Realistic Minimus-7 Measurements

[Gringoaudio1]

I seem to be having a hard time finding a simple circuit diagram of the improved crossover for the Minimus7. Not sure why. I find all sorts of discussion but no simple
image.

 

[restorer-john]

I seem to be having a hard time finding a simple circuit diagram of the improved crossover for the Minimus7. Not sure why. I find all sorts of discussion but no simple
image.

Have you heard of Google? It's quite a good search engine. Much better than Ask Jeeves, the Webcrawler or Alta Vista. And get a new modem, 14.4k won't cut it anymore.

Result 2:

How to Build The Minimus 7 PZ-2.1 Crossover

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...

audiokarma.org

 

[mhardy6647]

Have you heard of Google? It's quite a good search engine. Much better than Ask Jeeves, the Webcrawler or Alta Vista. And get a new modem, 14.4k won't cut it anymore.

I still kinda miss Dogpile...

 

[DWPress]

I still have a pair I've had around since the 80's and they're even in use outdoors on a small deck. They're mounted right up where the sidewall meets the eves and get a nice little boost from the wall reinforcement. Sometimes I'm amazed how well they sound 90 degrees off axis at low volumes. Had a pair of the wood ones too but they didn't survive the outdoors as well.

 

[coonmanx]

 

[Gringoaudio1]

Thanks I found that hifi haven link as well. And most of the image links are no longer valid on anything I found including the most of the AudioKarma pages on the topic. Have got enough now with your help and further Googling.

 

[MAB]

@MAB For reference, here's impedance sweeps of the two new old stock speakers from the photo above:

S/N 0492:
View attachment 400185

S/N 3375:
View attachment 400186

I digitize the S/N 0402 sample and compared to one of mine:

Pretty good correlation for speakers 2883 units apart and produced 9 months apart. (March 1988 vs December 1988)

Mine are model 40-2030C, compared to your 2030A versions. Across model runs the matching is remarkable. And mine are definitely not NOS.

 

[restorer-john]

I digitize the S/N 0402 sample and compared to one of mine:
View attachment 401172


Mine are model 40-2030C, compared to your 2030A versions. Across model runs the matching is remarkable. And mine are definitely not NOS.

Amazing. Especially since yours have been outside for 30 years.

The little speaker that could.

 

[EJ3]

You're most likely right on the 4558 vs 5532.

The thing is sitting there, staring at me, so I might have a bit of poke around and see what I can do. I've got a second unit down at my father's place. I might test them both to get baseline numbers and see if my recollections are valid in 2024. I'm pretty sure I reverted one of them to double insulated decades ago due to hum. It's been a long time...

Plenty of RS (Tandy's) equalizers had the same problem- they earthed them poorly (random screw to the chassis) for Australia and created hum loop monsters from designs that were not made with a star ground/earth design or even a consideration of issues that would crop up when the device was actually inserted in a tape/pre in/out loop with other earthed gear.

In the USA, I never had any hum problems with any Tandy/Radio Shack gear (from EQ's to the integrated amps & tuners).
And, caught on sale, they were usually relatively good for the price.

 

[mhardy6647]

In the USA, I never had any hum problems with any Tandy/Radio Shack gear (from EQ's to the integrated amps & tuners).
And, caught on sale, they were usually relatively good for the price.

That was the trick with R/S. They had monthly sales flyers. The minimus 7 (and its descendants), e.g., would be on sale once or twice a year at half-price, give or take. At half price, they were reasonable values. Not so much at full price ($79 @, give or take).
One of the two pairs here* was so acquired.

The other pair here is a much earlier one acquired as a close out from the R/S store in Acton, MA for $19 @.
Their only flaw -- both are missing their grille badges, for whatever reason. I suspect they were floor models that had gotten chucked into a corner and sat for a long time until discovered during a back room clean-out.

