The output voltge will depend on the primary inductance. If you want 3V rms output with 33:1 turn step-down ratio, 10 mA anode current and reasonably low distortion down to 20Hz you need at least 250-300H regardeless of what it is implemented up-stream the output stage. It has nothing to do with frequency response or gain.
The M7 original preamp without any transformers is miles better!
The M7 original preamp without any transformers is miles better!
Then, referring to your formula in #39, 112H would be enough.
Difficult to admit that the output stage is not so clever, huh?
No, the less current you swing the lower the distortion.
Then if you say that the declared output voltage of the M10 is 3V rms I really doubt the TURN ratio is 33:1. I said at the beginining this more likely the impedance ratio otherwise, without taking losses into account, the 5687 should provide AT LEAST 99V rms at the primary which is simply impossible with 300V supply....
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That is what I have been saying from the beginning! But someone else instists that it is.....
As I said, I have no idea. I have just found a schematic and it looks like that the input stage of the phono amp has only partial moderate cathode bypass, the second phono stage and the input line stage have no bypass at all.
Calculate the loss of the funny RIAA and see what you get. I am not willing to do that....
There is source selector, the input is low for phono, so you need higher gain, for other source there is even a input transformer, and volume attenuator go and read the sch.
Not so difficult to estimate, 45.
The phono stage has two voltage gain stages; input stage is a 6072 cascode, other stage is a 6072 SRPP.
Let's be pessimistic and assume that the phono stage voltage gain is 100 (RIAA equalization included).
With a standard input sensitivity of 5 mV it will present the output stage with 0.5 V, not unreasonable as the output stage should accept line level.
Then, with that output stage voltage gain and (maybe) 5.7:1 output transformer we certainly run into problems....
The phono stage has two voltage gain stages; input stage is a 6072 cascode, other stage is a 6072 SRPP.
Let's be pessimistic and assume that the phono stage voltage gain is 100 (RIAA equalization included).
With a standard input sensitivity of 5 mV it will present the output stage with 0.5 V, not unreasonable as the output stage should accept line level.
Then, with that output stage voltage gain and (maybe) 5.7:1 output transformer we certainly run into problems....
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No, read the schematic
All unbalanced signals (phono and line), has the volume control before entering the output stage.
There is an input transformer to accept balanced sources.
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It only says step-down ratio. If that is turn step down then it's no good. Nothing tedious. With just 300V supply and limited inductance it cannot be HiFi for general use. A HiFi preamp is supposed to give typically at least 2-3 V RMS with THD of 0.1-0.2% or less from 20Hz to 20KHz. That's the minimum! This is not going to be the case if 33:1 is the turn ratio and run the tube at 10 mA.
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Could you elaborate a bit more on the voltage gain of the 5687 stage?
I understand that the gain is lowered because of the unbypassed 1k cathode resistor, but by how much? (I am not good in interpreting sims...)
A gain of 1.4 (25:18???) seems very little.
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