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6J5 input swing

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Sure. I am designing a phono/pre and have a cascode on paper. With EQ it puts out 7Vrms below 1kHz with my MM cart giving occasional peaks of 70mV. I simply want the second stage to endure these peaks and I have had trouble with another amp that couldn't handle that level. The cascode seems to be happy with this level.
 
lndm said:
What is the best way to have a 6J5 accept a 7Vrms input cleanly whilst retaining a good operating point. I want to avoid an unbypassed Rk as I want a low rp for low noise.

If you don't want to use an unbypassed Rk, the only way to do what you want is to run at a very high Vpk. Since 7.0Vrms is a bit less than 10Vp, that's what you're looking at: Vgk= -10Vdc. From the plate characteristics, that'll be right around 250Vdc. Depending on how large the passive load is, the DC rail will go a lot higher than that (or use an active load).

Other than that, unbypassed Rk is the only other option.
 

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Below 1kHz the gain is 43dB. I am using an Ortofon OMB. I'm not aware of any specs for it, I just loaded the cartridge, played a few records and watched the screen. Most program material seems to be within 5-10mV with regular peaks at 30mV, some up to 50mV with some recordings, and occasionally 70mV.
 
lndm said:
Below 1kHz the gain is 43dB. I am using an Ortofon OMB. I'm not aware of any specs for it, I just loaded the cartridge, played a few records and watched the screen. Most program material seems to be within 5-10mV with regular peaks at 30mV, some up to 50mV with some recordings, and occasionally 70mV.

Yes, but that 70mV will comprise only high frequency components unless you're playing some record made with centimeter groove excursions. That 7V from a gain of 100 will be knocked down by a factor of ten, at the least. Even so, what about that next stage's gain (probably 20-23 dB)? Consider the poor power amp at the other end of some monstrous preamp hurling 70V at it...

No, really, you don't need 7V of input capability on that second stage.
 
OK, if the peaks are HF, then I probably have little to worry about. Would it be worth implementing the 3180us EQ at this point instead to be sure? It may reduce some of the signal to very low levels again, though.

What about direct coupling, are there any good ones? I'm thinking this could also help reduce the noise somewhat.
 
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