Why don't you apply this philosophy to your posts? You could edit the schematic and make it a lot simpler for us to understand what you did. This would probably get you more replies.Why can't we apply the KISS principle here, where KISS = Keep it Simple Stupid???
mstechca said:heh
I hope I caught your attention with the title haha.
ANYWAYS, I have a question.
I managed to make my superregen (see my 1/2 completed schematic on the superregen revisted thread) work. I can pick up the local TV station.
Here's the interesting part. As soon as I try modifying the amplifier portion of the radio, it seems that I'm getting an extra tuning control with my hand. As soon as my hand is at most 2 inches away from the actual tuner, the stations automatically change on me. I don't want this to happen.
Basically, my amplifier design is quite similar to Rick anderson's own version of the "Radio Shack powered amplifier". found at this link: **broken link removed**
BUT I have made a few modifications.
The amplification stage on the left is eliminated.
the 0.47uF is changed to 100pF because the results are clearer and sound less distorted (and less volume).
the 390K in the 2nd stage (of his circuit) is changed to a 1.5M. Another 1.5M is placed between base and ground.
Both 4.7K resistors are changed to 20K resistors, and the capacitors connected to them in parallel are removed.
the 0.47uF capacitor between Q2 and Q3 is changed to 0.1uF and the 27K resistor is shorted because I dont want to lose too much volume.
the 390K connected to Q3 is changed to a 470K.
the two diodes are changed to one diode and its part # is 1N4007
the 2.2K on the right is changed to 4.7K.
the 1K between Q3 and ground is changed to 12 ohms.
Transistors Q2 and Q3 are now BC547's instead of 2N3904's.
Transistors Q4 is now TIP-31 and Q5 is now TIP-32.
My power source is 6VDC.
So is there anyway I can improve the signal quality without losing a great amount of volume? and is there any way to minimize or prevent the stations from continuously changing as my hand moves anywhere within two inches of the tuning capacitor?
I think I need another capacitor.
You should have titled it, "How to ruin an amplifier design". Sorry.mstechca said:heh
I hope I caught your attention with the title haha.
Goodbye bass and most other audio frequencies.the 0.47uF is changed to 100pF because the results are clearer and sound less distorted (and less volume).
Less base current and the 1.5M from base to emitter has such a high value that it doesn't do anything.the 390K in the 2nd stage (of his circuit) is changed to a 1.5M. Another 1.5M is placed between base and ground.
Increasing the resistor's value increased the gain about 4 times for each one and agrees with the similar change of the bias you made with the 1.5M resistor.Both 4.7K resistors are changed to 20K resistors, and the capacitors connected to them in parallel are removed.
The cap change doesn't make much difference.the 0.47uF capacitor between Q2 and Q3 is changed to 0.1uF and the 27K resistor is shorted because I dont want to lose too much volume.
Its value should be adjusted for about half the supply voltage at the output transistors where they connect to the output capacitor. The resistance depends on Q3 because each transistor isn't the same.the 390K connected to Q3 is changed to a 470K.
Now you have crossover distortion. Two diodes are used in all audio amps to provide temperature compensated about 1.3V between the bases of the output transistors to keep them turned-on slightly.the two diodes are changed to one diode and its part # is 1N4007
The amp will have about twice the gain but its 390K resistor will need adjusting to compensate.the 2.2K on the right is changed to 4.7K.
This totally messes-up the DC bias. Use the 1K resistor as shown, and connect a 47 ohm resistor in series with a 100uF cap across the 1K resistor for much more gain and distortion.the 1K between Q3 and ground is changed to 12 ohms.
Same things but different pins layout.Transistors Q2 and Q3 are now BC547's instead of 2N3904's.
TIP power transistors have much less current gain than small audio transistors. They will work in this circuit but will produce a lower max output level and have more distortion.Transistors Q4 is now TIP-31 and Q5 is now TIP-32.
The max output level is reduced to about half.My power source is 6VDC.
Why not make the circuit as designed, removing the 0.01uF caps at Q1 and Q2. Add a bootstrap network as the load for Q3 for a higher max output level and much less distortion.So is there anyway I can improve the signal quality without losing a great amount of volume?
Use extremely short wiring to the cap and have its screw adjustment terminal connected to the bypassed side of its circuit. Having the circuit in a grounded metal box helps too, but it still will mis-tune when you get near its antenna.is there any way to minimize or prevent the stations from continuously changing as my hand moves anywhere within two inches of the tuning capacitor?
