Author Topic: Old Radio Shack mini amp?  (Read 509 times)

ljudsystem

Old Radio Shack mini amp?
« on: May 16, 2018, 04:00:07 AM »
Apparently Roy Nichols used a "Radio shack mini amp" on several Merle Haggard songs from the 70's like Working Man Can't Get Nowhere Today, Running Kind and Rainbow Stew.

It's a pretty cool sound. Tons of fuzz!  :D

Anybody know what kind of amp that is? I've learned from various forums that it was a cigarette pack sized amp and speaker that ran on a single 9v battery. I'm from Sweden so I've never been in a Radio Shack store.

I'm thinking it might make a good altoids tin project.

GibsonGM

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Re: Old Radio Shack mini amp?
« Reply #1 on: May 16, 2018, 05:07:02 AM »
I wasn't able to easily find a schematic for it, but I bet it's very similar to the Little Gem...LM386-based amp....I don't recall anything very special about them other than size.  With the right speaker, it might sound nice for recording; something different, a tiny amp turned way up.   
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ljudsystem

Re: Old Radio Shack mini amp?
« Reply #2 on: May 16, 2018, 05:56:39 AM »
I think it might be the Archer mini amplifier/speaker. This page has some gut shots:

http://www.hearingaidmuseum.com/gallery/Miscellaneous/Assistive%20Devices/Other%20Makes/info/archerminiamp.htm

I found two schematics floating around the web. Both of them single transistor and 386 design.








GibsonGM

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Re: Old Radio Shack mini amp?
« Reply #3 on: May 16, 2018, 06:03:23 AM »
I believe that's it.   Little transistor preamp up front, basic 386.  Have a go at it!
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thermionix

Re: Old Radio Shack mini amp?
« Reply #4 on: May 16, 2018, 06:13:08 AM »


That's a weird schematic.  Decimal points seem to have been replaced with spaces.  Not sure, but I think the electros list voltage first, then uF.

But yeah that's surely it.  Archer is (was) a Radio Shack brand, along with Realistic.
FDH

ljudsystem

Re: Old Radio Shack mini amp?
« Reply #5 on: May 16, 2018, 06:53:53 AM »
Yeah, I know. I've never seen capacitor values written like that before, but your probably right: voltage first then uF.

thnik I'm gonna try it without a speaker first, as a fuzz/preamp pedal.

GGBB

Re: Old Radio Shack mini amp?
« Reply #6 on: May 16, 2018, 07:38:29 AM »

GibsonGM

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Re: Old Radio Shack mini amp?
« Reply #7 on: May 16, 2018, 07:44:46 AM »
Yeah, I know. I've never seen capacitor values written like that before, but your probably right: voltage first then uF.

thnik I'm gonna try it without a speaker first, as a fuzz/preamp pedal.

I'd go off the bottom schematic you posted, it looks neater and the values aren't confusing.  If you want to try it as a 'fuzz' (booster), keep C9, of course, to block DC...these were a very popular little portable multi-purpose amp back then, and could have a lot of uses for troubleshooting with an audio probe, etc.
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ljudsystem

Re: Old Radio Shack mini amp?
« Reply #8 on: May 16, 2018, 07:56:03 AM »
GGBB: Thanks! The Realistic Micro Sonic looks cool but I don't have any transformers.

GibsonGM: Yeah, I'll use that one. From what I can gather it's an older version.

bluebunny

Re: Old Radio Shack mini amp?
« Reply #9 on: May 16, 2018, 08:08:17 AM »
There's one of these up for sale on eBay.  A snip at a mere $158.88!   :icon_eek:
Ohm's Law - much like Coles Law, but with less cabbage...

GibsonGM

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Re: Old Radio Shack mini amp?
« Reply #10 on: May 16, 2018, 08:33:13 AM »
There's one of these up for sale on eBay.  A snip at a mere $158.88!   :icon_eek:

Oh, but it's "vintage"...an "antique" now!  No way WE could ever reproduce something like that for $1.60 in parts!  Those caps - they're MAGIC!!  :)
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ljudsystem

Re: Old Radio Shack mini amp?
« Reply #11 on: May 16, 2018, 10:24:34 AM »
Sounds like a deal :icon_lol: ...especially when there's another guy on ebay selling a nos archer amp for 29 bucks.

Paul Marossy

Re: Old Radio Shack mini amp?
« Reply #12 on: May 16, 2018, 11:07:44 AM »
I have the guts of one from one that was given to me.... threw away the original case and rehoused it. It uses an LM386.

duck_arse

Re: Old Radio Shack mini amp?
« Reply #13 on: May 16, 2018, 11:23:23 AM »
I think it might be the Archer mini amplifier/speaker. This page has some gut shots:

http://www.hearingaidmuseum.com/gallery/Miscellaneous/Assistive%20Devices/Other%20Makes/info/archerminiamp.htm

I found two schematics floating around the web. Both of them single transistor and 386 design.









the pot at the input of these two circuits is 5k. might be a bit too low for guit input.
now you can get vintage spanners - who knew?

GibsonGM

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Re: Old Radio Shack mini amp?
« Reply #14 on: May 16, 2018, 12:13:08 PM »
Good eye, Stephen.
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thermionix

Re: Old Radio Shack mini amp?
« Reply #15 on: May 16, 2018, 07:01:41 PM »
Or maybe this one (the predecessor): https://www.radiomuseum.org/r/radioshack_realistic_microsonic_speaker_amplifier_cat_no.html.

Oh man that's hilarious looking.  And quite compact for 200 Megawatts!
FDH

ljudsystem

Re: Old Radio Shack mini amp?
« Reply #16 on: May 17, 2018, 02:34:50 AM »
Duck arse: the 5k pot sets the input impedance?

duck_arse

Re: Old Radio Shack mini amp?
« Reply #17 on: May 17, 2018, 10:20:47 AM »
arrgh! an impedance question. where's antonis when we need him?

the 5k pot will connect across (load) the guitar, if that is what you inplug. the guitar will see 5k when it would really like 500k for unrestricting highs. as it is connected as a volume control with respect to the guit, you should be able to replace it with pretty much any value you like. start with 100k, like many a fuzz pedal pregain pot.

I think. I'll stand for correction, tho.
now you can get vintage spanners - who knew?

GibsonGM

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Re: Old Radio Shack mini amp?
« Reply #18 on: May 17, 2018, 10:26:32 AM »
I think I read that the input itself, after the pot, is like 50k....obviously 10x lower input z than is ideal for guitar, but still  "ok"..some older effects have input z in that range.   

I thought the 5k pot would be in parallel with the 50k input Z of the circuit?   That gives us like 4.5k....WOAH, that is low.

Then, if you turn the axe or pot down, it gets worse...100k pot would give us 33k, a much better figure, at least as I calculate it (hey, I could be wrong, it's happened before...).   
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MaxPower

Re: Old Radio Shack mini amp?
« Reply #19 on: May 17, 2018, 02:34:37 PM »
Or maybe this one (the predecessor): https://www.radiomuseum.org/r/radioshack_realistic_microsonic_speaker_amplifier_cat_no.html.

Oh man that's hilarious looking.  And quite compact for 200 Megawatts!

Ah, if only it said powered by 9kv battery. They'd be flying off the shelves!
What lies behind us and what lies before us are tiny matters, compared to what lies within us - Emerson