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athos56 8th May 2009 12:22 AM

Gyrator Question
I wired up a gyrator and put in my 40v supply, it ended up with 4 volts at the output, I assume I miss wired it, however just to be sure I'm going to ask a quick question. I used this schematic
Do I hook this up between B+ and ground, or along the B+ rail like a normal choke?

Iain McNeill 8th May 2009 12:48 AM

Not speaking Dutch my guess is it's an in-line device. It's polarity sensitive so you gotta connect it the right way X1-1 to the +ve rail X1-2 to the load.

Also. it needs a current through it to work. Were you testing open circuit?

As you pull current through it, the cap charges up and "programs" the current source Q1-R3. The MOSFET regulates it's Rds to maintain said current.

Wavebourn 8th May 2009 12:53 AM

Right. And a voltage drop on it will be about 5V plus voltage drop on the resistor in source.
There was a thread recently about gyrators.

Here it is:

athos56 8th May 2009 12:54 AM

Ok, I read something that led me to believe it went the other way, I'll try it again, hopefully I didn't fry it :)

Hearinspace 8th May 2009 04:49 AM


There was a thread recently about gyrators.
Hi Wavebourn,
Why does the term Gyrator apply to your circuit? It's your original idea, why not give it an original name?

ErikdeBest 8th May 2009 10:07 AM

Hi Athos56

It is indeed a directional device: you should connect X1-1 to the B+, and X1-2 to the following cap in the PS circuit. In other words, X1-1 should be more positive (higher voltage) than X1-2.

The text is German, actually!


whitelabrat 8th May 2009 04:37 PM

I tried to build that gyrator myself and promptly smoked it. I haven't tried to repair it yet, but I believe my mistake was to work exclusively from the schematic. I'd suggest using the PCB layout as a wiring guide.

My test was done on a 300v +180ma circuit. Indeed X1-1 in your "In" and X1-2 is your "Out". The next test I'll do will be on a lower voltage/current circuit with a resistor load. Won't get a chance to play until after I get into my next house.

Pictures? I'm curious how you've done yours.

ErikdeBest 8th May 2009 06:41 PM

I have seen someone else complaining about the circuit, in that it oscillated wildly...maybe that also happened to Whitelabrat's circuit?

I have made a layout to build this unit on protoboard, but was not able to put it together, yet. I included space for a small resistor (couple R) in series with the drain as well as space for a gate stopper resistor (around 1k). I think that at least the gate-stopper is very important!

Let's see if I can put it together in the weekend and test it.

athos56 8th May 2009 06:52 PM

Well, so I tested my amp for the first time and got distorted output of music, removing the Gyrator will be my first troubleshooting measure.

whitelabrat 8th May 2009 08:07 PM

Could be that I didn't smoke it at all. I didn't think about oscillation. It sure sounded like that is what it was doing. It was almost as if it were amplifying the B+ noise instead of filtering it.

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