Minimus 7 PZ-2.2 Mod DIY Circuit Board by Pete Basel

Correct the leads of L1 do go right into holes in the board.
And the order of C1 and R1 do not matter, I just arranged them in the best
way for the layout. I didn't even think to make the schematic consistent,
thanks for doing that.
The one twist in the air connects C1 to R1 and that is it.
I would take another picture but mine are both closed up now.

How do you plan to make the PC board, or are you using another method?
 
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Ok Pete, thanks for the clarification as to the order of C1 and R1, theory is isn't my strong suit! I can proceed
with more confidence now...
 
Attached an actual sized layout drawing in .pdf format to the first post in this thread.
Use it as a drill and cut guide. it could even be used to drill a piece of masonite or
plastic to use as the XO board.
 
Pete .... you say that the PE inductor should not be glued down ... why ? I was thinking of taking your schematic and putting on a plain wood board and joining all the wires on the top and gluing all the parts on the top of the board. I like the idea of putting the speaker connectors on the board so that the board has a dual purpose.
 
Pete .... you say that the PE inductor should not be glued down ... why ? I was thinking of taking your schematic and putting on a plain wood board and joining all the wires on the top and gluing all the parts on the top of the board. I like the idea of putting the speaker connectors on the board so that the board has a dual purpose.

I intended to write that it should be glued down, but that if you use one off board
you should not also use one on the board it is one or the other - if that makes sense.
I'm not sure what is causing confusion but when we talk about the PE inductor we
usually mean the large one that doesn't fit on the board. The one that I called out
is also a surplus one from PE but it does fit and should be glued to the board. It is
not a PE brand part so we could refer to it as the surplus inductor.
 
I get the fact of it being either one or the other and on/off board. I see the inductor on PE (part# 269-2266). I appreciate your patience with my limited knowledge. This is my first attempt at building a crossover. I see the eBay sold solution (sold by Lawrence) somewhat expensive and difficult to install. Actually I'm surprised someone hasn't made a circuit board (minus the caps etc) and sold it ... something like what you made.
 
You're certainly on the right track, keep us up to date on your progress and don't
hesitate to ask questions. Building it on some masonite or whatever should work
fine. You can run the leads to the back of the board and just use the wires to hook
it all up, get some bare solid wire to hook up any that don't reach.
 
I'm attaching pictures of the much larger PE (by ERSE) 1.0 mH and the buyout/surplus (269-2266) 1.0 mH. The PE part is what Zilch used, I used something very similar to the buyout part.
 

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I'm attaching pictures of the much larger PE (by ERSE) 1.0 mH and the buyout/surplus (269-2266) 1.0 mH. The PE part is what Zilch used, I used something very similar to the buyout part.

Timely post. I was just set to ask about that buyout inductor. PE offers 2 types: 269-2266 and 269-2124.

Surplus_Is.jpg

I had assumed the laminated bar type to be the prescribed item, and had actually forgotten I had a couple of the other type until just now while rifling through parts bins. The ferrite core item superficially more closely resembles what you are using, causing a moment of doubt. Your post clarifies things nicely.

My build is moving along in fits and starts -- scheduling issues, not construction related. But I'm at the final assembly details. Here's an early pic of parts before assembly:

Xover_parts.JPG

I like to utilize the spare central casting for 3-point mounting, so tampered with layout a bit. No depth issue worries as I'm using stock woofers. Happened to have a 3/8" end mill that worked well to clear copper away from the mounting screw holes.

My choice to use L-Pads instead of pots necessitated notching the PCB. Even these little 15W L-Pads are MUCH larger than the 22 Ohm pots I would have otherwise used:

BIG.jpg

Pics of the final assembly hopefully to follow shortly.
 
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Nice work Stuart, please keep us up to date. Did you etch that board?
I had not noticed the 269-2124 inductor but laminated bar is
usually better. 269-2124 is 20 ga for slightly lower DC resistance but I'd still go
with the laminated bar, nothing wrong with trying either of them.
Jack Hidley from NHT has nothing good to say about ferrite core inductors, he
said something like he's never seen a good one. Yet the big Erse Super Q's are
solid, I think ferrite, core and they do measure well from some tests I've seen.

Found it, Jack Hidley wrote:
http://www.diyaudio.com/forums/mult...-interaction-4-way-system-31.html#post1589360
"All of the powdered iron core inductors I have ever measured have been junk. They
all have an order of magnitude more distortion than a laminated steel core at low drive
levels, exactly where you don't want it. "

There was an old Speaker Builder article where a number of different inductors were
measured for distortion and some of the Ferrites were quite bad.

The bar type that I used here IS a Ferrite but it came from a good company and the
power levels are low in this speaker - it sounds fine.
 
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I'm calling the schematic for use with an Lpad PZ-2.3 and it is attached, R2 should
be shorted and the Lpad hooked up directly in front of the tweeter. An Lpad is not
exactly like a pot, but that's how I drew it, just wire in and outs as shown.
 

