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.

2086020861

[CageyH]

I love the case!

[Edward]

Look like a Scottish Chocolate Chip prototype. What clan? :eyebrows:

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 (http://www.diyaudio.com/forums/pass-labs/301812-b1-rev-2-a.html).


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 (https://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? :eyebrows:

McClain clan, BTW!

[Arkless Electronics]

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.



McClain clan, BTW!

My buffer design, intended to beat the Pass buffer. Simon's will have my MkII circuit with no capacitors in the signal path.

I'll mention in passing, and for probably the 40th time, that the entire "linear supply versus SMPS" is a complete red herring in many ways.... The important thing is how the power is dealt with after the PSU, NOT the PSU itself. With a little thought as to how things are done there is no advantage to one type of supply over the other.

There is nothing in the use of matched FET's that reduce sensitivity to supply (most buffers are types of follower and have good PSRR anyway) and nothing in "Also,since it's just a buffer, the qualities of the potentiometer/attenuator will be passed through more directly than an active preamp"

[brucew268]

My buffer design, intended to beat the Pass buffer. Simon's will have my MkII circuit with no capacitors in the signal path.

I'll mention in passing, and for probably the 40th time, that the entire "linear supply versus SMPS" is a complete red herring in many ways.... The important thing is how the power is dealt with after the PSU, NOT the PSU itself. With a little thought as to how things are done there is no advantage to one type of supply over the other.

There is nothing in the use of matched FET's that reduce sensitivity to supply (most buffers are types of follower and have good PSRR anyway) and nothing in "Also,since it's just a buffer, the qualities of the potentiometer/attenuator will be passed through more directly than an active preamp"

Thanks for the clarification!

[RothwellAudio]

Also,since it's just a buffer, the qualities of the potentiometer/attenuator will be passed through more directly than an active preamp.
It is an active preamp. Having unity gain doesn't make it a passive preamp - it's still an active preamp.


I'll mention in passing, and for probably the 40th time, that the entire "linear supply versus SMPS" is a complete red herring in many ways.... The important thing is how the power is dealt with after the PSU, NOT the PSU itself. With a little thought as to how things are done there is no advantage to one type of supply over the other.
I agree. The two big advantages of switching power supplies are 1) they're cheap and easy to get, and 2) the noise is high frequency stuff which is easier to filter than 100Hz ripple.


Just as a general comment, you could easily get the impression from forums that Nelson Pass invented the buffer. He did not, and to be fair to him he does not claim he did. His original buffer circuit was just a bog standard JFET circuit which he offered as a simple DIY project. Nothing wrong with that but it's useful to put it into some perspective.

[brucew268]

There is nothing in... "Also,since it's just a buffer, the qualities of the potentiometer/attenuator will be passed through more directly than an active preamp"

Are you saying that opamps in most active gain stages don't have an influence on the sound character, let alone the influence of the shear number and config of components in many of the more complicated preamp circuits?


It is an active preamp. Having unity gain doesn't make it a passive preamp - it's still an active preamp.

Yeah, I know. I tend to sloppily, and inappropriately speak of preamps with no gain circuitry as passive even though they are powered. Thanks for differentiating. I suppose I should have said buffer vs. preamp with gain stages.

[Arkless Electronics]

It is an active preamp. Having unity gain doesn't make it a passive preamp - it's still an active preamp.


I agree. The two big advantages of switching power supplies are 1) they're cheap and easy to get, and 2) the noise is high frequency stuff which is easier to filter than 100Hz ripple.


Just as a general comment, you could easily get the impression from forums that Nelson Pass invented the buffer. He did not, and to be fair to him he does not claim he did. His original buffer circuit was just a bog standard JFET circuit which he offered as a simple DIY project. Nothing wrong with that but it's useful to put it into some perspective.

LOL yes indeedy!! Buffers are one of the most common electronic circuits and used in countless numbers of products (not just hi fi!!) and have been for virtually as long as electronics has existed!

Nelson Pass's circuit is a standard textbook circuit and in fact I was amazed he hadn't seen the obvious potential to use that circuit in its zero offset form and avoid coupling caps.... though I hear this has now been remedied...

On SMPS the wallwart I've used on the last few things I've built has only around 3mV ripple straight out the box!

[Arkless Electronics]

Are you saying that opamps in most active gain stages don't have an influence on the sound character, let alone the influence of the shear number and config of components in many of the more complicated preamp circuits?



Yeah, I know. I tend to sloppily, and inappropriately speak of preamps with no gain circuitry as passive even though they are powered. Thanks for differentiating. I suppose I should have said buffer vs. preamp with gain stages.

I'm afraid I can see no link between my comment which you quote and your following question:scratch: I'm certainly not saying that op amps and electronic components have no sound character! I will say that they generally have less than many people assume.... I would take reports of "night and day" differences between op amps and resistors with a whole sack of salt! Today's best IC op amps are also so good that it is, by and large, a waste of time and money to use discrete op amps any more unless you need to optimise particular parameters such as super low noise, high Voltage swing or super high current output...

An interesting point (well for some) is that many op amps have such good PSRR as to be virtually immune to the quality of the power they are supplied with. Many are so good in this respect that you could deliberately inject several Volts of interference on the Voltage rails and you would hear nothing but the intended music coming from the op amp circuitry. There are several ifs, buts and caveats to that which I am fully aware of but for the sake of simplicity it's pretty much correct.