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 27th March 2014, 12:11 AM   #1
diyAudio Member
 
Join Date: Mar 2014
Default Need help with college project - Trying to build a 3 stage amp but I'm lost

Basically the title. I tried a common emitter preamp which didn't work as the transistor I was using wasn't the correct one and I didn't know how to bias the one I had at my disposal correctly. I tried a non-inverting preamp but all I got on the oscilloscope screen was fuzz (I assume I intefaced the source and the preamp wrongly). The only thing I could get to work was the simple inverting design but even then I don't know how to interface it to the rest of my circuit. The output impedance of my source is 1kohm. I have TL081 op-amps at my disposal and I can find out the model number of the transistors tomorrow. Signal path looks like this. Whatever happens, I must keep the filters. It goes from left to right. I forgot to add it in, but you switch between the filters, direct line. Any help is appreciated. Cheers.
Click the image to open in full size.
  Reply With Quote
Old 27th March 2014, 04:06 AM   #2
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, on the east coast
Your block schematic shows an audio system - an integrated amplifier including the signal source. That's fine for illustration but a 3 stage amplifier generally refers to the electronic design category or architecture of just the power amplifier itself.

So what is your focus here - are you looking for an integrated amplifier design such as you find in commercial stereo amplifiers etc? Plenty of these are discussed constantly in threads here when repairs need to be explained to their owners but the schematics are often linked too and these are useful guides to putting together your own arrangement or version which won't be too different to countless products that are already out there.

It seems from your comments that you really need to bone up on the design issues rather than stumble about with designs that may well work in their original application but maybe not in your arrangement, whatever that may be. We often recommend the standard books on power amplifier design by Douglas Self Amazon.co.uk: Douglas Self: Books The Douglas Self Site
and Bob Cordell Amazon.co.uk: Bob Cordell: Books CordellAudio.com - Home
but the subjects of preamplifiers and tone controls are not well covered under solid state amplification. The low level audio processed here is often classed as "line level" or "small signal" processing and tends to get treated differently in other forums here. A more comprehensive reference would be a better start.

Here is our "go-to" site for many general design and construction matters arranged in various sections with DIY projects, articles and links to further reading. It's a big site with a lot of well proven information and discussion. Try it first - Elliott Sound Products - The Audio Pages (Main Index) and check out the articles on designing with op-amps.
__________________
regards
  Reply With Quote
Old 27th March 2014, 05:23 AM   #3
diyAudio Member
 
dchisholm's Avatar
 
Join Date: Mar 2011
Location: St Louis, Mo
Perhaps the first thing you need to do is sit down and do some "system engineering" - express your requirements in engineering terms. Then start describing each of the blocks in your diagram using engineering terms. Finally, expand each of the blocks into a stand-alone circuit, or a portion of a larger circuit.

Each of these steps adds details to the previous step. It's OK if you can't totally complete one step before moving to the next - you may move back and forth between steps several times before your design is complete. (Your comment that the attenuator "has to go somewhere" is actually a good example of this process. You made a design decision based on incomplete information, knowing that the decision needs to be reconsidered as more information becomes available.) After you have a more definite idea of what each of your "three stages" must do, it will be easier to design each of them.

Dale
  Reply With Quote
Old 27th March 2014, 07:40 AM   #4
diyAudio Member
 
Join Date: Mar 2014
Thanks for the help. I think an integrated amp type system is what I'm going for. A few questions if I may:
If I find the model number for the transistor I'm using and hence the data sheet could you give me some help on biasing it correctly and getting it to amplify?
Does the output of my source and the input of my preamp have to be matched?
Is the inverting design okay for use as an preamp? Sound quality is not a priority; it just has to work. Honestly, the filters are the most important part.
  Reply With Quote
Old 27th March 2014, 07:46 AM   #5
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by nxtgenlva View Post
Thanks for the help. I think an integrated amp type system is what I'm going for. A few questions if I may:
If I find the model number for the transistor I'm using and hence the data sheet could you give me some help on biasing it correctly and getting it to amplify?
Does the output of my source and the input of my preamp have to be matched?
Is the inverting design okay for use as an preamp? Sound quality is not a priority; it just has to work. Honestly, the filters are the most important part.
Transistor type is usually very uncritical for anything like this and a good design would work with "most" devices without change.

The source impedance should normally be much lower than the input impedance of the following stage. A TL081 has a very low output impedance (not to be confused with its ability to drive low impedance loads)

The majority of (active) tone controls need an inverting amp to function.

If this is for coursework then it seems like you need to understand more of the basics tbh
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 27th March 2014, 01:03 PM   #6
diyAudio Member
 
Join Date: Mar 2014
Yeah, I do tbh... though I'm in the deep if I cant get it done because its due in the 4th of april. The syllabus is awful to be fair, it teaches how to pass an exam rather than teaching practical skills to be used in making circuits. I have a circuit ready and I'm wondering whether or not it will function to begin with and how I may improve it. Also, jsut so I know the theory behind it, why should the impedance of the stage after the source be much higher than the output impedance of the source? Wouldnt they need to be matched to allow for maximum power transfer?

Click the image to open in full size.
  Reply With Quote
Old 27th March 2014, 02:17 PM   #7
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
OK, some practical points.

Impedances... we are not after maximum power transfer here. If we have (say) a 1 volt rms signal level at the first opamp output, then we want to ensure that the signal remains as clean and undistorted as possible. That means loading the first opamp relatively lightly because distortion tends to increase the "harder" the device works. Around 2k would be a lower limit for those devices. A second problem is that loading the opamp more heavily will at some cause the max voltage swing available to limit. It might swing -/+15 volts into 10k, perhaps only -/+10 volts into 1k and only around a couple of volts into 100 ohms.

