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Minimus 7 Loudspeakers - Measurements

I'd say try the amps that you have. I'd like to see 25 to 35 honest watts per channel into 8 ohms for these if you are trying to get the most out of them. Let us know what you think.
 
I put a T-amp in my Super minimus sevens, I think it was around 10 watts at 8 ohms, and it was totally fine.
 
Thanks

I have two t amps. One pushes about 5.5 watts of clean power and the other around 13. I was hoping to use the smaller amp as it runs off double A's. Right now the little amp is more than adequate with the unmodded M7s. We'll see.

I made my mounting boards yesterday using Stuarts design. I still need to buy a few things before I wire them up. Been fun. Thanks again.
 
I did an experiment once when I was thinking about how many people want small speakers and stacked a pair of Minimus 7s in our family room. No subs were used. The receiver was a Proton with the 6 dB of headroom feature for 500 msec like some NADs which was 40W/ch RMS and 160W/ch for 500ms. They sure sounded good, all things considered, with the right EQ curve. They did not last long, LOL when they were cranked up and I was not around to turn it down.
 
inductors etc.

jackgiff said:
My wife's new computer speakers were just finished today. The Minimus 7's that were modified are the 40-2030A's, which were built in Japan. As stock the rising treble response is very "in your face." The Zilch inspired PZ 2.1 crossover tames them quite nicely.

I laid out a simple PC board to replace the plastic mount used in the cabinet. The input terminals were cut out of the plastic mount, and held in by the circuit board which has a large cutout to clear the terminals. Both circuit boards were made from a single 4" X 6" board. I used 5 Watt resistors, since the Minimus 7 power capability is very limited. The two FR's are the before and after FR's.

The pics tell the story. Very easy fix, and well worth the doing. They will be powered by a 20 W per channel Sansui, which should provide all the volume the wife needs.

PS: I sure miss talking to Zilch.
Click to expand...

Hi,

I'm new to this forum. Thanks for posting the pictures! I seem to have the exact same model & build as yours (it looks the same inside, which is not necessarily true for all Minimus 7's, as I understand). Just got them from eBay last week after hearing them at my friends house. They sound pretty good with some music (e.g. what was playing at my friend's house at the moment) but generally not great, so I read up a little bit and decided to try to put in a real crossover.

Is there a reason the original inductor is air-core? I noticed that one of yours is, also (but you're not reusing the original one). Ferrite or permalloy would be more compact but possibly would introduce some distortion. I found some ferrite-core inductors on DigiKey I was going to use, but now I'm having second thoughts. The parts I found are rated for 1.6 A (390 uH, and I can just reuse the original part, I guess) and 2.5 A (1 mH, ferrite, toroidal). In this circuit, they should be more or less OK at max power for which these speakers are rated, which I don't intend to supply, anyway. The saturation current is not specified, so I assume the rated current determined by the wire gauge. These are general-purpose inductors, not advertised as super linear or "audio grade", although generally I'm pretty skeptical about magical audiophile parts. The inductor from Parts Express is pretty big and all they say is that it's "high grade" (I assume permalloy or something similar) and can "easily handle 250 Watts of power", which is basically illiterate. Which is not to say that that isn't a great part. Can anyone comment on this?

Aslo, would it make sense to try to add more filling? As far as I understand, this would increase the effective volume of the enclosure and thus lower the resonance at the cost of sensitivity, which would be fine by me. Has anyone tried this? Would it actually extend the bass response, and what other effects might it have besides lowering sensitivity?

And, finally, I noticed that the woofer is rated for "nominal 5 W / music 10 W max", while the speaker is rated for 40 W max. Has anyone else noticed this?

Thanks,

Sergei
 
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If you look at the summary thread, the bill of goods lists an I-core inductor.
The other inductor, the original one in the speaker is also used. It's small and you have it already.
http://www.audiokarma.org/forums/showthread.php?p=3671070#post3671070

attachment.php


Zilch was a great draftsman. : )

sergivs said:
Hi,

I'm new to this forum. Thanks for posting the pictures! I seem to have the exact same model & build as yours (it looks the same inside, which is not necessarily true for all Minimus 7's, as I understand). Just got them from eBay last week after hearing them at my friends house. They sound pretty good with some music (e.g. what was playing at my friend's house at the moment) but generally not great, so I read up a little bit and decided to try to put in a real crossover.

Is there a reason the original inductor is air-core? I noticed that one of yours is, also (but you're not reusing the original one). Ferrite or permalloy would be more compact but possibly would introduce some distortion. I found some ferrite-core inductors on DigiKey I was going to use, but now I'm having second thoughts. The parts I found are rated for 1.6 A (390 uH, and I can just reuse the original part, I guess) and 2.5 A (1 mH, ferrite, toroidal). In this circuit, they should be more or less OK at max power for which these speakers are rated, which I don't intend to supply, anyway. The saturation current is not specified, so I assume the rated current determined by the wire gauge. These are general-purpose inductors, not advertised as super linear or "audio grade", although generally I'm pretty skeptical about magical audiophile parts. The inductor from Parts Express is pretty big and all they say is that it's "high grade" (I assume permalloy or something similar) and can "easily handle 250 Watts of power", which is basically illiterate. Which is not to say that that isn't a great part. Can anyone comment on this?

Aslo, would it make sense to try to add more filling? As far as I understand, this would increase the effective volume of the enclosure and thus lower the resonance at the cost of sensitivity, which would be fine by me. Has anyone tried this? Would it actually extend the bass response, and what other effects might it have besides lowering sensitivity?

