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Yet Another Minimus 7 Upgrade Thread - Coronavirus Edition

Stuart Pedaso said:
Here's the schematic, traced off of PCB images posted on amazon.com.

View attachment 1808860

Inductor values shown are reported by Amazon reviewer RhythmJunky. Method for determining values is not reported, so take it for what it's worth.
Click to expand...

I know this is an old thread ... This 3500 Hz Amazon crossover (attachment above in quote) is specified 4-8 ohms. It can't be both ... Right? It's still on Amazon-
https://www.amazon.com/gp/product/B0BZP9VH8P/ref=ox_sc_act_title_1?smid=A2BWM8QI7O4H7Y&psc=1 (sold under bunch of different names, this is the cheapest one)

I know nothing of crossovers, so is this centered around 6 ohms? Or is it 4 OR 8?
 
I've always felt that the PZ mods built with new parts were too expensive and I often used
surplus parts. This is an excellent deal with a PAIR for about $13. I just ordered a pair.
Here's roughly what I would do:
Note that R3 was to flatten the input impedance, it is not needed. The order of the cap and resistor
to the tweeter do not matter once R3 is removed. The .4 mH value was simply reusing the value
from the original M7, who knows .35mH might work better.
2WAY uxcell_xover MOD.png
Edit: I found that adding 17 turns in the correct direction will bring it up to 1 mH, 18 to 20 ga is fine.
I measured the tweeter inductor as .30 mH, an option is to remove it and use the original .4 mH
from the M7. Getting very close to the correct values.
 
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Thank you Pete. So then I can be confident this is 3500hz- at 8 ohm? The description references nothing in terms of speaker impedances. Some of the others simply say 4-8 ohm. I see some questions were asked in the "Amazon questions" but no answers about the specific crossover point with 8 ohm drivers, or 4 ohm drivers.
 
Probably marketing wrote that to sell more.
If the values are close to the PZ mod then it will work with the M7.
 
Pete B said:
I've always felt that the PZ mods built with new parts were too expensive and I often used
surplus parts.
Click to expand...
Too expensive? One would have to be reeeealy pinching pennies for that to be expensive.

Here are mine. I don’t recall the exact price I paid through parts express for everything, but it was not much!! And I did 4 crossovers total!!

IMG_0692.jpeg IMG_0691.jpeg
 
The performance of the M7 even modified is not much and if you buy them for $10 or $20 a pair it doesn't
make much sense to put another $50 - $100 into them.
I bought the Sony SSCS5 PAIR on sale for $88, hard to beat that.

I also like to build the M7 mods with Lpads and those are now $10 each.

How much you want to spend is relative, I hardly ever use the M7 s that I have.
 
Crossovers arrived from Amazon, that was FAST.
The woofer inductor is steel laminated which is good, overall it is fairly small which
makes sense for a relatively low power speaker like this.
The tweeter inductor has a powdered iron sleeve inside of the plastic former, I prefer
air core but at low power it is probably fine.
Edit: Forgot to mention that we reused the stock inductor that came with the M7 s so people
can just replace the one on this board with the stock one.
I'll measure the inductors on my meter later tonight when I have a chance.

Wish there was a $3-5 dollar L-pad.
 
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Pete B said:
Crossovers arrived from Amazon, that was FAST.
The woofer inductor is steel laminated which is good, overall it is fairly small which
makes sense for a relatively low power speaker like this.
The tweeter inductor has a powdered iron sleeve inside of the plastic former, I prefer
air core but at low power it is probably fine.
I'll measure the inductors on my meter later tonight when I have a chance.

Looking forward to your opinion / measurement.
Click to expand...
 
Pete B said:
The performance of the M7 even modified is not much and if you buy them for $10 or $20 a pair it doesn't
make much sense to put another $50 - $100 into them..
Click to expand...

I don't see the correlation between upfront cost and how much $ one can justify putting into something. I don't see why low upfront cost equates to minimal future investment into whatever had a low upfront cost. I paid $50 for my Sansui 9090db. I put several hundred into it. Thats just one example.

