2 stage BJT amplifier - Page 2 - Electronic Circuits Projects Diagrams Free

Roff · 1st July 2008, 01:08 PM

Quote:

Originally Posted by Wond3rboy

sorry i asked that question to quickly here is another preamp i designed myself the o/p from the common emitter is fine 10v

It is definitely not fine. Post the waveform of the voltage on the collector of Q1.

Quote:

but the output from the emitter follower is very low.it should be 1 rite??but its not.decreasing the freq decreases the o/p and evern with 400 the emitter follower decreases the o/p to mv.

Your design has apparently assumed that the beta of Q2 is infinite. The default beta of the generic NPN in LTspice is 100. Think about what this does to the biasing of Q2. Probe the voltage on the base of Q2. Do you get what you expect (look at the DC level)? Better yet, run a DC Operating Point (DC op pnt) simulation.
If you did have infinite beta in Q2, you would be driving about 800mA DC through the speaker. This is not a good idea, to understate the case.

Wond3rboy · 3rd July 2008, 06:52 AM

i have uploaded the ckt itself.by the way also specify what effect increasing the frequency or decreasing it above the high pass filter.

Roff · 3rd July 2008, 12:35 PM

Quote:

Originally Posted by Wond3rboy

i have uploaded the ckt itself.by the way also specify what effect increasing the frequency or decreasing it above the high pass filter.

I downloaded your file and simulated it. Below are the waveforms on the Q1 collector and the Q2 base. Notice the distortion, and the DC level at the base of Q2. Why do you think this is happening?

Wond3rboy · 4th July 2008, 04:32 PM

i deletd teh capacitor and it seems to be working fine,but i chose the capacitor values accodrding to the 20hz filter!!

Roff · 4th July 2008, 08:43 PM

Quote:

Originally Posted by Wond3rboy

i deletd teh capacitor and it seems to be working fine,but i chose the capacitor values accodrding to the 20hz filter!!

Which capacitor?
If simulators were guns, you'd be dead by now!

Wond3rboy · 6th July 2008, 07:00 AM

sorry!!the capacitro c2.i deleted it and the o/p was k.what i dont understand is why the filter made by c2 and the r5parallelr6 distorting the o/p?have i miscalculated the value of the capacitor??sorry agaian!!!

Roff · 6th July 2008, 04:28 PM

Quote:

Originally Posted by Wond3rboy

sorry!!the capacitro c2.i deleted it and the o/p was k.what i dont understand is why the filter made by c2 and the r5parallelr6 distorting the o/p?have i miscalculated the value of the capacitor??sorry agaian!!!

The problem is with your emitter follower, Q2. You have attempted to bias the emitter at approx. half the supply voltage, but the 8 ohm resistor nearly shorts the emitter to ground. This also drags down the base voltage, because your base bias network cannot supply enough current to keep the base voltage up, and it lowers the input impedance for the positive half of your waveform, causing the distortion you see on the Q1 collector when C2 is in place. Delete the 8 ohm resistor and see what happens.
As I said before, it is not a good idea to drive a speaker with DC.

Wond3rboy · 7th July 2008, 05:27 AM

thanks very much!!until the next problem!

Hero999 · 7th July 2008, 09:59 AM

I've modified your circuit so it drives an 8

hm: speaker with no problem.

The forum wouldn't let me attach the .asc file so I've enclosed it in code tags. Just paste it into a text editor such as notepad of emacs, save it as a .asc file and open it in LTSpice.

Code:

