Booster amp

Thread Starter

Icanmakeit67

Joined Sep 23, 2018
97
I have a toy with a small sound effect that is quite weak. It is a “secret circuit” sealed. It is powered by a 9vdc battery and runs a 1.5” .5 watt 16 ohm speaker. Is there possibly a small simple circuit that could boost the signal at the speaker so I can replace the 1.5” diameter speaker with maybe a 3” speaker without harming the secret sealed source?
Thank You for any ideas….
 

Thread Starter

Icanmakeit67

Joined Sep 23, 2018
97
For a simple power boost you can try LM386 audio amplifier.
Ok, I thought the output of the toys “secret sealed” black box might not be compatible with just anything/amp. Would you have anything in the way of a schematic different from the manufacturer spec sheet?
Again Thanks
 

BobTPH

Joined Jun 5, 2013
8,967
The signal going to the speaker is always a varying voltage. The only compatibility issue is the level of that voltage.

The speaker voltage will likely be too high to give directly to the input of an LM386. It will need to be reduced by a simple voltage divider or a potentiometer.
 

Thread Starter

Icanmakeit67

Joined Sep 23, 2018
97
The signal going to the speaker is always a varying voltage. The only compatibility issue is the level of that voltage.

The speaker voltage will likely be too high to give directly to the input of an LM386. It will need to be reduced by a simple voltage divider or a potentiometer.
I contacted the toy manufacturer and was told the 1.4” 16ohm speaker could be replaced by any of three other speakers they sell of which I’d pick a 3”. They say the volume would be significantly louder. I’m wondering without a volume control is this a possible?
 

BobTPH

Joined Jun 5, 2013
8,967
Yes, it is possible that changing the speaker would give more volume.

If the speaker is not in an enclosure, putting it in one will also dramatically increase the volume, particularly at lower frequencies.

You can use any 16Ω speaker, there is nothing special about ones from the device’s manufacturer. Using an 8Ω speaker might also increase the output, or might not if the amp cannot provide any more current.
 

Thread Starter

Icanmakeit67

Joined Sep 23, 2018
97
Yes, it is possible that changing the speaker would give more volume.

If the speaker is not in an enclosure, putting it in one will also dramatically increase the volume, particularly at lower frequencies.

You can use any 16Ω speaker, there is nothing special about ones from the device’s manufacturer. Using an 8Ω speaker might also increase the output, or might not if the amp cannot provide any more current.
Thank you. This black box circuit sealed inside a black resin substance gives me no clues…..
 

Audioguru again

Joined Oct 21, 2019
6,692
The tiny speaker is rated for a maximum power of only 0.5W.
0.5W is fairly loud so maybe the signal level is low or the battery voltage is low?

We need the signal voltage and the battery voltage when playing to be measured by you.
We also need to know how much "more volume" you need.

With a 9V supply, an LM386 power amplifier maximum undistorted output power into a 16 ohms speaker is only 0.4W.
The power into an 8 ohms speaker is 0.56W.

A 9V battery will soon drop to 6V when the maximum powers above will be only 0.14W into 16 ohms or 0.25W.

10 times the power sounds twice as loud. Then you need an amplifier that produces much more power and/or uses much more battery voltage than only 9V.

Most suitable amplifiers are modern, stereo or quad and are in tiny packages that are difficult for you to solder.
 

Thread Starter

Icanmakeit67

Joined Sep 23, 2018
97
The tiny speaker is rated for a maximum power of only 0.5W.
0.5W is fairly loud so maybe the signal level is low or the battery voltage is low?

We need the signal voltage and the battery voltage when playing to be measured by you.
We also need to know how much "more volume" you need.

With a 9V supply, an LM386 power amplifier maximum undistorted output power into a 16 ohms speaker is only 0.4W.
The power into an 8 ohms speaker is 0.56W.

A 9V battery will soon drop to 6V when the maximum powers above will be only 0.14W into 16 ohms or 0.25W.

10 times the power sounds twice as loud. Then you need an amplifier that produces much more power and/or uses much more battery voltage than only 9V.

Most suitable amplifiers are modern, stereo or quad and are in tiny packages that are difficult for you to solder.
Yeah ok. The power to the toy is a 9 v battery. What ever I use if possible will also be the 9v battery. The tiny sealed amp is a siren but it’s really weak as to volume and I’d like to increase it. There is room for a 3” speaker to replace the the 1.4” original. I can measure the out put to the speaker when the siren is on and reply here shortly. Thank You
 

AnalogKid

Joined Aug 1, 2013
11,045
1. There is a chance that the "audio" signal out of the device is class-D. That is, a pulse-width modulated squarewave. This is not a big problem for an external amp, usually requiring nothing more than 1 extra capacitor.

2. All other things being equal (although they never are), a larger speaker is less efficient because a) the cone is larger, requiring more energy to move it; and b) the cone is in contact with and moving more air, requiring more energy to move it. In fact, cheap very small speakers often are pretty inefficient, so a small speaker size increase might get you more volume.

3. There is an amplifier configuration called Bridge-Tied Load (BTL). This uses two amplifiers for one mono channel. The speaker is connected between the two amp outputs. The two amps get the same signal input, but one of them is inverting. This effectively doubles the voltage across the speaker, for 4x the signal power from the same battery. A popular part for this is the TDA2822. Page 3 has the schematic.

https://r.search.yahoo.com/_ylt=Awr...822d.pdf/RK=2/RS=._Ltq1M0KLqxFgJwXW_7czpZpS0-
ak
 

Audioguru again

Joined Oct 21, 2019
6,692
We do not know how much power he has now "really weak" and we do not know how much power "more volume" he wants.
It is for a siren so low distortion is not needed then maybe 3V peaks of a squarewave into an 8 ohm speaker might be loud enough and kill the little 9V battery quickly.
 

Thread Starter

Icanmakeit67

Joined Sep 23, 2018
97
That is not what I wrote. This is what I wrote (emphasis new):



To the TS: There are other "stereo" low power amplifiers made by SGS, National Semiconductor, and Maxim. Or, I can just send you a couple.

ak
No expe with audio circuits so all you guy helping is very kind. I do want to try something
 

MisterBill2

Joined Jan 23, 2018
18,519
Another option, depending on how much distortion can be accepted, is to add a "class B"transformer coupled output stage, driven by the present output feeding the primary of the driver transformer. The secondary feeds the bases of the output stage, which is biased close to cutoff with no signal. Then with a signal a few watts can be delivered via a collector to collector output transformer. THAT should drive a 3 or 5 inch speaker quite well.
 
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