So… let's see.
CRC on the 6X4, with 20 V forward drop gives, and 10 μF → 5000 R → 100 μF → 3 ma load gives
262.5 VDC on first cap, with about –3.9 dBv (terrible) ripple, and –56
245.4 VDC on sec. cap, with about –56 dBv (OK) ripple.
If you install a CRCRC filter (i.e. another stage) you with 2k2 R and 100 μF C₃ then
238.6 VDC on thrd cap, with about –95 dBv (great!) ripple. And a fourth extension?
231.8 VDC on 4th cap, with about –130 dBv (wickd) ripple.
I got to wondering about "old fashioned" smaller caps, and the effect. Using nothing but 10 μF caps and 3k3 resistors in the CRCRCRC chain…
C₁ = 262.8 VDC, –4.03 dBv ripple
C₂ = 250.8 VDC, –32.7 dBv ripple
C₃ = 240.3 VDC, –55.3 dBv ripple
C₄ = 230.4 VDC, –74.8 dBv ripple
Hence why larger values of C make such a difference. And that weird old 10 μF, 22 μF, 33 μF, 47 μF rule that had its popular day?
C₁ = 261.9 VDC, –3.83 dBv ripple
C₂ = 250.6 VDC, –39.5 dBv ripple
C₃ = 240.5 VDC, –71.8 dBv ripple
C₄ = 230.4 VDC, –105. dBv ripple
C₄'s ripple is suitable for sensitive preamps, even using WW–2 generation parts. With our cheap-as-dirt 100 μF and higher caps, one hardly has to worry at all. But I would use a 3rd stage!
GoatGuy
CRC on the 6X4, with 20 V forward drop gives, and 10 μF → 5000 R → 100 μF → 3 ma load gives
262.5 VDC on first cap, with about –3.9 dBv (terrible) ripple, and –56
245.4 VDC on sec. cap, with about –56 dBv (OK) ripple.
If you install a CRCRC filter (i.e. another stage) you with 2k2 R and 100 μF C₃ then
238.6 VDC on thrd cap, with about –95 dBv (great!) ripple. And a fourth extension?
231.8 VDC on 4th cap, with about –130 dBv (wickd) ripple.
I got to wondering about "old fashioned" smaller caps, and the effect. Using nothing but 10 μF caps and 3k3 resistors in the CRCRCRC chain…
C₁ = 262.8 VDC, –4.03 dBv ripple
C₂ = 250.8 VDC, –32.7 dBv ripple
C₃ = 240.3 VDC, –55.3 dBv ripple
C₄ = 230.4 VDC, –74.8 dBv ripple
Hence why larger values of C make such a difference. And that weird old 10 μF, 22 μF, 33 μF, 47 μF rule that had its popular day?
C₁ = 261.9 VDC, –3.83 dBv ripple
C₂ = 250.6 VDC, –39.5 dBv ripple
C₃ = 240.5 VDC, –71.8 dBv ripple
C₄ = 230.4 VDC, –105. dBv ripple
C₄'s ripple is suitable for sensitive preamps, even using WW–2 generation parts. With our cheap-as-dirt 100 μF and higher caps, one hardly has to worry at all. But I would use a 3rd stage!
GoatGuy
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Just to thank all the late contributions and to clarify that the preamp has an only tube (5687) for both channels, Either I'm misinterpreting some posts or this is not clear.
I aslso have a Kondo style preamp based on 5687 or alike. My first version was a single tube where I tried a lot of 5687 types and yes, some of them were really microphonic. There was no way to get rid of the strange noise but replacing the tube with a different type. I found the Raytheons the best, no microphonic, the GEs were neither mic.
Later I supplemented the schematics with a cathode follower as an improvement.
Later I supplemented the schematics with a cathode follower as an improvement.
Thanks BarG01,
Your info is invaluable. Could you share with me the mods you did to the preamp?
Regards,
Raul
Your info is invaluable. Could you share with me the mods you did to the preamp?
Regards,
Raul
Hi Raul,
As I mentioned above, i added a cathode follower 5687 after the anode follower, with direct coupling. The cathode resistor is the same value as the anode resistor, 13K 2W Shinkoh type. It seems overdesign but I apply a 5U4GB for rectifier and it's really worth to try! Output capacitor is 0,22u because in my system this is enough but in general application it should be higher, at least 0,47u or 1u to drive a solid state.
As I mentioned above, i added a cathode follower 5687 after the anode follower, with direct coupling. The cathode resistor is the same value as the anode resistor, 13K 2W Shinkoh type. It seems overdesign but I apply a 5U4GB for rectifier and it's really worth to try! Output capacitor is 0,22u because in my system this is enough but in general application it should be higher, at least 0,47u or 1u to drive a solid state.
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