Zobel and notch combined

[Klimon]

When using both a parallel notch filter and a zobel filter, is it critical which comes first in the chain?

I've been using a zobel for a little while now but I can't hear any difference when I insert a 50µF cap + 7ohms resistor or the standard (textbook value for the claimed self-inductance of beyma 8ag/n) 10µ + 7ohms. I thought it was possible to 'over-compensate' but my ears don't agree, unless the notch is screwing the zobel performance up The amp is a triode-strapped el84 se.

And another one: does anyone know a different method to calculate zobels; I've come accross a zobel for Beyma 8ag/n that uses 4,7µF + 22ohms ????? I can only find equations that recommend the measured DC resistance of the drivers for the resistor value...

Now we're at it : is DCR of a parallel notch filter coil critical?

Muchas gracias

Simon

[lndm]

Originally posted by Klimon
[B]When using both a parallel notch filter and a zobel filter, is it critical which comes first in the chain?

Just so I don't misunderstand, you mean a filter with the components in parallel, and the entire filter is in series with the driver, right?

A zobel that is intended to equalise the driver's impedance should go closest to the driver.

Now we're at it : is DCR of a parallel notch filter coil critical?

To a point, this will lower the Q of the resonance just as the resistor in parallel with the coil does. Therefore, the resistor in parallel can be made a little larger to compensate for a coil with a high DCR.

OTOH, it does make the circuit behave differently below the resonance frequency as the DCR is in series with the driver. It is just as desirable to use a low DCR inductor here as with any time you use a series inductor, IMO.

[Klimon]

Just so I don't misunderstand, you mean a filter with the components in parallel, and the entire filter is in series with the driver, right?

Yep!

OTOH, it does make the circuit behave differently below the resonance frequency as the DCR is in series with the driver. It is just as desirable to use a low DCR inductor here as with any time you use a series inductor, IMO.

That's what I hoped for, a good quality coil has 1/10 DCR of the coil I'm using now. Room for improvement.

Cheers,

Simon