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?
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?
Hi DaviRuz,DaViruz said:
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)😉
Re: Re: Oscillating amp.
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
Will upload it instead, i usually put all images and stuff on a friends box, but it's down at the moment.
Elso Kwak said:
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
I did call it a silly language ;-)Elso Kwak said:
Will upload it instead, i usually put all images and stuff on a friends box, but it's down at the moment.
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
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
No idea, i just picked one.LennyK said:
I'm using a ATX supply, since that's the only thing i've got that i can get +/-12V from at .7A
Thanks. 🙂
Headphone Amp
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.😉
Hi Daviruz,DaViruz said:
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.😉
Re: Headphone Amp
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.
Elso Kwak said:
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.
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.
Jam
P.S. I suspect the output needs to be taken from the emitter of Q1.
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"
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"
DaViruz said:
DaviRuz,
Just trying to be helpfull, OK?
Try to workout the base voltage of Q2. I assume you used R2,3,4 to put the base at around ground? Won't work, remember the Vbe is something of .7V (unless broken) so your Q2 base will be at -11.3V, which means that the whole bias is out of whack. So, use an emittor resistor for Q2. This will bring down the gain, and to restore it decouple this resistor with a parallel cap to make it zero resistance for ac. If you want to get fancy, only partially shunt the emittor resistor.
Example: say you want a gain of 5 in Q2, with a collector current of 5mA. Since collector voltage should be halfway pos supply, use Rc of 6v/5mA=1.2k. For gain of 5, the undegenerated Re should be 1/5 of Rc=200 Ohms. But the emitter should be close to gnd, so approximately for dc the Re should be 11.3v/5mA=approx 2.2k. We had already 200 ohms, so we need another 2k. This one needs to be shunted by a cap. For a lower Ft of 10Hz calculate the cap to be 2k at 10Hz (see tread on opamp bandwidth).
Now, Q1's base is at about +6V, remember, so it's emitter is at +5.3, so Re has 17.3v across it. Say you want a standing (class A) bias current of 100mA in Q1. That makes Re 17.3/100mA about 173 Ohms. Now, what will be the power dissipation in this resistor and Q1? You tell me.
Jan Didden
Yea, just realized that R2/3 was pretty much useless too 🙂 Since i have C1, there isn't be any reason at all to try to make the input 0V, is it?janneman said:
Can't i just use the 33 ohm and use a standing current of 0.363A as i intended in the first place? A lot of power for a couple of headphones maybe, but i could always warm my hands on it in the winter 🙂
what is your definition of the term, the word "amplifier"
for me it is an adaptor
connected in between 3 things
a signal - a signal source
a supplier of energy, power
a load, a thing that need energy, power to do its WORK
to make the adoptation in the good way
you need information about what is needed
to be adopted together
the better information you have about the 3 things
the better chance to manage well in your design
try to figure out, what the need is
for those 3 items
use the "worst case" scenario
and try to design from that
when I need a system, to do THE WORK
I seldom go to the shop and buy the adaptor first
and buy the gear to fit the adaptor
I guess however, that this is the way some like to do it
/halojoy sweden 2002
could be copied
in fact
it should be
brought to common knowledgde - for common good
shared happiness is always more happiness
shared burdon is always less of a burdon
for me it is an adaptor
connected in between 3 things
a signal - a signal source
a supplier of energy, power
a load, a thing that need energy, power to do its WORK
to make the adoptation in the good way
you need information about what is needed
to be adopted together
the better information you have about the 3 things
the better chance to manage well in your design
try to figure out, what the need is
for those 3 items
use the "worst case" scenario
and try to design from that
when I need a system, to do THE WORK
I seldom go to the shop and buy the adaptor first
and buy the gear to fit the adaptor
I guess however, that this is the way some like to do it
/halojoy sweden 2002
could be copied
in fact
it should be
brought to common knowledgde - for common good
shared happiness is always more happiness
shared burdon is always less of a burdon
Um, check your supply too! The -12V line on most ATX supplies is a trickle only (100mA or less).
DaViruz said:
Sure, whatever you fancy. But if you go to class A much beyond the max current that your load asks, you cause more dissipation without more *quality*.
Jan Didden
DaViruz said:
Close. Probably just 0.92 😉
But why the pot? Put the base to gnd with a resistor, and you can probably DC-couple the input.
Jan Didden
Re: what is your definition of the term, the word "amplifier"
Halojoy,
I get your point, and you are right. But observe: if a painter gets the urge to make a painting, do you think he will start to worry about the exact size of the linen, or do you think he grabs anything that seems OK and starts to paint? Sometimes we need to let go of our right brain half (or was it the left half?)
Jan Didden
halojoy said:
Halojoy,
I get your point, and you are right. But observe: if a painter gets the urge to make a painting, do you think he will start to worry about the exact size of the linen, or do you think he grabs anything that seems OK and starts to paint? Sometimes we need to let go of our right brain half (or was it the left half?)
Jan Didden
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