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In Reply to: RE: strange phono stage posted by Best audiotransformers on August 25, 2024 at 12:08:20
Thank you very much!!!
Very good tips i try these capacitors and values
is c 3 not needed for dc protection of the cartridge ?
and c7 where is this capacitor needed for ? and what voltage should this have 47 uF is is mostly really big in higher voltages
I now c5 and 9 are coupling caps they are directly in the signal
i real appreciate you're helpful post
Follow Ups:
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Edits: 09/20/24
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Have Fun and Enjoy the Music
"Still Working the Problem"
hello Tre i have no transformer in the phono stage but its possibly in the future that i use afstand alone step up
I see now that you did say that. Oops.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
thank you so much for all the help both of you that is perfect for me
i have one more question about c7 i will try different values but what voltage should i take for this ?
and do someone have a tip for me that i can try here ?
I would leave that one alone. That cap is playing into R5 (1.5k) and that resistance is in parallel with the cathode impedance of the tube's cathode.
The two in parallel might be as low as 500 ohms. That cap needs to be large if you want 20Hz un-altered by the filter that is created by that cap playing into that load.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
hello Tre and its not a problem that this (c7)is an elco?
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Edits: 09/20/24
C7 will form a high pass filter with the total cathode impedance of the tube V1T. The total cathode impedance value is the cathode resistor value, R5, in parallel with the impedance of the cathode itself. This will not be a very large number. Without working all the math my educated guess is about 500 ohms. 160uf gives a -3db point of that filter of 2Hz which leaves 20Hz unmolested.So yes, the 220uf that is there now could be made smaller but not much smaller.
Here's the equation,
The "total" cathode impedance Zk is cathode resistance of the triode Zk` in parallel with cathode resistor Rk.
Triode cathode resistance is Zk`= (Rl+rp)/(mu+1)
Where mu is amplification factor and rp is anode resistance in concrete operating point. Rl is load resitance for AC, and this is anode resistor (in preamp stage) or reflected primary load of the OPT (Za) in output stage. Note that actual Rl can be Ra//Rg, or anode resistor in parallel with second stage grid resistor.
The final formula for Zk (Zk`//Rk) is:
Zk = (rp + Rl) / ((mu + 1 + (rp + Rl)/Rk)
And Zk is what C7 is seeing.I built it into a spreadsheet so I can just enter values.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/29/24 08/29/24 08/29/24 08/29/24
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Edits: 09/20/24
Well whatever the output impedance of the RIAA feedback filter is, it's in parallel with R6 (1.5k) so the total output impedance can't be all that high. It will be something less than 1.5k. I'm not sure what that has to do with the -3db point of the high pass filter I was talking about?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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Edits: 09/20/24
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Edits: 09/20/24
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