Version 4
SHEET 1 880 680
WIRE 304 -240 -336 -240
WIRE -448 -192 -592 -192
WIRE -336 -192 -336 -240
WIRE -336 -192 -448 -192
WIRE -144 -192 -336 -192
WIRE -16 -192 -144 -192
WIRE -448 -176 -448 -192
WIRE -592 -144 -592 -192
WIRE -16 -144 -16 -192
WIRE 304 -112 304 -240
WIRE -144 -96 -144 -112
WIRE -80 -96 -144 -96
WIRE -144 -32 -144 -96
WIRE -16 -32 -16 -48
WIRE -448 48 -448 -96
WIRE -368 48 -448 48
WIRE -144 48 -144 32
WIRE -144 48 -304 48
WIRE -16 64 -16 48
WIRE 48 64 -16 64
WIRE 144 64 112 64
WIRE -144 80 -144 48
WIRE -16 80 -16 64
WIRE -448 96 -448 48
WIRE -784 144 -944 144
WIRE -592 144 -592 -64
WIRE -592 144 -720 144
WIRE -512 144 -592 144
WIRE -592 192 -592 144
WIRE -144 208 -144 144
WIRE -80 208 -144 208
WIRE 144 208 144 64
WIRE -944 224 -944 144
WIRE -448 224 -448 192
WIRE -144 224 -144 208
WIRE -944 336 -944 304
WIRE -592 336 -592 272
WIRE -592 336 -944 336
WIRE -512 336 -592 336
WIRE -448 336 -448 304
WIRE -448 336 -512 336
WIRE -352 336 -448 336
WIRE -144 336 -144 304
WIRE -144 336 -352 336
WIRE -16 336 -16 256
WIRE -16 336 -144 336
WIRE 144 336 144 288
WIRE 144 336 -16 336
WIRE -512 352 -512 336
WIRE -352 400 -352 336
WIRE 304 400 304 -32
WIRE 304 400 -352 400
FLAG -512 352 0
SYMBOL npn3 -512 96 R0
SYMATTR InstName Q1
SYMBOL res -608 -160 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -608 176 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res -464 208 R0
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL Misc\\signal -944 208 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 .5 400)
SYMBOL res -464 -192 R0
SYMATTR InstName R4
SYMATTR Value 1k
SYMBOL res -160 -208 R0
SYMATTR InstName R5
SYMATTR Value 1k
SYMBOL res -160 208 R0
SYMATTR InstName R6
SYMATTR Value 1k
SYMBOL npn -80 -144 R0
SYMATTR InstName Q2
SYMBOL Misc\\battery 304 -128 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 20
SYMBOL res 128 192 R0
SYMATTR InstName Speaker
SYMATTR Value 8
SYMBOL cap -304 32 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 10µ
SYMBOL pnp -80 256 M180
SYMATTR InstName Q3
SYMBOL diode -160 -32 R0
WINDOW 0 39 32 Left 0
WINDOW 3 -28 29 Left 0
SYMATTR InstName D1
SYMBOL diode -160 80 R0
WINDOW 0 42 30 Left 0
WINDOW 3 -29 30 Left 0
SYMATTR InstName D2
SYMBOL res -32 -48 R0
SYMATTR InstName R7
SYMATTR Value 1
SYMBOL res -32 64 R0
SYMATTR InstName R8
SYMATTR Value 1
SYMBOL Misc\\EuropeanPolcap 48 80 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName C3
SYMATTR Value 1000µ
SYMBOL cap -720 128 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C1
SYMATTR Value 10µ
TEXT -752 -32 Left 0 !.tran 0 5 1 1

Roff · 7th July 2008, 03:29 PM

Quote:

Originally Posted by Hero999

I've modified your circuit so it drives an 8

hm: speaker with no problem.

The forum wouldn't let me attach the .asc file so I've enclosed it in code tags. Just paste it into a text editor such as notepad of emacs, save it as a .asc file and open it in LTSpice.

Code:

Version 4
SHEET 1 880 680
WIRE 304 -240 -336 -240
WIRE -448 -192 -592 -192
WIRE -336 -192 -336 -240
WIRE -336 -192 -448 -192
WIRE -144 -192 -336 -192
WIRE -16 -192 -144 -192
WIRE -448 -176 -448 -192
WIRE -592 -144 -592 -192
WIRE -16 -144 -16 -192
WIRE 304 -112 304 -240
WIRE -144 -96 -144 -112
WIRE -80 -96 -144 -96
WIRE -144 -32 -144 -96
WIRE -16 -32 -16 -48
WIRE -448 48 -448 -96
WIRE -368 48 -448 48
WIRE -144 48 -144 32
WIRE -144 48 -304 48
WIRE -16 64 -16 48
WIRE 48 64 -16 64
WIRE 144 64 112 64
WIRE -144 80 -144 48
WIRE -16 80 -16 64
WIRE -448 96 -448 48
WIRE -784 144 -944 144
WIRE -592 144 -592 -64
WIRE -592 144 -720 144
WIRE -512 144 -592 144
WIRE -592 192 -592 144
WIRE -144 208 -144 144
WIRE -80 208 -144 208
WIRE 144 208 144 64
WIRE -944 224 -944 144
WIRE -448 224 -448 192
WIRE -144 224 -144 208
WIRE -944 336 -944 304
WIRE -592 336 -592 272
WIRE -592 336 -944 336
WIRE -512 336 -592 336
WIRE -448 336 -448 304
WIRE -448 336 -512 336
WIRE -352 336 -448 336
WIRE -144 336 -144 304
WIRE -144 336 -352 336
WIRE -16 336 -16 256
WIRE -16 336 -144 336
WIRE 144 336 144 288
WIRE 144 336 -16 336
WIRE -512 352 -512 336
WIRE -352 400 -352 336
WIRE 304 400 304 -32
WIRE 304 400 -352 400
FLAG -512 352 0
SYMBOL npn3 -512 96 R0
SYMATTR InstName Q1
SYMBOL res -608 -160 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -608 176 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res -464 208 R0
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL Misc\\signal -944 208 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 .5 400)
SYMBOL res -464 -192 R0
SYMATTR InstName R4
SYMATTR Value 1k
SYMBOL res -160 -208 R0
SYMATTR InstName R5
SYMATTR Value 1k
SYMBOL res -160 208 R0
SYMATTR InstName R6
SYMATTR Value 1k
SYMBOL npn -80 -144 R0
SYMATTR InstName Q2
SYMBOL Misc\\battery 304 -128 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 20
SYMBOL res 128 192 R0
SYMATTR InstName Speaker
SYMATTR Value 8
SYMBOL cap -304 32 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 10µ
SYMBOL pnp -80 256 M180
SYMATTR InstName Q3
SYMBOL diode -160 -32 R0
WINDOW 0 39 32 Left 0
WINDOW 3 -28 29 Left 0
SYMATTR InstName D1
SYMBOL diode -160 80 R0
WINDOW 0 42 30 Left 0
WINDOW 3 -29 30 Left 0
SYMATTR InstName D2
SYMBOL res -32 -48 R0
SYMATTR InstName R7
SYMATTR Value 1
SYMBOL res -32 64 R0
SYMATTR InstName R8
SYMATTR Value 1
SYMBOL Misc\\EuropeanPolcap 48 80 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName C3
SYMATTR Value 1000µ
SYMBOL cap -720 128 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C1
SYMATTR Value 10µ
TEXT -752 -32 Left 0 !.tran 0 5 1 1