The pz crossover costed closer to $20 each, per crossover. Or roughly $40 per pair. Not much. I can easily justify that.[/QUOTE]
 
@z-adamson I don't really care to discuss this it is just my opinion. I remember the cost being more,
but this is really not a high priority of mine. How do you find the time to debate such trivial things?
There was a time when the 1mH was significantly more because the one from Dayton was not available.
 
OK, the woofer inductor is .82mH and adding 16 turns of wire that's one gauge thicker (what I had as scrap)
brings it to .97 mH close enough make it 17 turns to get even closer.
Edit: The DC resistance is .48 ohms which is just fine for the M7.

The tweeter inductor measures .3 mH on my very decent meter. Did not try to wind it up.
Edit: Just remembered that in the PZ mods we reused the original inductor for the tweeter so, just swap that in.
 
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Pete B said:
How do you find the time to debate such trivial things?
Click to expand...
For the designer of an improved crossover to put lots of time into testing, r+d etc. then publish the schematic for others to follow…to then turn around and say that it is not worth it because the cost is too great and the performance is too poor is no “trivial thing.” Many, many folks have done this xover. You are saying all these people that built YOUR xover overspent and ended up with a poor performing speaker. That’s not trivial.
 
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Well there you go again.
I'm saying yes it is an improvement but if you are starting from scratch the Sony's that I
referenced are much better. If you love to DIY, and don't mind spending the money have
fun with the M7 s it is not so black and white. Also the M7s are tiny, if one has the requirement
for tiny then go ahead.
As I said, I don't use my 3 pairs of M7s much but I DO use the cheap Sony's that we have.
And, I also already said that this cheap crossover does make sense when modded for the M7.
I built all of mine so far from mostly surplus parts, so mine were very cheap.
 
Pete- Thanks for adding the inductor info.

Question, since I've never wound any inductors ... What is a good all around gauge (or diameter) to have around to do what you did with the woofer inductor?

Question 2, since the search fuction isn't working yet apparently ... Do you have a thread running about the Sony SSCS5?
 
Let me measure the DCR of the woofer inductor in this XO and then talk about wire gauge.
If you google "sony sscs5 audiokarma" the thread is the 3rd hit. Here it is:
https://audiokarma.org/forums/index...e-cheap-bookshelf-speaker-sony-ss-cs5.953908/

Unfortunately we did fairly extensive listening tests about a year or two ago but I never got around
to posting about them here and I didn't write down any notes. Let me say that they are VERY
good, I preferred them over KEF LS50 s in most ways - hard to believe. I'll go try to post what
I remember. There are many rave YouTube reviews that you can check out.
 
Pete, thank you, but don't knock yourself out on that inductor wire gauge question. It looks to be maybe 18 gauge in a photo on Amazon in someone's hand. I decided to order a pair tonight, so I'll figure it out. It looks like the 3.3uf HF cap is the most off the mark component anyway compared to the PZ 2.2 2.0uf , don't know if this is the reason they can rate this as 4 to 8 ohm applicable or not.

And again thanks for the Sony link, I will be interested to read up. But I'm just know realizing these are ported. Never fell in love with a ported design. perhaps it's the out of phase (?) reflection of the port?? Don't need them to go "artificially" low. Preference has always been sealed. But if I see a pair used for a price I could resell and not lose I'll give them a go. And hopefully they're not "bright" or "in your face", that I run from.
 
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I edited post #31 to add the woofer DRC which is .48 ohms - just fine for the M7.

To refresh everyone's memory, I did my mod to the M7 in about a 3 hour session were I "designed" it
by hooking the drivers up to my measurement system with a cap switch box and selected values that
provided a logical electrical transfer function.
I did a very quick acoustical measurement to confirm that the response was reasonably flat.
And then I listened to one in mono with one of my sons and we trimmed the tweeter pad for the
best balance to our ears. This was what I gave to Zilch and he tweaked things around but more or
less roughly came back to my suggestions.
I used a 2.7uF tweeter cap in the original.
Yes, 3.3uF is off but give it a listen and see what you think, or change it whatever works for you.
 
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