Convert TDA2030 to DC Coupled, Wholely Positive Voltage Output

[pnielsen]

Many of you would be familiar with the TDA2030 audio amplifier IC. Here is a typical circuit application. **broken link removed**

I would like to modify this into a DC coupled amplifier in which the output waveform is complete (not clipped) but offset to only swing between 0V and the 15V positive rail. I realize as a result the output wattage will be halved.

To restate this. I want to remove the negative-going polarity from the output signal while still leaving the original waveform intact. I prefer to use the TDA2030 because this is a modification to existing equipment.

The input signal would be from the push pull stage of an MP3 player, so that may also need to be offset prior to the amp.

Can anyone please propose a straightforward design approach? I will then draw and post for further comments.

 

[ronsimpson]

As far as DC coupling see below. Removed the input capacitor. Often there is a output capacitor to remove.

To restate this. I want to remove the negative-going polarity from the output signal while still leaving the original waveform intact.

Is this what you want?

swing between 0V and the 15V

The amplifier can not swing to the 15V rail. It can not swing to the negative rail. I can not find what the max output is but I think with a 0 & 15V supply the output must be about 3V to 11V.
What is your power supply voltage(s)?
---edited----
What are you doing?

 

[pnielsen]

Thank you for your reply. I would like the output waveform to be identical to the input (not clipped as you show in red), but offset to swing entirely above 0V, and as close to the positive rail as practical.

Power supply is +/-15VDC as per previous circuit diagram.

What I want to do is simulate, using the TDA2030, what used to be termed a "single ended" amplifier. In other words, the output is monopolar and does not cross into negative voltage region. The DC coupling is to allow passage of sub-audio frequencies.

I reralize the TDA2030 was not intended for this type of use, but I do not want to entirely rebuild the existing circuit.

 

[ronsimpson]

Like this?

 

[ronsimpson]

If the above picture is right; The output needs to be raised 6 volts. Pulling down on the (-) input a little will do that. (or pulling up on the (+) input.
The gain is about 31. 47K/1.5K=31. Need to move up 6V. So 6v/31=0.2v.

Just so you know this does not guarantee the output will not go negative. It only moves the "0" point up to 6V.

 

[pnielsen]

Yes, exactly that.

Please note that it is not feasible to use a transformer to offset the output because I need to pass sub-audio as well as audio.

 

[ronsimpson]

You can make the -0.2V with a 500 ohm pot and a 14k resistor to -15V.
One end of the variable resistor connected to ground. Wiper arm connected to 1.5k resistor. This will make about 0.5V across the pot and allow you to adjust the offset.

 

[pnielsen]

You just answered my next question as I was writing it.

So a 500R trimmer as a voltage divider, one side connected to the negative rail through a 14K resistor and the other to ground, with the center tap to the circuit's existing 1K5 resistor.

If this is done correctly, is there anything remaining that could cause the TDA2030 output to swing negative?

 

[ronsimpson]

is there anything remaining that could cause the TDA2030 output to swing negative?

I added a diode that will look for a case where the output goes -0.8V. If the output goes a little negative it will pull down on the (-) input causing the output to stop its downward movement.

 

[pnielsen]

Thank you for your generous and detailed advice. I will built this circuit over the weekend, and now expect no difficulties in getting it working.

 

[audioguru]

If you put an average of 6VDC into an 8 ohm speaker then the resulting 750mA of DC will push the cone to one side and also cause 4.5W of heating both the speaker and in the TDA2030. Which will melt first?

 

[ronsimpson]

8 ohm speaker

We do not know what he is driving. I asked. Probably not a speaker. "Sub sonic"

 

[pnielsen]

As part of an experiment, I intend to drive a solenoid coil ... through a 12R 30W resistor to avoid overloading the TDA2030.

With regard to audioguru's comment about a speaker coil overheating, this seems to imply that a speaker can only be safely driven by a complimentary output stage. My understanding is that speakers are sometimes driven by a monopolar signal.