And, finally, I noticed that the woofer is rated for "nominal 5 W / music 10 W max", while the speaker is rated for 40 W max. Has anyone else noticed this?

Thanks,

Sergei
Click to expand...
 
skywave-rider said:
If you look at the summary thread, the bill of goods lists an I-core inductor.
The other inductor, the original one in the speaker is also used. It's small and you have it already.
Click to expand...

Thanks, I did see the summary and I did actually try to look at the specs of that inductor. One of my questions was whether it's any better in terms of linearity and hysteresis than a smaller and cheaper ferrite-core one. For example, this:

http://search.digikey.com/us/en/products/1410516C/811-1343-ND/1924840

The only obvious problem with this one is that it's 10% tolerance, vs. the declared 5% of the inductor from Parts Express.
 
sergivs said:
Thanks, I did see the summary and I did actually try to look at the specs of that inductor. One of my questions was whether it's any better in terms of linearity and hysteresis than a smaller and cheaper ferrite-core one. For example, this:

http://search.digikey.com/us/en/products/1410516C/811-1343-ND/1924840

The only obvious problem with this one is that it's 10% tolerance, vs. the declared 5% of the inductor from Parts Express.
Click to expand...

Another obvious problem is that the Murata inductor has roughly three times the DC resistance as the Parts Express one spec'ed in the Zilch crossover. The Murata's DCR is .419 Ohms, while the PE unit's is .17 Ohms.
 
jackgiff said:
Another obvious problem is that the Murata inductor has roughly three times the DC resistance as the Parts Express one spec'ed in the Zilch crossover. The Murata's DCR is .419 Ohms, while the PE unit's is .17 Ohms.
Click to expand...

That's a good point, but where are the PE specs?
 
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Zilch's legacy lives on.

My experience is that even someone completely new to the world of modding speakers (or anything electric, for that matter) can do this mod.

After finally getting all the parts together (the 1 mh inductor seems to constantly be on back order). I assembled everything and it worked!

I used Stuart's layout for the most part but I used new inductors rather than the old stock inductors (bought them not knowing I could reuse the originals). I still have to tap the center lug to fully secure the cross-over board, but otherwise I have completed one speaker. The cross-over on the other speaker just needs to be soldered and mounted.

I left one speaker stock to A/B test. High frequency definitely smoothed out. Very even presentation overall. It is a little quieter, but my t-amp is still able to push it to an acceptable levels in my portable rig.

Thanks to everyone who helped on this.

Oh, one other tip to anyone stumbling upon this thread as I did and not having an previous experience. Print out Zilch's diagram and trace the tweeter circuit and the woofer circuit with different color highlighters. This allowed me to understand what was going on and make slight tweaks to the board layout and still make it work.
 
Minimus 7 Convert

I too have recently been exposed to Minimus 7 speakers. I've been on a vintage stereo equipment jag. I purchased a Hitachi HMA/HCA-6500 amp/pre-amp setup. A co-worker mentioned his Minimus 7's so we hooked them up and gave it a listen. I was sold! I immediately checked craigslist and found a white pair nearby for $20.

After getting my new white units connected side by side with my friend black units, we found something odd. Besides the colors ;^) of course. His sounded much brighter while mine were subdued. I had read about the crossover mods and was giving it consideration. So I opened my 7's and low and behold they had been modded.

The mod doesn't have the same quality of components (only one inductor, small resistors, and cheap looking caps). Will better components result in less attenuation of the brightness?

So I have a couple of questions:
1. Is the lack of brightness what I can expect from the new crossover?
2. Regarding the resistors. The one in my minimus are quite small. One is maybe a 3 watt the other two are probably 1 watt. Why does the list of parts have such beefy (10w) resistors?

Thanks for looking and Minimus 7's ROCK!
 
Maybe you have those eBay crossovers? Zilch had little good to say about them, but I think maybe they're better than the stockers.
 
Zonker92 said:
Maybe you have those eBay crossovers? Zilch had little good to say about them, but I think maybe they're better than the stockers.
Click to expand...
Doubt it. The ebay xo has a big sand cast resistor. I would be afraid of a fire hazard with tiny resistors. I've seen even 5 watt sand cast go up in smoke! XO resistors should be 10 to 12 watts.
Kent
 
Yes! They should sound much better and naturally balanced since it is based on my design.

Kent, since the entire Minimus 7 cannot handle much power it is reasonable to use lower power resistors, 5W should be fine here. It does also depend on the design of course and what percentage of power ends up in the resistors.
 
I've attached a photo of my finished crossover as a way of returning the favor for all the great info I found on this thread. I really enjoyed this project.

The resemblance to Stuart's XO should tell you he's onto something; it works well. In my case, stiff cardboard did the trick.

If I learned anything not already said, it's that self-tapping screws might work after drilling the center boss, although I had a tap on hand so I went that route. Also, I used foam insulation to make sure the XO board had a vibration proof seal against the cabinet mounting area.

My only question is this: I used tiny bolts in the plastic housing of the I-core inductor to secure it to the board. Are they far away enough from the inductor to not effect the specs? I can remove them and slather with glue.

So thanks everyone.
 

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I have a pair of these speakers . There ok . but they sound tinny to me . Im using sansui 771 receiver in my bedroom . I would not use there for anything else for sound . I not a fan of how they sound . My niegbor has mach 2 speakers from the day . I heard these at radioshack when they sold stereo equipment , Not the phoneshack like they are nowdays . But I bet these speakers are beter built than what they are selling now in time .But if I had to use then in outside where they would not get wet , then yes I think they would be ok for use as outdoor speakers for entertanment .
 
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