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Old 8th May 2009, 08:34 PM   #11
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Quote:
Originally posted by Hearinspace

Hi Wavebourn,
Why does the term Gyrator apply to your circuit? It's your original idea, why not give it an original name?
Thanks
Thanks;
I don't invent a terminology usually. But I have to think about it, thank you!
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Old 8th May 2009, 10:56 PM   #12
athos56 is offline athos56  United States
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Ok, well that solves that problem. Taking the gyrator out solved the problem of the distortion, mostly. My tube section is running about 25v hot and the mosfets are about 16v hot. So I need to go back in and increase the resistors in my RC sections. Hopefully that will bring the distortion down even further. However, even through the minor distortion thats still left I can tell this amp is going to kick my Kt-88 amp in terms of bass response.
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Old 14th May 2009, 03:57 PM   #13
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Yesterday I put the gyrator together. I used a IRFBC30... which has an insulated TO220 'body'. I am using a 4R resistor in series with the drain, a 1k2 gate stopper and a ferrite bead in series with the sources (all measures to decrease chance of oscillation). The cap employed is a 10uF one...

I works and it makes the supply quiet! I tested it in a small PP amp that was running with a standard choke. With 200mA through the gyrator, it was dropping 16V. Just for comparison I replaced it with a 80R resistor (80R x 200mA also drops 16V) and the hum was audible. So indeed, it works and filters some ripple away...
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Old 14th May 2009, 04:55 PM   #14
athos56 is offline athos56  United States
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Did you follow the schematic or the lay out you get when you click on the picture at the bottom? I remade mine using the lower layout. I was really tired when I posted my last observation and since found that my RC sections were way off and that my mosfets were only getting 4v not the 50 something I thought they were. So I fixed that problem and I hooked my Gyrator back up and burnt out R3.... So I upped the wattage of R3, I'm going back to the split rail to lessen the load, made 2 gyrators and am going to try it again. I'll report back...
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Old 14th May 2009, 05:26 PM   #15
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R3 should indeed be relatively large... in my case (with 200mA draw by the amp) it burns around 1,5W. I used a 3W MOX unit...

I followed the schematic, and layed components so that distances were minimized. I took a picture, attached, with values. The picture is crap, but you get the idea about the layout. The black traces indicate how components are connected together, under the board.

One thing to reconsider is the positioning of the 10uF cap... it will get quite hot from the 33R resistor...

I hope this helps, but feel free to ask!
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File Type: jpg gyrator.jpg (61.9 KB, 1002 views)
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Old 14th May 2009, 05:36 PM   #16
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This is how I would implement a Gyrator. Output voltage is set by adjusting R3. Note, devices and component values are random choice.
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Old 14th May 2009, 06:06 PM   #17
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I'd call that a voltage regulator ;-)

Michael
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Old 14th May 2009, 06:11 PM   #18
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MJK,
This way we get two functions in one: Gyrator AND regulator .

Also due to the CCS, there will be very little ripple on the gyrators gate, this should make it even better.
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Old 14th May 2009, 06:37 PM   #19
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I'm trying to understand the purpose of R1 and C1 providing a high
AC impedance when that circuit node has a 100uF cap to AC ground.
What happens if R1 and C1 (and C3 for that matter) are removed?

I think if this were on a PCB and had 2 or 3 different connections to
R1, it could be built as a screen regulator, a high impedance fixed
voltage anode load, mu-follower, anti-triode, etc. It's a nice set
of functions to have in one place..

On a related note, I'm looking at a DC filament gyrator as an
alternative to filament chokes or VCCS. The circuit looks similar
to yours but without C3. It would provide fixed voltage (on a
controlled ramp) and present a (relatively) high AC impedance
to the signal current on the filament.

Cheers,

Michael
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Old 14th May 2009, 06:49 PM   #20
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Thanks for the picture. That helps. I used a huge resistor for 33ohm too:

Picture here
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