Building the Sjöström's extreme phon preamp

[sinigersky]

Hi,

I am intending to build the extreme phono preamp project of Per-Anders Sjöström:

http://sjostromaudio.com/_unsql/hifi/qsxm2/index.html

I want to have a universal "killer" phono preamp, which I'll use to test different equipment. The QXM2 is preferably used with MM pickups.
I am looking for good input transistors to be able to get the "ultra" performance for MC pickup, too. I will be glad to get ideas and recommendations. Has anyone experience with 2SA1455K/2SC3722K? They look good (found them in the forums here), but the problem is I cannot find a supplier to buy them. Any hints about these transistors?

Another solution for MC I am thinking of is using a "head-amp" from here:

http://users.ece.gatech.edu/mleach/headamp/

...for instance the Common-Base Circuit. Has anybody built it? Will the input perform better than the MC-version of the Sjöström preamp? Would it be a good idea to parallel transistors in this schematics? And use floating super regulator with own transformer instead of the battery...

Best Regards,
Angel Sinigersky

[KJ42]

Originally posted by sinigersky
... Has anyone experience with 2SA1455K/2SC3722K? They look good (found them in the forums here), but the problem is I cannot find a supplier to buy them. Any hints about these transistors?

Hi,
I have no experience with Sjöströms designs (except that I have studied them for inspiration), so I have no comment to his RIAA- phono preamps. Regarding the trannies, I believe LC-Audio in Denmark has been using them in their kits, may be they have a surplus for sale?

...
Another solution for MC I am thinking of is using a "head-amp" from here:

http://users.ece.gatech.edu/mleach/headamp/

...for instance the Common-Base Circuit. Has anybody built it? Will the input perform better than the MC-version of the Sjöström preamp? Would it be a good idea to parallel transistors in this schematics? And use floating super regulator with own transformer instead of the battery...
...

Back to LC-audio, they have a MC/RIAA phonopreamp which uses a variation of the common base Leach head-amp. I am using a previous iteration of the LC-audio MC RIAA phono preamp (where the PCBs for the head amp and MM RIAA phono preamp are separated) together with a Ortofon MC 25 FL (low output low impedance MC-pickup. LC-audios twist is that they power the head amp with a set of photodiodes in their forward «mode» (no batteries and «total» isolation from the rest of the PSU). I am very satisfied with the performance, very low noise, high immunity to radiated EMI/RFI noise, and clean sounding. I have had some reliability problems (the lamps powering the photodiodes had a tendency to blow); they were solved some 8 years ago, and it has been working flawlessly since. I believe the Leach head-amp design is more suited for low-impedance MC-pickups (i.e. below with a source impedance below about 30 ohm or so), than for high impedance MC-pickups, though I have never tried any high impedance MC-pickups my self.

By the way, I am currently in the design process of an overly ambitious direct input MC/RIAA phono heavily inspired by the Leach head amp, and a previous LC-Audio design or rather a Lars Claussen design - The Air as published by the Danish magazine High Fidelity. My design has differential input, amplification, RIAA-EQ and output. It is a discrete three-stage no-global feedback approach, whith a two-stage/split RIAA-network. I hope to be «publishing» soon (the progress of the actual design has been published in Norwegian at AV-Forum for those interested), though I have been tinkering with the design concept for over 10 years, so don’t hold your breath ... The electronic design as such is more or less finalised, but I sincerely need a hefty push to get on with designing PCBs.

best regards
KJ

PS sorry for the heavy «marketing» of LC-audio (DK). I have no commercial interest in them, I’m just a happy consumer who has some experience with their products, and I like their approach to DIY-/KIT-design and marketing. Their designs are pretty close to «open source», and their marketing in my experience has been non-intrusive and characterised with full information about their products.

[phn]

All of the above should be good.

Jean Hiraga has dropped the tubes and uses a DIY current-source (FET I believe) amp these days. Hiraga FET MC Phono.

Hiraga's choice of phono stage today is the 47 Labs Phonocube. So this should be another performer.