Hi mitsos,mitsos said:...So, I started wondering about trafo loading and zobels... The EA2622 is a 1:7 trafo, yet the recommended RL (150K) is the same as for the Cinemag 75101, which is 1:10... This would give you an input impedance of 3K vs 1K5 with the Cinemag. Does this not make a difference in the sound? I'm assuming Ed (who knows much more than I do about trafos) was the one to suggest this value and I'm curious to know why/how.
Of course, I did not consider the zobel. I know you select zobels by passing a square wave through the trafo while the trafo is in the circuit, right? But how does the zobel resistor affect the overall load on the trafo? Meaning if you use the values Jeff suggests, (RL=150K, zobel = 10K + 220pF) what is the effective load on the EA2622 and what is the input impedance?
Thanks!
For the values I mentioned, they were recommended by the old API crew as that is how they populated my input channels. ;D My channels have original AP2622's. I figured I would use their original Zobel and load R as a starting point for my VP26 pre's with Ed's 2622's and tune with the ear as suggested by CJ. I asked Ed about this early on. He had sent me this in an email.
"for the zobel, i've also seen 22k in series with 100pf, in parallel
with a 100k loading resistor -- that is what was on the card that i
removed the 2622 i used for research from. any of these values will
work, but the frequency response will be slightly different."
I also have a 1K series R between the Zobel and a 33uf coupling cap, then the 150K shunt R and a 27pf decoupling cap.
Depending upon the pad configuration, I assume that will contribute to the imput impedance calculation as well?
Cheers, Jeff