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I get the fact of it being either one or the other and on/off board. I see the inductor on PE (part# 269-2266). I appreciate your patience with my limited knowledge. This is my first attempt at building a crossover. I see the eBay sold solution (sold by Lawrence) somewhat expensive and difficult to install. Actually I'm surprised someone hasn't made a circuit board (minus the caps etc) and sold it ... something like what you made.

Al, some people use red fiberglass board (GP03 material) that you can find
on Ebay but is cheaper at McMaster Carr. Might not be worth it if you already
have some suitable material.
 
I'm attaching pictures of the much larger PE (by ERSE) 1.0 mH and the buyout/surplus (269-2266) 1.0 mH. The PE part is what Zilch used, I used something very similar to the buyout part.

So the preferred component is 269-2266?
 
I'm using stock woofers currently. Might fab a temporary adapter plate to experiment with the MCM woofers. But they're ultimately destined for custom box builds -- once this deluge that's soaking the west coast passes and I can pull out woodworking tools. Maybe I'll build an ark instead. Anyone know how long a cubit is?

I am just reading this whole thread so please excuse my multiple replies...

I purchased a couple pairs of the MCM 55-1856 woofers as replacements for those damaged in my M7s. I have one set in a M7 box with the PZ2.1 and love them as near field speakers at my work bench. Having a second set of the woofers has prompted the idea of using them in a custom wood enclosure (bluetooth enabled portable cabinet). I first thought about using the M7 tweeter in the custom box and this crossover to emulate the improved M7 performance but the M7 tweeter is pretty big for my target from factor. It is more about the magnet size than the faceplate as could remove the faceplate and rear mount the tweeter....but then would need to find the correct length screws to mount the tweeters. So the 2nd and 3rd order effect start to add up and turns what is supposed to be a simple project of using what is on hand into a full custom job.

Now I am wondering if I can use the MCM woofer with different tweeter and still use this crossover to good effect (as I have all the components on hand except a .4mH inductor to replace the surplus used in the M7). The tweeter I am considering is 275-030. https://www.parts-express.com/dayton-audio-nd20fa-6-3-4-soft-dome-neodymium-tweeter--275-030
 
Now I am wondering if I can use the MCM woofer with different tweeter and still use this crossover to good effect (as I have all the components on hand except a .4mH inductor to replace the surplus used in the M7). The tweeter I am considering is 275-030. https://www.parts-express.com/dayton-audio-nd20fa-6-3-4-soft-dome-neodymium-tweeter--275-030

I really can't say, depends on how close that tweeter is to the original.
I'm planning to do something with the ND16FA-6 tweeter but it will be down the road.

I mentioned it here but will probably not get to this for several years:
http://audiokarma.org/forums/index.php?threads/minimus-7-with-mcm-1853-woofer.755200/
 

Not sure about that, seems Stuart has the actual part and it does not match that picture.
Stuart? Anyone know?

I purchased mine in March of last year. PE has since switched out that inductor with another of similar specs, reusing the same part number. And recently, I suspect. Look at the Q&A section below the part -- someone with a question posted reference pics, capturing the original part offered:

ferrite.jpg

Parts Express has been known to recycle part numbers, even for items bearing no similarity to the original. I purchased some of these long-shaft 15W L-Pads with part no. 269-270 back in '93:

PartNo.jpg

Today that number is assigned to something completely different:

SameNo.jpg
 
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Here's an update of my PZ-2.3 build:

I machine-cut all copper removed from the PCBs similar to Pete's proposed method. Used a table saw for the long vertical cuts, which works very nicely. The short horizontal cuts were made with a 1/8" carbide end mill in a hand held Dremel with a small router-like attachment running along a straight edge. Did this just to try it out since I had those tools at hand. These cuts aren't as perfectly smooth and straight as with the table saw, but it's easy to control the stop point without overshooting the vertical cut. And the result is every bit as functional. I used 3"x4" .060 fiberglass PCBs with 2oz. copper -- plenty stout with lots of metal.

I installed a jumper in place of R2, realizing afterward that for version PZ-2.3 I could have simply not cut away the copper normally bridged by R2 in the first place. Ah well, something learned for next time ...

PZ-2.3_LPad.jpg

All parts except resistors are strapped down with small gauge zip ties. Resistors are raised to enhance cooling as Pete recommended:

pcb_assembly.jpg

Note that this whole assembly, including L-pad, displaces hardly more than a stock early style crossover:

pz_vs_stock.jpg

And it installs nearly as easily. Placement of the L-pad is constrained due to its size and by bosses cast inside the cabinet. There's little choice except where I ended up mounting it (though could be on either side) after notching the PCB for clearance. I used a 1-1/2"OD x 3/8"ID rubber washer under it for a seal.

PZ_installed.jpg

A view from the rear offers the only tell-tale signs that this ain't your daddy's Minimus-7.

PZ-2.3_rear.jpg

Cabinets of this early Silver pair are sound but cosmetically challenged. They're slated for painting once I settle on a colour. I'm leaving the stock crossover in one for a bit so I can A/B compare the before and after between these twins of identical vintage. Won't happen today though (much to my chagrin) -- as I'm quite soon to be dragged away to other commitments. Too much of that lately. Really need to retire and enjoy some music ... :music:
 
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