# 741 Op Amp Question

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#### BobaMosFet

Jan 1, 1970
0
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?

R

#### Richard Seriani

Jan 1, 1970
0
BobaMosFet said:
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

Good luck and have fun experimenting.

Richard Seriani, Sr.

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#### Eeyore

Jan 1, 1970
0
BobaMosFet said:
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?

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

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#### YD

Jan 1, 1970
0
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?

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

- YD.

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#### Phil Allison

Jan 1, 1970
0
"BobaMosFet"
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.

** Be a nice Sony electret mic built into that.

They make professional grade examples too - see the ECM-CS10.

http://www.ogormans.co.uk/micropho.htm

All these mics have an internal pre-amp, so there aint any 741s doing
magic.

........ Phil

Oct 21, 2006
1,325
let me see how about $1.00 for a amp stereo phones hearing spy made in china all packaged into a 3/4" by 1/4". i cannot buy the amp for that. C #### [email protected] Jan 1, 1970 0 Hello BobaMosFet, 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? Bell & Howell Sound Amplifier - Model #: 7667$20 usd

http://www.heartlandamerica.com/browse/item.asp?PIN=20023&DL=OVR1&#

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,

* * *
Christopher

Temecula CA.USA
http://www.oldtemecula.com

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