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How to Build The Minimus 7 PZ-2.1 Crossover

Pete B

Pete B

AK Member
Subscriber
I'm posting this because people are often asking how to build this crossover. I've reposted
Zilch's diagrams in the long Minimus 7 thread but new posts keep pushing them back down.
Link to the original thread for those who want to read the long history:
https://audiokarma.org/forums/index.php?threads/minimus-7-loudspeakers-measurements.199790/

I'd like to ask people to please make posts here just about how to build the crossover and do the modification.

My PZ-2.2 revision that adds a tweeter control:
I strongly suggest using Stuart's L-Pad if you choose this:
https://audiokarma.org/forums/index...2-mod-diy-circuit-board-by-pete-basel.750334/

Continue below to build the PZ-2.1 version if you do NOT need a tweeter level control:

This is an older how to build it thread with a more step by step guide:
https://audiokarma.org/forums/index.php?threads/minimus-7-pz2-1-installation-guide-review.900518/

Zilch used the ERSE 1.0 mH but now there is a nearly exact copy under the Parts Express (PE)
brand for much lower cost. Edit: Both 1.0 mH are out of stock at PE I will look for an alternate.
Edit: The Dayton steel laminate 1.0 mH is back in stock as of 9-24-2023, they go in and out of stock.
The schematic was finalized in post #121 at the top of page 7:
https://www.audiokarma.org/forums/i...mus-7-loudspeakers-measurements.199790/page-7

Schematic:
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Note that this is an old BOM but at least you get the idea:
BOM: Note that you may use cheaper NPE caps to reduce cost.
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Layout Sketch:
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Picture of Zilch's Layout:
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Picture of Installed Mod:
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Before/After Frequency Response:
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Another Excellent Build by Stuart:
https://audiokarma.org/forums/index...kers-measurements.199790/page-15#post-2726526

Another Build Diagram Found on Ebay:
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Parts Express is out of the 1.0 mH steel laminate inductor from both Erse and Dayton.
Here is a 19 ga version directly from Erse, this will work fine:
https://www.erseaudio.com/ELC54-19-1000?whence=

Here's a BOM for purchasing all the parts directly from ERSE, however it doesn't meet
the $20 minimum order being about $12 so people might want to combine orders or
form a group buy to get over the minimum.

Also, note that the inductor is 19ga rather than 18ga,
The tweeter pad resistor is 2.2R rather than 2.0 or 10% high.
The tweeter cap is 2.2uF or 10% high over the design value of 2.0 uF.
These are very minor deviations used because the design values were not in stock as of 2-18-2022:
M7 ERSE BOM - Copy.JPG
 
With the different versions of this speaker, the mod is for the version with the metal flanged tweeter? I'll have to keep an eye out for a couple of these.
 
Lavane said:
With the different versions of this speaker, the mod is for the version with the metal flanged tweeter? I'll have to keep an eye out for a couple of these.
Click to expand...

I don't think I've ever seen a pair with the metal flanged tweeter, mine were all plastic.
And I've not seen any mention of the mod not working with certain revisions of the M7,
it is certainly possible that they made changes to the drivers but we've not measured any.
 
Lavane said:
With the different versions of this speaker, the mod is for the version with the metal flanged tweeter?
Click to expand...
I've modded both metal and plastic faced tweeter models with the same glorious results.

There are disassembled SD-50 (steel) and SD-60 (plastic) tweeters here on the bench. Construction and materials of their component parts other than faceplate appear identical (earlier aluminium faceplate SD-13 might be a different matter). The move to plastic was likely about meeting production demand as much as cost-cutting.

Steel plates can be stamped out quickly but still need paint and drying time. A typical 300 tonne injection moulding machine can turn out 8 of these per shot. And they drop out of the mould ready to install. A single machine running 2 shifts just 5 days a week could comfortably produce about 33,000 per month.

Diecast models (after the original 40-2030) with metal faceplate tweeters have the extra threaded boss inside, affording a convenient three-point screw mounting option for crossover assemblies.
 
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I must be missing something, the diagram above will yield a 42 ohm load at the speaker terminals?

Update; completed one but did something wrong. Back to the bench!
 
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We are trying to keep this thread about sourcing parts, and building/installing the XO.
Please post about listening impressions in the original or a new thread.
A new thread about listening impressions would be great since the title makes it easy to find.
 
I scored a 2 pairs of Minimus 7 speakers from a rummage sale a week ago in mint condition. The tweeters and woofers look brand new, not dried out and the rubber surround is still shiny. One set has the metal face plate on the tweeters and one set has plastic. This will be interesting to try. I did a similar crossover with a pair of Optimus Pro 110 and they were excellent near field speakers. I'll have to dig for the crossover schematic to those if anyone has a pair of the Pro 110's. They were the last version of the Minimus 77 but in oak. My particular pair had to be refoamed due to age. Still sound great.

Pro 110.jpg Image1.jpg
 
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Thank you!
I have also seen another schematic where R3 is 47 Ohm instead of 40 Ohm. Which value is correct?
Thanks again,
--Mark--
 
Here's my build. I bought this pair of Minimus 7W's back in 1987. they have the metal flange tweeter.
Components are held in place with hot glue. Hot glue was also used to seal the cabinet in the back by the new binding posts.

P1048149-X3.jpg


P1048151-X3.jpg


And here's my BOM. All from Parts Express:

Dayton Audio IC181 1.0mH 18 AWG Laminated Iron Core Inductor
Part #: 257-650
Quantity: 2

Jantzen Audio 0.40mH 20 AWG Air Core Inductor Crossover Coil
Part #: 255-032
Quantity: 2

Dayton Audio DNR-40 40 Ohm 10W Precision Audio Grade Resistor
Part #: 004-40
Quantity: 2

Dayton Audio DNR-3.0 3 Ohm 10W Precision Audio Grade Resistor
Part #: 004-3
Quantity: 2

Dayton Audio DNR-2.0 2 Ohm 10W Precision Audio Grade Resistor
Part #: 004-2
Quantity: 2

Dayton Audio DMPC-4.7 4.7uF 250V Polypropylene Capacitor
Part #: 027-422
Quantity: 2

Dayton Audio DMPC-2.0 2.0uF 250V Polypropylene Capacitor
Part #: 027-414
Quantity: 2

Parts Express Dual Binding Post Banana Jack 1 Red 1 Black
Part #: 090-475
Quantity: 2

--Mark--
 
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