1st attempt at 2 stage amp with questions. need help

Started by ibanezts808, August 18, 2006, 12:49:33 PM

Previous topic - Next topic

ibanezts808

To start, the darn thing works, but it may only be because I have it running through a transformer.  I first designed a single stage amplifier then I though, maybe I can make two stages.  I tried and tried and couldn't get it.  Well then I found a book that mentioned coupling and decoupling.  I have a fairly if not prebasic understanding of how to apply the concepts of coupling and decoupling.  I guess what I'm trying to say is, if you see anything needless, or if you see something that I do need, please do mention.  thanks a lot!

Sorry about the quality of the pictures...

The Two leds off to the right are for the clipping stage, but I'm having trouble figuring out how to load the second stage to push the signal over to the clipping stage... if that makes any sense at all.



This is a closer view of the amplifier:


and here is the schematic via my sweet Paint skills.


Okay now the important parts.  These are the voltages I read across q1, and q2. 
Q1:
B - 3.4v
C - 2.9V
E - 2.74

Q2:
B - 4v
C - 8.5v
E - 3.81
I know there is a problem with both.  On Q1 you can quite clearly see the collector has .5 volts less than base and in q2 the emitter is .19 volts less than base when it should be about .6-.7(right?)  now this whole contraption is breadboarded onto a radioshack learning lab dealy so naturally I did what the book provided does and I run my amp into a transformer into a speaker.  which may be why I hear anything at all.  So please let me know what's up with this whole thing, I have a feeling I may have to go completely back to the drawing boards. :(  to make me feel better, I'm going to brag about my organizational skills:



yeah, that's what happend when I got frustrated with my amp, I organized my resistors... and labeled them.
Hi Paul.  Welcome.  We are all Stompboxaholics

I am so cool.

ibanezts808

I forgot to put the voltages in but they are now there, sorry guys  :icon_redface:
Hi Paul.  Welcome.  We are all Stompboxaholics

I am so cool.

petemoore

  C4 is jumpered, can be removed.
  the resistor connected to the base are equal size, perhaps a base bias arrangement like the LPB
http://www.generalguitargadgets.com/diagrams/lpb2_sc.gif...
  Just a glancing suggestion...
  But
  B - 3.4v 
C - 2.9V
E - 2.74
  This ones base is highest, emitter and collector are about the same...bias problem here.
Q2:
B - 4v
C - 8.5v
E - 3.81  This one is shown as connected [but can't be] to Gnd. = 0V according to the schematic.

Convention creates following, following creates convention.

ibanezts808

#3
 :icon_redface: :icon_redface: :icon_redface:

now I feel dumb, I was in such haste that I forgot to connect Q2's emitter to ground.  Lol.  I'll have to check the new votages sometime tomorrow and maybe I can report.  I appreciate the response. I'll update this thread with new voltages if there are still questions.
Hi Paul.  Welcome.  We are all Stompboxaholics

I am so cool.