Solderless audio amplifier

Ok thanks Tim, I figured that the answer would probably be something like that but it would still be nice to have a symbol for a variable resistor which takes two fixed resistance values for the parts above and below the slider.

Old Guy

Reply to
John Smith
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Den torsdag den 30. januar 2014 00.43.06 UTC+1 skrev John Smith:

just click the little running man in the tool bar and put in a stop time

-Lasse

Reply to
Lasse Langwadt Christensen

but you can do something like this:

Version 4 SHEET 1 880 680 WIRE 272 80 96 80 WIRE 96 128 96 80 WIRE 528 160 272 160 FLAG 96 208 0 FLAG 272 240 0 FLAG 528 160 out IOPIN 528 160 Out SYMBOL voltage 96 112 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 1 SYMBOL res 256 64 R0 SYMATTR InstName R1 SYMATTR Value {10k*(1-a)} SYMBOL res 256 144 R0 SYMATTR InstName R2 SYMATTR Value {10k*a} TEXT 272 288 Left 2 !.step param a = 0.001 0.999 .1 TEXT 62 308 Left 2 !.tran 1

Reply to
Lasse Langwadt Christensen

Put a voltage source at the input, set up as either AC (for AC analysis) or with a sine wave (right-click then push the "advanced" button). If you have crossover distortion the AC analysis will be messed up -- you need to have some standing current in the output transistors for AC analysis to be sensible.

Rename one or the other of your 'C3' to 'C7', or 'C42', or whatever.

Put a resistor in for the speaker, lest your gain be infinite.

Then hit the little running man like Lasse said.

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Reply to
Tim Wescott

Thanks Tim

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I set the DC operating point for an idle current of 50mA by setting R13 to

22 ohms.

It took me a while to figure out how to do an AC plot but it looks like the value of C6 is a bit low for an audio amplifier.

Old Guy

Reply to
John Smith

Your power filter of R8 and C3 is definitely not right. The voltage difference between the two circuit halves is going to modulate TR4 via R3. It will thump during power-on and probably motor-boat when the battery is low. The only thing that needs filtering is the voltage divider on your input. Everything else is running in constant current mode and is fine with unregulated voltage.

I don't know what current is flowing through TR3, but it should be adjusted so that C6 charges and discharges symmetrically. Sometimes you can put a long wire on the input and adjust the current until you stop hearing AM radio stations :)

Unless it's there to be educational, replace whole constant current regulator around TR3 with a simple resistor. You only have +/- 0.4V of input swing to reach full modulation. The current through a resistor should be close enough.

Reply to
Kevin McMurtrie

Many thanks for your comments. I moved the power filter to the input voltage divider. 330uF is probably overkill. I've also given the battery a 2 ohm internal resistance.

TR3 was mostly intended to be educational but for the present circuit I have replaced TR3 with a 4.7k resistor. The LTspice model says that the current in the resistor is 0.82 mA.

Can I use the LTspice model to find out whether C6 is charging and discharging symetrically?

The current circuit is here:

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Quick view here:
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I've also added an equivalent circuit for a loudspeaker which came from here:

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I've no idea how close that is to my real loudspeaker but it may be closer than an 8 ohm resistor.

A bode plot of V(input)/V(output) from 5Hz to 3MHz shows the expected 20dB voltage gain. The gain and phase are fairly flat over the audio range but the unity gain frequency appears to be about 2.3 MHz. Is there any advantage in reducing that for an audio amplifier? Apart from reducing the potential for amplification of AM radio signals?

Does annyone know whether any of the models on this page can ne used in LTSpice?

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Old Guy

Reply to
John Smith

Thanks Lasse. I ran your ciruit and found a nice sine wave at the output.

Now I want to put some pulses in to see how it handles fast rise and fall times.

Old Guy

Reply to
John Smith

Thanks Tim. I can see the sinewave at Vout.

Old Guy

Reply to
John Smith

I haven't put my two cents in yet but here it is :

First of all, C4 should be nowhere near 4700 uF. You are not driving a 12" woofer with it. Look at those good old stereo console pieces of junk, they got by with as low as like 220 uF. Since it isn't in the feedback loop anyw ay, forget about phase shift, it means nothing.

Next, you are not submitting this thing for evaluation by the IHF (are the even still around ?) or Hifi magazine (same question) so you can totally el iminate Q2 and just send the feedback (DC and AC) straight to the emitter o f Q1. I would suggeast lower values for the voltage divider to yield a lowe r impedance, off the top of my head use 4.7K for R7 and 470 for R5. Elimina te C2 of course or the thing won't work.

