Most piezo transducers have a max allowed sine-wave signal of 24V RMS which is 68V peak-to-peak.It is a bridged power amplifier which injects 24V to the transducer.
A bridged car amplifier has an output of 14 watts into 4 ohms which is 21V peak-to-peak. If the amplifier is not bridged then the signal is about 11.2V peak-to-peak into 8 ohms which is only 1.96 Watts RMS at clipping.What are you meaning by 2W out of of a 30W amplifier for an speaker?
A step-up transformer driven from two small transistors can be used. A power amplifier is not needed since the power to the piezo transmitter transducer is very low.So whats the solution please?
The ratio of the feedback resistor to R10 determines the gain. C2 stops the opamp from amplifying the DC voltage.what are those resistor/capacitor (R10 & C2) in your last circuit that are in series?
Most piezo transducers have a max allowed sine-wave signal of 24V RMS which is 68V peak-to-peak.
A bridged car amplifier has an output of 14 watts into 4 ohms which is 21V peak-to-peak. If the amplifier is not bridged then the signal is about 11.2V peak-to-peak into 8 ohms which is only 1.96 Watts RMS at clipping...
A step-up transformer driven from two small transistors can be used. A power amplifier is not needed since the power to the piezo transmitter transducer is very low...
But it amplifies the dc Offset, or maybe I misunderstood you?The ratio of the feedback resistor to R10 determines the gain. C2 stops the opamp from amplifying the DC voltage.
Audio power is measured with a sine-wave input and the volume control is increased until the amplifier clips the sine-wave.The power supply is a 12 to 14V DC so whats the peak to peak output for the audio which Is not a pure sine??? I am getting confused!
The datasheet for the transducer lists its impedance which is probably 10k ohms. You do not need to know the impedance. Simply feed it with enough voltage swing. An 8 ohms to 1k ohms transformer steps up the voltage 11.2 times.I have to know the impedance of the transducer. Does a ohm meter do it for me
C2 blocks DC, so the gain to the 9V modulator bias (R3 and R4) is 1. C2 is a very low impedance (<<10k) at audio frequencies, so the gain is 1+R11/R10.
You have pin3 input of the opamp at 13.5VDC which is way too high. The opamp will not work if it is higher than about 11V (with your 14V supply). Ron has it at 10.5V.Ron,
I simulated your last modification circuit by Pspice. Bellow is the result.
I think there is a Small fault yet? Please take a look at the waveform at the time domain. Why the modulated signal is not so good at peaks or envelopes or whatever you call them, that seems to be clipped at peaks?!
Besides when I change the value of the R9 and use a higher resistor I get a strange waveform?!
Why do you ask for help, and then change the op amps and the modulator bias voltage?Ron,
I simulated your last modification circuit by Pspice. Bellow is the result.
I think there is a Small fault yet? Please take a look at the waveform at the time domain. Why the modulated signal is not so good at peaks or envelopes or whatever you call them, that seems to be clipped at peaks?!
Besides when I change the value of the R9 and use a higher resistor I get a strange waveform?!
Why do you ask for help, and then change the op amps and the modulator bias voltage?
LT1366 is a rail-to-rail op amp. I chose it for this application. If you want to use TL072, you will have to live with less output swing, which is probably not a bad thing.
Did you try simulating exactly what I posted, before you made the modifications?please do not be angry Ron,
First I tried Your bias So I changed the values of those resistors to inject more offset to see if the waveform wants to be ok.
Besides In your before modification You used a pot For those 2 resistors so I thought they are a Pot yet.
You don't need high speed op amps for the two that are in the schematic.Are you talking about that behaviuor of several op amps that audioguru told about it before? If so I must say that a looked around for a high speed opamp to use instead of tl072, I just found LM318, When I used it I had a distored bad output.
auduguru, What is your idea of using LM833 instead tl072?
You don't need high speed op amps for the two that are in the schematic.
For 100% modulation, the upper sine wave needs to swing from vcc/2 to vcc, and the lower sine wave needs to swing from vcc/2 to 0V. In order to make this happen, the DC bias on the upper sine wave needs to be 75% of Vcc if you are using rail-to-rail op amps. When you invert the upper sine wave around vcc/2, the lower sine wave will be biased at 25% of vcc, which is what you need.Ron,
A technical question, How did you notice that those resistor values must be used there (R3 & R4 at your modification)? Just using a voltage divider formula?
Their spec's are almost identical.auduguru, What is your idea of using LM833 instead tl072?
For 100% modulation, the upper sine wave needs to swing from vcc/2 to vcc, and the lower sine wave needs to swing from vcc/2 to 0V. In order to make this happen, the DC bias on the upper sine wave needs to be 75% of Vcc if you are using rail-to-rail op amps. When you invert the upper sine wave around vcc/2, the lower sine wave will be biased at 25% of vcc, which is what you need.
If you are not using rail-to-rail op amps, tell us what you want to use and we can tell you the bias voltage that will give you the highest possible amplitude 100% modulation without audio distortion or overmodulation.
Below is a simulated output waveform of my last circuit, but with Vcc=+14V and Vin=0.7V p-p (0.35V peak). This is the highest-level 100% modulation waveform you can achieve with a 14V supply. If you make the bias voltage lower, you can still get 100% modulation, but at a lower amplitude. If you make the bias voltage higher, you will not be able to achieve 100% modulation without clipping the peaks of the audio.
The ratio of R3/R4 is calculated from this relationship:
R3/(R3+R4)=0.75
Their spec's are almost identical.
The same power bandwidth and very low distortion.
The TL072 has FET inputs so it has a very low bias current and has low noise at high source resistances.
The LM833 has ordinary transistors at the input for normal bias current and has low noise at low source resistances.
They sound the same.
You have seen from the waveform that I posted that it works. Do you think it should be different? You should be able to study the waveform and the explanation I posted to understand it.Thanks Ron,
I agree with you about that Vc/2, but can not understand why you inserted the 75% and 25% when the modulation index is 100% yet?
What supply voltage do you want to use?I want to use TL072 as single ended (using resistor dividers).
You have seen from the waveform that I posted that it works. Do you think it should be different? You should be able to study the waveform and the explanation I posted to understand it.No I d not think so, Just wanted to know the reason.
What supply voltage do you want to use?
I use 14V as power supply
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