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Those Radio Shack Mini Amps ...

atmasphere said:
Schematics of the SA-175 don't seem to exist in any form on the web so I thought I'd supply it here.
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Blast said:
No, they do not. Thanks for that draw-up!
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+1 ..:thumbsup:
Much appreciated.
atmasphere said:
The SA-10, SA-100c and SA-101 use variants of this circuit. They usually do not included the output coupling cap in the loop, and often the cap used to kill buzz is tied to the output of the amp rather than the base of the top output device.
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Is the top output transistor in SA-175 a PNP? That would be another variation from other Tandy minis, which have the NPN device in that position.
 
Stuart Pedaso said:
+1 ..:thumbsup:
Much appreciated.

Is the top output transistor in SA-175 a PNP? That would be another variation from other Tandy minis, which have the NPN device in that position.
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Actually no- got the transistors backwards. I also put the 43K feedback resistor on the collector of the driver transistor rather than the base :rolleyes:
 
OH MAN! A thread after my own heart! I am a Rat Shack fan.....see my sig! Thanks for all the great info!:bowdown:
 
Been reading through this thread and many thanks to the informative comments from @atmasphere and others.

I have a SA-175C and would like to remove the loudness circuit. I think I read a cap and a resistor are all that’s needed.

Can anyone help with the cap and resistor values and procedure? I’m a complete novice.
 
It looks like it’s as simple as removing the cap and resistor that are encased in a clear plastic on each volume tap (left and right). Anyone done this? Do I have this correct?

It’s a nice sounding amp but the bass is just way too much.
 
I don’t know if anyone is paying attention to this thread but can share that I removed the cap and resistor, which I believe is the loudness circuit. It’s a .047uf green cap (mica?) and a resistor. In my 175-C, these were encased in a clear plastic sheathing.

There is still a 250pf ceramic cap tied to each channel on the pot. Anyone know what this is for?

This Realistic 175-C now seems more detailed, expressive, and punchy. Bass seems a little less and lot more room to dial in the bass tone control. Not noticing a significant increase in gain on the volume control. Will need more listening than the ten minutes for this assessment.

I may take to a friend of mine to consider the mods that @atmasphere graciously offered here. My understanding of what has been written is above my pay grade.

I’m specifically wondering if the bass can be tightened up. I have obviously heard better bass performance on other amplifiers but I knew that going in.

I purchased this amplifier recapped. It was recapped with a 2200uf main filter capacitor and two 1000uf capacitors, which I assume for DC blocking. Plenty willing to change these if it helps tighten the bass.

Overall, this is a great amplifier. Sound is similar to my Kenwood KA-2002. Very impressive on Klipschorns.

Love this forum…so much knowledge here!
 
Stuart Pedaso said:
... get a surprising amount of buzz in these forums. It's commonly understood they are lo-fi, entry level audio from a bygone era. Yet there seems to be a pervasive fascination for the little things.

View attachment 1243979

I pondered on this recently while watching my collection grow by a few new additions -- which is alarming enough to conduct a Usage-to-Hoarding ratio check.

My set includes an SA-101, two SA-150's, three SA-155's and four very humble SA-10's, with a smattering of TM-150 and TM-155 tuners. Most of these are either used in some capacity, or staged for a specific planned purpose.

Some examples:

Wifey feeds an SA-150 with audio from the wall mounted bedroom TV. She switches between either headphones or very-near-field speakers for late night sound that won't disturb the household. The amp is left on 24/7. One burned out recently. Took mere seconds to replace since I had a spare at hand.

One mini-amp resides on the workbench as a diagnostic and repair tool.

An SA-155 and TM-155 with some NOS RCA PRO-X33AV mini speakers will become my youngest grandson's first component stereo system when he turns 6 next month.

SA-10's are for a project that may warrant a new thread if successful. And if not, ... never happened.

So I'm not ready to check into a hoarders' rehab center just yet. But the situation is being closely monitored.

I've constructed a simple graphic timeline of Radio Shack's solid state mini stereo amplifiers. Helps me keep track of model chronology. Thought it might be worth sharing.

There are really two concurrent timelines from 1969 through 1994: small, budget-friendly models vs even smaller BOTL models. From 1995 only brand variants of SA-155 remain in the lineup:

View attachment 1533521

Some data still needs to be firmed up. Such as, what year did SA-102 go from discrete transistors to the LA4440 chip amp? And likewise for SA-10's transition to chip amps. Also, exact years SA-155 wore the "Radio Shack" brand is somewhat mysterious as catalogs were no longer published after 2002. At least model chronology is in the correct order for general reference.

So what say you, RS mini-amp aficionados? What's the appeal of these small wonders? Is it performance? Utility? Vintage cuteness? Or, on the flip side, are you filled with disgust and loathing for these wretched little urchins? Does apparent interest that percolates through these forums suggest some consensus? Or are we drawn -- or repulsed -- purely from our own diverse perspectives? I invite your comments.
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I'm using one of these little guys with a pair of SPEAKERLAB point ones with my computer with surprising results! I paid $4.00 for the SA-10 at a local thrift store and $10.00 for the point ones at a garage sale.I must say that I wouldn't call it "reference" quality sound,it's not too far off.This is in a "near field" situation mind you. Bass and sound stage location detail is very good...MUCH better than I would ever guess from Radio Shack's BOTL amp!
 
YTthedrummer said:
I'm using one of these little guys with a pair of SPEAKERLAB point ones with my computer with surprising results! I paid $4.00 for the SA-10 at a local thrift store and $10.00 for the point ones at a garage sale.I must say that I wouldn't call it "reference" quality sound,it's not too far off.This is in a "near field" situation mind you. Bass and sound stage location detail is very good...MUCH better than I would ever guess from Radio Shack's BOTL amp!
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I had one of the later silver model SA-10's. I used in in my garage for a short time. Years some years back an AK'r was looking for another like the one I had since his had died and he used it with the matching little tuner.
He liked the little setup, so I gave him my amp and sent it to him.
I had other amps and used one of them in my garage to replace it.
 
Kolner said:
It looks like it’s as simple as removing the cap and resistor that are encased in a clear plastic on each volume tap (left and right). Anyone done this? Do I have this correct?

It’s a nice sounding amp but the bass is just way too much.
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That's what I ran into as well. All you have to do is disconnect everything from the loudness tap and you're all set.

If you've not already done so, replace all the 1M resistors in the amp. When the amp was new they were known for failure. Any that have lasted this long are probably not at the correct value.
 
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