The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to weather conditions here in Ontario) so I thought I'd try my hand at making my own audio amplifier kit.
The requirements were as follows:
Must use components I already have. I couldn't find any 1N4148 but did find packets of 1N4001 so that's what I used. Also I could only find one resistor under 1 ohm so another is made from two in parallel.
Must be simple enough to fit on one piece of breadboard but not be a trivial design.
Must deliver enough power to make an 8 ohm speaker cone move visibly.
Must run from a single 9V battery.
Must be quick to design with minimal calculation.
Any soldering must be done in advance of taking it into a school and getting a little guy to build it.
Doesn't need high voltage gain as it will be driven from an ipod so I designed for a gain of about 10.
Low distortion is not essential as long as there's no obvious issue below clipping level.
With those requirements in mind I got a piece of paper out and drew this:
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Then I did the layout:
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Then I built and tested it:
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Actually there was much overlap between those three things.
I set VR2 to zero resistance and measured an idle current of 60mA, so I didn't adjust VR2. I then connected a signal source from a computer, adjusted VR1 and the requirements seemed to have been met.
I'm aware that there are people here who can comment on my amplifier design skills, or lack of them, and maybe some component values can be tweaked for better performance.
Are there any free tools available which can run a simulation of this circuit? What is the lower and upper 3dB bandwidth? Is my wild guess at a value for C6 reasonable?
On a sunny day (Wed, 29 Jan 2014 13:02:18 -0500) it happened "John Smith" wrote in :
Only thing is an emitter resistor in TR4 to make it a more of a real current source. I think R8 is asking for trouble, just short it, but keep C3. C4 is big relatve to the supply decoupling caps, maybe works with a good battery / voltage source.
LT spice.
LT spice will tell you, but if you use some soundcard with a sweep audio file any scope will tell you. If you do not have a frequency sweep audio file I can make one available for download.
Wow. Lots of components for not much amplification -- but if you're eschewing op-amps and coils, and want a class-AB output stage, I guess that's what you need to do.
Check out LTSpice, from Linear Technology. It's supposed to be a tool for marketing their power supply chips, but it's a great all-around simulation tool.
I'd suggest you answer your questions about bandwidth and C6 with LTSpice, if you can't just do the circuit analysis yourself.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Wow.. I was just at that page... trying to recall how he did the class A th ing.
To John Smith. I was going to say that if the students are going to understand it then a s imple class A type design might be better. (though wastful of the battery) I wonder if you need any voltage gain at all? Would using an audio transformer be OK?
One thing that struck me is that you are not going to get taht much power f rom a 9V battery. (What's the internal resistance of the battery? I stuck 100 ohms across a 9V and Vout dropped to ~8V, but this is an old battery t hat's been sitting on my bench for a while) So perhaps a beefier battery o r a higher impedance speaker.
Thanks for your comments. I could have used an op amp but I think the breadboard area required would be roughly the same. There is probably a single chip power op amp available which could do it with no other active devices at all but that would talke some of the fun out of building it.
It's more about having fun bulding it and watching it work. The student isn't likely to be able to fully understand how it works yet.
Possibly but I don't have any audio transformers except those on some old amplifier boards I have from the days when designers were still thinking tubes and used both a driver tansformer and an output transformer with a pair of transistors, usually germanium devices.
It's true that the battery isn't likely to last long. It will be interesting to see what happens as it runs down.
In my experience that's always how I start, but when I actually try both I end up finding that the op-amp solution takes less space.
I'm shooting off the cuff here, but I think you could take out everything from just to the left of C1 all the way to, and including, TR4 and C6, and replace it with an op-amp, possibly with an emitter-follower into the base of TR5.
Some audio guy will come on and tell you that yes, I guessed right or no, I'm full of holes.
I certainly agree for you and me. A kid raised on video games may run out of patience before they get your circuit hooked up, though.
I'd go with one little black bug, then have an "advanced" class for the kids that stick around, or maybe have your protoboard with all the transistors ready to pull out and try.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
A little guy is going to build that? Cut 'im some slack! Do something like this:
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TIP29/30 or 31/32 will do for the outputs, 2N3904 will do for the gain. Umm, you'll want to adjust the values a little for 9V operation, and obviously it won't give 10W then.
