Active vs Passive Hi Pass Filter for Audio

[AltAudio]

LT Spice

Well I've downloaded this very versatile tool and I can't believe it's free. For hi/low pass filter designs however, am I able to tweak component specs in more of an itemized field listing such that I can quickly simulate outcome. I remember seeing a window that lists Freq, Mag, Phase and Group Delay fields. What is this window/feature called?

 

[AltAudio]

Flyback Type Inverter Circuit

Hello,

Using LT Spice I created this schematic. Everything works as expected-the collector outputs 18KHz pulses as desired, however trying to create a flyback type inverter as described in previous post

You can have DC on one side of a transformer primary if the other side of the primary is periodically switched to ground, which forms a flyback type inverter circuit. That type of inverter is typically used to achieve high secondary voltages.

- the DC creeps onto both sides of transformer, and actually backs up to collector output.

How would I be able to implement this flyback type inverter?

 

[AltAudio]

Measuring Impedance

Having trouble determining current at a specific point in circuit. In two different setups, o-scope registers 5V for both, but the current is different. How does one go about measuring this current at various spots within circuit?

 

[crutschow]

Using LT Spice I created this schematic. Everything works as expected-the collector outputs 18KHz pulses as desired, however trying to create a flyback type inverter as described in previous post - the DC creeps onto both sides of transformer, and actually backs up to collector output.

How would I be able to implement this flyback type inverter?

The transistor is acting as a switch and thus should have no collector or emitter resistor but must have a base resistor. The transistor then periodically connects one transformer input to ground for a period sufficient to built up the transformer current until the transformer is near saturation (the time for this to occur is determined by the voltage and the transformer primary inductance). When the transistor turns off, the inductive kickback voltage will be converted by the transformer turns ratio to give the output voltage.

(Note: This voltage can become quite high if the output is open circuited and can zap the transistor. Thus you would likely want to put a zener across the transistor collector to ground, with a breakdown voltage rating somewhat less than the transistor voltage rating).

 

[AltAudio]

Very interesting thank you Carl. I will implement Zeners too.

 

[AltAudio]

Single Power Supply for Op Amp

Trying to build a single power supply(right now I have bi-polar with 2 9V batteries). Am I able to hook two 9V in series? I suppose I'm questioning whether or not multiple batteries in series increases the voltage. I'm thinking it does not, only increases current. As such, I need to get a 12V source, is this correct?

 

[MikeMl]

(Equal voltage) Batteries in parallel increase the battery capacity (Ah), and allow a larger current to be drawn. Batteries in connected in series (- of first to + of second) add their respective voltages, while the capacity is no better than the worst of the two batteries.

 

[AltAudio]

Single Power Supply for Op Amp

Ok thanks, makes sense. Referring to sticky https://www.electro-tech-online.com/threads/basic-opamp-circuits.35258/, I am trying to build a single supply inverting circuit to coincide with the second stage of attached schematic. The first stage is inverting hi pass, while second stage is non-inverting signal amplification. In trying to build single power supply, am I correct using inverting rail of 2nd stage?

 

[MikeMl]

I see several problems. The signal from the first stage swings symmetrically both above and below ground. Your second stage and the transistor is referenced to ground, so will turn on only for the positive half cycles of the filtered signal. Is that what you are trying to do?

What is B1 supposed to be?

Why are both sides to the transformer primary shorted to V+?

Missing power supply connections on both opamps?

 

[audioguru]

The negative swing of the opamp exceeds the max allowed emitter-base voltage of 6V causing the emitter-base to have avalanche breakdown with slow damage occuring.

Is this the thread where the OP wants to "tingle" himself (or zap himself) with the stepped-up music signal?

 

[AltAudio]

Ok, here's a more updated schematic. The first stage atenuates anything below 12KHz from input audio, so I'm not sure what is meant by 'swings symmetrically' - this is in fact what I anticipated. The second stage is a non inverted amplification of filtered signal. Because the current was not strong enough, I added a LM386 Audio Amp directly after 2nd stage. Measuring the signal on output of 386 yields a very narrow width inverted pulse, which is exactly what is needed, and that is fed into left primary of transformer. Now with the right primary, through sheer trial and error, I was able to get the desired dc bias(not 100%) with a capacitor connected to 2N collector.

That being said, I thought I could hook a single power supply to non-inverted input of 2nd op amp(basically the feed from stage one). Is this possible, or should I use one of the remaining two op amps to create single power supply?

 

[audioguru]

The opamps are not powered.
The "bipolar" power supply connects both negative terminals to the audio input source and one positive terminal connects to the LM386.
The power supply does not connect to ground so the LM386 also is not powered.
The negative power supply is shown backwards and connects to nothing.
The positive and negative power supplies have no voltage so they are useless.
The lousy old LM324 opamp has trouble above only 2kHz.
The transistor does nothing.
The diode shorts half the signal from the LM386.

 

[AltAudio]

Ok does this look better?

I removed the transistor and made some adjustments to schematic. What exactly does this mean...

The lousy old LM324 opamp has trouble above only 2kHz.

I did notice that I hear a wispy pulsing sound emanating from the op amp. This is undoubtedly the bmp signal being filtered. Is this what is meant by unwanted oscillation?

 

[AltAudio]

MikeML, after reading...

The signal from the first stage swings symmetrically both above and below ground,

I thought to switch the order of the hi pass/gain op amps. Would this have any bearing on signal characteristics? As I was receiving the desired output, I did not realize the first stage was not inverting signal.

 

[audioguru]

The highpass filter has a cutoff at 12kHz so it needs an opamp that works well up to 100kHz. But the lousy old LM324 has trouble above 2kHz as shown on its datasheet.
The diode will charge the output capacitor and nothing will discharge it so the output will work for only a second or two.

Is the input signal level so low that the amplifier needs the gain of 1160?

 

[AltAudio]

Light Emitting Diode in this Circuit

Trying to hook an LED in this circuit and find it saps output current noticeably. The circuit that I'm trying to mimic has one side of LED getting signal from pulse signal from transistor collector, while other side receives V+ signal from source. There is also a forward threshold diode directly after V+ connection. Is this something I can leverage to make the LED work without losing current?

 

[audioguru]

The collector of the transistor has a capacitor to ground so it does not have a signal.
The base and emitter of the transistor connect to nothing so the transistor does nothing.
The diode short circuits the output of the LM386 amplifier.

Make the circuit like this:

 

[AltAudio]

Ok thank you.

 

[AltAudio]

Amazing audioguru- this design you suggested is producing the intended DC/AC configuration on transformer. I only added a jumper from voltage source to left primary and this somehow maintains a DC 5V on left side.The LED, with its forward threshold characteristics must be acting as some sort of buffer in this instance.

Many thanks for your input.

 

[audioguru]

The output impedance of the LM386 amplifier is extremely low like all modern amplifiers, maybe 0.04 ohms so the LED has no effect on its output.