Zobel Networks

[KTea88]

I have been looking at zobels, my question is this.
I run my system active so the woofer is fed directly by a KAT88 amp.
the DC of the Tannoy driver type 1667 is 4.3 ohms and inductance 0.83 mH
works out that I need 28.73uF caps and 5.38 Ohm resistors not a problem.

Putting in a Zobel would this help the amp in seeing a more level load ?

would it smooth things out in the 2khz area nat resonance of driver ?

[waaza]

Originally Posted by KTea88

I have been looking at zobels, my question is this.
I run my system active so the woofer is fed directly by a KAT88 amp.
the DC of the Tannoy driver type 1667 is 4.3 ohms and inductance 0.83 mH
works out that I need 28.73uF caps and 5.38 Ohm resistors not a problem.

Putting in a Zobel would this help the amp in seeing a more level load ?

would it smooth things out in the 2khz area nat resonance of driver ?

seems to me the capacitor value you calculated is very high, usually they are about 0.1µF, if I remember correctly. Surely, if you use the value you quote, it will indeed smooth out frequencies in the 2kHz region, smooth them into oblivion, I wouldn't be surprised. Please recheck your calculations, and/or equations, and their dimensions, nF rather than µF ?
cheers
Waaza

[Richard]

Originally Posted by KTea88

I have been looking at zobels, my question is this.
I run my system active so the woofer is fed directly by a KAT88 amp.
the DC of the Tannoy driver type 1667 is 4.3 ohms and inductance 0.83 mH
works out that I need 28.73uF caps and 5.38 Ohm resistors not a problem.

Putting in a Zobel would this help the amp in seeing a more level load ?

would it smooth things out in the 2khz area nat resonance of driver ?

Hi,

Morgan Jones says similar values for exactly this job, using the formula,

C zobel = L voice coil/R squared DC where R used for the zobel is the same as the voice coil R,

C = .00083/4.3 squared = .000044 = 44uF

So, a zobel of 4R3 with 44uF. Did yours come from this calc ?

(Waaza, are you thinking of the high frequency stability RC network on the output of an amp which will have different values?)

It would level the load the amp sees, and prevent any instability from rising impedance, but whether it will affect the driver characteristic I don't know.

Worth a try though and not hard to do if you're already active.

The component values won't be critical (the combined impedance will still be very much flatter than without the zobel) so I'd try standard values such as 4R7 with 33uF or similar.

Rich

[KTea88]

thanks guys, I got my calcs from a couple of zobel calculators on the net
I tried two just to make sure.

http://www.mhsoft.nl/spk_calc.asp

and

http://www.carstereo.com/help/Articles.cfm?id=36

I can get spot on with standard value components from WD.
at a tenner per speaker its not going to break the bank.

[Primalsea]

I would be careful with high value caps in a zobel network on a power amp. An amp I built had its zobel resistors go into meltdown because a preceeding peice of hifi was putting out high frequency oscillations. The 100n caps become almost a short meaning the power of the amp was being fed into the resistors.

Having higher value caps will mean you can get a short at a much lower frequency. You only need some thing to throw out alot of high frequency energy and your resistors will burn up.