______________
* Actually a pair of the later, ported "Optimus PRO 7" morph. They are also, technically, not here any more, but they are still in the family. They were given to our daughter in her college days (ahem, turn of the century ) and, other than a visit here when they were moving house last year, have been in her family room with their TV since she got married (over) 15 years ago. [N.B. edited for accuracy! sorry...]

source: https://www.radioshackcatalogs.com/flipbook/1994_radioshack_catalog.html

 

[mhardy6647]

Having noticed that the 1994 Optimus PRO 7 "specification" references a frequency "range" of 100 to 20k Hz , I thought it would be amusing to look back at the original, sealed box version as introduced in 1978.
From above:

1994: "Increased Bass" -- Response 100-20,000 Hz

source: https://www.radioshackcatalogs.com/flipbook/1978_radioshack_catalog.html
1978: "50 Hz bass". umm-hmm.

Some fuzzy maths.

 

[Power Pop 23]

Having noticed that the 1994 Optimus PRO 7 "specification" references a frequency "range" of 100 to 20k Hz , I thought it would be amusing to look back at the original, sealed box version as introduced in 1978.
From above:
View attachment 401240
1994: "Increased Bass" -- Response 100-20,000 Hz


View attachment 401238
source: https://www.radioshackcatalogs.com/flipbook/1978_radioshack_catalog.html
1978: "50 Hz bass". umm-hmm.

Some fuzzy maths.

I would wait for Radio Shack to hold a half-price sale to pounce on select gear with a decent review. I am impressed the list price for the Minimus-7/Optimus Pro 7 increased by only 20 percent over 16 years.

 

[EJ3]

Having noticed that the 1994 Optimus PRO 7 "specification" references a frequency "range" of 100 to 20k Hz , I thought it would be amusing to look back at the original, sealed box version as introduced in 1978.
From above:
View attachment 401240
1994: "Increased Bass" -- Response 100-20,000 Hz


View attachment 401238
source: https://www.radioshackcatalogs.com/flipbook/1978_radioshack_catalog.html
1978: "50 Hz bass". umm-hmm.

Some fuzzy maths.

Maybe that is the result of the "New Math" that they had been trying to teach in grade school in the late "60's".
That "New Math" might even be why I failed algebra when I was a High School sophomore but was able to use trigonometry at my job in real life (during my Senior year of high school).
Having learned to do things a bit differently in mathematics while in Austria (from my Austrian mother [to get to the same answer]), the teachers weren't happy with the way I showed my work when I was asked to do so. "You got the answer right but that's not the way you do it" was a typical response. And then they would attempt to teach (once again) me the "proper" way to do it, which only confused me.
In school, it also did not help to have undiagnosed (at the time) dyslexia (which seemed to affect me much more when dealing with numbers than with words).
But at work, I could visualize how something worked or needed to work (whether it was a plumbing run used in the building of apartments or the need to phase an array of antennas so that the power went more in a certain direction).
To put this back on track, I always used mine with a Radio Shack sub-woofer, which I believe was crossed over somewhere between 150-200 Hz.
The earlier one was a (walnut?) wood veneer that kinda' matched the wood Minimus 7's, the later sub-woofer was a much larger black veneer (oak?). Both were down firing 12" ones. I do not remember if the earlier one was ported (gave it to a friend) but the black ones are supposedly tuned to 29 Hz. I have a pair that I have modified that I currently use with a Pioneer car audio competition dual 4 ohm voice coil running in a 4 ohm circuit in each one.
The FR is 20-80Hz, and they are crossed over at 60 LF & 80HF. (with my Dahlquist M-905's handling above that.

