I just think it's kind of silly to get too carried away (of course I've done a few realy silly things in my time, and I'm sure I'll do a few more before I'm done).
I know some of you guys here really like the M7, and this may not be very popular, but you've basically got a couple of really cheap drivers in a too small enclosure and no amount of crossover fiddling is going to change that. If you absolutely have to have tiny speakers for low volume near field use they're OK, but IMO there are so many other good speakers around that it really isn't worth putting very much time, money, or effort into a pair of Minimus 7s. Having said that, I do have a pair with the simple crossover mod outlined above, and I don't plan on getting rid of them any time soon. I just think it's kind of silly to get too carried away (of course I've done a few realy silly things in my time, and I'm sure I'll do a few more before I'm done).
ByrdWyngs said:
I've got a pair of Optimus pro AV44X, which are the same as Minimus 7's but sheilded and ported, I did exactly the same mod as soon as I got them, can't comment on improvement because I didn't listen to them 'standard', I did it because the idea of the woofer running full range just seems wrong to me.
As has been said already, they are not great speakers but they are quite special for such a small package, surprisingly good for nearfield use but for anything else the lack of bass soon becomes apparent, I'm using mine as rears in a 5.1 setup, they work very well but there is room for improvement.
I've been wondering if the designers added a bass refex port to compensate for losing some cabinet volume due to the extra magnets for sheilding.
lukiedog
Super Member
I agree that they aren't really that great, the wife insisted I swap back to the Paradigm Titans in the computer room after I hooked them up for a listen, really a no-brainer, but I like the idea of tinkering and was thinking they may match up nicely with the Sonic Impact T-amp if they ever sell them again. I emailed the company and they said it was going to ship in December, but PE has moved their available date to January...
Well, back to the M7, I found some discussion on AA, what was recommended was to replace the 4.7uF stock with as close to 7.75uF (let's say a 7.5 Dayton poly and a .22 film) and put a .4mH in series with the woofer. This lowers the crossover point from about 4500 Hz to 2700 Hz, for a first order crossover and you can confirm these numbers here:
http://www.ajdesigner.com/crossover/crossoverfirst.php if you assume 7.6 ohm DC resistance on the drivers. The inductor in series with the driver adds some resistance and you can put a 150 ohm resistor in parallel with the woofer to bring it back to 7.6 ohm (or whatever you measure on yours).
Well, back to the M7, I found some discussion on AA, what was recommended was to replace the 4.7uF stock with as close to 7.75uF (let's say a 7.5 Dayton poly and a .22 film) and put a .4mH in series with the woofer. This lowers the crossover point from about 4500 Hz to 2700 Hz, for a first order crossover and you can confirm these numbers here:
http://www.ajdesigner.com/crossover/crossoverfirst.php if you assume 7.6 ohm DC resistance on the drivers. The inductor in series with the driver adds some resistance and you can put a 150 ohm resistor in parallel with the woofer to bring it back to 7.6 ohm (or whatever you measure on yours).
lukiedog
Super Member
Micropassatman said:
I have heard good things about this unit used as a full ranger, it is a Tang Band, alot of DIYers have made computer speakers with them:
http://www.madisound.com/cgi-bin/index.cgi?cart_id=2409665.7295&pid=1757
Parts Express has several other Tang Bands, they are suppose to be decent and cheap. For a bathroom, you might want to get a poly cone or "hodge podge" the paper cone for additional protection. Make sure your box is deep enough...
I've seen the same (from 7.2 to 8.0uf), and that might give slightly better freq. response, but it also leaves the tweeter fairly vulnerable. You'll need to be careful not to feed it too much power crossed over that low.lukiedog said:
Anyway here's the crossover that was in the Speaker Builder article, and that the eBay seller is basing his upgrade on, for those of you that want to try something a bit more complex (still pretty simple really).
Attachments
lukiedog
Super Member
Thanks. If you look here:
http://support.radioshack.com/productinfo/
You can see that this same tweeter has been crossed over as low as 2500Hz, but it looks like in the posted scheme, the crossover is actually raised, rather than lowered.
http://support.radioshack.com/productinfo/
You can see that this same tweeter has been crossed over as low as 2500Hz, but it looks like in the posted scheme, the crossover is actually raised, rather than lowered.
Micropassatman
Swollen Member
lukiedog said:
Thanks Lukie!
Are all the T-B drivers fullrange? I'll do some more investigating and see what I can come up with!
lukiedog
Super Member
Micropassatman said:
The 3" and 4" are full rangers, usually, with compromises of course. Here is an article with more ideas:
http://www.zaphaudio.com/minitest/
It is just that the NS3-194-8E is pretty cheap at $10.50!
lukiedog
Super Member
lukiedog said:
Well, I finally got around to doing this project, put a 3uF dayton poly in parallel with the existing 4.7uF to get 7.7uF and re-wired the inductor to be in series with the woofer. Results? A bust. The stock arrangement was far superior, better bass and more clarity overall. The more time I spent comparing the two, the better the stock sounded. I was doing a blind test, too, did not know which was which. Disappointing, because it was kind of a pain to do the mods, its tight in there. If you are going to do any kind of crossover mod, the previously posted schematic or purchasing the kit from eBay would be the way to go.
I'm not sure I would bother with the expense and trouble to rebuild or significantly alter the crossover.
I have found that just replacing the original electrolytic capacitor with a polypropylene cap of the same value made a significant improvement. Cheap and easy!
I have found that just replacing the original electrolytic capacitor with a polypropylene cap of the same value made a significant improvement. Cheap and easy!
Bump!
I'm in trouble. I have a pair of Minimus 7s that are blown. I haven't had the heart to find out what is scorched, but the sound is awful. Please don't make me confess to how I did it, but be kind! I did while trying to repair a preamp for someone I didn't even know.
Suffice it to say, I want to heal them but where on earth do I get replacement drivers?
As always, Thanks in advance!
.
I'm in trouble. I have a pair of Minimus 7s that are blown. I haven't had the heart to find out what is scorched, but the sound is awful. Please don't make me confess to how I did it, but be kind! I did while trying to repair a preamp for someone I didn't even know.
Suffice it to say, I want to heal them but where on earth do I get replacement drivers?
As always, Thanks in advance!
.
Interesting thread. I have 8 or 10 of the 7's that I have picked up at garage/estate sales, don't believe I have ever found one that was blown or ever paid more than $5 for a pair. I use them with Radio Shack DSP40's which is a 5 watt out digital signal processor and use them with my shortwave receivers. They are great for that purpose as well as the stereo bit.
I recently picked a pair of Minimus 1's (gave $7 for the pair). They are about twice the size as the 7's and in wood cabinets/have removeable grills and sound really great with my Sansui 2000X. I have ran surches on the one's and find absoutly no info on them. I suspect they are probably 30 or better years old but the surrounds are in great shape.
I recently picked a pair of Minimus 1's (gave $7 for the pair). They are about twice the size as the 7's and in wood cabinets/have removeable grills and sound really great with my Sansui 2000X. I have ran surches on the one's and find absoutly no info on them. I suspect they are probably 30 or better years old but the surrounds are in great shape.
Crapola! I didn't get notification of these replies. Ok:
Shrinkboy, I was so mad I didn't determine what was blown. I would expect both tweeters are bad. But I will bookmark the woofer at PE.
I will check and see.
Thanks,
Shrinkboy, I was so mad I didn't determine what was blown. I would expect both tweeters are bad. But I will bookmark the woofer at PE.
I will check and see.
Thanks,