That will set your feedback at about 1/10th of the center voltage at R10 an d 11. With your voltage divider there, make the voltage at the base of Q1 a bout that, just add schoch for the drain of Q1. It really doesn't have to b e all that accurate. Accuracy comes later.

Increase R1 and C3 to charge slowly and reduce the turnon transient. Whate ver the voltage divider feeding the base of Q1, figure the bottom resistor against the input coupling cap to give the desired lower frequency limit, t here is no reason to be concerned about anything below 100 Hz unless your s peakers are going to reproduce it. If they are, that can be done later. (yo u might want heftier transistors and a realer battery at that point)

Reply to
jurb6006

I worded that worng but you know what I mean.

Reply to
jurb6006

Den torsdag den 30. januar 2014 20.44.39 UTC+1 skrev John Smith:

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if you hover over the component you get the amp meter

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P31A

The easiest way (keeping everything in the same file), is to change the nam e of the transistor to the models name Qtip31 and then add the model as a s pice directive on the schematic

Version 4 SHEET 1 1728 680 WIRE 560 -64 256 -64 WIRE 256 0 256 -64 WIRE 256 112 256 80 WIRE 560 112 560 -64 WIRE 496 160 256 160 WIRE 256 208 256 160 WIRE 560 224 560 208 WIRE 256 336 256 288 WIRE 560 336 560 304 FLAG 256 112 0 FLAG 256 336 0 FLAG 560 336 0 SYMBOL voltage 256 -16 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL npn3 496 112 R0 SYMATTR InstName Q1 SYMATTR Value Qtip31 SYMBOL voltage 256 192 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 -485 52 Left 2 SYMATTR InstName V2 SYMATTR Value PULSE(0 1.7 1m 500m 500m 10m 20m 1) SYMBOL res 544 208 R0 SYMATTR InstName R1 SYMATTR Value 1 TEXT 64 312 Left 2 !.tran 1 TEXT 904 -120 Left 2 !.MODEL Qtip31 npn\n+IS=1e-09 BF=3656.16 NF=1.23

899 VAF=10\n+IKF=0.0333653 ISE=1e-08 NE=2.29374 BR=0.1\n+NR=1.5 VAR=100 IKR=0.333653 ISC=1e-08\n+NC=1.75728 RB=6.15083 IRB=100 RBM=0.00113049\n+RE=0.0001 RC=0.0491489 XTB=50 XTI=1\n+EG=1.05 CJE=3.26475e-10 VJE=0.446174 MJE=0.464221\n+TF=2.06218e-09 XTF=1 5.0842 VTF=25.7317 ITF=0.001\n+CJC=3.07593e-10 VJC=0.775484 MJC=0 .476498 XCJC=0.750493\n+FC=0.796407 CJS=0 VJS=0.75 MJS=0.5\n+TR =9.57121e-06 PTF=0 KF=0 AF=1

-Lasse

Reply to
Lasse Langwadt Christensen

Thanks for your comments. I used that capacitor because I had it available, it's probaby between 30 and 40 years old.

Before I saw your post I experimented with removing Q2 as follows:

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Quick View:
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I adjusted the component values for what seemed to be reasonable DC operating conditions with correct center voltage and same voltage gain. The bode plot looks reasonable over the audio range, unity gain frequency is now about 1MHz.

I haven't looked in the time domain yet to see if there are any other issues.

I was going to ask if there was any good reason to keep Q2.

Old Guy

Reply to
John Smith

Interesting. Your method seems perfect for one-offs. Thank you for sharing. Another way is to add TIP31A as a component into LTSpice. This way the TIP31A always appears under component misc TIP31A

The TIP31A.asc file shown below uses the TIP31A component.

------------------------------------------------------------------------ These lines go into C:\Program Files\LTC\LTspiceIV\lib\sub\TIP31A.sub

------------------------------------------------------------------------

*NPN silicon power transistor: TIP31A SUBCKT TIP31A 1 2 3 ************** C B E Q1 1 2 3 NMOD MODEL NMOD NPN(IS=1e-09 BF=3656.16 NF=1.23899 VAF=10 +IKF=0.0333653 ISE=1e-08 NE=2.29374 BR=0.1 +NR=1.5 VAR=100 IKR=0.333653 ISC=1e-08 +NC=1.75728 RB=6.15083 IRB=100 RBM=0.00113049 +RE=0.0001 RC=0.0491489 XTB=50 XTI=1 +EG=1.05 CJE=3.26475e-10 VJE=0.446174 MJE=0.464221 +TF=2.06218e-09 XTF=15.0842 VTF=25.7317 ITF=0.001 +CJC=3.07593e-10 VJC=0.775484 MJC=0.476498 XCJC=0.750493 +FC=0.796407 CJS=0 VJS=0.75 MJS=0.5 +TR=9.57121e-06 PTF=0 KF=0 AF=1 ) ENDS TIP31A

