N.Pass B1 Buffer DIY preamp!

[brucew268]

Danilo's post on a thread in April got me checking into simple N.Pass preamp designs, and I built a pre-amplifier from an Alps Blue Velvet pot and a B1r2 buffer that uses JFETs in a push-pull config. Amazing! For just a handful of parts I'm getting some pretty amazing sound, which beats a lot of what I've heard including, to my ears, the Glasshouse Seiden Takman Rex kit.

Really silent and sound emerge with a natural ease. There are good details and imaging, even at lower volumes. There is just such a musical-ness and breath of life in its presentation, a realistic sense of space between the musicians that doesn't seem to be just about staging depth and separation. I also got a bit more bass, low and high bass, so had to move the speakers a little to rebalance with the room.

I put it in a biscuit tin for my proof-of-concept phase, powered from a SMPS laptop supply and a simple voltage divider to get +10v/-10v. A few experiences with the biscuit tin: being flimsy, chassis vibration is a delicate issue. With no damping, things were just a bit nervous and congested in lively, complex music. Add some Silent Coat 2mm butyl-based damping and everything went a bit over the top in the euphonic department, but lost all the harmonics and leading edge of sounds. Dropped back to just two 1cm squares with a little experimentation on placement.

And tis is all with a basic Alps Blue Velvet. I haven't even gotten to consider fancy attenuators yet.

It's sounding pretty good now, way better than I could imagine for the cost and use of an SMPS, but it's time to put in a proper enclosure and build a proper linear supply and see what that does to the sound.

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[CageyH]

I love the case!

[Edward]

Look like a Scottish Chocolate Chip prototype. What clan?

What is the unique selling point of the Nelson Pass preamp design?

[brucew268]

What is the unique selling point of the Nelson Pass preamp design?

Do you mean the idea of a buffer-based preamp, or his specific approach to one?

[CageyH]

It looks like a good DIY project to get started on.
I assume the build was fairly easy?

[Edward]

Do you mean the idea of a buffer-based preamp, or his specific approach to one?

His specific approach.

[brucew268]

It looks like a good DIY project to get started on.
I assume the build was fairly easy?

I was. I built it on strip board though one could do pad board, perfboard, point to point. As you can see, a pretty small number of parts, where the buffer fit easily on 50x80mm and the voltage divider also on 50x80mm. The main complication for a first timer is that the JFETs have to be matched. DIYAUDIO has them in their store and a Kim Bay Smidt also has a couple matched sets for sale in their Swap Meet section.

The schematics and thread are at this thread.


Pass's B1 Buffer uses matched JFETs and some capacitors for a simple build that one can dress up with the choice of caps. EnjoytheMusic reviewed it with rather high praise, and that when powered by an SMPS. People who put a linear supply in it reported further improvement over already choice SQ.

Pass's B1 rev 2 Buffer is capacitorless and uses JFETs in a push-pull configuration.

Nelson Pass generally is know for his elegant designs and focuses his amplifiers on the Class A world.

[brucew268]

I should give a link to the paper explaining his original B1 Buffer design www.passdiy.com/project/preamplifiers/b1-buffer-preamp.

[Simon_LDT]

Nice enclosure!

Jez is building me a passive pre with his buffer design included. Quite excited to try it out.

[brucew268]

Nice enclosure!

Jez is building me a passive pre with his buffer design included. Quite excited to try it out.

Did you mean Jez's buffer design, or Nelsons Pass' design? I've been curious why reviews confirm what I've heard, such high marks for a preamp using a cheap switcher power supply. Not that I know anything about it, but I wonder if it is related to the use of matched JFET's making it less sensitive to supply... or maybe that if it's that good with an SMPS, what league it will be with a well designed linear supply? Also,since it's just a buffer, the qualities of the potentiometer/attenuator will be passed through more directly than an active preamp. Still I wonder that I liked the buffer+Alps RK27 better than the completely passive Glasshouse Takman Rex or the Glasshouse TVC. YMMV.

Look like a Scottish Chocolate Chip prototype. What clan?

McClain clan, BTW!