Simulation of 12-Watt Amp Help

[kbyrne]

AS a newbi to electronics I have a simulation question. Am I correct that total amps can be measured in attached circuit accurately? Schematic  called for 2 Amps but did not include RC circuit addition for hum
problem. Transistors used were ProtoLab ideal as the program is limited in choices. Ideal or 2N2907 ect.

[Hero999]

Why do you have what looks like a current source and voltage source connected in parallel?

It will inject 2A into the voltage source so the ammeter's reading will be equal to the amplifier's total current consumption (which is almost nothing when there's no signal) minus 2A.

Is the 10R resistor supposed to be the load? If so Why is it in series with 0.1uF?

[kbyrne]

Becuase I am new to this. How to do this the right way? That is why I post. Not due to my being a person
who is a know it all type. How would you show a student the right way? Thanks for the post thou, I do not
get mad at anything. I need all the help I can get.

[Hero999]

Becuase I am new to this. How to do this the right way? That is why I post. Not due to my being a person
who is a know it all type. How would you show a student the right way? Thanks for the post thou, I do not
get mad at anything. I need all the help I can get.

I wouldn't show a student the right way. Believe it or not, that wouldn't be helping them at all in the long run. It may help them pass the assignment but it wouldn't help them with the exam or when they get a job and have to do it for real. I'd help the student by giving hints about what they're doing wrong and let them figure it out.

I've never heard of ProtoLab so I can't help you with the specifics. If you can't find the model for the transistors you used, I suggest you create your own from the parameters given on the datasheets.

You need to label the schematic properly. Give each component an indent, i.e. C1, C2, Tr1, Tr2, R1, R2 etc. That way people helping you can refer to the components on your schematic. You could flip some of the components to make it easier to read and save the schematic as a .PNG or .GIF file. JPG is designed for photographs and is a lossy format so gets fuzzy after a few saves.

Going back to the schematic. On the right you have a 2A constant current source (call it I1), connected in parallel with the 36V power supply (V1), with the ammeter connected in series (M1) and reads 1.62A.

Can you figure out the current actually drawn by your circuit?

Try removing I1 and noting the the reading on M1.

[kbyrne]

Thankyou for the post. I am busy for the moment but will print your reply and study it carefully. I am new but accept critism well enough. Tanks

[audioguru]

I fixed the schematic:
1) I removed the horrible dark background that was covered with dots.
2) I cropped it.
3) I straightened all the "dog legs".
4) I put the PNP transistors right side up and left to right.
5) I marked "X" on one useless resistor.

EDIT: The 0.1uF capacitor in series with the 10 ohms resistor at the output is a Zobel network to prevent oscillation.

[kbyrne]

Thankyou. I have downloaded your piece of work and will study all your posts today. One question concerning the two 100ohm resistors. Is the milliamps to the TO-92 transistors right per ohms law and data sheets? I receive different replys conserning that am trying to study the circuit with ProtoLab to figure that aspect of circuit design. The  design works but with hum. The additional capacitor and 1k RC circuit are for that purpose.
A capacitance mutliplier power supply is also being designed for a revised box.

[audioguru]

Doesn't your schematic look awful with the dark green background covered in dots and with backwards and upside down transistors?

I think the hum comes down the extra 2.2k resistor directly into an input. The extra 2.2k resistor is not needed because the right side input transistor is biased from the 10k feedback resistor.

I would change the 100 ohm resistors to 1k so that the driver transistors do not get too warm.

I would bootstrap the 5.6k resistor or change it to a high impedance current source then the open loop gain will be much higher, the distortion will be much lower and the maximum power at clipping will be higher.  

[kbyrne]

The schematic is a ProtoLab simulation program. Problem is the transistors are Ideal not the specified
2N3906, 2N3904, Tip31C & Tip32C. Do you know and can recomend a better simulation program where I can stipulate the correct part # and data sheet? I am askeing you because I have been following your
name for a while and like your advise. I am printing this topic and studying it to redo a plastic box in
metal till final box no hum. Thankyou

[Hero999]

LTSpice is one of the most popular simulators in hobbyist circles. It's a powerful SPICE simulator and you can easilly creat your own models from the datasheets.

[kbyrne]

I will check your Spice advise ASAP Thankyou. As far as useless 2.2k resistor and changing the other 2.2k to 1k and finally adding the capacitor a question arises. The construction article in G. Randy Sloans book
states that both resistors are used to keep the supply voltage at 18.0 volts at the center node to keep the voltage at emitters of Q4 & Q6 close to 18.0 volts. If that is necessary why remove the voltage devider
and raise the voltage at emitter legs? What is bootstraping as I cannot find that Termonology or definition
anywhere. Thankyou

[audioguru]

As far as useless 2.2k resistor and changing the other 2.2k to 1k and finally adding the capacitor a question arises. The construction article in G. Randy Sloans book states that both resistors are used to keep the supply voltage at 18.0 volts at the center node to keep the voltage at emitters of Q4 & Q6 close to 18.0 volts.

No.
The input voltage divider at the input with two 22k resistors sets the center node at 18V. The 2.2k voltage divider fed hum into the negative feedback input and messed up the voltage at the center node.
The negative feedback through the 10k resistor from the output to the input of transistor 2 lets the center node adjust itself.

What is bootstraping as I cannot find that Termonology or definition anywhere.

Spelled correctly as "Bootstrapping (electronic)" then Google finds many definitions like this one:
http://en.wikipedia.org/wiki/Bootstrapping_(electronics)

Bootstrapping allows the output to swing symmetrically, adds open-loop voltage gain and reduces distortion.

[kbyrne]

Thanks for the info, I am trying out LTSpice ASAP. The attachment is some work I did with voltages and currents and Beta. Are my firures right as the two output transistors in ProtoLab are Ideal not Tip31C &
Tip32C. You schematic put the voltages right on the money thou. I will research the link you gave me also.
Either way a new metal box with a capacitance multiplier power supply is in the near future.