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Old 25th September 2012, 05:08 PM   #1
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Default I finally made a good working transistor amplifier

I actually finally got it working!
it runs off exactly 6 volts from only 4 double A batteries no more no less
it has only one resistor and one capacitor.
there is zero background noise
and it has enough power to drive a 12 inch subwoofer and gets some real bass!
it has zero distortion and I'm not even sure how long the batteries last but I'm sure they will last for a long time
there is only one teeny tiny drawback is that there is a small amount of dc flowing to the output speaker but it's not even noticeable with such a large 12 inch subwoofer
and the transistor doesn't even get warm
the capacitor is set on the base and the input from my computer but only to keep the DC from the batteries from flowing back to my computer
it works absolutely great and there is no buzzing sound when you touch the end of the input plug like the other amplifiers.
the sound quality is outstanding and it's fairly loud to the point when my mom tells me to turn it down lol.
i'm not exactly sure what value the resistor has but I was trying to get the perfect biasing so I have perfect output quality with no distortion and not too much flowing dc to the speaker output so I just tested a bunch of random resistors until I found one that makes it sound perfect and not have too much dc voltage flowing to the speaker output to make a difference..
I have placed it all in a cardboard box and taped it all together so it looks really nice.
the only physical things in my simple amplifier are 3 things.. one the transistor.. two. a single resistor. and three the capacitor to the input.
i could somehow draw a super simple diagram of how I have everything wired up if anyone wants to know exactly how I made it.
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Old 25th September 2012, 06:02 PM   #2
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while i do understand your statisfaction, i still have to remaind you that this is chipamps section.
transistor based amps do not belong here.
and as a side note, that single transistor amp is surely a design that can use a whole lot of upgrades.
at best it would get you prehaps a watt.

maybe -since you are intrested in electronics- ask around for books on the subject, it is great to expermient with stuff but.. surely a solid basic knowledge would lead to roughly lightyears better results.

Your achivement is a great start never the less, maybe you should make some pictures of it, draw what you conected and how, i'm sure some of the responses will suggest nice additions to the amplifier.
as an example, i can give you one right away. A larger value capacitor connected in series with the speaker will block all DC from the speaker.

Probably You should do some research on simple transistor circuits.
Not that realy hard or costly to build a single transistor unit with voltage gain, and a nother stage with current gain for some real power. (like 5 watt or so would most probably be a big difference).
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Old 25th September 2012, 06:45 PM   #3
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my problem is I only have 6 volts going one direction..... it needs to have another 6 volts going the other way too to have the full sinewave
and I tried that with the capacitor on the output to the speaker but when I try that all my sound goes away and I get no power at all going to my speaker. it fixes the DC problem but then I get extremely quiet sound since it's still only pushing the speaker one way..
by the way i'm already using a two in one darlington transistor so gain is not an issue :P
and I don't know how to find the transistor based amp section wherever that is can someone help me on that i'm still new here.

Last edited by realflow100; 25th September 2012 at 06:48 PM.
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Old 25th September 2012, 06:53 PM   #4
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Quote:
Originally Posted by Arty View Post
while i do understand your statisfaction, i still have to remaind you that this is chipamps section..........
He's excited to have a working project

OK, so this in now in the solid state forum... so how about posting a circuit so we can all see this beastie
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Old 25th September 2012, 06:58 PM   #5
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by realflow100 View Post
..............I have placed it all in a cardboard box and taped it all together so it looks really nice.
the only physical things in my simple amplifier are 3 things.. one the transistor.. two. a single resistor. and three the capacitor to the input.
i could somehow draw a super simple diagram of how I have everything wired up if anyone wants to know exactly how I made it.
how about a couple of pictures
If your not sure how to attach anything to a post just ask.
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Old 25th September 2012, 07:21 PM   #6
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witch is a fantastic thing.
i hope to see the schematic too, surely that amp can get better

bit on the technical stuff::
single supply does not mean the amplifier moves the speaker cone to one direction only.
The loss of power when connecting a capacitor can be for the following:
not connected series with the speaker, and/or the capacitor value is too low.
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Old 25th September 2012, 07:37 PM   #7
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The transistor is a darlington (or that's what someone told me and when I looked at the data sheets of it.

sorry my wiring is so messy i'm no good with a solder gun so i just use a lot of wires instead!

I'll draw a really quick diagram of how I have it set up and then i'll upload it soon.
i know something is totally out of place like the resistor or the power supply or possibly both including the speaker.. but it works mostly and sounds really loud and clear except for the DC flowing to the speaker
but I want to make it more beefier more bass and without the DC flowing to the speaker. (that's the difficult part)
Attached Images
File Type: jpg one.jpg (46.8 KB, 764 views)
File Type: jpg two.jpg (42.9 KB, 736 views)
File Type: jpg three.jpg (68.8 KB, 718 views)
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File Type: jpg six.jpg (55.1 KB, 189 views)
File Type: jpg seven.jpg (57.4 KB, 187 views)
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Old 25th September 2012, 07:52 PM   #8
Mooly is offline Mooly  United Kingdom
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Thanks for the pictures

It reminds me of my first projects... a headphone amp I made using a single AD149 germanium power transistor. Mine lived a small plastic picnic sandwich box. Trouble is it leads to bigger things

Nothing beats hearing sound from something you first make.

Its a bit hard to make out from the pictures but from your description I think I can visualise the circuit.
To get rid of the DC in the speaker means adding more parts and reducing the efficiency but it is the way forward to a better design.
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Old 25th September 2012, 08:03 PM   #9
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i think i can describe it better than i could draw a diagram so here goes..
the positive input wire goes to the base or pin 1 (lets lable the transistors leads pin 1 2 and 3)
and there is a resistor between pins 1 and 2
pin 2 goes to the positive wire of the power supply
the negative wire of the power supply goes to the positive speaker wire
and the negative wire of the speaker wire goes to the negative of the input. and the negative of the input goes to pin 3 of the transistor.
and there is a capacitor between the positive of the input and pin 1 of the transistor.

a little complicated but it works perfectly fine at only 6 volts four double A batteries.
trust me it won't work with any more or any less or it does weird things
(super heats the transistor or massive distortion if i take away one battery or add one more battery)
it works fine except for the amount of DC flowing to the speaker constantly wasting a bit of power
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Old 26th September 2012, 07:06 AM   #10
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Hmmm... Nelson Pass had better watch out

So this is what I think you have come up with. The two transistors here make a single "Darlington". The 6 ohm resistor is the speaker and the 47K is chosen to bias the transistor optimally.

It works and the distortion is even harmonic. The two traces show the input voltage and the output across the speaker. Plenty of voltage gain Connecting the input ground to the emitter rather than the battery negative changes the amp from an emitter follower (look it up) to a common emitter configuration.

Increase the supply and the power consumption rises dramatically as you have found. Decrease and you get distortion. You would have to alter the value of the 47K for each and every change in supply voltage with a circuit like this.

The biggest problem is the DC current in the speaker coil.
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File Type: jpg Circuit.JPG (102.6 KB, 496 views)
File Type: jpg One transistor amplifier.JPG (134.1 KB, 437 views)
File Type: jpg Circuit 2.JPG (108.5 KB, 200 views)
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