Simple mod: "Q capacitor" to the top of the 1k (add another resistor in series) to bootstrap the pullup.
Den onsdag den 29. januar 2014 20.53.09 UTC+1 skrev John Smith:
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copy paste into file *.asc run in ltspice
Version 4 SHEET 1 880 680 WIRE -512 -288 -656 -288 WIRE -352 -288 -512 -288 WIRE -240 -288 -352 -288 WIRE -160 -288 -240 -288 WIRE -96 -288 -160 -288 WIRE 64 -288 -16 -288 WIRE 256 -288 64 -288 WIRE 560 -288 256 -288 WIRE -656 -256 -656 -288 WIRE -512 -256 -512 -288 WIRE -160 -256 -160 -288 WIRE 64 -192 64 -288 WIRE 560 -192 560 -208 WIRE -512 -144 -512 -176 WIRE -16 -144 -512 -144 WIRE 0 -144 -16 -144 WIRE 256 -144 256 -288 WIRE 128 -96 64 -96 WIRE 192 -96 128 -96 WIRE -848 -48 -992 -48 WIRE -16 -48 -16 -144 WIRE 16 -48 -16 -48 WIRE 128 -48 128 -96 WIRE 128 -48 80 -48 WIRE 256 -32 256 -48 WIRE -992 -16 -992 -48 WIRE -848 -16 -848 -48 WIRE 128 0 128 -48 WIRE -512 32 -512 -144 WIRE -352 32 -352 -288 WIRE -848 80 -848 64 WIRE -752 80 -848 80 WIRE -656 80 -656 -176 WIRE -656 80 -688 80 WIRE -576 80 -656 80 WIRE -96 80 -288 80 WIRE -80 80 -96 80 WIRE 256 80 256 48 WIRE 256 80 0 80 WIRE 432 80 256 80 WIRE 560 80 496 80 WIRE 640 80 560 80 WIRE 720 80 640 80 WIRE -848 96 -848 80 WIRE 128 96 128 64 WIRE 256 112 256 80 WIRE -432 128 -512 128 WIRE -352 128 -432 128 WIRE -240 128 -240 -288 WIRE -96 128 -96 80 WIRE 128 176 128 160 WIRE -432 192 -432 128 WIRE 256 208 256 192 WIRE -848 224 -848 176 WIRE -96 224 -96 208 WIRE -240 240 -240 208 WIRE -240 240 -368 240 WIRE 192 256 128 256 WIRE -240 272 -240 240 WIRE 128 304 128 256 WIRE -656 320 -656 80 WIRE -432 320 -432 288 WIRE -240 368 -240 336 WIRE 560 384 560 80 WIRE 560 384 128 384 WIRE -656 464 -656 400 WIRE -432 464 -432 400 WIRE -432 464 -656 464 WIRE -240 464 -240 432 WIRE -240 464 -432 464 WIRE -96 464 -96 288 WIRE -96 464 -240 464 WIRE 256 464 256 304 WIRE 256 464 -96 464 FLAG 256 464 0 FLAG 640 160 0 FLAG -848 224 0 FLAG -160 -192 0 FLAG 560 -192 0 FLAG -992 64 0 FLAG -992 -48 input IOPIN -992 -48 In FLAG 720 80 output IOPIN 720 80 Out SYMBOL npn 192 -144 R0 SYMATTR InstName Q1 SYMATTR Value BC547B SYMBOL pnp 0 -96 M180 SYMATTR InstName Q2 SYMATTR Value BC557B SYMBOL npn -576 32 R0 WINDOW 3 -38 -21 Left 2 SYMATTR InstName Q3 SYMATTR Value BC547B SYMBOL npn -288 32 M0 WINDOW 3 -36 -23 Left 2 SYMATTR InstName Q4 SYMATTR Value BC547B SYMBOL npn -368 192 M0 SYMATTR InstName Q5 SYMATTR Value BC547B SYMBOL pnp 192 304 M180 SYMATTR InstName Q6 SYMATTR Value BC557B SYMBOL res -448 304 R0 SYMATTR InstName R1 SYMATTR