# Increase volume on store-bought prop...



## RowlandHarris (Sep 11, 2009)

I'm trying to amplify the volume of purchased props. In the past, I've hooked them up to amplifiers (module amps and computer amps). While that works great, I'd like to see if there's a simpler way. 

I just tried two different speakers on a new store-bought prop. I tried a small one I had sitting around, and a big one used for a stereo (both were 8 ohm speakers). Of course, the big sounds better but it's not much louder. 

Has anyone tried to change the speaker impedance, e.g., replacing the 8 ohm speaker with a 4 or 2 ohm speaker? I know that might tax the on-board amp, but since it's not on for long, it may work.

If you have an opinion, let me know before I buy a 4 ohm speaker to try... Thanks!


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## David_AVD (Nov 9, 2012)

I doubt decreasing the speaker's impedance would have any benefit. Any gains from the reduced impedance would likely be countered by extra losses in the output stage of such a simple circuit. I thing the external amp is the only real option. You can get bare amp modules for a few dollars off eBay.


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## DarkOne (Oct 16, 2012)

I second the amp. Changing the impedance of the speaker could damage the circuit, depending on how it was engineered.


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## RowlandHarris (Sep 11, 2009)

Oh fine! Just shatter my hopes for a 5 minute upgrade!!!

So, this morning I pulled out an amp module
https://smile.amazon.com/gp/product/B00C4MT274/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
and hooked it up to my phone (I used only 6V battery power). Very loud and very clear sound - quite amazing for $7! Then I hooked it directly up to my prop. The sound was mediocre with more hiss than when I hooked the speaker up directly, and, using my phone's sound level meter, the speaker alone was slightly better than with the amp in between!

This afternoon, I'll try to put a resistive voltage divider at the input to the amp and see if that improves the quality and volume (I may be overdriving the amp). I also have another amp:
http://www.dx.com/p/tda2030-audio-amplifier-module-404662#.W2h9SNIzphE
that I'll try. I want to use battery power so I don't have to run yet another extension cord...


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## David_AVD (Nov 9, 2012)

The speaker output of the prop could be designed to run into a load. If you remove the speaker (and don't add a resistor to take its place) its operation could change dramatically.


The other thing to watch out for is that the speaker -ve is likely NOT to be connected to the battery -ve. In fact, the speaker +ve may even be connected to the battery +ve ! This can cause all sort of magic smoke to escape if you tie the -ve of the prop to the -ve of the amplifier.


Using a small audio transformer to couple the output of the prop to the input of the amplifier is the safest way to go. I've done this to record the prop audio into the aux input of a PC and it worked very well. You can pick up 600 Ohm transformers on eBay for less than $1 each. I'm sure I posted about this in another thread in the last year or two.


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## RowlandHarris (Sep 11, 2009)

David_AVD: I'm getting some audio transformers. Is there a reason that you recommend a 600 ohm? Shouldn't the output of the amplifier be matched to the speaker impedance, e.g., 8 ohm?


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## David_AVD (Nov 9, 2012)

You don't need to match the impedance in an application like this. You could use a lower one, but they don't tend to come in 1:1 ratios at 8 Ohms whereas the 600 Ohm ones are super cheap and available.


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## Batbuddy (Sep 3, 2014)

Your prop is outputting a speaker level Signal most likely and if you input that into an amp of any kind you are highly likely to over drive the signal and get distortion and clipping of the signal. You really need to attenuate the signal before sending it into an amp


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