I have done a smd version of the phono preamp on a PCB 20x45 mm [ see here https://www.patreon.com/posts/68149559 ] . Do you think it must be even smaller, or is that enough to fit inside your turntable close to the tonearm? IMHO it is better than Phaedrus active cartridge solution
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Marcel proposed an original circuit Fig5, but the non-differential signal pickup from the input stage adds noise of the current generator transistor BC550 and the 422 Ohm resistor in its emitter. It is too noisy and his fine idea on active inpur resistance is far from being fully implemented.
Actually it's not that noisy...but you can use 2sc1845 instead...I think that a Wireless World article need to adress a wider audience and outline the principles of operation. That differential is actually a true differential as in the famous APT Holman just not symmetrical if judged by input impedance . As for the 422 ohms running 6.5 mA through it sounds better than 330 ohms run at 17mA...
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There is an error in figure 5, one section of the 30 dB/40 dB switch is drawn in the wrong state.
The noise of the tail current source is effectively in parallel with the channel noise of the JFET. I designed it in the mid 1990's and I don't remember all the details, but I'm sure I must have chosen the tail current degeneration such that the JFET dominates.
In any case, it's good enough for me, but if you or anyone else wants to improve it further, be my guest.
The circuit is just my implementation of the Hoeffelman and Meys configuration from around 1978, so it is not that original. Electronic cooling even dates back to 1939.
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Marcel, can you suggest links to these interesting works of 78 and 39?
W. S. Percival, "An electrically "cold" resistance", The wireless engineer, vol. 16, May 1939, pages 237...240
Jean M. Hoeffelman and René P. Meys, "Improvements of the noise characteristics of amplifiers for magnetic transducers", Journal of the Audio Engineering Society, vol. 26, no. 12, December 1978, pages 935...939, see also Ernst H. Nordholt, "Comments on "Improvement of the noise characteristics of amplifiers for magnetic transducers"", Journal of the Audio Engineering Society, vol. 27, no. 9, September 1979, pages 680...681
Jean M. Hoeffelman and René P. Meys, "Improvements of the noise characteristics of amplifiers for magnetic transducers", Journal of the Audio Engineering Society, vol. 26, no. 12, December 1978, pages 935...939, see also Ernst H. Nordholt, "Comments on "Improvement of the noise characteristics of amplifiers for magnetic transducers"", Journal of the Audio Engineering Society, vol. 27, no. 9, September 1979, pages 680...681
Just a little bit of scolar justice for some :
https://patents.google.com/patent/US4470020A/en
https://www.diyaudio.com/community/...plifier-part-ii.146693/page-3592#post-4413675
with reserves... as quoting smart peopled doesn't automatically makes us equally smart...
I appreciate other's work if it doesn't nullify the importance of the giant's shoulders they're built on.
https://patents.google.com/patent/US4470020A/en
https://www.diyaudio.com/community/...plifier-part-ii.146693/page-3592#post-4413675
with reserves... as quoting smart peopled doesn't automatically makes us equally smart...
I appreciate other's work if it doesn't nullify the importance of the giant's shoulders they're built on.
Here's where I found a hint to 1984 patent which proved to be Mohr's:
http://waynestegall.com/audio/riaa.htm#mozTocId495677
He's heads and shoulders above my mental gymnastics abilities, but I hope you will enjoy his work more than I can.His spice models reveal the circuits values.
What's even more strange is that Mohr's circuit resembles the AD844 internal guts...while we know now that Win Palmer designed the AD844.
http://waynestegall.com/audio/riaa.htm#mozTocId495677
He's heads and shoulders above my mental gymnastics abilities, but I hope you will enjoy his work more than I can.His spice models reveal the circuits values.
What's even more strange is that Mohr's circuit resembles the AD844 internal guts...while we know now that Win Palmer designed the AD844.
I do have a measurement by Hans of an ortofon S-120. This is a DJ cart, but interested me as it has a fancy suspension to improve tracking thats in the 700mH range and really needs a load in the range of 100k and 100pF to not drop like a stone above 10kHz.
Steven's analysis is one I do not agree with and hoping to show some evidence he was incorrect in his conclusions
To be clear, due to time pressures of life I've not been able to measure much at all but am being helped by some great friends who do. All the results are being posted in the mechanical resonance thread as I don't want to cross post too much or derail this thread other than to point out cartridges are a far more complex equivalent circuit than the literature until now might have suggested.
I do not think so. Because in Kenwood L-02 the current generator noise of Q30 Q28 is distributed as equally correlated currents to the input differential stage Q18 Q20 Q22 and then it is perfectly compensated as a common mode signal by the second differential stage Q38 Q40. In Marcel's circuit, the noise current of the current generator is not compensated in this way and is added to the input transistors noise.
In my book of 1985 [ freely here: https://www.patreon.com/posts/67628599 ] I have strictly mathematically shown on pages 72 and 73 that the input-referenced noise of the differential stage with an active uncompensated (via next differential stage) current generator is 1.8 dB higher than that with a resistive supply of the differential stage
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Hence the No load amplifier ideea a friend of mine had:
https://www.diyaudio.com/community/threads/no-active-load-amplifier.300887/#post-4928591
https://www.diyaudio.com/community/threads/no-active-load-amplifier.300887/#post-4928591
And there is also on page 73: the input-referenced noise of the differential stage with an active uncompensated current source is 4.8 dB higher than that with a compensated by the next differential stage.