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Gyrator and capacitance multiplier .

H

hp1

pfm Member
I see that a good upgrade for the naim circuits is a gyrator but as far as I can gather a gyrator is a
way of making inductance from a capacitor, a few resistors and a transistor .

Is the term gyrator being used loosely and is actually more like a capacitance multiplier in this context?

Any circuit diagrams for the type suitable naim constant current source would be appreciated.
 
You are correct it is a 'capacitance multiplier'.

But even that is a poor description. What the approach amounts to, is an RC filter, with an emitter-follower wrapped-around it to drop the output impedance to something useful. Think of it in those terms, and they are useful.


Second part of your post - these are not usually used in that context; the fix for the Naim CCS is easier: you split the the bias - side 'tail' resistor into two equal parts and bypass to the reference rail with a cap from the mid-point of your two new resistors. Very effective for the effort.
 
ThankYou for the info Martin. What do You think would be the most suitable cap in that position please? and would the mod be suitable for the circuit powered by a split rail power supply ie +12v,0,-12v . I know that Les W has been known to fit what he terms as gyrators in place of or in series with the 27r 47uf power supply filters of say a snaxo .
 
Such things work best (esp when the ciruit has low current demand, such as replacing the 27r/47uF filter) when you keep series R fairly low in value, in order to also keep the RC+emitter-follower output impedance usefully-low.

You could re-use the 47uf, with an R of 1000ohms, add a transistor and that'd be a very effective filter from 3Hz upwards. And simple.
 
Cascading them is very effective and helps to maintain low z to much lower frequency. A load resistor to force it to operate at higher current can be an effective improvement also as transconductance is increased and hence Z out reduced still further.
 
ThankYou gents.

would a 10uf polarised cap suffice between the bias splitter? and for the RC network if an 1000ohm resistor works down to 3hz would it be fair to say a 100ohm would be down to 30hz? Thanks again.
 
The bigger the better cap wise but cap quality best if film cap used which is large but available in 10uF or 22uF usually. Resistance is also larger the better but limited by transistor bias current and input impedance requirements.
I don't know the precise schematic you're thinking of to be any more precise.
 
FWIW I've said nothing as I have no idea of the details of the circuit the gyrator is intended for and how it will be used!
 
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