Hi - I have an amp that I made based on the "little gem" amplifier circuit (LM386-based). I want to try to run it through a speaker from an old AM radio, which is a reed-type speaker supposedly with an impedance of 550 ohms (though I might be misunderstanding the schematic). Is there any way to do this while getting a reasonable amount of volume out of the amp/speaker?
Thanks in advance for your help.
Little Gem Schematic: littlegem.html
Thanks in advance for your help.
Little Gem Schematic: littlegem.html
Interesting... and I might be way off the mark here but if the AM radio was a mains powered unit then the 'Reed' type speaker may be such high impedance because it is intended to be used without a matching transformer. In other words it could run off what would be a high impedance point like the anode of an output valve.
If so then I'm thinking that the high impedance means you will not get much useful volume from it on a low voltage amp such as the LM386.
Have you tried it just for fun?
If so then I'm thinking that the high impedance means you will not get much useful volume from it on a low voltage amp such as the LM386.
Have you tried it just for fun?
All you can do is try it. It is obviously designed for a low voltage amp (which I wasn't sure on).
Would anyone have any idea what the minimum impedance might be?
Would anyone have any idea what the minimum impedance might be?
Might not be the best sounding speaker. Instead of a voice coil that can push and pull this one mostly has a little tension on the rod pulling back on the middle of the cone.
Agreed - I'll be interested to see if it gives a cool lo-fi sound. Certainly not something I'd expect to sound objectively "good."
The point of G.E.'s reed speakers was that they were VERY efficient and would make decent sound on very small amplifiers.
I am sure you will get "some" sound. Enough to hear across the room.
FWIW: I have a reed in my ear. So do many stage musicians. The balanced armature (reed) earpiece is used in all good hearing-aids and most in-ear monitors. Yes, it has severe limitations compared to voice-coil drivers but within limits makes 5X to 10X the sound power per electrical milliwatt. OTOH it is fussy about alignment and may not have aged well.
https://www.knowles.com/subdepartment/dpt-ba-receivers/subdpt-hearing-instruments-receivers
https://www.knowles.com/subdepartme...sound-balanced-armature-receiver-and-speakers
https://knowles-cms.ae-admin.com/do...ry/wp03_science_of_premium_sound.pdf?sfvrsn=0
Well, I got no sound. I think the voltage output is just too small to move this thing. Would be interesting to try to make it work with a step-up transformer, but I don't have one lying around. Fun experiment anyway.
At least you tried 
You could try it across a bigger amp, perhaps with a series 5 to 10 ohm to protect the amp just in case the speaker was/went/is short circuit.
You could try it across a bigger amp, perhaps with a series 5 to 10 ohm to protect the amp just in case the speaker was/went/is short circuit.
Have you checked its Ohms?
Scratch it on a 1.5V battery (with clip leads). Steady 1.5V is silent (or smoke) but a tap-scratch should make "static".
