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Guitar Amp Modification

N_Hound

Jun 5, 2017
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Hey guys,

I have an 'Orange Micro Crush', and I had fun with it, but it seems the speaker blew. So, I was looking online to possibly place the speaker for a better one as a project. The amplifier runs off a 9v battery, and the speaker has an impedance of 8 ohms and it states the 'Power' is 2 Watts RMS. That's about all I know. I came across a few 3-4 inch speakers that seem to be an improvement. I was just curious if it would work since most the other speakers I found have a 20-30 Watt RMS. I'm not sure if that's too much of a power demand for the 9v battery. If I could get any insight on this, it would be really appreciated.
 

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davenn

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speakers I found have a 20-30 Watt RMS. I'm not sure if that's too much of a power demand for the 9v battery.

the power rating of the speaker is kinda irrelevant
it will still work, the 2 W amp will just give it 2 watts
there is no power demand going on :)

Dave
 

hevans1944

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Jun 21, 2012
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The image you uploaded shows the device runs from a 9V to 12 V "wall wart" power supply capable of supplying up to 500 mA, and that the amplifier provides up to 3 watts RMS output power over the stated range of input voltages. That current and voltage works out to 4.5 watts for 9 V input, and 6 watts for 12 V input.

Either way, 500 mA is waaay beyond the capacity of a typical "9 V battery." See this Google result page. Use a wall wart to power up this puppy. Note the center post is negative while the barrel shell is positive. Check wall-wart polarity before you plug it in and apply power to your micro Crush guitar amplifier.

The speaker "power rating" is what a speaker can safely handle without damage. If the replacement speaker has the same 8 ohm impedance as the original, then the power applied to it by the guitar amplifier will be the same. The maximum power sent to your speaker will be limited by the power output capability of the guitar amplifier, NOT the power handling capability of whatever 8 ohm speaker you connect to it. However, a speaker rated for a maximum power of 20-30 watts RMS may not be as efficient in converting electrical power to audible sound. Try to match a replacement speaker to the maximum power capability of the original speaker, about 3 - 4 watts.
 

N_Hound

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I know it can use a wall power supply, but i'd like to use a 9 volt battery so it can be mobile. So, if I use the speaker with a 20 watt RMS, it might not be as loud. If I use a speaker with a 4 ohm impedance, how would that affect the sound/volume?
Thanks for all of the help!
 

hevans1944

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Jun 21, 2012
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If you want to "be mobile" consider using a 12 V sealed lead-acid battery. These are popular for use in emergency exit lights. It should run for at least an hour before requiring a re-charge, depending on battery size. Of course you will need a lead-acid battery charger, so I don't know how that affects mobility. You could also consider wiring six or eight D-size alkaline cells in series, but that gets pretty expensive.

The amplifier is designed to drive the 8 ohm speaker shown in your image. It may not provide full output power when driving a lower impedance, such a 4 ohm speaker, but it probably won't hurt it either. Battery life is going to be very poor if you consistently drive this guitar amplifier to its full rated output. Consider switching to an acoustic guitar and ditching the amplifier. This will force your audience to be quieter and to pay close attention to your playing.
 

davenn

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s
but i'd like to use a 9 volt battery so it can be mobile.

the small 9V batteries are only for very small loads. you would be lucky to get 5 minutes out of it
they just don't have the current capacity

hevan1944 said a 12V battery :) just to expand on that......
get yourself a 7.2Ah 12V sealed lead acid battery and use a buck converter to drop the 12V to 9V
with the minimum of loss
there's a zillion DC-DC buck converters on ebay for a few $$ each
 

hevans1944

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A 12 V SLA will work "as is" since the guitar amp has a supply voltage range of 9 V to 12 V according to OP's image.
 

davenn

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A 12 V SLA will work "as is" since the guitar amp has a supply voltage range of 9 V to 12 V according to OP's image.

I didn't look too close at the image haha
was going by his 9V requirement comment
 

Audioguru

Sep 24, 2016
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An ordinary single-ended amplifier powered from 12V produces an output of about 1.5W into 8 ohms at fairly low distortion.
If the volume is turned up too high then the horribly distorted squarewaves produce 3W. The cheap little 2W speaker was doomed. A 3" or 4" cheap little speaker is used in a cheap clock radio. My computer speakers use high quality 3" speakers rated at 5W.

Powered with a new 9V battery the output of your amplifier is about 0.88W and is 0.3W when the battery voltage has dropped to 6V.
 
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