I do not see why the cone would have to move both ways, but if not doing so is a problem, would adding more series resistance solve it? How would this be calculated?

 

[ronsimpson]

I think AudioGuru is saying; audio amps spend most of the life at 0 volts and 0 power. (or close to zero)
When you park the output at 6V there is power loss with no signal.

In your case the load is 12 ohms plus maybe 10 more ohms in the solenoid. So the power will be much less with 22 ohms then 8 ohm load.

Many speakers can not really handle the power they are rated for. Turn up the volume until the loudest part of music is 30 watts but the average might be 3 watts. The speaker coil heats to only 3 watts. You can, now with your DC coupled amplifier, place a DC voltage that will heat up the speaker to 30 watts. It was never designed to do that for very long.

 

[pnielsen]

What I had originally envisioned was for the amp output to sit at 0V and swing upward toward the positive rail.

Having looked at the TDA2030 type architecture, I can now see why this will not work. https://proxy.duckduckgo.com/iu/?u=...2015/04/The-schematic-diagram-TDA2050.jpg&f=1

Unless there is another solution, I will build the circuit Ron kindly provided and try doubling the load resistance to compensate for the DC offset.

Or maybe I would be better off building something simple from scratch, like an LM358 and 2N3055 emitter follower.

 

[ronsimpson]

Having looked at the TDA2030 type architecture, I can now see why this will not work.

why?
Maybe you should tell me what you are doing.
You said you want what is in post #4 but not what is in #2. They you say "output to sit at 0V". That is not consistent.
What about this? With no signal the output is at 0V. Input =+ out=+, input =- out=+.

I think you want audio to pull in a solenoid.
What is the pull in voltage and the hold voltage of the solenoid? And resistance.

 

[audioguru]

Of course you do not need an audio amplifier IC. You just need a variable DC voltage driving a power emitter follower transistor. If the emitter-follower is fully turned on then it will not get hot. It gets hot if it is partially turned on.

 

[pnielsen]

Excuse me for not being entirely clear. By "solenoid", I was referring to the winding configuration of the coil. Its purpose is simply to emit a magnetic field at frequencies between sub audio and the low audio range.

From what I have learned, the output of the TDA2030 circuit, previously linked to, swings between the plus and minus rails. Offsetting the 0V to half the positive rail, or around 6V, as you first suggested does not make the signal monopolar. I did mention in my first post that I wanted to "remove the negative-going polarity".

Since there appears to be no way to change this from the input side, what I was looking for is a method to DC offset the output external to the amp. I have seen this done with a biasing voltage (see link, pg. 3), but this is not suitable for my application since sub-audio frequencies would not pass the transformer. https://literature.cdn.keysight.com/litweb/pdf/5990-3466EN.pdf

I was hoping for a solution involving only passive components, but am now unsure if this is possible. Any further suggestions would be much appreciated.

 

[rjenkinsgb]

Its purpose is simply to emit a magnetic field at frequencies between sub audio and the low audio range.

Why not use a single-supply audio amp circuit, that works between 0V and positive supply to start with? Leave off the output coupling can and you have a unipolar varying drive to your coil.
Starting with a dual supply is part of the problem and over-complicating things, i think...

You can even use the TDA2030 if you want, with a minimum 12V supply -
**broken link removed**

 

[Nigel Goodwin]

With regard to audioguru's comment about a speaker coil overheating, this seems to imply that a speaker can only be safely driven by a complimentary output stage. My understanding is that speakers are sometimes driven by a monopolar signal.

Yes, but NOT permanent DC through the coil, which is what AG was referring to - for single supply amplifiers you simply connect the speaker via a large capacitor to remove the DC component.

However, I'n still extremely vague as to EXACTLY what you're trying to do?, other than it seems you're trying to do it in the most difficult way you can find, using something completely unsuitable for the task.