 

[beagleman]

Maybe that is the result of the "New Math" that they had been trying to teach in grade school in the late "60's".
That "New Math" might even be why I failed algebra when I was a High School sophomore but was able to use trigonometry at my job in real life (during my Senior year of high school).
Having learned to do things a bit differently in mathematics while in Austria (from my Austrian mother [to get to the same answer]), the teachers weren't happy with the way I showed my work when I was asked to do so. "You got the answer right but that's not the way you do it" was a typical response. And then they would attempt to teach (once again) me the "proper" way to do it, which only confused me.
In school, it also did not help to have undiagnosed (at the time) dyslexia (which seemed to affect me much more when dealing with numbers than with words).
But at work, I could visualize how something worked or needed to work (whether it was a plumbing run used in the building of apartments or the need to phase an array of antennas so that the power went more in a certain direction).
To put this back on track, I always used mine with a Radio Shack sub-woofer, which I believe was crossed over somewhere between 150-200 Hz.
The earlier one was a (walnut?) wood veneer that kinda' matched the wood Minimus 7's, the later sub-woofer was a much larger black veneer (oak?). Both were down firing 12" ones. I do not remember if the earlier one was ported (gave it to a friend) but the black ones are supposedly tuned to 29 Hz. I have a pair that I have modified that I currently use with a Pioneer car audio competition dual 4 ohm voice coil running in a 4 ohm circuit in each one.
The FR is 20-80Hz, and they are crossed over at 60 LF & 80HF. (with my Dahlquist M-905's handling above that.

I owned that Radio Shack sub for several years. 12" dual voice coil. The real crossover frequency was closer to about 200 or so, but OMG that was the most boomy bass sub/low frequency speaker I have EVER heard.
The box was ported and obviously too small for the high Qts sub they used.

If was fun to use, but had a huge huge peak in the 50-90hz range, that added huge bass to just about any music, but often left it almost unbearable at times!

 

[EJ3]

I owned that Radio Shack sub for several years. 12" dual voice coil. The real crossover frequency was closer to about 200 or so, but OMG that was the most boomy bass sub/low frequency speaker I have EVER heard.
The box was ported and obviously too small for the high Qts sub they used.

If was fun to use, but had a huge huge peak in the 50-90hz range, that added huge bass to just about any music, but often left it almost unbearable at times!

As to the Minimus 7's, I still have several and use a walnut pair in my mother's (she is 90) home system with an ADVENT 300 receiver (she only plays LP's of listens to the radio.
Radio Shack made 2 different subs, a walnut one and later on, a substantially larger black one that was tuned to 29 HZ.
I had both: the later ones (I had/have 2 of them, I pulled the woofers out and replaced them (many years ago) with a pair of 12" Pioneer car audio competition speakers (I do not remember the model) but had dual 4 OHM voice coils (which I converted to a single 4 ohm circuit) an FR of 20-80HZ, 96 Db for 1 watt and could handle 1800 watts each.
I run a Low Pass filter at 60Hz & a High pass filter at 70Hz.
I run each one with a bridged mono NAD 2200 (producing over 1000 watts each).
With EQ, they are just fine.

MOD NOTICE- I HAVE REMOVED A SWATHE OF OFF TOPIC MEASUREMENTS FOR THE NAD AMP

 

[EJ3]

Still has to do with Radio Shack Minimus 7's (why I bought the Radio Schack subs to begin with, as that is one way that Radio Shack recommended them).
Then: what I eventually did with the Minimus 7's & the the Subs that Radio Shack paired with them.
Now, all this Minimus 7 information makes me want to redo the crossovers in my six pair of these things (two pair of which are the walnut ones)
I do not think that I went off topic at all.
I guess that I come from a time and place where we weave stories that are loosely connected and you do not.
Hopefully: we can just respectfully agree to disagree.

 

[Fahzz]

So i should have kept my late father's Minimus('s)???

 

[restorer-john]

So i should have kept my late father's Minimus('s)?

You can't keep everything in life. Minimus 7s are cute, but you can do a whole lot better in 2024.

(and that's coming from someone with probably ~10 pairs)

 

[beagleman]

So i should have kept my late father's Minimus('s)???

The "Idea" and the looks of them are honestly better than the reality of them.

They are very common, and I think today mostly nostalgia driven. Not horrible but just not as good as the memories.

 

[Fahzz]

I definitely should have grabbed his vintage Sansui receiver and the Infinity tower speakers.