No more tuners please [read]

[mstechca]

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.

 

[Roff]

Why can't we apply the KISS principle here, where KISS = Keep it Simple Stupid???

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.

 

[stevez]

There is a limit to what you can expect from this approach - though as you've demonstrated, some improvements can be made. You are turning up many of the reasons that this kind of circuit isn't often used. Taking a closer look at how the circuit actually functions would help you understand the limitations better.

A metal enclosure might help with some of the problems though it is possible that the metal enclosure could also affect the operation significantly. Improving mechanical rigidity of components, especially inductors and capacitors will reduce the impact of vibration or movement.

 

[Nigel Goodwin]

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.

Welcome to the world of super regen radio receivers!.

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.

Why?, I hesitate to use the term 'random changes' again, but this appears to be what you have done again?.

The amplification stage on the left is eliminated.

Fair enough!, if you only need low gain you can remove that stage.

the 0.47uF is changed to 100pF because the results are clearer and sound less distorted (and less volume).

BAD MOVE - 100pF is FAR too small, 0.47uF should be fine, leave as 0.47uF!.

the 390K in the 2nd stage (of his circuit) is changed to a 1.5M. Another 1.5M is placed between base and ground.

BAD MOVE, the 390K provides local negative feedback, your change will reduce the quality and upset the DC conditions of the stage.

Both 4.7K resistors are changed to 20K resistors, and the capacitors connected to them in parallel are removed.

Sounds another BAD MOVE, why did you do this?, and what is the collector voltage now?, an dwhat was it originally?.

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.

SERIOUSLY, SERIOUSLY BAD MOVE! - the 27K resistor is one of the gain setting components (along with the 390K) - you should refit the 27K, and I see no reason to change the 0.47uF, all it will do is reduce your bass response.

the 390K connected to Q3 is changed to a 470K.

Again WHY?, you've already ruined the operation of the stage, so it can't really make it any worse!.

the two diodes are changed to one diode and its part # is 1N4007

Again WHY?, they set the idle current of the output stage, doing this will give MUCH higher distortion at low volumes.

the 2.2K on the right is changed to 4.7K.

Why?.

the 1K between Q3 and ground is changed to 12 ohms.

Another BAD MOVE - presumably for no good reason?.

Transistors Q2 and Q3 are now BC547's instead of 2N3904's.

No problem with that.

Transistors Q4 is now TIP-31 and Q5 is now TIP-32.

Or that!.

My power source is 6VDC.

Probably NOT a good move, more voltage is always better, 6V is pushing this type of amplifier a bit.

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 need to build a 'proper' radio, rather than a regen, or fit it in a screened metal box, plus rebuild the amplifier as the original circuit was (not that it's great?, but your changes have made it greatly worse!).

 

[audioguru]

heh

I hope I caught your attention with the title haha.

You should have titled it, "How to ruin an amplifier design". Sorry.

the 0.47uF is changed to 100pF because the results are clearer and sound less distorted (and less volume).

Goodbye bass and most other audio frequencies.

the 390K in the 2nd stage (of his circuit) is changed to a 1.5M. Another 1.5M is placed between base and ground.

Less base current and the 1.5M from base to emitter has such a high value that it doesn't do anything.

Both 4.7K resistors are changed to 20K resistors, and the capacitors connected to them in parallel are removed.

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.
The caps reduced high audio frequencies and it probably sounds better without them.

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 cap change doesn't make much difference.
Shorting the 27k resistor makes the amp have about twice the gain. It works because the output impedance of the preceding transistor is about 20k. It won't work if the transistor had a low output impedance.

the 390K connected to Q3 is changed to a 470K.

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 two diodes are changed to one diode and its part # is 1N4007

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.
With a single diode or no diode, the transistors are off until a high enough signal level abruptly turns an output transistor on.
The 1N4148 diode spec'd closely matches the base-emitter diode of the transistors. The big 1N4007 rectifier doesn't.

the 2.2K on the right is changed to 4.7K.

The amp will have about twice the gain but its 390K resistor will need adjusting to compensate.
The max output level will be reduced.

the 1K between Q3 and ground is changed to 12 ohms.

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.

Transistors Q2 and Q3 are now BC547's instead of 2N3904's.

Same things but different pins layout.

Transistors Q4 is now TIP-31 and Q5 is now TIP-32.

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.

My power source is 6VDC.

The max output level is reduced to about half.
The biasing of all stages must be adjusted by a similar amount since they were designed for 9V.

So is there anyway I can improve the signal quality without losing a great amount of volume?

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.

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?

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.

I think I need another capacitor.

I used tiny little variable caps in my FM transmitter and they don't cause your problem.

Add a filter cap across the power supply. All battery powered circuits should have one. :lol:

 

[mstechca]

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?