I used tiny little variable caps in my FM transmitter and they don't cause your problem.I think I need another capacitor.
Why not make the circuit as designed?
mstechca said:Why not make the circuit as designed?
Because the original circuit was intended to operate at VHF, and I want to enter UHF. And I thought I got more gain by increasing the negative feedback resistors in each transistor stage.
Thanks for the circuit.
In your last circuit, is the impedance of the signal entering Q3 27K, 31.7K, 4.7K, or am I lost?
mstechca said:A properly designed tuner will have the same output level at UHF that it has at VHF so you won't need more audio gain.Because the original circuit was intended to operate at VHF, and I want to enter UHF. And I thought I got more gain by increasing the negative feedback resistors in each transistor stage.
The negative feedback resistor in a single transistor stage affects its DC bias operating point, and is used because of the wide range of current gain in a make of transistor and in case the supply voltage changes. It affects AC amplification very little because the transistor has an input impedance of about 3k to 10k which is so much less than its value.
The bootstrapping in my last posted circuit increases the AC amplification of Q3 to a high amount, therefore with negative feedback through the 390k resistor the input impedance of Q3 is very low. The 27k resistor determines the input impedance of the Q3 to Q5 output amplifier.In your last circuit, is the impedance of the signal entering Q3 27K, 31.7K, 4.7K, or am I lost?
I think you would understand DC biasing, AC gain, clipping and crossover distortions much better if you used an oscilloscope and a sine-wave generator to see what happens when you change something in an audio circuit:
1) You could change the negative feedback resistor in a single transistor stage and watch its collector voltage change with it, until the transistor is cutsoff when you will see the top part of the sine-wave get clipped, or until the transistor saturates when you will see the bottom part of the sine-wave get clipped.
2) You could also see a high level output of a high output impedance single transistor stage get reduced by being loaded-down from connecting a low impedance circuit to its output.
3) You could also see the interaction of stages and see the gain of the Q3 to Q5 output amplifier get reduced by increasing the value of its 27k input resistor when you expect more gain from the preceding single transistor stage since it wouldn't be loaded-down so much.
4) You could short one or both bias diodes in a complementary emitter-follower output stage of an amplifier and see the crossover distortion that is produced. :lol:
mstechca said:Can someone tell me every single equation involved in the circuit, and then maybe something is off.
also, I think that I am tuned to some ridiculously high frequency. why? because if the capacitor (from base of Q3 to ground) acts as a low pass filter and I'm obtaining greater volume, I think I'm hearing harmonics.
Where and when do I apply Capacitive and Inductive reactance, and what values are optimal and why?Ohms law.
Capacitive reactance.
Inductive reactance.
Resonance of a tuned circuit.
What is the maximum reactance I can have at audio frequencies? and what is the limit on reactance at RF?The capacitor from base to ground acts as a decoupling capacitor at RF, setting the conditions of the transistor as common base - at audio frequencies it's reactance will be far too high to act as a decoupler.
That's about all I know about impedance, as well as determining reactance from frequency and one of capacitance and inductance.You don't need a course 'just for impedance', you need a basic electronics course - if you don't even know what impedance is then you haven't done even a very basic beginners course.
Impedance is to AC what resistance is to DC, so a 1K resistor will have a resistance of 1K AND an impedance of 1K (as a resistor is non-reactive).
I like that explanation. Maybe some of the equations I use work after all.A coil will have a DC resistance of one value, and a different impedance value, which changes with frequency - the impedance will always be higher than the DC resistance, and will increase with frequency.
A capacitor will not have a DC value, it 'should' be completely open circuit, but at AC it will have an impedance value, decreasing as frequency increases.
You basically told me everything I knew in general.Essentially capacitance and inductance are opposites, it should be easy to see that if you use the two together there will be a frequency when their impedances (reactances) are the same - this is how a tuned circuit works.
It's somewhat more complicated than that, but that should give you some idea of what it's all about.
mstechca said:But I have a question, and I'll say it again.
What is the maximum reactance I can have at audio frequencies? and what is the limit on reactance at RF?
mstechca said:I think capacitors are a benefit to my design. I just added another one between base and +ve of the NPN transistor driving the push-pull pair.
there was already one between base of the same transistor and ground.
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