Value 470 SYMBOL res -256 112 R0 SYMATTR InstName R2 SYMATTR Value 22k SYMBOL res 240 96 R0 SYMATTR InstName R3 SYMATTR Value .5 SYMBOL res 240 -48 R0 SYMATTR InstName R4 SYMATTR Value .5 SYMBOL res -528 -272 R0 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL res -672 -272 R0 SYMATTR InstName R6 SYMATTR Value 22k SYMBOL res -672 304 R0 SYMATTR InstName R7 SYMATTR Value 22k SYMBOL diode -256 368 R0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode -256 272 R0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL cap 80 -64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 470p SYMBOL diode 144 0 M0 WINDOW 3 -72 0 Left 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL diode 144 96 M0 WINDOW 3 -82 30 Left 2 SYMATTR InstName D4 SYMATTR Value 1N4148 SYMBOL res 112 160 R0 SYMATTR InstName R8 SYMATTR Value 50 SYMBOL res -112 112 R0 SYMATTR InstName R9 SYMATTR Value 1k SYMBOL res 16 64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R10 SYMATTR Value 10k SYMBOL cap -80 288 R180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C2
SYMBOL cap 496 64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3
SYMBOL res 624 64 R0 SYMATTR InstName R11 SYMATTR Value 8 SYMBOL res 112 288 R0 SYMATTR InstName R12 SYMATTR Value 330 SYMBOL cap -688 64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4
SYMBOL res -864 80 R0 SYMATTR InstName R13 SYMATTR Value 22k SYMBOL res -864 -32 R0 SYMATTR InstName R14 SYMATTR Value 22k SYMBOL cap -176 -256 R0 WINDOW 3 39 37 Left 2 SYMATTR InstName C5
SYMBOL res 0 -304 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R15 SYMATTR Value 100 SYMBOL voltage 560 -304 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 9 SYMBOL voltage -992 -32 R0 WINDOW 3 -328 54 Left 2 WINDOW 123 -328 82 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value SINE(0 1 1000 0 0 0 1000) SYMATTR Value2 AC 1 TEXT -1320 448 Left 2 !.tran 1
On a sunny day (Wed, 29 Jan 2014 14:31:54 -0600) it happened "Tim Williams" wrote in :
The voltage at the speaker will swing below ground by itself, the bootstrap is already there. The price is a very small DC current in the speaker, no problem.
"Lasse Langwadt Christensen" wrote in message news: snipped-for-privacy@googlegroups.com... Den onsdag den 29. januar 2014 20.53.09 UTC+1 skrev John Smith:
Thanks for going to that much effort Lasse but I've got started with drawing the schematic myself in LT Spice and will compare it with yours when I'm done figuring out which function key does what. How do I change a designator? i.e. change Q3 into Q4?
