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Old 14th October 2012, 02:22 AM   #41
sreten is offline sreten  United Kingdom
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Hi,

Shown is your amplifier redrawn.

As it stands it has a DC current through the loudspeaker, not good.

The DC current depends on R1 and transistor Beta and is temperature dependent, not good.

Added is how to measure it and how to AC couple the speaker.

rgds, sreten.
Attached Images
File Type: jpg AUDIO AMPLIFIER CIRCUIT REDRAWN.JPG (14.9 KB, 207 views)
File Type: jpg AUDIO AMPLIFIER CIRCUIT Measure.JPG (17.9 KB, 204 views)
File Type: jpg AUDIO AMPLIFIER CIRCUIT AC Coupled.JPG (25.7 KB, 203 views)
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Last edited by sreten; 14th October 2012 at 02:49 AM.
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Old 14th October 2012, 03:01 AM   #42
sreten is offline sreten  United Kingdom
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Hi,

Here is a 5V amplifier schematic to play with :

Click the image to open in full size.

Not that I'm saying its a good circuit, it isn't.

rgds, sreten.

12V supply and a 4 ohm driver cant do more than about 4 watts.
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Last edited by sreten; 14th October 2012 at 03:21 AM.
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Old 14th October 2012, 07:41 AM   #43
Mooly is offline Mooly  United Kingdom
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Using more than one transistor has to be the way forward now. You have taken the single transistor design as far as it can go.

Read, learn and experiment.
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Old 14th October 2012, 10:32 AM   #44
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by realflow100 View Post
I'm still confused .................. I hooked up the 12 volt power supply and it bumps my subwoofer showing at least half inch excursion it's insane everything in my house is vibrating like crazy
it's showing what looks like at LEAST 25-55 watts!!.........r...
start with some simple analysis of what is happening.
If the available supply is 12Vdc, then the maximum AC voltage available to the load is +6Vk to -6Vpk. This is normally written as 12Vpp.
That 12Vpp is roughly equivalent to 4Vac. (12Vpp/2 = 6Vpk, 6Vpk/Sqrt[2] ~4.2Vac)

The maximum power, if your amplifier can actually deliver 4Vac, into your 8ohms speaker would be Pmax = Vac^2 / Rload = 4*4 / 8 = 2W.

Note, this is no where near your estimate of
Quote:
at LEAST 25-55 watts.
Learn about what you are doing instead of grabbing at any silly notion that comes into mind.
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Last edited by AndrewT; 14th October 2012 at 10:38 AM.
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Old 14th October 2012, 10:36 AM   #45
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That last statement is pretty good advice IMO.

But hey, he may have a ways to go with the engineering stuff but he's got the marketing down pat.
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Old 14th October 2012, 03:00 PM   #46
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wow... 4 watts pumping a 4ohm 12 inch 175 watt rms 500 watt max subwoofer.... at half an inch excursion?
yes my subwoofer is 4 ohms..
I say...
and yeah I seriously need to get rid of the DC going to the output! Ouch!!! It's not good for my speaker or the amplifier!
I think a good audio transformer would be the way to go.
but that's just my opinion.
If you want you can post a schematic of how I could get rid of the DC from my current circuit and make it better.
or a point to point wire to wire diagram would be helpful also... as I'm still not that good with schematics that much..
but an audio transformer would work wonders just by itself..

Last edited by realflow100; 14th October 2012 at 03:05 PM.
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Old 14th October 2012, 04:22 PM   #47
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by realflow100 View Post
wow... 4 watts pumping a 4ohm 12 inch 175 watt rms 500 watt max subwoofer.... at half an inch excursion?
If the speaker is just in free space and not in a cabinet then you would see a lot of cone movement due to there being no "air pressure" for it to push back on. Thats part of what mounting speakers in a box does

I doubt you'll come up with a suitable transformer. Did you try the AC coupled version I posted earlier. It will work but you need the correct value resistors.
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Old 14th October 2012, 04:29 PM   #48
AndrewT is offline AndrewT  Scotland
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Try a 1.5V C cell.
That would be ~ 3/4W across the Re=3r0.
That will move the cone a fair distance. and the effective voltage at the speaker will actually be a lot less than 1.5Vdc due to internal resistance in the C cell.
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Old 14th October 2012, 04:52 PM   #49
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My subwoofer is definitally in a subwoofer box
huge 2 and a half inch port on it major bass! still get half inch excursion never taken it out of the box since I put it in.
and sorry I have no clue how to AC couple my amplifier or whatever that is..

if I try using a capacitor in series with my subwoofer I get absolutely nothing at all
all I get is some tiny faint swishing pulsing sound that has no use.
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Old 14th October 2012, 06:30 PM   #50
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by realflow100 View Post
My subwoofer is definitally in a subwoofer box
huge 2 and a half inch port on it major bass! still get half inch excursion never taken it out of the box since I put it in.
and sorry I have no clue how to AC couple my amplifier or whatever that is..

if I try using a capacitor in series with my subwoofer I get absolutely nothing at all
all I get is some tiny faint swishing pulsing sound that has no use.
As I keep saying, it's all in post #22 on how to AC couple the speaker. You would need a 6 ohm or thereabouts resistor and an assortment of resistors to get the base bias correct.

Your speaker cone moves 1/2" purely because of the DC current. It either pulls or pushes the cone depending on polarity. If the same voltage were an AC equivalent (its RMS value) and a low frequency sine wave then above some frequency determined by the speaker and its box you would find the cone movement much less.
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