AVC measurements?
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And here is the FFT for the full lam stack, this time only -6dB attenuation but the input signal is the same as before @ -18dBFS (-3dB is 2Vrms). Distortion is zero. That little pip @ 2kHz was not a harmonic since it was just part of the noise floor. I just happened to hit "print screen" when it was up. This is really outstanding performance! I'm very pleased!
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docali wrote:Hello Dirk!
Very nice measurements!
But as such results much depends on the source impedance would you please tell us what was the source impedance of you function generator and what was the schematic for measurement? Was this device loaded?
Thanks!
Docali
the circuit is the AVC as an input, with an opamp set to unity gain directly connected to the output of the AVC. power was by 9V batteries. so no, the AVC is unloaded on the output since the unity gain opamp presents an infinite load (effectively) to the AVC. This is basically the way I intend to use it.
Source impedance for the FFT's is unknown, but low. I used a Tascam UH-7000 for those. For the square wave results, I used an analog oscillator that has a 600 ohm source impedance. It's a Kenwood oscillator.
Hello Dirk!
You state that the source impedance of the oscillator is about 600 Ohms. In this case it is no wonder that there is less ringing. The 600 Ohms damps the TVC quite good. But what when you drive it with abot 200 Ohms or even 50 Ohms? Then you see the truth
You can do this while driving the oscillator into an resistor divider 560R-56R and drive the TVC around the 56R resistor. The ringing should be much more pronounced. These TVCs should be driven from fairly low source impedances. I doubt that 600 Ohms will do the best job but Dave can maybe say more about what should be the source impedance of the driving stage.
Thanks!
Bernd
You state that the source impedance of the oscillator is about 600 Ohms. In this case it is no wonder that there is less ringing. The 600 Ohms damps the TVC quite good. But what when you drive it with abot 200 Ohms or even 50 Ohms? Then you see the truth
You can do this while driving the oscillator into an resistor divider 560R-56R and drive the TVC around the 56R resistor. The ringing should be much more pronounced. These TVCs should be driven from fairly low source impedances. I doubt that 600 Ohms will do the best job but Dave can maybe say more about what should be the source impedance of the driving stage.
Thanks!
Bernd
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I'm not concerned with ringing, so I'm not going to do the test you describe, thanks. I checked it with a digital generator that has very low source impedance and it performed very well as I recall. It's not an issue for me.
What is an issue is DC balance for the following gain stage after the AVC. Since I use op amps and feedback, I need to make the feedback network have equivalent DC resistance as the AVC. This is not possible with resistors, so I have to use an inductive feedback network in order to achieve low enough DC resistance there. I am in the process of developing such a network myself, however, the cost for the entire product will be much higher because of that. I do not make, nor am I interested in, passive preamps.
What is an issue is DC balance for the following gain stage after the AVC. Since I use op amps and feedback, I need to make the feedback network have equivalent DC resistance as the AVC. This is not possible with resistors, so I have to use an inductive feedback network in order to achieve low enough DC resistance there. I am in the process of developing such a network myself, however, the cost for the entire product will be much higher because of that. I do not make, nor am I interested in, passive preamps.
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Still no ringing. I used a nice digital oscillator with very low output Z and there was no ringing. They were perfect square waves.docali wrote:Hello Dirk!
You state that the source impedance of the oscillator is about 600 Ohms. In this case it is no wonder that there is less ringing. The 600 Ohms damps the TVC quite good. But what when you drive it with abot 200 Ohms or even 50 Ohms? Then you see the truth
You can do this while driving the oscillator into an resistor divider 560R-56R and drive the TVC around the 56R resistor. The ringing should be much more pronounced. These TVCs should be driven from fairly low source impedances. I doubt that 600 Ohms will do the best job but Dave can maybe say more about what should be the source impedance of the driving stage.
Thanks!
Bernd