Old Guy
copy paste into file *.asc run in ltspice
Version 4 SHEET 1 880 680 WIRE -512 -288 -656 -288 WIRE -352 -288 -512 -288 WIRE -240 -288 -352 -288 WIRE -160 -288 -240 -288 WIRE -96 -288 -160 -288 WIRE 64 -288 -16 -288 WIRE 256 -288 64 -288 WIRE 560 -288 256 -288 WIRE -656 -256 -656 -288 WIRE -512 -256 -512 -288 WIRE -160 -256 -160 -288 WIRE 64 -192 64 -288 WIRE 560 -192 560 -208 WIRE -512 -144 -512 -176 WIRE -16 -144 -512 -144 WIRE 0 -144 -16 -144 WIRE 256 -144 256 -288 WIRE 128 -96 64 -96 WIRE 192 -96 128 -96 WIRE -848 -48 -992 -48 WIRE -16 -48 -16 -144 WIRE 16 -48 -16 -48 WIRE 128 -48 128 -96 WIRE 128 -48 80 -48 WIRE 256 -32 256 -48 WIRE -992 -16 -992 -48 WIRE -848 -16 -848 -48 WIRE 128 0 128 -48 WIRE -512 32 -512 -144 WIRE -352 32 -352 -288 WIRE -848 80 -848 64 WIRE -752 80 -848 80 WIRE -656 80 -656 -176 WIRE -656 80 -688 80 WIRE -576 80 -656 80 WIRE -96 80 -288 80 WIRE -80 80 -96 80 WIRE 256 80 256 48 WIRE 256 80 0 80 WIRE 432 80 256 80 WIRE 560 80 496 80 WIRE 640 80 560 80 WIRE 720 80 640 80 WIRE -848 96 -848 80 WIRE 128 96 128 64 WIRE 256 112 256 80 WIRE -432 128 -512 128 WIRE -352 128 -432 128 WIRE -240 128 -240 -288 WIRE -96 128 -96 80 WIRE 128 176 128 160 WIRE -432 192 -432 128 WIRE 256 208 256 192 WIRE -848 224 -848 176 WIRE -96 224 -96 208 WIRE -240 240 -240 208 WIRE -240 240 -368 240 WIRE 192 256 128 256 WIRE -240 272 -240 240 WIRE 128 304 128 256 WIRE -656 320 -656 80 WIRE -432 320 -432 288 WIRE -240 368 -240 336 WIRE 560 384 560 80 WIRE 560 384 128 384 WIRE -656 464 -656 400 WIRE -432 464 -432 400 WIRE -432 464 -656 464 WIRE -240 464 -240 432 WIRE -240 464 -432 464 WIRE -96 464 -96 288 WIRE -96 464 -240 464 WIRE 256 464 256 304 WIRE 256 464 -96 464 FLAG 256 464 0 FLAG 640 160 0 FLAG -848 224 0 FLAG -160 -192 0 FLAG 560 -192 0 FLAG -992 64 0 FLAG -992 -48 input IOPIN -992 -48 In FLAG 720 80 output IOPIN 720 80 Out SYMBOL npn 192 -144 R0 SYMATTR InstName Q1 SYMATTR Value BC547B SYMBOL pnp 0 -96 M180 SYMATTR InstName Q2 SYMATTR Value BC557B SYMBOL npn -576 32 R0 WINDOW 3 -38 -21 Left 2 SYMATTR InstName Q3 SYMATTR Value BC547B SYMBOL npn -288 32 M0 WINDOW 3 -36 -23 Left 2 SYMATTR InstName Q4 SYMATTR Value BC547B SYMBOL npn -368 192 M0 SYMATTR InstName Q5 SYMATTR Value BC547B SYMBOL pnp 192 304 M180 SYMATTR InstName Q6 SYMATTR Value BC557B SYMBOL res -448 304 R0 SYMATTR InstName R1 SYMATTR Value 470 SYMBOL res -256 112 R0 SYMATTR InstName R2 SYMATTR Value 22k SYMBOL res 240 96 R0 SYMATTR InstName R3 SYMATTR Value .5 SYMBOL res 240 -48 R0 SYMATTR InstName R4 SYMATTR Value .5 SYMBOL res -528 -272 R0 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL res -672 -272 R0 SYMATTR InstName R6 SYMATTR Value 22k SYMBOL res -672 304 R0 SYMATTR InstName R7 SYMATTR Value 22k SYMBOL diode -256 368 R0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode -256 272 R0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL cap 80 -64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 470p SYMBOL diode 144 0 M0 WINDOW 3 -72 0 Left 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL diode 144 96 M0 WINDOW 3 -82 30 Left 2 SYMATTR InstName D4 SYMATTR Value 1N4148 SYMBOL res 112 160 R0 SYMATTR InstName R8 SYMATTR Value 50 SYMBOL res -112 112 R0 SYMATTR InstName R9 SYMATTR Value 1k SYMBOL res 16 64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R10 SYMATTR Value 10k SYMBOL cap -80 288 R180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C2
SYMBOL cap 496 64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3
SYMBOL res 624 64 R0 SYMATTR InstName R11 SYMATTR Value 8 SYMBOL res 112 288 R0 SYMATTR InstName R12 SYMATTR Value 330 SYMBOL cap -688 64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4
SYMBOL res -864 80 R0 SYMATTR InstName R13 SYMATTR Value 22k SYMBOL res -864 -32 R0 SYMATTR InstName R14 SYMATTR Value 22k SYMBOL cap -176 -256 R0 WINDOW 3 39 37 Left 2 SYMATTR InstName C5
SYMBOL res 0 -304 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R15 SYMATTR Value 100 SYMBOL voltage 560 -304 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 9 SYMBOL voltage -992 -32 R0 WINDOW 3 -328 54 Left 2 WINDOW 123 -328 82 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value SINE(0 1 1000 0 0 0 1000) SYMATTR Value2 AC 1 TEXT -1320 448 Left 2 !.tran 1
Here: Cut and paste the following into a text file, save it as "audio.asc", then open it with LTSpice. Making a reduced-part-count op- amp stage is left as an exercise to the reader.
