I will be using a triode-connected D3A as the input stage for my LCR phono preamp.
The input stage will utilize a MC-SUT, with a secondary winding impedance of around 70,000 ohms. The primary winding will match a 250 ohm input impedance.
My question here relates to the -3dB response of the input stage due to the series resistance/impedance presented to the high-u D3A by the MC-SUT, and it's effect in conjunction with the Miller capacitance of the tube. This of course can be easily determined once the Miller Effect input capacitance of the D3A has been determined, which I have done.
I want to determine the -3dB response of this stage, when driven by this particular MC-SUT. This can be easily calculated by the standard equation 1/6.28 (RC). However, I need to know how to determine the value of R (or Z) presented to the grid of the D3A input stage, when using an input transformer.
Is the series impedance presented to the input stage grid the impedance of the secondary of the MC-SUT? Or does the issue of reflected impedance come into play here, that being the source impedance of the MC cartridge?
The input stage will utilize a MC-SUT, with a secondary winding impedance of around 70,000 ohms. The primary winding will match a 250 ohm input impedance.
My question here relates to the -3dB response of the input stage due to the series resistance/impedance presented to the high-u D3A by the MC-SUT, and it's effect in conjunction with the Miller capacitance of the tube. This of course can be easily determined once the Miller Effect input capacitance of the D3A has been determined, which I have done.
I want to determine the -3dB response of this stage, when driven by this particular MC-SUT. This can be easily calculated by the standard equation 1/6.28 (RC). However, I need to know how to determine the value of R (or Z) presented to the grid of the D3A input stage, when using an input transformer.
Is the series impedance presented to the input stage grid the impedance of the secondary of the MC-SUT? Or does the issue of reflected impedance come into play here, that being the source impedance of the MC cartridge?
"However, I need to know how to determine the value of R (or Z) presented to the grid of the D3A input stage, when using an input transformer."
The input transformer designed for 47k secondary impedance.
The input transformer designed for 47k secondary impedance.
The simplest practical model is to include the MC's (usually very small) inductance in series with the reflected leakage inductance of the transformer. Refer both to the secondary, and you can usually ignore resistances, so consider the source impedance to the grid inductive and the shunt load at the grid to be the sum of various capacitances.
Makes a two-pole network with the various resistances providing damping. Very similar to the fundamental resonance of a speaker driver in a sealed box.
All good fortune,
Chris
Makes a two-pole network with the various resistances providing damping. Very similar to the fundamental resonance of a speaker driver in a sealed box.
All good fortune,
Chris
Step Up Transformer Calculations
Visit this site, it shows how to calculate Rload, X and other params.
X=SQR(70000/250=280)=16.72, is this correct turn ratio of your setup xformer? What brand and model of MC you using? What is MC catridge load impedance? When you have these params then you can calculate the Rload resistor. The calculator is based on 47k grid resistor of phono preamp, can be changed to your own value.
Step Up Transformers SUT for Moving Coil Cartridges Explained - SUT Series Part 1 - YouTube
Visit this site, it shows how to calculate Rload, X and other params.
X=SQR(70000/250=280)=16.72, is this correct turn ratio of your setup xformer? What brand and model of MC you using? What is MC catridge load impedance? When you have these params then you can calculate the Rload resistor. The calculator is based on 47k grid resistor of phono preamp, can be changed to your own value.
Step Up Transformers SUT for Moving Coil Cartridges Explained - SUT Series Part 1 - YouTube
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