I used to have a Sony cassette recorder in the early 80s that if you wore headphones and pressed record, you could literally here a pin drop in the room. I took this apart back then and the circuit for this used a 741 op amp chip. I have some of these and have found some schematics and put them together on my breadboard, but none of them have the gain that the cassette recorder had. Does anyone have a schematic that will produce this high gain?
There is more to answering your request than simply providing "a schematic that will produce this high gain".
How high a gain are you trying to achieve? What are your input and output devices and what are their characteristics? What supply voltages are you using?
You are likely needing different circuits for input and output, and they may not both be op-amp circuits.
To get you started, try a Google search on "op-amp tutorial". There are several, including some specifically for the 741. You might even be able to find something about frequency conversion (or, at least. frequency-to-voltage and voltage-to-frequency conversion) to answer your other question. While you are at it, get a copy of the 741 datasheet, if you don't already have it.
Good luck and have fun experimenting.
Richard Seriani, Sr.
I think your perception of it being so quiet that you could "hear a pin drop" must have been optimistic.
741 op-amps are horribly noisy for mic preamp stages. There's far far better.Let's start with what kind of mic you want to use. Let's have its source impedance, is it balanced or unbalanced, moving coil, capacitor or electret etc.... Does it need phantom power ?
Graham
Late at night, by candle light, BobaMosFet penned this immortal opus:
The 741 can't have been the only active part in it, there must have been a lot of other stuff there. If all you want is a high gain phone amp with mic input there are oodles of schems on the net, do a search and take your pick.
- YD.
-- Remove HAT if replying by mail.
"BobaMosFet"
** Be a nice Sony electret mic built into that.They make professional grade examples too - see the ECM-CS10.
All these mics have an internal pre-amp, so there aint any 741s doing magic.
....... Phil
Bell & Howell Sound Amplifier - Model #: 7667 $20 usd
These do work good in the forest and ghost hunting. They have a couple of other models on that page.
I bought a toy Spy Tek listener with two ear buds in the toy section of Thrifty Drug store. Also check our Walmart if you are in the states. For $5 you can get a clear plastic belt mounted enclosure and circuit board with one button battery.
Good luck,
Temecula CA.USA
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