Hi all!
I was interested in experimenting with a Zobel network across the secondary of my 1:20 step-up transformer to address some brightness/coherence issues at high frequencies in my phono setup. I am using a Denon DL-303 MC cartridge (40 Ohm impedance and ~0.20 mV output) and a couple of different SUTs, but mainly a Fidelity Research FRT-3. The output of the SUT goes into a Hagerman Bugle 2 phono preamp.
My questions:
1. To find the cuttoff frequency (Fc) of the Zobel, I am using Fc = 1/(2πRC). What ballpark cutoff frequency (Fc) and values of C and R are good to start with?
From the Sowter website for their 1:20 SUT, they use 9.2kOhms and 330pF which gives an Fm = 52kHz. I've copied this and built a few Zobel networks using an Fm of about 50 kHz, but using capacitance values over 100pF seems too large for my needs. My cursory testing leads me to think that capacitance in the 10-50pF range might be better, but I might be losing some bass response... I'm assuming the objective is to find the smallest value of capacitance and the highest value of resistance that will remove any potential overshoot/ringing issues in the SUT (as per the recommendation an old post I found written by Jensen Technician Dale Roche). Is this reasonable?
2. Is there any need to parallel a resistor to the Zobel network or should one be used only to change the resistive load "seen" by the cartridge?
Sorry for all the questions but I super appreciate any help!! I tried first using just resistive loading across the secondary, but to make things sound balanced, I am losing too much gain and squashing the dynamics. Thanks!!!
I was interested in experimenting with a Zobel network across the secondary of my 1:20 step-up transformer to address some brightness/coherence issues at high frequencies in my phono setup. I am using a Denon DL-303 MC cartridge (40 Ohm impedance and ~0.20 mV output) and a couple of different SUTs, but mainly a Fidelity Research FRT-3. The output of the SUT goes into a Hagerman Bugle 2 phono preamp.
My questions:
1. To find the cuttoff frequency (Fc) of the Zobel, I am using Fc = 1/(2πRC). What ballpark cutoff frequency (Fc) and values of C and R are good to start with?
From the Sowter website for their 1:20 SUT, they use 9.2kOhms and 330pF which gives an Fm = 52kHz. I've copied this and built a few Zobel networks using an Fm of about 50 kHz, but using capacitance values over 100pF seems too large for my needs. My cursory testing leads me to think that capacitance in the 10-50pF range might be better, but I might be losing some bass response... I'm assuming the objective is to find the smallest value of capacitance and the highest value of resistance that will remove any potential overshoot/ringing issues in the SUT (as per the recommendation an old post I found written by Jensen Technician Dale Roche). Is this reasonable?
2. Is there any need to parallel a resistor to the Zobel network or should one be used only to change the resistive load "seen" by the cartridge?
Sorry for all the questions but I super appreciate any help!! I tried first using just resistive loading across the secondary, but to make things sound balanced, I am losing too much gain and squashing the dynamics. Thanks!!!
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