Nelson Pass Labs B1 Buffer Pre-Amplifier Update DIY



Having sold the last B1 buffer I built I ended up building another. I had a spare pcb sitting around for a while and since it is such a good pre-amp, easy to build and the fact I had 90% of the parts already it was a situation of... might as well. It also meant I could use one of those nice aluminium cases from modshop in Italy to match my copland cd player and the lightspeed pre-amp case. Solid state builds such as this simple design do not have much to go wrong and testing is safe unlike tube gear. A big difference working on 18V here rather than 300V plus. The B1 is the ideal project for a beginner since it is safe and the parts are easy to fine along with 3rd party pcb's. Most parts can be found on eBay.

 

Matched Vs Unmatched

In the first build I used a quad matched set of FET's having read forums saying the pre sound better with a matched set. Anyhow seeing as I has some FET's already but not matched I ignored the usual chatter and just built it with what I had. I can honestly say that in my build it makes no obvious difference. Channels are still balanced and it has the same character B1 sound. Infact this time I had some better output caps so it sounds even better.

 

Sound

As expected and same as the previous build it is fairly neutral. Don't expect a big bold warm sound but equally it is not bright and brittle as some solid state can be. It has a clean sound typical of class A with a sense of purity, no grain or harshness. If I have one criticism is that it is not super dynamic and does not provide that dynamic boost that some pre-amps can do. Also sometimes a little colouration is an advantage if you need to balance other components that may be too warm or bright and you need a pre-amp to counter balance that. If your system is already well balanced and flat sounding then this pre-amp is ideal.

 

Gain Reduction and Impedance Matching

A good use of the B1 is to act as an impedance matcher or gain reducer if your source output is too high for your main amplifier. For example on my Yamaha AS-1000 integrated with a pioneer F91 tuner I have very little volume control and 1/4 way is just too loud for my bookshelf speakers. I have some Rothwell style attenuators (Harrison Labs -6db) which I have used but the results are very mixed and can be detrimental. However with the B1 after the tuner there is no degradation of sound and it gives perfect impedance matching.

You do not need to build this as a stand alone pre-amp with volume control and selector but can build it as a 1:1 buffer with a single set of inputs and outputs and chain it between your source and existing pre-amp / integrated. It is also possible to install the B1 pcb inside any existing amplifier build such as a power amp or tube pre-amp were you need better matching if space is permitting.

Note to self... must not sell this one.

 

Nelson Pass Labs B1 Buffer
Nelson Pass Labs B1 Buffer
Nelson Pass Labs B1 Buffer
Nelson Pass Labs B1 Buffer
Nelson Pass Labs B1 Buffer