Project files: BUF-03 revisited

What is it?
As I mentioned in my post on my still work-in-progress “Ring” amplifier, I am planning to use (at least initially) a version of my BUF03-buffer as the input stage. Since I have now build and tested the revised boards and they seem to work well, I thought I’d publish the files as an update to the original. Key changes are:

  • In/Out connections are now grouped together as single 3-pin headers instead of the previous 2 x 2 configuration.
  • PSU connector has been uprated to a screw clamp type which is easier to work with. Also, there is now only one PSU entry instead of two.
  • The diameter of the decoupling electrolytics has been reduced to 8mm which should still be plenty for low-ESR types (Panasonic FC/FM are what I normally use). The smaller caps make the board look a little less cramped.
  • There is now a provision for a resistor at the input. This sets the input impedance and may be useful in applications where no volume pot is used. It is optional if you either want to use a volume pot immediately before the buffer or just want the previous stage to see the natural input impedance of the BUF03 (which is quite high).

How big are the boards?
The board measures 2.55×1.45″ (app. 65x37mm) – same as the original.

What is the status of the boards?
The board is now in rev. 1.5 as I’ve only made minor changes (described above). Both the original version and this one have been tested and work fine.

Does it use any special/expensive/hard-to-find parts?
Yes. The BUF-03 IC was discontinued several years ago. They are often available as used or NOS on ebay, but as always be wary of the risk of counterfeit/substandard parts in ebay listings.

Anything else I need to know?

  • DO NOT attempt to use this board with the BUF634 or any other buffer IC as that will not work.
  • The BUF-03 ICs are internally biased to class A and will get (quite) hot during normal operation. Small TO-5 heatsinks are recommended if you can find them.
  • The board can be used with the (equally hard to find) BUF-04 from Analog Devices, as long as you note the different pinouts (different location of the DC offset adjust pins).
  • Remember to measure and adjust the DC-offset with the inputs shorted, preferably like this: Apply the power, measure offset and adjust to zero with the trimmer. Once done, disconnect power and let the buffers cool down. Once they are cold, reapply power and check that the offset does not “drift” too much when they heat up (leave them on for 5-10 mins. at least).

Download design files here

Related information:
See the two original posts for some more information and links.
Note: Always read the “intro post” for additional important information about my designs.



2 Responses to Project files: BUF-03 revisited

  1. Marco says:

    Good morning. Very great and high end sound and abosolutely no hum.
    But with 10KB volume pot it is necessary to install a resistor (10K)from potentiometer out to BUF03 input, otherwise it is impossible to null offset and the preamplifier it is very noisy.
    Thanks and kind regards.
    Marco – Italy

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