Oscillating amp. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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
Reply
 
Thread Tools Search this Thread
Old 2nd December 2002, 09:12 PM   #1
diyAudio Member
 
Join Date: Jun 2002
Location: Sweden
Default Oscillating amp.

I just had my first go at drawing a class A headphone amplifier, this is what i came up with:
http://hem.passagen.se/jocke999/classas.gif
(open it in a new window, if you get a funny error message in a silly language, just place the cursor at the address bar and press enter)

Don't laugh :-), it is the first audio amp i've ever drawn, my main goal was to make it actually amplify the sound, quality of the sound being extremely low priority.
I just built the darn thing, when i finally managed to cool it enough to get a stable DC offset near zero, i hooked up a pair of old crappy $5 headphones and powered it up, and got scared to death. The output was oscillating at about 500Hz, fairly loud.
Anyone got any pointers on how to solve this?
  Reply With Quote
Old 2nd December 2002, 09:16 PM   #2
Banned
 
Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Send a message via Yahoo to Elso Kwak
Default Re: Oscillating amp.

Quote:
Originally posted by DaViruz
I just had my first go at drawing a class A headphone amplifier, this is what i came up with:
Click the image to open in full size.

Don't laugh :-), it is the first audio amp i've ever drawn, my main goal was to make it actually amplify the sound, quality of the sound being extremely low priority.
I just built the darn thing, when i finally managed to cool it enough to get a stable DC offset near zero, i hooked up a pair of old crappy $5 headphones and powered it up, and got scared to death. The output was oscillating at about 500Hz, fairly loud.
Anyone got any pointers on how to solve this?
Hi DaviRuz,
I would like to give some free advice but your schematic did not show even not with a right mouse click.
http://hem.passagen.se/jocke999/classas.gif
Apart from the fact that you call Swedish a funny language, which I find funny , something goes wrong with your link to the picture. What works best on this forum is uploading the picture from your PC. If necessary resample/resize with the program : www.irfanview.com (free of charge)
  Reply With Quote
Old 2nd December 2002, 09:19 PM   #3
diyAudio Member
 
Join Date: Jun 2002
Location: Sweden
Default Re: Re: Oscillating amp.

Quote:
Originally posted by Elso Kwak

I would like to give some free advice but your schematic did not show even not with a right mouse click.
http://hem.passagen.se/jocke999/classas.gif
Try entering the url in the address bar and press enter, it's the damn host that refuses all requests with the wrong http-referer.


Apart from
Quote:
Originally posted by Elso Kwak
the fact that you call Swedish a funny language, which I find funny , something goes wrong with your link to the picture. What works best on this forum is uploading the picture from your PC.
I did call it a silly language ;-)

Will upload it instead, i usually put all images and stuff on a friends box, but it's down at the moment.
  Reply With Quote
Old 2nd December 2002, 09:24 PM   #4
LennyK is offline LennyK  Poland
diyAudio Member
 
LennyK's Avatar
 
Join Date: Nov 2002
Location: Gdansk - best part of Poland :)
why you use OE on the output?
maybe try amplyfing signal on the input with BC546 and thn use BD177 as OC follower

if you don't want to do so then try adding some local feedback - put smal resistor from BD177 emiter to -12V

PSU regulated?

good luck

Lenny
  Reply With Quote
Old 2nd December 2002, 09:28 PM   #5
diyAudio Member
 
Join Date: Jun 2002
Location: Sweden
Here is the pic, sorry for the hassle.
Attached Images
File Type: gif classas.gif (4.2 KB, 386 views)
  Reply With Quote
Old 2nd December 2002, 09:31 PM   #6
diyAudio Member
 
Join Date: Jun 2002
Location: Sweden
Quote:
Originally posted by LennyK
why you use OE on the output?
No idea, i just picked one.
Quote:

maybe try amplyfing signal on the input with BC546 and thn use BD177 as OC follower

if you don't want to do so then try adding some local feedback - put smal resistor from BD177 emiter to -12V

PSU regulated?
I'm using a ATX supply, since that's the only thing i've got that i can get +/-12V from at .7A
Quote:

good luck
Lenny
Thanks. :-)
  Reply With Quote
Old 2nd December 2002, 09:44 PM   #7
Banned
 
Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Send a message via Yahoo to Elso Kwak
Smile Headphone Amp

Quote:
Originally posted by DaViruz
Here is the pic, sorry for the hassle.
Hi Daviruz,
No problem, I now see a very clear schematic.
First you will need a coupling cap between your headphone and the amps output as otherwise it has a large offset voltage upon it.
Furthermore with Darlington connected transistors it is very unusual to take the ouput at the collector. It is usually taken from the emittor and the gain provided by some earlier, i.e. upstream stage.
  Reply With Quote
Old 2nd December 2002, 09:49 PM   #8
diyAudio Member
 
Join Date: Jun 2002
Location: Sweden
Default Re: Headphone Amp

Quote:
Originally posted by Elso Kwak

Hi Daviruz,
No problem, I now see a very clear schematic.
First you will need a coupling cap between your headphone and the amps output as otherwise it has a large offset voltage upon it.
Furthermore with Darlington connected transistors it is very unusual to take the ouput at the collector. It is usually takan from the emittor and the gain provided by some earlier, i.e. upstream stage.
Do i really need the dc blocking cap at the output when i can adjust the dc offset with VR1?
Will redraw it to take the output from the emitter too, since that seems to be a more usual approach. By the way, why is that? Is the more powerfull transistors more unsuitable for voltage amplifing then the small signal trannies?

Thanks for the help so far, much apriciated.
  Reply With Quote
Old 2nd December 2002, 09:51 PM   #9
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Try a small value resistor in series with the base of Q2 and Q1(500 ohms). Also add decoupling caps 10uf (tantalums if possible) to the supply lines (as close to the circuit as possible). You may also try some degeneration on Q1.

Jam

P.S. I suspect the output needs to be taken from the emitter of Q1.
  Reply With Quote
Old 2nd December 2002, 10:51 PM   #10
halojoy is offline halojoy  Sweden
On Hiatus
 
Join Date: Nov 2002
Thumbs up Bra start, DaViruz - alla är vi barn i början

Good Start, DaViruz
This is how we do when we first try to figure out
how amplification with this thing called transistors works.

This time next year,
you might shows us all some new ideas.
And teach some new beginners how to do the trick
of designing an amplifier!
(While you are experimenting! Please use an 100-470uF Capacitor in series with your headphone output.
One of mine headphones took the shortcut to the heaven of headphones)

The Times They Are A'Changin' /Dylan 1964
Things Have Changed /Dylan 2000

"People are crazy and times are strange
I'm locked in tight, I'm out of range
I used to care, but things have changed"
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
6j4 oscillating? Klimon Tubes / Valves 2 18th January 2008 09:32 PM
PSU oscillating apolon34 Power Supplies 3 24th June 2005 02:20 PM
oscillating...always oscillating WoulYaShassu Solid State 30 9th April 2004 05:31 PM


New To Site? Need Help?

All times are GMT. The time now is 10:49 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2