------------------------------------------------------------------------ These lines go into C:\Program Files\LTC\LTspiceIV\lib\sym\Misc\TIP31A.asy

------------------------------------------------------------------------

Version 4 SymbolType CELL LINE Normal 44 76 36 84 LINE Normal 64 96 44 76 LINE Normal 64 96 36 84 LINE Normal 40 80 16 64 LINE Normal 16 80 16 16 LINE Normal 16 32 64 0 LINE Normal 16 48 0 48 WINDOW 0 56 32 Left 0 WINDOW 3 56 68 Left 0 SYMATTR Value TIP31A SYMATTR Prefix X SYMATTR Description Bipolar NPN transistor SYMATTR SpiceModel TIP31A SYMATTR ModelFile TIP31A.sub PIN 64 0 NONE 0 PINATTR PinName C PINATTR SpiceOrder 1 PIN 0 48 NONE 0 PINATTR PinName B PINATTR SpiceOrder 2 PIN 64 96 NONE 0 PINATTR PinName E PINATTR SpiceOrder 3

------------------------------------------------------------------------ These lines go into TIP31A.asc

------------------------------------------------------------------------ Version 4 SHEET 1 880 680 WIRE 240 32 48 32 WIRE 400 32 240 32 WIRE 400 64 400 32 WIRE 48 80 48 32 WIRE 240 80 240 32 WIRE 400 160 400 144 WIRE 240 256 240 160 WIRE 320 256 240 256 WIRE 240 320 240 256 WIRE -80 368 -208 368 WIRE 48 368 48 160 WIRE 48 368 -16 368 WIRE 176 368 48 368 WIRE -208 400 -208 368 WIRE -208 528 -208 480 WIRE 240 528 240 416 FLAG 400 160 0 FLAG 240 528 0 FLAG -208 528 0 SYMBOL voltage 400 48 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 10V SYMBOL res 224 64 R0 SYMATTR InstName R1 SYMATTR Value 1K SYMBOL res 32 64 R0 SYMATTR InstName R2 SYMATTR Value 580K SYMBOL cap -16 352 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 1\xc2\xb5 SYMBOL cap 384 240 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 1\xc2\xb5 SYMBOL Misc\\signal -208 384 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value SINE(0 25mV 1K) SYMBOL Misc\\TIP31A 176 320 R0 SYMATTR InstName Q1 TEXT -232 104 Left 2 !.tran 10ms

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Reply to
Don Kuenz

and 40 years old. "

It might be better off as the main filter, though still overkill. The probl em is that it is going to take a while to charge and discharge, so you woul d want to have the input side also charge slowly. Then you are capable of d riving at subwoofer frequencies. If your source has a bass boost it'll eat all the power up in notime. I would let the low end response roll off at ma ybe 100 Hz. If you get a bigger speaker then modify it.

When I said jump out C2 the intent was to lower the DC voltage required at the base of Q1 so it wouldn't take forever to charge. Actually the way you have it is just fine and has the advantage of being less susceptable to cha nges in Vbe on Q1. More stable as the battery dies as well, I would say kee p it that way.

You almost don't really need R1 and C3, but they will help reduce the turno n transient. Let C3 charge slow. I don't feel like figuring the time consta nt right now, but you want it slower than C4 charges. (do lower that C4 val ue !) Other than that it is not critical.

On something like this, simplicity is wonderful. Remember what they used to tell engineers - don't waste silicon. (eyeing D3 or D4 with an evil eye... )

Reply to
jurb6006

snip

the much simpler way is to add it to the file

....\LTC\LTspiceIV\lib\cmp\standard.bjt

then it'll be in the list of transistor you can choose

-Lasse

Reply to
Lasse Langwadt Christensen

Some do realtime interaction... EWB, and the "circuit simulator" module in GCompris would be two examples. I would not recommend the latter.

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Reply to
Jasen Betts

As long as you don't need to share the model with anybody. For client work I generally cut'n'paste the model right into the .ASC file, and then hide the text.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

indeed, keeping every thing in a single file so it'll run anywhere makes life a lot easier when you have to share or run on multiple computers

would be nice with an option to embedded all the models in .asc file automatically

-Lasse

Reply to
Lasse Langwadt Christensen

Your way is the best way. I just need to figure out how to use CVS or something to keep track of the changes to standard.bjt in order to preserve my additional models after Linear releases a newer version of LTSpice. Thank you for sharing.

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Reply to
Don Kuenz

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