 

[Nigel Goodwin]

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.

The tuner part only requires changes to the tuning circuit to try and make it work at a higher frequency, but I thought you were looking for channel 11?, which is VHF band 3.

You can't just go changing values without knowing what you are doing, you're more likely to make things worse - not better. One place where this doesn't really apply 100% is with opamp circuits, their design is such that you can effectively ignore the chip and concentrate on the external components (feedback etc.).

Thanks for the circuit.

Yes, I'd have added the bootstrap circuit as well, it's a VERY simple change, and will increase the power capability of the output stage quite dramatically (particularly with the low supply rail).

In your last circuit, is the impedance of the signal entering Q3 27K, 31.7K, 4.7K, or am I lost?

The input impedance of the power amplifier will be roughly 27K (the value of the input resistor), it's basically a simple inverting opamp circuit.

It's not usually simple to calculate input and output impedances, except in opamp circuits! - it's usually far easier (and more accurate) to measure them. I would measure the preamp stages, rather than try and calculate them.

 

[audioguru]

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.

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.
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.

In your last circuit, is the impedance of the signal entering Q3 27K, 31.7K, 4.7K, or am I lost?

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.

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]

I can see an oscilloscope as a good tool to have, but I can't afford it! god, 1/2 the time I can't even afford my lunch because my income is spent on rent, and no, I'm not living in a fancy hotel. LOL

Here's the interesting part. In Rick's original superregen, (see below)

**broken link removed**

he has a 0.47uF capacitor in series with a 12K resistor. Along with my other modifications, I even modified this part. I knocked off the 12K resistor, and I played with this capacitor. It seems that the capacitor can make a huge difference. I find that anything under 100 pF causes a ton of distortion, and anything above 680 pF causes lower volume, but better quality.

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.

I am so lost on equations. The only one I seem to know is Ohms Law.

 

[Nigel Goodwin]

Can someone tell me every single equation involved in the circuit, and then maybe something is off.

As already explained, MANY times, you can't do calculations on these types of circuit, because stray capacitance and inductance make up a large part of the values. The circuit of a super-regen itself is also fairly 'obscure' which makes life even more difficult.

But the only equations you really need to know are:

Ohms law.
Capacitive reactance.
Inductive reactance.
Resonance of a tuned circuit.

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.

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.

 

[mstechca]

Ohms law.
Capacitive reactance.
Inductive reactance.
Resonance of a tuned circuit.

Where and when do I apply Capacitive and Inductive reactance, and what values are optimal and why?

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.

What is the maximum reactance I can have at audio frequencies? and what is the limit on reactance at RF?

 

[audioguru]

Bye.
I like to talk about complicated modern circuits that do their job well, not simple fundamental basics that should be learned in an electronics course.
Jumping from this post about ordinary transisors and audio amps then suddenly back over to the super-regen revisited post is the end for me.
This simple super-regen is just a crappy toy.

 

[mstechca]

wtf!

No one ever taught me impedance in school!

How am I supposed to know stuff that was never taught?

it would be highly insane for me to search for a special college that has a course that talks about impedance!

:shock: :shock: :shock:

 

[Nigel Goodwin]

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).

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.

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]

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).

That's about all I know about impedance, as well as determining reactance from frequency and one of capacitance and inductance.

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.

I like that explanation. Maybe some of the equations I use work after all.

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.

You basically told me everything I knew in general.

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?

 

[Nigel Goodwin]

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?

There is no set maximum or limit, but above (or below) certain values the changes cease to make any difference.

For an example, consider a simple high pass filter - a series capacitor, and a resistor from the output down to ground.

When the frequency is such that the reactance of the capacitor equals the resistance of the resistor, the signal passing through will be attenuated by half - a simple potential divider with equal values.

As the frequency increases, the reactance of the capacitor decreases, and the attenuation of the potential divider decreases. You will eventually reach the point where the attenuation is negligible - increasing the frequency further will have no further noticeable effect.

Incidently, this simple high pass filter is one of the design elements you were altering by changing the coupling capacitors.

 

[mstechca]

I think there is a catch,

but I'll take your word for it and I'll see if my design improves.

 

[mstechca]

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.

It seems that station quality at VHF improves from this.
Now its a matter of finding perfect values.

 

[Nigel Goodwin]

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.

This is what I mean by 'random changes', you appear to have no idea what the capacitor you've added is supposed to do, nor if it should be there or not?.

In actual fact it's simply in parallel with the lower one!, depending on it's value it's probably giving treble cut?.

 

[mstechca]

If I only had a cap from base to ground, then I would get more treble. If I had both capacitors, it seems that more bass is applied, and therefore, the sound is more normal.