Tube DIY Asylum

strange phono stage

85.147.53.253

horny

A

Hello i buy a tube phono amplifier and i find the schematic i was shocked it is not terrible sounding but look at the capacitors the values it are elco's! i can not believe it that it not sounds awful but not bad
what can i do to made a decent phono stage from this ?
i mean what caps and values
i have no transformer in front it is just the mm stage but the elco in front is there
why should someone design such phono stage with these high value elco's instead of normal capacitors ?

Follow Ups:

All you need at the grid is R3 - Tre' 15:34:53 08/26/24 (0)
C9 only needs to be big enough for the high pass filter's -3db point to be 2Hz (if you want 20Hz untouched by the filter). So the value necessary will depend on the input impedance of whatever you are driving with that preamp.
If that load is 100K then .8uf will do.

C5 could be .15uf and pass 20Hz perfectly.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
- https://www.digikey.com/en/resources/conversion-calculators/ (Open in New Window)
Edits: 08/26/24 08/26/24
RE: strange phono stage - Best audiotransformers 12:08:20 08/25/24 (14)
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Edits: 08/25/24 08/25/24 09/20/24
- RE: strange phono stage - horny 14:46:34 08/25/24 (13)
  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
  - RE: strange phono stage - Best audiotransformers 03:03:34 08/26/24 (0)
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    Edits: 09/20/24
  - DC won't got through a transformer. nt - Tre' 15:12:14 08/25/24 (11)
    .
    Have Fun and Enjoy the Music
    "Still Working the Problem"
    - RE: DC won't got through a transformer. nt - horny 22:36:24 08/25/24 (10)
      hello Tre i have no transformer in the phono stage but its possibly in the future that i use afstand alone step up
      - "Tre i have no transformer in the phono stage" - Tre' 15:26:52 08/26/24 (9)
        
        In Reply to: RE: DC won't got through a transformer. nt posted by horny on August 25, 2024 at 22:36:24
        
        I see now that you did say that. Oops.
        
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        RE: "Tre i have no transformer in the phono stage" - horny 10:00:21 08/27/24 (8)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by Tre' on August 26, 2024 at 15:26:52
        
        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 ?
        
        RE: "Tre i have no transformer in the phono stage" - Tre' 19:49:04 08/27/24 (6)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by horny on August 27, 2024 at 10:00:21
        
        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"
        
        RE: "Tre i have no transformer in the phono stage" - horny 11:10:08 08/28/24 (5)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by Tre' on August 27, 2024 at 19:49:04
        
        hello Tre and its not a problem that this (c7)is an elco?
        
        RE: "Tre i have no transformer in the phono stage" - Best audiotransformers 14:22:48 08/28/24 (4)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by horny on August 28, 2024 at 11:10:08
        
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        Edits: 09/20/24
        
        RE: "Tre i have no transformer in the phono stage" - Tre' 16:35:25 08/29/24 (3)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by Best audiotransformers on August 28, 2024 at 14:22:48
        
        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
        
        RE: "Tre i have no transformer in the phono stage" - Best audiotransformers 12:22:12 08/30/24 (2)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by Tre' on August 29, 2024 at 16:35:25
        
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        Edits: 09/20/24
        
        RE: "Tre i have no transformer in the phono stage" - Tre' 13:27:26 08/30/24 (1)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by Best audiotransformers on August 30, 2024 at 12:22:12
        
        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"
        
        RE: "Tre i have no transformer in the phono stage" - Best audiotransformers 11:01:53 09/01/24 (0)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by Tre' on August 30, 2024 at 13:27:26
        
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        Edits: 09/20/24
        
        RE: "Tre i have no transformer in the phono stage" - Best audiotransformers 14:02:47 08/27/24 (0)
        
        In Reply to: RE: "Tre i have no transformer in the phono stage" posted by horny on August 27, 2024 at 10:00:21
        
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        Edits: 09/20/24

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