I know some people (maybe you aren't saying this) claim that Gyrators don't store energy - but as far as I can see this isn't the whole story. Gyrators do store energy. They store it in the capacitor. They store less energy than the equivalent inductor, but they can still store a lot of energy.
As I understand, a capacitor stores the energy in the electric field between it's plates, the inductor in the magnetic field. The key difference is the way in which the energy is stored and then released.
An inductor stores energy when current flow generates a magnetic field. It then releases the energy when the magnetic field collapses back down and in doing so it induces a voltage in the coil. The voltage is mostly limited by the load impedance, so it can rise to a higher voltage than the supply rails. This fact is exploited in tube amps. So, energy goes in via a current flow, comes back out as a voltage that drives a current through an impedance.
A capacitor stores energy when a voltage is held across it's plates, which drives a current to accumulate charge on the plates. It then releases energy when the charge flows out as a current through an external load. The key difference here is that the discharge current is voltage driven so the voltage can not ever exceed the supply rail that was used to charge the capacitor in the first place. So the gyrator can never properly mimic an inductor even if it can store a good deal of energy.
Or maybe I've got this wrong
Capacitor stores, but gyrator does not. It is an electronic device that is powered and draws power in order to work. You are absolutely right.
Here is a gyrator similar to what we used in ICs to build equalizers:
http://upload.wikimedia.org/wikipedia/commons/1/16/Op-Amp_Gyrator.svg
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For now on I shall say the TeddyRegs "seem to have" a capacitance multiplier...or I better say nothing!
Call it "RC filter with emitter follower", everyone would understand you!
Sure, for up to 500V of voltage. And don't forget to protect it's gate by Zener between gate and source.
I use similar transistors to regulate voltages for vacuum tube amps.
Edit: or do you mean the schemo in the 1'st post? Sure! 20N50D were first devices I tried in exactly such follower many years ago. Sounded fantastishe. With this driver: http://wavebourn.com/images/audio/Tower-I.gif
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Beatifull. I will have to wait until the kids are gone to play with tubes
Maybe an IXYS 20N50D power follower deserves its own thread in the future...
Vgs is 30V so the PS shall be +60VDC?
Apart, to Hugh and Wavebourn: a voltage reference for the second Mosfet, the CCS, shall sound different if built based on LEDs or on Zener?
Maybe an IXYS 20N50D power follower deserves its own thread in the future...
Vgs is 30V so the PS shall be +60VDC?
Apart, to Hugh and Wavebourn: a voltage reference for the second Mosfet, the CCS, shall sound different if built based on LEDs or on Zener?
Beatifull. I will have to wait until the kids are gone to play with tubes
Maybe an IXYS 20N50D power follower deserves its own thread in the future...
Vgs is 30V so the PS shall be +60VDC?
No.
It depends on how much power do you agree to dissipate on your MOSFETs and what is load resistance.
It does not matter really. It will sound nice even with a resistive divider shunted by a capacitor.
Thank you Hugh, I lived in apartment then, and my ex was "happy" about my electronics projects. However, she tolerated them because hoped to get a huge profit.
I did not. Because I have my barn where I have my laboratory, my metalworking workshop, woodworking workshop, and a warehouse.
Oh Anatoliy,
I can see my working table is nothing compared to yours
It's Ok Pavel; I knew that you are mostly a theoretician!
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Ahh, but there is no DC going through the inductor! There is a funny looking AC current going through the inductor. Since the L resists the changes in the current, it tends to flatten the waveform so the current charging the cap after the L tends to become more "constant" (but not DC because it stops and starts 100 or 120 times per sec). Therefor, the voltage on that cap becomes more ripple free but also lower because the average value of the current also gets lower.
Download PSU designer from Ben Duncan, you can play with it and see the waveforms.
jd
even i am OT here...
I have an interesting problem now.
I am running the follower from a 20v-0-20v/4A rated EI transformer and this current rating with 40v output is the maximum available from retailers here.
The transformer becomes hot after almost an hour of operation and thermally stabilizes at about 75-80 degrees Celsius, which I think is really hot; barely touchable. It's almost the end of winter here and maximum midday temperature is about 24-28 degrees C. In the Summer it becomes and remains more than 30 deg C. for many days and midday temp often rises to 45 deg C.
With the current darw of ~2.5A I think the transformer will get too hot in summer and probably will fail.
So I thought of a workaround as the summertime fail-safe. The configuration is depicted in the picture below.
The dissipation in the transformer decreases with the lower voltage output. I think this will do good in summer. The current through the follower is still ~2.5A. Adding another 1ohm resistor increases it to 3A, which too doesn't seem to stress the transformer too much.
My question is that whether this lower voltage have any adverse effect on the distortion figures of the follower. Listening tests didn't show any quality loss in output other than clipping at less volume.
Thanks.
I have an interesting problem now.
I am running the follower from a 20v-0-20v/4A rated EI transformer and this current rating with 40v output is the maximum available from retailers here.
The transformer becomes hot after almost an hour of operation and thermally stabilizes at about 75-80 degrees Celsius, which I think is really hot; barely touchable. It's almost the end of winter here and maximum midday temperature is about 24-28 degrees C. In the Summer it becomes and remains more than 30 deg C. for many days and midday temp often rises to 45 deg C.
With the current darw of ~2.5A I think the transformer will get too hot in summer and probably will fail.
So I thought of a workaround as the summertime fail-safe. The configuration is depicted in the picture below.
The dissipation in the transformer decreases with the lower voltage output. I think this will do good in summer. The current through the follower is still ~2.5A. Adding another 1ohm resistor increases it to 3A, which too doesn't seem to stress the transformer too much.
My question is that whether this lower voltage have any adverse effect on the distortion figures of the follower. Listening tests didn't show any quality loss in output other than clipping at less volume.
Thanks.
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