Power supply... you understand the supply type required for the circuit as drawn ?

Resistor values... although the above about loading holds true there are other problems going to high. Noise, prone to stray pickup of interference and worst of all, severe high frequency loss due to in circuit capacitances at the circuit nodes. If you make the 1megs 10k and scale accordingly it will be much better.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 27th March 2014, 10:49 PM   #8
diyAudio Member
 
dchisholm's Avatar
 
Join Date: Mar 2011
Location: St Louis, Mo
Quote:
Originally Posted by nxtgenlva View Post
. . . I'm in the deep if I cant get it done because its due in the 4th of april. . . .
I don't know how extensive your assignment is - e.g., are you required to create printed wiring boards, a comprehensive test report, compare measured performance to rigorous mathematical analysis, etc - but a week may be enough time if you don't have a lot of the other demands typical to college students (such as girlfriends, beer runs, all-night poker games, etc). In some cases, washing and waxing your instructor's car may get you a deadline extension.
Quote:
Click the image to open in full size.
I see some good progress here! Can you explain - at least to your own satisfaction, though ultimately you'll have to satisfy your instructor - how you arrived at these component values? (I don't expect you to actually post your entire analysis and calculations here, unless there's a particular detail you don't understand, or calculation you'd like to have checked.)

Your diagram doesn't show the transistor amplifier stage you mentioned in previous posts. Where is it used, what is its function, and what performance is required of it?

Quote:
. . . I have a circuit ready and I'm wondering whether or not it will function to begin with and how I may improve it . . . .
  • First, make it perform some semblance of what you expect it to do.
  • Then, measure what it is doing.
  • Decide what qualifies as an "improvement".
  • Use your understanding in conjunction with your intuition to suggest a change that may lead to an improvement.
  • Finally, repeat the above steps as necessary.
What tools are available to you for evaluating your design's functionality and performance? "Mooly" (http://www.diyaudio.com/forums/members/mooly.html) and I have differing philosophies on this, but I'd start with a decent circuit simulator. If you haven't been using something like Multisim or LTSpice or gEDA in your coursework up to this point, it probably isn't time to get acquainted with such tools - or perhaps it is. If you have assembled a circuit on a solderless experimenter's board or soldered it together on a vectorboard, posting a few clear, close-up, photos of your creation plus a complete schematic of what you intended to build will give others an opportunity to check your work.

Quote:
. . . The syllabus is awful to be fair, it teaches how to pass an exam rather than teaching practical skills to be used in making circuits . . .
You have more urgent things to do with your time than argue this point here. I have spent quite a bit of time on both sides of the classroom podium and know both sides of this claim. Students are often preoccupied with exams and grades because they perceive these things as the official coinage of the academic realm where they live, and there is some truth to that. Instructors see exams and grades as merely a superficial sampling of the material they teach, and even the material they taught is simply a step toward something much greater. As Dr. Jacob Bronowski, a 20th century physicist, said about recognizing when you truly understand something:
"The most powerful drive in the ascent of man is his pleasure in his own skill. He loves to do what he does well and, having done it well, he loves to do it better.

. . .

We have to understand that the world can only be grasped by action, not by contemplation. The hand is more important than the eye ... the hand is the cutting edge of the mind."
Dale
  Reply With Quote
Old 28th March 2014, 12:03 AM   #9
diyAudio Member
 
Join Date: Mar 2014
I have come on leaps and bounds, I have a far more comprehensive circuit diagram which I hope should work. A couple of things though:
Click the image to open in full size.
I am using this to help me build my circuit. May I ask what the 47nF cap does and also the 0.1uF+1R resistor tying the positive terminal to ground do?

I do have the full version of a program called livewire in college that I can use to simulate. I am currently using the trial version to build my circuit schematic. I can put the schematic on a pendrive and simulate tomorrow though before any building occurs.

I will explain values and the like when I have posted the final (hopefully) circuit diagram.

Last edited by nxtgenlva; 28th March 2014 at 12:13 AM.
  Reply With Quote
Old 28th March 2014, 12:27 AM   #10
diyAudio Member
 
Join Date: Mar 2014
Click the image to open in full size.
Here we go. The pairs of switches aren;t meant to be two separate pairs of switches. They are meant to to be single pole triple throw switches. I also had to use an op-amp for the LM380 chip. the line tied to ground comprises pins 3,4,5,6,10,11,12, input is pin 2, output is pin 3 and PSU pin is 14. 1, 9 and 12 are not connected. I don't see any real reason why this circuit shouldnt work. I will post explanations of values once I am up to date on my write up. It's going to be a long night

E. R4 should be 10K

Last edited by nxtgenlva; 28th March 2014 at 12:29 AM.
  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
[HELP] DIY College project Fraco Construction Tips 3 21st August 2010 12:34 AM
Help with a College Design Project... Phil Bhoy Everything Else 3 3rd April 2010 01:21 PM
My GhettoBlaster college Project vinaltap Full Range 5 17th May 2009 03:01 PM
Amplifier suggestion for college project tguzella^TuX64 Solid State 23 18th May 2005 09:50 AM
Build or buy? Logitech Z-680 & College student donga Multi-Way 3 19th August 2004 08:09 PM


New To Site? Need Help?

All times are GMT. The time now is 05:04 AM.


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