Got Bored Today

DoomPixie · 13th June 2006, 09:00 PM

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

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
I got bored	danielwritesbac	Chip Amps	11	6th January 2009 06:48 PM
Any bored custom amp builders need a project?	troystg	Car Audio	3	16th January 2007 12:22 AM
Bored...2n3055e amp?	ThSpeakerDude88	Solid State	27	25th March 2006 01:56 PM
I'm bored, I need a project	SkinnyBoy	The Lounge	9	3rd August 2004 01:56 PM
Unemployed and Bored, what should I make for cheap?	PHilgeman	Parts	7	12th February 2004 04:17 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

13th June 2006, 09:03 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

13th June 2006, 09:22 PM	#4
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	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?

13th June 2006, 09:30 PM	#5
DoomPixie diyAudio Member Join Date: Jun 2005 Location: Aberystwyth / Llanelli (wales)	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

13th June 2006, 09:43 PM	#7
DoomPixie diyAudio Member Join Date: Jun 2005 Location: Aberystwyth / Llanelli (wales)	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

13th June 2006, 10:19 PM	#8
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Another vote for me using my glasses? I'd go for fixed resistors. The nework will load the input a bit. -Chris

13th June 2006, 10:52 PM	#9
DoomPixie diyAudio Member Join Date: Jun 2005 Location: Aberystwyth / Llanelli (wales)	true.. I will see how it works soon, hopefully i can get some kind of cheap little speaker to test it with tommorow...

14th June 2006, 12:53 AM	#10
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	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

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)