(Some real audio guy will laugh at me for this, I'm sure).
Version 4 SHEET 1 880 680 WIRE 288 -96 -512 -96 WIRE 288 -48 288 -96 WIRE 128 0 -80 0 WIRE 224 0 128 0 WIRE 128 64 128 0 WIRE 288 64 288 48 WIRE 128 160 128 128 WIRE 288 176 288 144 WIRE 352 176 288 176 WIRE 384 176 352 176 WIRE 480 176 448 176 WIRE 496 176 480 176 WIRE -80 192 -80 0 WIRE 288 208 288 176 WIRE 128 240 128 224 WIRE 496 256 496 176 WIRE 288 304 288 288 WIRE -80 320 -80 272 WIRE -80 320 -160 320 WIRE -512 336 -512 -96 WIRE 128 352 128 320 WIRE 224 352 128 352 WIRE -80 368 -80 320 WIRE 128 384 128 352 WIRE -512 496 -512 416 WIRE -80 496 -80 448 WIRE 128 496 128 464 WIRE 288 496 288 400 WIRE 496 496 496 336 FLAG 128 496 0 FLAG 288 496 0 FLAG 496 496 0 FLAG -80 496 0 FLAG -512 496 0 FLAG 480 176 Vout FLAG -160 320 Vin FLAG 352 176 Ve SYMBOL npn 224 -48 R0 SYMATTR InstName Q1 SYMATTR Value 2N4401 SYMBOL pnp 224 400 M180 SYMATTR InstName Q2 SYMATTR Value 2N4403 SYMBOL res 272 48 R0 SYMATTR InstName R1 SYMATTR Value .47 SYMBOL res 272 192 R0 SYMATTR InstName R2 SYMATTR Value .47 SYMBOL diode 112 64 R0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 112 160 R0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL res 112 368 R0 SYMATTR InstName R3 SYMATTR Value 330 SYMBOL cap 448 160 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1
SYMBOL res 480 240 R0 SYMATTR InstName R4 SYMATTR Value 8 SYMBOL res 112 224 R0 SYMATTR InstName R5 SYMATTR Value 0 SYMBOL voltage -512 320 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 9 SYMBOL voltage -80 176 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 5.5 SYMBOL voltage -80 352 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value SINE(0 3 2000 0 0 0 0) TEXT -360 504 Left 2 !.tran 100m
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Or one, yes. Your VR2 is really just one resistor that changes when you turn a knob. Usually in LTSpice (or any SPICE) such user input isn't modeled -- it's up to you to enter the resistance that would be there.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Many thanks to Lasse Langwadt Christensen and Tim Wescott for posting LT spice files.
I haven't looked at them yet because I wanted to get familiar with drawing a schematic in LT spice. I've used schematic capture systems before. I was pleasantly surprised with the LT spice schematic capture interface even if it does remind me of Windows 3.0
Here is my first ever LT spice schematic.
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Now I will have a look at Lasse and Tim's files and see if I can run a simulation.
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