does it work like this ?edit: or forget that below witht he series caps. Use one cap tied between the gate of J1 and 2.
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Just in advance of bimo's reply, I recommend the initial grounding plan better. It serves many other issues.
Well that floats the JFET gates and phono cartridge completely, so the common-mode will be all over the place with DC offset and mains hum - you need some resistance to ground.
Yo can do it also in this way: no floating anymore - but there is no problem in bimo's way.
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good common mode rejection ignores the problem? maybe a dc servo to handle very low f ?
Well the devices may drift to forward bias the gates, or swing with mains hum between the end-stops - you need to tie it down with something to prevent this, you don't want the cartridge being an antenna.
Since there are a common and easy mitigation techniques, as That has recomended for example, It seemed worth mentioning. A little attention to the low hanging fruit could make a big difference in performance.
Common mode noise is not the main consideration of my design. Because of non global negative feedback and use of LTP as input, the connection for input is balanced. The goal is how using non global negative feedback pre-amplifier with passive RIAA equalizer.
You cannot optimize the S/N ratio if you using same schematic for MM and MC cartridge. MM cartridge have high impedance and it need very low input current noise. Usually it use low noise JFET for input which input current noise almost none and input voltage noise below 1n/√Hz or using low rBB BJT with collector current around 100uA as input.
MC cartridge have very low impedance and it need very low input voltage noise. Usually it use low rBB BJT with collector current around several mA.
Hi,
Phono Pres using INAs from TI, ADI and THAT are able to perform very low-noise with almost any existing cartridge.
Commercial incarnations from Lehmann, Clearaudio, Blueamp and more ...my own designs for purist and audiospecials included.... have proven to perform top notch in many reviews, as have done some DIY pres.
And while the noise figures fall just short of the absolute best limits, this doesn't play a role in praxis ... as they are noise-transparent under almost all circumstances.
SN figures are always way above the requirements and possibilities of Vinyl.
The great versatility of these input stages outweighs by far this minor 'flaw'.
jauu
Calvin
Phono Pres using INAs from TI, ADI and THAT are able to perform very low-noise with almost any existing cartridge.
Commercial incarnations from Lehmann, Clearaudio, Blueamp and more ...my own designs for purist and audiospecials included.... have proven to perform top notch in many reviews, as have done some DIY pres.
And while the noise figures fall just short of the absolute best limits, this doesn't play a role in praxis ... as they are noise-transparent under almost all circumstances.
SN figures are always way above the requirements and possibilities of Vinyl.
The great versatility of these input stages outweighs by far this minor 'flaw'.
jauu
Calvin
Hi,
I agree ... but optimization to me rather means juggling with parameters to achieve a good compromise ;-)
And if improving on noise figures doesn´t play an important role any more due to the restrictions of the medium, other parameters may become more important or may offer more reward.
jauu
Calvin
I agree ... but optimization to me rather means juggling with parameters to achieve a good compromise ;-)
And if improving on noise figures doesn´t play an important role any more due to the restrictions of the medium, other parameters may become more important or may offer more reward.
jauu
Calvin
For me, in amplification of very small voltage signal, the signal to noise ratio is the most important.
But it is subjective, because some people can enjoy 60 dB S/N ratio pre-amplifier.
Distortion is not important because it is small signal and operating as class A, but low distortion still desirable.
Head room and RIAA precision are important.
Hi,
come on Bimo .... we're both not talking about 60dB S/N Pres here, but rather about the upper 10%.
And for these circuits, that perform considerably better than the maximal 67dB we can get out of Vinyl, the quest for the last 2-3dBs is rather academic as it doesn't offer a practical advantage any more.
I agree on the importance of RIAA precision and would add equality of the stereo channels to the list.
jauu
Calvin
come on Bimo .... we're both not talking about 60dB S/N Pres here, but rather about the upper 10%.
And for these circuits, that perform considerably better than the maximal 67dB we can get out of Vinyl, the quest for the last 2-3dBs is rather academic as it doesn't offer a practical advantage any more.
I agree on the importance of RIAA precision and would add equality of the stereo channels to the list.
jauu
Calvin
Fair enough. Though if the common mode noise rejection could easily, and inexpensively be made better by a minor circuit alteration that doesn't negatively affect the performance aspects you value, then it would sure be a shame to miss the opportunity.