That's weird. .ASC is listed as a valid attachment type, and I have attached them with no problem.
Disclaimer: I am not an audio guru.

You can drive a speaker with that, but the gain is low and I think the distortion will be high if you want enough power to actually hear it.

audioguru · 7th July 2008, 04:08 PM

I tried adding negative feedback around the entire circuit and many other things but the output transistors do not have enough OOMPH.

I cannot make an attachement because it say that I have exceeded my attachments quota!!!!!
Again. Last time i deleted all my attachments then admin removed the quota. Now the quota is back!

Wond3rboy · 7th July 2008, 04:21 PM

well thanks roff making a power amplifier for running my 8ohm speaker was my seond task.i am practising making amplifier and different types of circuits.any hints??

Hero999 · 7th July 2008, 04:56 PM

The circuit I posted isn't perfect, I just made the bare minimum number of changes to enable it to drive an 8

hm: speaker.

I certainly don't plan to remove any of my attachments.

Attachmets are a good thing but they aren't really needed, an external hosting service is all that's required.

**Nigel Goodwin** · 7th July 2008, 06:38 PM

Quote:

Originally Posted by audioguru

I tried adding negative feedback around the entire circuit and many other things but the output transistors do not have enough OOMPH.

I cannot make an attachement because it say that I have exceeded my attachments quota!!!!!
Again. Last time i deleted all my attachments then admin removed the quota. Now the quota is back!

Before you get carried away (like some have already!), PM Electromaster and tell him, presumably it's the default setting on the last software upgrade.

Wond3rboy · 8th July 2008, 05:19 AM

[quote=audioguru;325591]I tried adding negative feedback around the entire circuit and many other things but the output transistors do not have enough OOMPH.

OOMPH?? and if you dont mind me asking why we dont use a class c or d amplifier because i have seen most of the people make clas ab amps as power amplifiers.AND from where can i learn about class c and d amps?

Which external service are you talking about?

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4th July 2008, 04:32 PM	(permalink)
Wond3rboy	i deletd teh capacitor and it seems to be working fine,but i chose the capacitor values accodrding to the 20hz filter!!

6th July 2008, 07:00 AM	(permalink)
Wond3rboy	sorry!!the capacitro c2.i deleted it and the o/p was k.what i dont understand is why the filter made by c2 and the r5parallelr6 distorting the o/p?have i miscalculated the value of the capacitor??sorry agaian!!!

7th July 2008, 05:27 AM	(permalink)
Wond3rboy	thanks very much!!until the next problem!

7th July 2008, 04:08 PM	(permalink)
audioguru	I tried adding negative feedback around the entire circuit and many other things but the output transistors do not have enough OOMPH. I cannot make an attachement because it say that I have exceeded my attachments quota!!!!! Again. Last time i deleted all my attachments then admin removed the quota. Now the quota is back! __________________ Uncle $crooge Last edited by audioguru; 7th July 2008 at 04:12 PM.

7th July 2008, 04:21 PM	(permalink)
Wond3rboy	well thanks roff making a power amplifier for running my 8ohm speaker was my seond task.i am practising making amplifier and different types of circuits.any hints??

7th July 2008, 04:56 PM	(permalink)
Hero999	The circuit I posted isn't perfect, I just made the bare minimum number of changes to enable it to drive an 8hm: speaker. I certainly don't plan to remove any of my attachments. Attachmets are a good thing but they aren't really needed, an external hosting service is all that's required. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

8th July 2008, 05:19 AM	(permalink)
Wond3rboy	[quote=audioguru;325591]I tried adding negative feedback around the entire circuit and many other things but the output transistors do not have enough OOMPH. OOMPH?? and if you dont mind me asking why we dont use a class c or d amplifier because i have seen most of the people make clas ab amps as power amplifiers.AND from where can i learn about class c and d amps? Which external service are you talking about?