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DoomPixie 13th June 2006 09:00 PM

Got Bored Today
 
2 Attachment(s)
Hey guy's!
I got bored earlier and decided to try something a little "strange"... I built an amplifier that is based around a single Tip110 darlington transistor.. Just because i had a couple in my parts pox and i was bored..
I have NOT tested this amplifier yet as i'm at my g/f's in harpenden and didnt bring a speaker with me **DOH!!** Also she uses a mac and i havent been able to find a visual spice simulator that will run on it yet (mac os x if anyone knows one that will work?)
I have powered it up and nothing caught fire and no magic smoke escaped which is a good sign i think..
Am i missing anything obvious? is there an obvious reason why this will not work?

anatech 13th June 2006 09:03 PM

Hi DoomPixie,
I'd bias the base at a fixed voltage and couple the input capacitively at the base instead. Your speaker will pump as you adjust the volume otherwise.

-Chris

AKN 13th June 2006 09:16 PM

Quote:

Originally posted by anatech
Hi DoomPixie,
I'd bias the base at a fixed voltage and couple the input capacitively at the base instead. Your speaker will pump as you adjust the volume otherwise.

-Chris

hi!

I think that is what he has just done. It's not a volume pot, instead it's DC working point pot.

/ Anders

bigwill 13th June 2006 09:22 PM

Am I right in thinking that when the wiper on that pot is close to ground it will also shunt a lot of the signal to ground?

DoomPixie 13th June 2006 09:30 PM

the pot isnt a volume pot...
when it is set towards ground it will feed signal to ground aswell.. hopefully it will never be anywhere near ground though.. as i said, i have no way to simulate it and no speaker to test it so it is very likley that i will have to change the values and change the layout a bit to get it working right.. if it will work atall...
Owen

AKN 13th June 2006 09:35 PM

Quote:

Originally posted by bigwill
Am I right in thinking that when the wiper on that pot is close to ground it will also shunt a lot of the signal to ground?

Yes and not just close to ground, the same thing will happen close to Vcc. You could add resistor from base to center of pot to get a min resistanse approx to value of resisor (not involving base current).

But on the otherhand the pot should be close to center to get working point close to half of supply voltage. Pot could be replaced by two resistors.

/ Anders

DoomPixie 13th June 2006 09:43 PM

true, i could just replace it with two resistors.. Or i mabey i could use 15V supply and referance input and output to ground and do away with the pot altogether? the power supply i am runing this prototype from has outputs for 15V...
Owen

anatech 13th June 2006 10:19 PM

Another vote for me using my glasses?

I'd go for fixed resistors. The nework will load the input a bit.

-Chris

DoomPixie 13th June 2006 10:52 PM

true.. I will see how it works soon, hopefully i can get some kind of cheap little speaker to test it with tommorow...

sawreyrw 14th June 2006 12:53 AM

DoomPixie,

This amp will amplify the input signal if the 10K pot is adjusted so that the TIP110 is in it's active region. The ideal gain of the amp will be 8, but if the input swings more than a few tenths of a volt the output will be badly distorted. This is the reason almost all solid state amps use negative feedback. In addition, the 500 ohm collector load can't drive much current to whatever is on the output side of the 2200uF cap. Good idea, but it won't do what you want.

Rick


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